JP2002148288A - Current-detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current-detecting device which can precisely detect current, without being affected by power source and can be made small-sized. SOLUTION: This device is provided with a power MOSFET 11, which is inserted in series into the main path where the current to be detected flows; a diode 12 which is provided to the power MOSFET side by side across an insulating thin film and varies in characteristics with the temperature; a constant-current circuit 20 which supplies a constant current to the diode 12, independently of the current flowing through the main path; a storage device 21 which stores the value of the voltage across the diode when the power MOSFET is turned on, a voltage detecting circuit 22 which detects the value of the voltage across the diode, while the power MOSFET is held on; and a difference detecting circuit 23, which detects the value of the difference voltage between the voltage value stored in the storage device and the voltage value detected by the voltage detecting circuit and detects the current flowing to the main circuit, according to the difference voltage value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a current detecting device for detecting a current flowing in an electric circuit.

[0002]

2. Description of the Related Art Conventionally, a resistor having a known value is inserted into a main path through which a current to be detected flows, and a voltage between both ends of the resistor when a current flows through the main path is measured, so that the main path is measured. 2. Description of the Related Art A current detection device that detects the magnitude of a flowing current is known.

Further, a shunt path through which a very small current flows with respect to the current flowing through the main path is provided, a resistor having a known value is inserted into the shunt path, and a resistance when a current flows through the shunt path is set. There is also known a current detection device that detects the magnitude of the current flowing in the main path by measuring the voltage between both ends of the current path. Hereinafter, a technique for detecting a current flowing through the main circuit using these resistors will be referred to as “first prior art”.

On the other hand, in order to prevent the semiconductor element from being destroyed, it is determined whether or not the chip temperature has reached a temperature near the element breakdown limit region based on a voltage between both ends of a diode provided in proximity to the semiconductor element. 2. Description of the Related Art There is known a semiconductor device having an overheat shut-off function of stopping operation just before a breakdown temperature is reached and protecting the device from destruction. In this semiconductor device, a constant current is applied to the diode to monitor the voltage between both ends thereof, and the chip temperature is detected based on the absolute value, or a constant voltage is applied to the diode to monitor the current flowing to the diode. The chip temperature is detected based on the absolute value, and overheating is shut off based on the detected temperature. In this case, the diode provided in the semiconductor element can be considered as a current detection device. Hereinafter, this technology is referred to as “No.
Of the prior art.

As a second prior art, for example, Japanese Patent Application Laid-Open No. 5-129598 discloses a "power device" which is formed on a semiconductor substrate such as a control power IC and detects an abnormal temperature of a power device included in the power IC. Overheat detection circuit ". In addition, Japanese Patent Application Laid-Open No. Hei 5-13543
Japanese Patent Application Laid-Open Publication No. H11-15095 discloses a power supply system for supplying power to an internal circuit from a power supply pad and a power supply voltage supply control means capable of controlling supply / interruption of a power supply voltage. Discloses a "semiconductor integrated circuit" that stops supply of a power supply voltage when an abnormal temperature rise of a chip is detected.

[0006] Further, Japanese Patent Application Laid-Open No. 6-232410 discloses that
A "MOS semiconductor device" including a diode for preventing destruction at the time of overload or increase in ambient temperature is disclosed. Furthermore, Japanese Patent Application Laid-Open No. Hei 8-254071 discloses a "power window regulator circuit" provided with a shunt resistor for detecting a current value.

[0007]

However, in the above-mentioned first prior art, a space for mounting a resistor is required, so that downsizing is difficult. Further, in a configuration in which a resistor is provided in the main path, the resistance generates heat when a current flows, so that there is a problem that a measure for heat treatment must be taken. Further, since a resistor is mounted on a main path through which a current to be detected flows, the resistance is affected by the power supply voltage, and power supply voltage dependency occurs.

In the second prior art, since the semiconductor element and the diode inserted in the main path operate on the same power supply, they are affected by the power supply voltage. Further, since the chip temperature is determined based on the voltage between both ends of the diode, the temperature dependency of the diode itself is affected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a current detecting device which can accurately detect a current without being affected by a power supply and which can be downsized. And

[0010]

In order to achieve the above object, the present invention is directed to a power transistor inserted in series in a main path through which a current to be detected flows, and an insulating thin film provided on the power transistor. A temperature-sensitive element whose characteristics change according to temperature, a constant current circuit that supplies a constant current to the temperature-sensitive element independently of the current flowing through the main path, and a power transistor that is turned on. A storage device for storing a voltage value between both ends of the temperature-sensitive element when
A voltage detection circuit that detects a voltage value between both ends of the temperature sensing element while the power transistor is turned on, and a voltage value stored in the storage device and a voltage value detected by the voltage detection circuit. And a difference detection circuit for detecting a current flowing through the main circuit based on the difference voltage value.

According to the first aspect of the invention, independently of the current flowing through the main path, the main path of the main path is determined based on the voltage between both ends of the temperature sensing element generated by the constant current supplied from the constant current circuit. Since the current flowing through the power transistor is detected, it is not affected by the power supply voltage. as a result,
The current flowing in the main path can be accurately detected. Further, even if noise is generated in the main circuit, it is not affected by the noise, so that the configuration for protecting the temperature sensing element and its peripheral circuit can be simplified. Further, since the current flowing through the main path is detected based on the difference voltage value, the temperature dependency of the temperature-sensitive element due to the surrounding environment can be eliminated. Furthermore, since no resistor is inserted in series in the main path as in the prior art, there is no problem of mounting space or heat generation.

The invention described in claim 2 is the first invention.
In the invention described in (1), a control circuit for turning off the power transistor when a difference voltage value from the difference detection circuit exceeds a predetermined value is further provided.

According to the second aspect of the present invention, whether or not an overcurrent or an overload is detected based on the difference voltage value, and if the overcurrent or the overload occurs, the power transistor is turned off. Therefore, in addition to the effect of the first aspect of the present invention, it is possible to prevent the system including the power transistor from being destroyed due to overcurrent or overload.

According to a third aspect of the present invention, there is provided a resistor which is inserted in series in a main path through which a current to be detected flows, and which has a characteristic according to temperature, which is provided in parallel with the resistor via an insulating thin film. A temperature-sensitive element that changes, a constant current circuit that supplies a constant current to the temperature-sensitive element independently of the current flowing through the main path,
A storage device for storing a voltage value between both ends of the temperature sensing element when current supply to the resistor is started, and both ends of the temperature sensing element while current supply to the resistor is continued A voltage detection circuit for detecting a voltage value between the two, and a difference value between a voltage value stored in the storage device and a voltage value detected by the voltage detection circuit, and the main circuit is detected based on the difference voltage value. And a difference detection circuit for detecting a current flowing through the circuit.

According to the third aspect of the invention, independently of the current flowing through the main path, the main path of the main path is determined based on the voltage between both ends of the temperature sensing element generated by the constant current supplied from the constant current circuit. Since the current flowing through the resistor is detected, it is not affected by the power supply voltage. As a result, the current flowing through the main path can be accurately detected. Further, even if noise is generated in the main circuit, it is not affected by the noise, so that the configuration for protecting the temperature sensing element and its peripheral circuit can be simplified. Also, since the current flowing through the main path is detected based on the differential voltage,
The temperature dependency of the temperature sensing element due to the surrounding environment can be eliminated.

Further, the invention according to claim 4 is the same as the invention according to claim 3.
In the invention described in (1), a control circuit for interrupting a current flowing through the resistor when the difference voltage value from the difference detection circuit exceeds a predetermined value is further provided.

According to the fourth aspect of the present invention, whether or not an overcurrent or an overload is detected based on the difference voltage value, and if the overcurrent or the overload occurs, the current flowing through the resistor is cut off. Therefore, in addition to the effect of the third aspect of the present invention, the destruction of the system including the resistor due to overcurrent or overload can be prevented.

The invention described in claim 5 is the first invention.
5. The invention according to any one of Items 4 to 4, wherein the temperature-sensitive element is a temperature-sensitive diode.

According to the fifth aspect of the present invention, since the temperature-sensitive diode is used as the temperature-sensitive element, the temperature-sensitive element can be formed at a low cost and in a small size.

According to a sixth aspect of the present invention, there is provided a power transistor which is inserted in series in a main path through which a current to be detected flows, and which has a characteristic according to temperature which is provided in parallel with the power transistor via an insulating thin film. A first temperature-sensitive element that changes, and a heat-insulated side-by-side attached to the first temperature-sensitive element;
A second temperature-sensitive element whose characteristics change according to temperature, a constant current circuit that supplies a constant current to the first temperature-sensitive element and the second temperature-sensitive element independently of the current flowing through the main path; A difference detection circuit that detects a difference voltage value between a voltage value stored in a storage device and a voltage value detected by the voltage detection circuit, and detects a current flowing through the main circuit based on the difference voltage value. It is characterized by the following.

According to the sixth aspect of the present invention, in addition to the operation and effect of the first aspect, the invention according to the first and second aspects is used as a reference voltage for detecting a differential voltage value. Is not the voltage value stored in the storage device like
Since a voltage value obtained in real time from the second temperature sensing element is used, an accurate current value can be detected even when the ambient temperature changes.

The invention described in claim 7 is the same as the invention in claim 6
In the invention described in (1), a control circuit for turning off the power transistor when a difference voltage value from the difference detection circuit exceeds a predetermined value is further provided.

According to the present invention, whether or not an overcurrent or an overload is detected based on the difference voltage value, and if the overcurrent or the overload occurs, the power transistor is turned off. Therefore, in addition to the effect of the first aspect of the present invention, it is possible to prevent the system including the power transistor from being destroyed due to overcurrent or overload.

The invention according to claim 8 is characterized in that a resistor inserted in series in a main path through which a current to be detected flows, and a resistor provided in parallel with the resistor via an insulating thin film, according to temperature. Are changed, a second temperature-sensing element that is thermally insulated from the first temperature-sensing element and has a characteristic that changes according to the temperature, and a current flowing through the main path are: A constant current circuit for independently supplying a constant current to the first temperature sensing element and the second temperature sensing element; and a difference voltage value between a voltage value stored in the storage device and a voltage value detected by the voltage detection circuit. And a difference detection circuit for detecting a current flowing through the main circuit based on the difference voltage value.

According to the eighth aspect of the present invention, in addition to the operation and effect of the sixth aspect, the reference voltage for detecting the differential voltage is used as the reference voltage of the third and fourth aspects of the present invention. As described above, not the voltage value stored in the storage device but the voltage value obtained in real time from the second temperature sensing element is used, so that an accurate current value can be detected even when the ambient temperature changes.

The invention according to claim 9 is the same as the invention according to claim 8.
In the invention described in (1), a control circuit for interrupting a current flowing through the resistor when the difference voltage value from the difference detection circuit exceeds a predetermined value is further provided.

According to the ninth aspect of the present invention, whether or not an overcurrent or an overload is detected based on the difference voltage value, and if the overcurrent or the overload is detected, the current flowing through the resistor is cut off. Therefore, in addition to the effect of the invention described in claim 8, it is possible to prevent the system including the resistor from being destroyed due to overcurrent or overload.

Further, the invention according to claim 10 is the invention according to any one of claims 6 to 9, wherein the first temperature sensing element and the second temperature sensing element are temperature sensing diodes. Features.

According to the tenth aspect of the present invention, since the temperature-sensitive diode is used as the temperature-sensitive element, the temperature-sensitive element can be configured at a low cost and in a small size.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a current detecting device according to an embodiment of the present invention will be described in detail with reference to the drawings. In the following, description will be made assuming that this current detection device is applied to an automobile. Further, in each of the embodiments described below, the same or corresponding parts will be denoted by the same reference characters.

(First Embodiment) In a current detection device according to a first embodiment of the present invention, a detection element including a power MOSFET and a temperature-sensitive diode is used.

This current detecting device, as shown in FIG.
It comprises a detection element 10, a power supply 13, a load 14, a detection circuit 15, and a control circuit 16. The detection circuit 15 includes a constant current circuit 20, a storage device 21, a voltage detection circuit 22, and a difference detection circuit 23. Also, the control circuit 1
Reference numeral 6 includes a determination circuit 30 and a gate drive circuit 31.

The detecting element 10 comprises an N-channel type power MOSFET 11 and a temperature-sensitive diode (hereinafter simply referred to as “diode”) 12. Power M
The OSFET 11 corresponds to the power transistor of the present invention, and functions as a heating element that generates heat according to the magnitude of the current flowing between the source and the drain. In addition, power MOS
The FET is not limited to the N-channel type but may be a P-channel type.

The diode 12 corresponds to the temperature sensing element of the present invention, and functions as a current detection element whose characteristics (for example, voltage) change with temperature. Note that the temperature-sensitive element of the present invention is not limited to a diode, and an element whose characteristics change with temperature, such as a thermistor or a thermocouple, can also be used.

The detection element 10 includes a power MOSFET 11
The diode 12 is integrated on the polysilicon layer with an insulating thin film of high thermal conductivity that is electrically insulated. Thereby, the detection element 10
It is realized as a power semiconductor with a built-in diode in which a heating element, an insulating thin film and a temperature sensing element are integrated.

The power supply 13 supplies a current to the drain of the power MOSFET 11 included in the detecting element 10. The source of the power MOSFET 11 is connected to one end of the load 14, and the gate is connected to a gate drive circuit 31 included in the control circuit 16. Although not shown, the power supply 13 also supplies power to the detection circuit 15 and the control circuit 16.

The load 14 is composed of, for example, lamps such as headlights and tail lamps, and motors for driving wipers, windows and the like. This load 14
Is grounded. From the power supply 13 to the detecting element 1
The path leading to the load 14 via 0 corresponds to the main path of the present invention.

Gate drive circuit 3 included in control circuit 16
1 generates a gate signal to be supplied to the gate of the power MOSFET 11 in response to an external input signal from a console switch or the like (not shown). Power MOSFET 11
Turns on when the gate signal from the gate drive circuit 31 is set to a high level (hereinafter, referred to as “H level”), and is turned off when the gate signal is set to a low level (hereinafter, referred to as “L level”). The gate signal controls whether to supply a current to the load 14.

When a P-channel type is used as the power MOSFET 11, the gate drive circuit 31 generates a gate signal opposite to the above level. The gate signal generated by the gate drive circuit 31 is stored in the storage device 2
1 and the voltage detection circuit 22 (the details will be described later). Further, the gate drive circuit 31 receives a gate-off signal from the determination circuit 30 as described later. The gate drive circuit 31 responds to the gate-off signal by
The gate signal is forced to the L level.

Constant current circuit 20 included in detection circuit 15
Generates a constant current independently of the output of the power supply 13 in response to the external input signal. The constant current circuit 20 keeps outputting a constant current while the gate signal is at the H level. The current generated by the constant current circuit 20 is supplied to the anode of the diode 12. The cathode of the diode 12 is grounded. With the above configuration, the diode current IF flowing through the diode 12 and the anode-cathode voltage VF
Changes only depending on its temperature and is not affected by the power supply voltage.

The anode of the diode 12 is further connected to a storage device 21 and a voltage detection circuit 22.
A voltage (anode-cathode voltage) VF across the diode 12 is supplied to the storage device 21 and the voltage detection circuit 22. As shown in FIG. 2, the voltage VF between both ends of the diode 12 elapses, that is, the power MOSFET 11
Gradually decreases as the temperature rises.

The storage device 21 included in the detection circuit 15
For example, it can be constituted by a memory, a buffer, a register, a peak hold circuit and the like. As shown in FIG. 2, the storage device 21 stores the voltage VF across the diode 12 in synchronization with the rising change of the gate signal from the gate drive circuit 31.
Is stored. Therefore, in the storage device 21,
The voltage between both ends of the diode 12 before the temperature rise of the power MOSFET 11 is stored. Hereinafter, the storage device 2
The voltage corresponding to the voltage value stored in 1 is called a VF reference voltage.

The storage device 21 holds a voltage value representing the VF reference voltage while the gate signal from the gate drive circuit 31 is at the H level. The voltage value representing the VF reference voltage stored in the storage device 21 is supplied to the difference detection circuit 23.

Voltage detection circuit 22 included in detection circuit 15
Detects the voltage between both ends of the diode 12 while the gate signal from the gate drive circuit 31 is at the H level. The voltage value detected by the voltage detection circuit 22 is supplied to the difference detection circuit 23.

The difference detection circuit 23 comprises a subtractor. The difference detection circuit 23 subtracts the voltage value detected by the voltage detection circuit 22 from the voltage value representing the VF reference voltage stored in the storage device 21. The difference voltage value ΔVF obtained by the subtraction represents a change in the temperature of the power MOSFET 11, in other words, a change in the current flowing between the source and the drain. This difference voltage value ΔVF is determined by the determination circuit 3
0 is supplied.

The discriminating circuit 30 included in the control circuit 16
It is determined whether the difference voltage ΔVF from the difference detection circuit 23 has become larger than a predetermined overcurrent reference voltage,
When it is detected that the voltage exceeds the overcurrent reference voltage, a gate-off signal is generated and supplied to the gate drive circuit 31. Thus, the gate drive circuit 31 forcibly sets the gate signal to the L level.

As shown in FIG. 3, a semiconductor device generally includes a normal operation region and a destruction region. The normal operation region further includes a normal operation region, an overload (overcurrent) region, and an overheat protection region. Have been. Each of these areas is determined by the load.

The normal operation region is a region where the semiconductor element saturates with a certain amount of heat and operates in a preferable state. The overload (overcurrent) region is a region where the semiconductor element operates normally but is in an overload (overcurrent) state and a temperature rise is caused. The overheat protection region is a region where the temperature rise is at a limit and further temperature rise should be suppressed.
The destruction region is a region where the semiconductor element is destroyed due to a temperature rise.

The overheat protection function is a function of detecting a boundary region between the destruction region and the normal operation region to prevent the destruction of the semiconductor element. The determination circuit 30 determines the overload (overcurrent) in a range outside the normal operation area and not reaching the overheat protection area, that is, the current value and the voltage value belonging to the overload (overcurrent) area. It is stored as a reference value. Accordingly, the determination circuit 30 determines whether the load 14 has become overcurrent or overloaded, and feeds back the determination result to the gate drive circuit 31.

The transient heat generated in the detecting element 10 is equivalent to the power. Since the transient heat is directly detected as the difference voltage ΔVF which is the amount of change in the voltage between both ends of the diode 12, the normal operation area and the overheat protection area The overload (overcurrent) can be easily determined by having a voltage (overcurrent reference voltage in FIG. 2) which is a boundary with the reference value as a reference value.

Next, the operation of the current detecting device configured as described above will be described.

When an external input signal is supplied from a console switch or the like (not shown), the constant current circuit 20 generates a constant current and supplies it to the diode 12. In this state, the power MOSFET 11 operates as a switch. That is, the gate drive circuit 31 changes the gate signal from the L level to the H level, and the storage device 21 and the power M
It is supplied to the gate of the OSFET 11.

As a result, the memory device 21 synchronizes with the rising change of the gate signal to store the diode 1 at that time.
In addition to storing the voltage VF between both ends, that is, a voltage value representing the VF reference voltage, the voltage value representing the VF reference voltage is supplied to the difference detection circuit 23.

On the other hand, the power MOSFET 11 is turned on, and the current from the power
Flows to the load 14 via the source-drain of the IGBT. At this time, since there is always an on-resistance between the source and the drain of the power MOSFET 11, power is consumed by the on-resistance. The excessive heat generated by this power consumption is conducted to the diode 12 and raises the temperature of the diode 12 over time. As shown in FIG. 2, the voltage VF between both ends of the diode 12 decreases as the temperature rises.

The voltage detection circuit 22 includes the diode 12
Is supplied to the difference detection circuit 23. The difference detection circuit 23 subtracts the voltage value from the voltage detection circuit 22 from the voltage value from the storage device 21 and outputs the result as a difference voltage value ΔVF. Therefore, the difference voltage value ΔVF increases as time passes, as shown in FIG. This difference voltage value ΔVF is supplied to the determination circuit 30.

The determination circuit 30 constantly monitors whether the difference voltage value ΔVF from the difference detection circuit 23 has become larger than the overcurrent reference voltage. Then, the differential voltage value ΔV
When it is determined that F has become larger than the overcurrent reference voltage, the gate-off signal is activated, and the fact is notified to the gate drive circuit 31. In response to this, the gate drive circuit 31 changes the gate signal to L level, and turns off the power MOSFET 11. This prevents the power MOSFET 11 from being destroyed and prevents an overcurrent from flowing through the load 14.

With the above configuration, the temperature characteristics of the diode 12 due to the environment, that is, the influence of the temperature of the atmosphere in which the diode 12 is installed can be offset, so that the amount of change in the temperature from the reference value is always detected. Since the amount of change and the current flowing through the main path have a one-to-one relationship,
The current flowing in the main path, in other words, the current flowing through the load 14 is detected with high accuracy.

Here, a current detecting device for detecting the current flowing to the load based on the voltage VF across the diode, and the current flowing to the load based on the differential voltage ΔVF calculated according to the voltage VF across the diode. In order to make a comparison with the current detection device according to the first embodiment, a change in the characteristics of the diode due to the power supply voltage was examined, and will be described below.

FIG. 4 shows that the power supply voltages are 8, 10, 12, 14
And the relationship between the voltage VF across the diode and the current Id flowing through the main path when the voltage is changed to 16 V and 16 V. Each plot point is 4 points after turning on the power MOSFET 11.
This is the value after 0 millisecond. Referring to FIG. 4, the voltage VF between both ends of diode 12 greatly varies depending on the power supply voltage. Therefore, it can be understood that the result of detecting the current flowing through the main path also has a large variation.

On the other hand, FIG.
The relationship between the difference voltage ΔVF and the current Id flowing through the main path when the voltage is changed to 0, 12, 14, and 16 V is shown. The difference voltage ΔVF is, as described above, the power MOSFET 1
1. The voltage VF between both ends of the diode 12 before the temperature rise of 1
This is a difference voltage from the voltage VF between both ends of the diode 12 after the temperature rise due to the current flowing. Each plot point is a value 40 ms after the power MOSFET 11 is turned on. Referring to FIG. 5, it can be seen that even if the power supply voltage supplied to the main path changes, the difference voltage ΔVF hardly changes. Therefore, it can be understood that if the current flowing through the main path is detected based on the difference voltage ΔVF, the current can be accurately detected.

As described above, according to the current detection device of the first embodiment, the current from the power supply 13 flows through the power MOSFET 11 and the load 14 (the system to be detected), but the diode 12 (the detection system). ), A constant current from the constant current circuit 20 flows independently of the current from the power supply 13. Therefore, since the detection system is not affected by the power supply voltage of the detected system, the current flowing to the load 14 via the power MOSFET 11 can be accurately detected.

Further, since the detected system and the detection system are independent, even if a surge or the like is applied to the detected system (main path), the detection system is not affected. Therefore, the configuration for protecting the detection system is unnecessary or can be simplified. Further, since there is no need to insert a resistor into the main path or the branch path as in the related art, a space for mounting the resistor is not required.

Furthermore, since the current flowing through the main path is detected based on the difference voltage ΔVF, the influence of the temperature characteristics of the diode 12 due to the surrounding environment can be canceled, and the temperature dependency of the diode 12 can be eliminated.

More specifically, the characteristics of the diode 12 generally fluctuate greatly depending on the ambient temperature. FIG.
Shows the temperature characteristics of the voltage VF between both ends of the diode 12 at the respective ambient temperatures of −40 ° C., 0 ° C., 20 ° C., and 85 ° C. Each plot point is a value 40 ms after the power MOSFET 11 is turned on. As is apparent from FIG. 6, even when the current flowing through the main path is constant, the voltage VF between both ends of the diode 12 changes when the ambient temperature changes.

On the other hand, FIG. 7 shows that the ambient temperature of the detecting element 10 used in the first embodiment is -40.degree.
5 shows the temperature characteristics of the differential voltage ΔVF at ° C, 20 ° C, and 85 ° C. According to FIG. 7, even when the current (horizontal axis) flowing through the main path is constant, it appears that the difference voltage ΔVF changes with temperature.
This is due to the temperature dependence of the power consumed by the OSFET 11.

The power consumption P of the power MOSFET 11 is represented by “P = I ² R _on ”. Where I is the power M
The current flowing through the OSFET 11 and R _on is the power M
This is the on-resistance of the OSFET 11. Power MOSFET
The power consumed at 11 varies depending on the ambient temperature, as shown in FIG. This is the power MOSFET 11
This is due to the temperature dependence of the on-resistance of the transistor.

The change in the difference voltage ΔVF shown in FIG.
The temperature dependency of the power MOSFET 11 is caused by the temperature dependency of the diode 12 in practice. Therefore, when a temperature correction circuit is added to the detection circuit 15, it is not necessary to consider the temperature dependency of the diode 12, and only the temperature correction circuit of the power MOSFET 11 needs to be added, so that the correction circuit can be simplified.

(Second Embodiment) In a current detection device according to a second embodiment of the present invention, a detection element including a resistor and a temperature-sensitive diode is used. In the following, a description will be given focusing on portions different from the first embodiment.

This current detecting device, as shown in FIG.
It comprises a detection element 10a, a power supply 13, a load 14, a detection circuit 15, and a control circuit 16a. Detection circuit 15
Is a constant current circuit 20, a storage device 21, a voltage detection circuit 22
And a difference detection circuit 23. The control circuit 16a includes a discrimination circuit 30, a switch control circuit (SW
(Control circuit) 32 and a switch 33.

The detecting element 10a comprises a resistor 17 and a diode 12. The resistor 17 functions as a heating element that generates heat according to the magnitude of the current flowing between both ends. Further, the diode 12 corresponds to the temperature sensing element of the present invention, and functions as a current detection element whose characteristics (for example, voltage) change with temperature.

As the diode 12, it is preferable to use a composite diode in which a plurality of diodes are connected in series. With this configuration, the change in the diode forward voltage with respect to the temperature change increases, so that the detection sensitivity can be increased. In this case, the voltage VF between both ends of the diode 12 (anode-cathode voltage) is “forward voltage of the diode 12 × number of diodes”, and this voltage fluctuates depending on temperature.

The detecting element 10a is constituted by integrating a diode 12 with a highly insulated thin insulating film having high thermal conductivity interposed between resistors 17. Thus, the detection element 10a is realized as a semiconductor in which the heating element, the insulating thin film, and the temperature sensing element are integrated. According to this configuration, since the diode 12 and the main path are electrically insulated, noise in the main path does not directly affect the diode 12.

The power supply 13 supplies a current to one end of the resistor 17 of the detecting element 10a via the switch 33. The other end of the resistor 17 is connected to one end of the load 14. The other end of the load 14 is grounded. The path from the power supply 13 to the load 14 via the switch 33 and the resistor 17 corresponds to the main path of the present invention.

The configuration and operation of the detection circuit 15 are the same as those of the first embodiment except that the gate signal is generated by the switch control circuit 32.

As described above, the control circuit 16a includes the discrimination circuit 30, the switch control circuit 32, and the switch 33. The determination circuit 30 is the same as that in the first embodiment.

The switch control circuit 32 generates a gate signal in response to an external input signal from a console switch or the like (not shown) and supplies the gate signal to the switch 33. The gate signal controls whether to supply a current to the load 14. The gate signal generated by the switch control circuit 32 is also supplied to the storage device 21 and the voltage control circuit 22 (details will be described later). Further, the switch control circuit 32
, A gate-off signal is input from the determination circuit 30 as described later. The switch control circuit 32 forcibly sets the gate signal to the L level in response to the gate-off signal.

The switch 33 is composed of, for example, a relay. The switch 33 is closed when the gate signal from the switch control circuit 32 is set to H level,
It is opened by being set to L level. This allows
Whether the current is supplied to the load 14 is controlled. The switch 33 is not limited to a relay, but may be another mechanical switch, a semiconductor switch, or the like.

Next, the operation of the current detecting device configured as described above will be described.

When an external input signal is supplied from a console switch or the like (not shown), the constant current circuit 20 generates a constant current and supplies it to the diode 12. In this state, the switch control circuit 32 changes the gate signal from the L level to the H level and supplies the gate signal to the switch 33, the storage device 21, and the voltage detection circuit 22.

As a result, the switch 33 is turned on,
From the power supply 13 to the switch 33 and the resistor 1 of the detection element 10
A current flows through the load 14 via the switch 7. At this time, power is consumed by the resistor 17. The heat generated by this power consumption is conducted to the diode 12 and the diode 12
Is raised over time. Diode 1
2, the voltage VF between both ends decreases as the temperature rises, as shown in FIG.

The storage device 21 stores the voltage VF across the diode 12 at that time, that is, a voltage value representing the VF reference voltage, and stores the VF reference voltage in synchronization with the rising change of the gate signal. The represented voltage value is supplied to the difference detection circuit 23.

The voltage detection circuit 22 supplies a voltage value representing the voltage VF between both ends of the diode 12 to the difference detection circuit 23. The difference detection circuit 23 subtracts the voltage value from the voltage detection circuit 22 from the voltage value from the storage device 21 and outputs the result as a difference voltage value ΔVF. Therefore, the difference voltage value ΔV
F increases as time passes, as shown in FIG. This difference voltage value ΔVF is supplied to the determination circuit 30.

The determination circuit 30 constantly monitors whether the difference voltage value ΔVF from the difference detection circuit 23 has become larger than the overcurrent reference voltage. Then, the differential voltage value ΔV
When it is determined that F has become larger than the overcurrent reference voltage, the gate-off signal is activated to notify the switch control circuit 32 of that fact. In response to this, the switch control circuit 32 changes the gate signal to L level, and opens the switch 33. Thereby, the load 14
The overcurrent is prevented from flowing.

As described above, according to the current detection device according to the second embodiment, the conventional problems of space and heat generation are not solved, but the system to be detected (main path) and the detection system are independent. Therefore, the detection system is hardly affected by the main route. As a result, the influence of the power supply voltage on the detection system is reduced, so that an accurate current can be detected.

In the conventional current detection device, a protection circuit is required because the power supply voltage may affect the detection system especially when the current detection device is used on the high side. According to the current detection device, since the detection target system (main path) and the detection system are independent, the protection circuit provided as a peripheral circuit can be simplified.

In the second embodiment, the switch 33 is provided on the upstream side of the detecting element 10a (on the side of the power supply 13). However, the switch 33 may be provided on the downstream side of the detecting element 10a (on the side of the load 14). . In this case, the same operation and effect as described above can be obtained.

(Third Embodiment) In a current detection device according to a third embodiment of the present invention, a detection element including a power MOSFET and two temperature-sensitive diodes is used. In the following, a description will be given focusing on portions different from the first embodiment.

As shown in FIG. 10, the current detecting device includes a detecting element 10b, a power source 13, a load 14, a detecting circuit 1
5a and a control circuit 16. Detection circuit 1
5a includes a constant current circuit 20a and a difference detection circuit 23a. Further, the control circuit 16 includes a determination circuit 30
And a gate drive circuit 31.

The detecting element 10b comprises an N-channel type power MOSFET 11, a first diode 12a and a second diode 12b. Power MOSFE
T11 corresponds to the power transistor of the present invention, and functions as a heating element that generates heat according to the magnitude of the current flowing between the source and the drain. The power MOSFET is not limited to the N-channel type, but may be a P-channel type.

Further, the first diode 12a and the second diode 12b correspond to the first temperature sensing element and the second temperature sensing element of the present invention, respectively. In general, as shown in FIG. 11, the voltage VF between both ends of the diode changes depending on the temperature if the current IF flowing through the diode is constant. Therefore, the first diode 12a and the second diode 12b function as current detecting elements whose characteristics (for example, voltage) change with temperature. The first diode 12a is used to detect heat generation in the main path. The second diode 12
b is used to generate a reference voltage V _ref corresponding to the ambient temperature. Note that the first and second temperature sensing elements of the present invention are not limited to diodes, but may be elements such as thermistors and thermocouples whose characteristics change with temperature.

The detection element 10b includes a power MOSFET 1
The first diode 12a is integrated on one polysilicon layer with an electrically insulated thin insulating film having a high thermal conductivity interposed therebetween, and the power MOSFET 11 and the first diode 1 are further integrated.
The second diode 12b is integrated at a position thermally insulated from the second diode 12a. As a result, the detection element 10b is realized as a power semiconductor with a built-in diode in which the heating element, the insulating thin film, the first temperature sensing element and the second temperature sensing element are integrated.

The power supply 13 and the load 14 are the same as those of the first embodiment. From the power supply 13 to the detecting element 1
The route to the load 14 via 0b corresponds to the main route of the present invention.

Gate drive circuit 3 included in control circuit 16
1 generates a gate signal to be supplied to the gate of the power MOSFET 11 in response to an external input signal from a console switch or the like (not shown). Power MOSFET 11
Is turned on when the gate signal from the gate drive circuit 31 is set to the H level, and turned off when the gate signal is set to the L level. With this gate signal, load 1
4 is controlled.

When a P-channel type is used as the power MOSFET 11, the gate drive circuit 31 generates a gate signal opposite to the above level. The gate signal generated by the gate drive circuit 31 is also supplied to the difference detection circuit 23a (details will be described later). Further, a gate-off signal is input from the determination circuit 30 to the gate drive circuit 31 as described later. Gate drive circuit 31 forcibly sets the gate signal to L level in response to the gate-off signal.

Constant current circuit 20 included in detection circuit 15a
a generates a first constant current and a second constant current independently of the output of the power supply 13 in response to the external input signal. The constant current circuit 20a keeps outputting the first and second constant currents while the gate signal is at the H level. The first and second constant currents generated by the constant current circuit 20a are the anode of the first diode 12a and the second diode 12a.
b, respectively. First diode 1
Each cathode of the 2a and the second diode 12b is grounded. With the above configuration, the first and second diodes 1
The diode current IF and the anode-cathode voltage VF flowing through each of 2a and 12b change only depending on the temperature, and are not affected by the power supply voltage.

The anode of the first diode 12a is connected to the difference detection circuit 23a, and supplies a voltage (anode-cathode voltage) VF across the first diode 12a to the difference detection circuit 23a. As shown in FIG. 12, the voltage VF between both ends of the first diode 12a gradually decreases as time passes, that is, as the temperature of the power MOSFET 11 rises.

Similarly, the anode of the second diode 12b is connected to the difference detection circuit 23a, and supplies a voltage (anode-cathode voltage) VF _ref across the second diode 12b to the difference detection circuit 23a. The voltage VF _ref between both ends of the second diode 12b is determined by the ambient temperature, and lapse of time, that is, the power MOSFET 1
1 keeps a substantially constant voltage even when the temperature rises.

The difference detection circuit 23a is constituted by a subtractor. As shown in FIG. 12, while the gate signal from the gate drive circuit 31 is at the H level, the difference detection circuit 23a calculates the voltage VF across the second diode 12b from the voltage value representing the voltage VF across the first diode 12a. _The voltage value representing _ref is subtracted. The difference voltage value Δ obtained by this subtraction
VF represents a change in the temperature of the power MOSFET 11, in other words, a change in the current flowing between the source and the drain. This difference voltage value ΔVF is supplied to the determination circuit 30. The configuration and operation of the discrimination circuit 30 are the same as those of the first embodiment.

Next, the operation of the current detecting device configured as described above will be described.

When an external input signal is supplied from a console switch or the like (not shown), the constant current circuit 20a generates first and second constant currents and supplies them to the first diode 12a and the second diode 12b, respectively. In this state, the power MOSFET 11 operates as a switch. That is, the gate drive circuit 31 changes the gate signal from the L level to the H level and supplies the gate signal to the gate of the power MOSFET 11 and the difference detection circuit 23a.

As a result, the power MOSFET 11 is turned on, and the current from the power supply 13 is changed to the power MOSFET.
The current flows to the load 14 via the source and drain of T11. At this time, since there is always an on-resistance between the source and the drain of the power MOSFET 11, power is consumed by the on-resistance. The excessive heat generated by the consumption of the electric power is conducted to the first diode 12a, and raises the temperature of the first diode 12a over time. As a result, the voltage VF between both ends of the first diode 12a decreases as the temperature rises, as shown in FIG.

The voltage VF between both ends of the first diode 12a is
The difference is supplied to the difference detection circuit 23a. On the other hand,
12b is a voltage between both ends corresponding to the ambient temperature at that time.
VF _refIs output. Voltage VF between both ends_refIs the difference detection
It is supplied to the output circuit 23a.

The difference detection circuit 23a includes the first diode 1
The voltage value from the second diode 12b is subtracted from the voltage value from 2a and output as a difference voltage value ΔVF. Therefore, as shown in FIG. 12, this difference voltage value ΔVF increases with time. This difference voltage value ΔVF
Is supplied to the determination circuit 30.

The determination circuit 30 constantly monitors whether the difference voltage value ΔVF from the difference detection circuit 23a has become larger than the overcurrent reference voltage. And the difference voltage value Δ
When it is determined that VF has become larger than the overcurrent reference voltage, the gate-off signal is activated, and the fact is notified to the gate drive circuit 31. In response, the gate drive circuit 31 changes the gate signal to L level,
The power MOSFET 11 is turned off. This prevents the power MOSFET 11 from being destroyed and prevents an overcurrent from flowing through the load 14.

With the above configuration, the temperature characteristic of the first diode 12a due to the environment, that is, the influence of the temperature of the atmosphere in which the first diode 12a is installed can be offset, so that the amount of change in the temperature from the reference value is always detected. Is done. Since the amount of change and the current flowing through the main path have a one-to-one relationship, the current flowing through the main path, in other words, the current flowing through the load 14 is accurately detected.

As described above, according to the current detecting device according to the third embodiment, the current from the power supply 13 flows through the power MOSFET 11 and the load 14 (the system to be detected). Second diode 12b
A constant current from the constant current circuit 20a flows through the (detection system) independently of the current from the power supply 13. Therefore, since the detection system is not affected by the power supply voltage of the detected system, the current flowing to the load 14 via the power MOSFET 11 can be accurately detected.

Further, since the detected system and the detection system are independent, even if a surge or the like is applied to the detected system (main path), the detection system is not affected. Therefore, the configuration for protecting the detection system is unnecessary or can be simplified. Further, since it is not necessary to insert a resistor in the main path or the branch path as in the related art, a space for mounting the resistor is not required.

Since the current flowing in the main path is detected based on the difference voltage ΔVF, as described in detail in the first embodiment, the first diode 12a
Can be canceled out, and the temperature dependence of the first diode 12a can be eliminated. As a result, when a temperature correction circuit is added to the detection circuit 15a, it is not necessary to consider the temperature dependency of the first diode 12a, and only the temperature correction circuit of the power MOSFET 11 needs to be added, so that the correction circuit is simplified. it can.

Further, according to this current detection device, thermal energy based on the current flowing through the power MOSFET is detected through the thin film. Therefore, even if an impulse current due to noise or the like flows through the detected system, the energy is small. , The difference voltage ΔVF becomes smaller. As a result, the influence of the impulse current on the detection system is reduced, so that a filter for removing noise generated in the power supply can be simplified.

Further, according to this current detection device, the reference voltage for detecting the difference voltage ΔVF is not the voltage value stored in the storage device 21 as in the first and second embodiments, but the reference voltage. Since a voltage value obtained in real time from the two diodes 12b is used, an accurate current value can be detected even when the ambient temperature changes.

(Fourth Embodiment) In a current detection device according to a fourth embodiment of the present invention, a detection element including a resistor and two temperature-sensitive diodes is used. Below,
The following description focuses on the differences from the third embodiment.

As shown in FIG. 13, this current detecting device comprises a detecting element 10c, a power source 13, a load 14, a detecting circuit 1
5b and a control circuit 16a. The detection circuit 15b includes a constant current circuit 20a and a difference detection circuit 23a. Further, the control circuit 16a includes a discrimination circuit 30, a switch control circuit (SW control circuit) 32, and a switch 33.

The detecting element 10a comprises a resistor 17, a first diode 12a and a second diode 12b. The resistor 17 functions as a heating element that generates heat according to the magnitude of the current flowing between both ends. Also, the first
The diode 12a and the second diode 12b correspond to the first temperature sensing element and the second temperature sensing element of the present invention, respectively, and function as current detection elements whose characteristics (for example, voltage) change with temperature.

In the detecting element 10c, the first diode 12a is integrated on the resistor 17 with an electrically insulated thin insulating film having a high thermal conductivity interposed therebetween, and furthermore, the first diode 12a is thermally connected to the resistor 17 and the first diode 12a. The second diode 12b is integrated at a position insulated from the second diode 12b. Thereby, the detection element 10c is realized as a semiconductor in which the heating element, the insulating thin film, the first temperature sensing element, and the second temperature sensing element are integrated. According to this configuration, the first diode 12a
And the main path are electrically insulated, so that noise in the main path does not directly affect the first diode 12a.

The power supply 13 supplies a current to one end of the resistor 17 of the detection element 10c via the switch 33. The other end of the resistor 17 is connected to one end of the load 14.
The other end of the load 14 is grounded. The path from the power supply 13 to the load 14 via the switch 33 and the resistor 17 corresponds to the main path of the present invention.

The configuration and operation of the detection circuit 15b are the same as those of the detection circuit 15b except that the gate signal is generated by the switch control circuit 32.
This is the same as that of the third embodiment.

The configuration and operation of the control circuit 16a are as follows. The gate signal generated by the switch control circuit 32 is
This is the same as that of the second embodiment except that it is supplied to 3a.

Next, the operation of the current detecting device configured as described above will be described.

When an external input signal is supplied from a console switch or the like (not shown), the constant current circuit 20a generates first and second constant currents and supplies them to the first diode 12a and the second diode 12b, respectively. In this state, the switch control circuit 32 changes the gate signal from L level to H level and supplies the gate signal to the switch 33 and the difference detection circuit 23a.

As a result, the switch 33 is turned on,
From the power supply 13 to the switch 33 and the resistor 1 of the detection element 10
A current flows through the load 14 via the switch 7. At this time, power is consumed by the resistor 17. The excessive heat generated by the consumption of the electric power is conducted to the first diode 12a,
The temperature of the diode 12a is increased over time. As a result, the voltage VF between both ends of the first diode 12a
Falls as the temperature rises, as shown in FIG.

The storage device 21 stores the voltage VF across the diode 12 at that time, that is, a voltage value representing the VF reference voltage, and stores the VF reference voltage in synchronization with the rising change of the gate signal. The represented voltage value is supplied to the difference detection circuit 23.

The voltage VF between both ends of the first diode 12a is
The difference is supplied to the difference detection circuit 23a. On the other hand,
12b is a voltage between both ends corresponding to the ambient temperature at that time.
VF _refIs output. This voltage VF between both ends_refIs the difference
It is supplied to the minute detecting circuit 23a.

The difference detection circuit 23a includes the first diode 1
The voltage value from the second diode 12b is subtracted from the voltage value from 2a and output as a difference voltage value ΔVF. Therefore, as shown in FIG. 12, this difference voltage value ΔVF increases with time. This difference voltage value ΔVF
Is supplied to the determination circuit 30.

The determination circuit 30 constantly monitors whether or not the difference voltage value ΔVF from the difference detection circuit 23a has become larger than the overcurrent reference voltage. And the difference voltage value Δ
When it is determined that VF has become larger than the overcurrent reference voltage, the gate-off signal is activated, and the switch control circuit 32 is notified of this. In response to this, the switch control circuit 32 changes the gate signal to L level, and opens the switch 33. Thereby, the load 14
The overcurrent is prevented from flowing.

As described above, according to the current detecting device of the fourth embodiment, the same effects as those of the third embodiment can be obtained.

According to this current detecting device, the conventional problems of space and heat generation are not solved. However, as in the second embodiment, an accurate current can be detected and a protection circuit provided as a peripheral circuit can be provided. Can be simplified.

According to this current detecting device, the reference voltage for detecting the difference voltage ΔVF is not the voltage value stored in the storage device 21 as in the third embodiment, but the second diode 12b. Since a voltage value obtained in real time is used, an accurate current value can be detected even when the ambient temperature changes.

In the above-described fourth embodiment, the switch 33 is provided on the upstream side (the power supply 13 side) of the detection element 10c, but may be provided on the downstream side (the load 14 side) of the detection element 10c. . In this case, the same operation and effect as described above can be obtained.

The current detection devices according to the first to fourth embodiments of the present invention configured as described above can be used to realize a function of preventing pinching in a power window system of an automobile. In this power window system, when a foreign object is caught during the closing operation of the power window, a motor lock current flows to the motor, and when this current value reaches a certain value, the current supply to the motor is cut off. Therefore, the anti-jamming function can be realized by reversing the power window motor upon detecting that the current supply has been interrupted.

When this current detection device is used in a power window system, when the power window is fully closed or fully opened, a motor lock current flows through the detection element and the current supply to the motor is automatically cut off. Therefore, a sensor for full closing or full opening becomes unnecessary. This current detector is
It can also be applied to inrush current control when the lamp is lit and detection of lamp disconnection.

[0131]

As described in detail above, according to the first aspect of the present invention, both ends of the temperature sensing element generated by the constant current supplied from the constant current circuit independently of the current flowing through the main path. Since the current flowing through the power transistor in the main path is detected based on the inter-voltage, there is no influence of the power supply voltage. As a result, the current flowing through the main path can be accurately detected. Further, even if noise is generated in the main circuit, it is not affected by the noise, so that the configuration for protecting the temperature sensing element and its peripheral circuit can be simplified. Further, since the current flowing through the main path is detected based on the difference voltage value, the temperature dependency of the temperature-sensitive element due to the surrounding environment can be eliminated. Furthermore, since no resistor is inserted in series in the main path as in the prior art, there is no problem of mounting space or heat generation.

According to the second aspect of the present invention, whether or not an overcurrent or an overload is detected based on the difference voltage value, and if the overcurrent or the overload is detected, the power transistor is turned off. As a result, in addition to the effect of the first aspect of the present invention, the destruction of the system including the power transistor due to overcurrent or overload can be prevented.

According to the third aspect of the present invention, independently of the current flowing through the main path, the main path is generated based on the voltage between both ends of the temperature sensing element generated by the constant current supplied from the constant current circuit. Since the current flowing through the resistor is detected, it is not affected by the power supply voltage. As a result, the current flowing through the main path can be accurately detected. Further, even if noise is generated in the main circuit, it is not affected by the noise, so that the configuration for protecting the temperature sensing element and its peripheral circuit can be simplified. Also,
Since the current flowing through the main path is detected based on the difference voltage value, it is possible to eliminate the temperature dependency of the temperature sensing element due to the surrounding environment.

According to the fourth aspect of the present invention, whether or not an overcurrent or an overload is detected based on the differential voltage value, and if the overcurrent or the overload is detected, the current flowing through the resistor is detected. Since the cutoff is performed, in addition to the effect of the third aspect of the present invention, it is possible to prevent the system including the resistor from being broken due to the overcurrent or the overload.

According to the fifth aspect of the present invention, since the temperature-sensitive diode is used as the temperature-sensitive element, the temperature-sensitive element can be configured at low cost and small size.

According to the invention of claim 6, in addition to the effect of claim 1 described above, the reference voltage for detecting the differential voltage is as in the invention of claims 1 and 2. Since the voltage value obtained in real time from the second temperature sensing element is used instead of the voltage value stored in the storage device, an accurate current value can be detected even when the ambient temperature changes.

According to the seventh aspect of the present invention, whether or not an overcurrent or an overload is detected based on the differential voltage value, and if the overcurrent or the overload is detected, the power transistor is turned off. As a result, in addition to the effect of the first aspect of the present invention, the destruction of the system including the power transistor due to overcurrent or overload can be prevented.

According to the eighth aspect of the present invention, in addition to the effect of the sixth aspect, the reference voltage for detecting the differential voltage is the same as that of the third and fourth aspects. Since the voltage value obtained in real time from the second temperature sensing element is used instead of the voltage value stored in the storage device, an accurate current value can be detected even when the ambient temperature changes.

According to the ninth aspect of the present invention, whether or not an overcurrent or an overload is detected based on the difference voltage value, and if the overcurrent or the overload is detected, the current flowing through the resistor is detected. Since the cutoff is performed, in addition to the effect of the invention described in claim 8, it is possible to prevent the system including the resistor from being destroyed due to overcurrent or overload.

Furthermore, according to the tenth aspect of the present invention,
Since a temperature-sensitive diode is used as the temperature-sensitive element, the temperature-sensitive element can be configured inexpensively and compactly.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a current detection device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a voltage VF across a diode used in the current detection device shown in FIG. 1 and a gate signal.

FIG. 3 is a diagram for explaining a normal operation region and a destruction region of a general semiconductor element.

4 is a diagram showing a relationship between a voltage VF between both ends of a diode and a current Id flowing through a main path when a power supply voltage is changed in the current detection device shown in FIG.

5 is a diagram showing a relationship between a difference voltage ΔVF and a current Id flowing through a main path when the power supply voltage is changed in the current detection device shown in FIG.

6 is a diagram showing temperature characteristics of a voltage VF across the diode at a plurality of ambient temperatures in the current detection device shown in FIG. 1;

7 is a diagram showing temperature characteristics of a differential voltage ΔVF at a plurality of ambient temperatures of a detection element used in the current detection device shown in FIG.

8 is a diagram illustrating a power MO in the current detection device shown in FIG.
FIG. 3 is a diagram illustrating a relationship between power consumed by an SFET and current.

FIG. 9 is a block diagram illustrating a configuration of a current detection device according to a second embodiment of the present invention.

FIG. 10 is a block diagram illustrating a configuration of a current detection device according to a third embodiment of the present invention.

FIG. 11 is a diagram for explaining temperature characteristics of a general diode.

12 is a diagram showing a relationship among a voltage VF between both ends of a diode used in the current detection device shown in FIG. 10, a difference voltage ΔVF, and a gate signal.

FIG. 13 is a block diagram illustrating a configuration of a current detection device according to a fourth embodiment of the present invention.

[Explanation of symbols]

 10, 10a, 10b, 10c Detection element 11 Power MOSFET 12 Diode 12a First diode 12b Second diode 13 Power supply 14 Load 15, 15a, 15b Detection circuit 16, 16a Control circuit 17 Resistor 20, 20a Constant current circuit 21 Storage device Reference Signs List 22 voltage control circuit 23, 23a difference detection circuit 30 discrimination circuit 31 gate drive circuit 32 switch control circuit 33 switch

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Makiko Hisaga 1500 Onjuku 1500, Susono City, Shizuoka Prefecture Inside (72) Inventor Ryo Serizawa 1500 Onjuku 1500, Susono City, Shizuoka Prefecture F-term (reference) 2G032 AA10 AB19 AC03 AD01 AK11 AL14 2G035 AA20 AA26 AB02 AC08 AC15 AD02 AD04 AD07 AD23 AD26 AD56 5F038 AR00 AV04 AV06 AV13 AZ08 AZ10 BH04 BH16 CD16 DF01 DF05 DF06 DT12 DT17 DT18 EZ20

Claims (10)

[Claims] 1. A power transistor inserted in series in a main path through which a current to be detected flows, a temperature-sensitive element provided in parallel with the power transistor via an insulating thin film and having a characteristic that changes according to temperature, A constant current circuit that supplies a constant current to the temperature sensing element independently of a current flowing through the main path; and a storage device that stores a voltage value between both ends of the temperature sensing element when the power transistor is turned on. A voltage detection circuit for detecting a voltage value between both ends of the temperature sensing element while the power transistor is turned on; a voltage value stored in the storage device and a voltage value detected by the voltage detection circuit And a difference detection circuit for detecting a difference voltage value between the first and second signals and detecting a current flowing through the main circuit based on the difference voltage value. 2. The current detection device according to claim 1, further comprising a control circuit for turning off the power transistor when a difference voltage value from the difference detection circuit exceeds a predetermined value. . 3. A resistor inserted in series in a main path through which a current to be detected flows, a temperature-sensitive element provided in parallel with the resistor via an insulating thin film and having a characteristic that changes according to temperature, A constant current circuit that supplies a constant current to the temperature sensitive element independently of a current flowing through the main path; and a voltage value between both ends of the temperature sensitive element when current supply to the resistor is started. A storage device, a voltage detection circuit that detects a voltage value between both ends of the temperature sensing element while current supply to the resistor is continued, a voltage value stored in the storage device, and the voltage detection circuit A difference detection circuit that detects a difference voltage value from the voltage value detected in step (a) and detects a current flowing through the main circuit based on the difference voltage value. 4. The current according to claim 3, further comprising a control circuit for interrupting a current flowing through the resistor when a difference voltage value from the difference detection circuit exceeds a predetermined value. Detection device. 5. The current detection device according to claim 1, wherein the temperature sensing element is a temperature sensing diode. 6. A power transistor inserted in series in a main path through which a current to be detected flows, and a first temperature-sensitive element having a characteristic that changes in accordance with temperature, provided in parallel with the power transistor via an insulating thin film. A second temperature-sensitive element, which is thermally insulated and provided with the first temperature-sensitive element, and whose characteristics change in accordance with temperature; and the first temperature-sensitive element and the current independent of the current flowing through the main path. A constant current circuit for supplying a constant current to the second temperature sensing element; detecting a difference voltage value between a voltage value stored in the storage device and a voltage value detected by the voltage detection circuit; And a difference detection circuit for detecting a current flowing through the main circuit based on the current detection device. 7. The current detection device according to claim 6, further comprising a control circuit for turning off the power transistor when a difference voltage value from the difference detection circuit exceeds a predetermined value. . 8. A resistor inserted in series in a main path through which a current to be detected flows, and a first temperature-sensitive element having a characteristic that changes according to temperature, which is provided in parallel with the resistor via an insulating thin film. A second temperature-sensitive element, which is thermally insulated and provided with the first temperature-sensitive element, and whose characteristics change in accordance with temperature; and the first temperature-sensitive element and the current independent of the current flowing through the main path. A constant current circuit for supplying a constant current to the second temperature sensing element; detecting a difference voltage value between the voltage value stored in the storage device and the voltage value detected by the voltage detection circuit; And a difference detection circuit for detecting a current flowing in the main circuit based on the current detection device. 9. The current according to claim 8, further comprising a control circuit for interrupting a current flowing through the resistor when a difference voltage value from the difference detection circuit exceeds a predetermined value. Detection device. 10. The temperature sensing diode according to claim 6, wherein the first temperature sensing element and the second temperature sensing element are temperature sensing diodes.
The current detection device according to any one of the above.