JP3642699B2 - DC stabilized power circuit protection circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a protection circuit for a DC stabilized power supply circuit.
[0002]
[Prior art]
FIG. 5 shows a conventional DC stabilized power supply circuit and its protection circuit. Q1 is a PNP output transistor, the emitter of which is connected to the DC power supply input terminal 1 and the collector of which is connected to the output terminal 2. The base is connected to the collector of an NPN type drive transistor Q2.
[0003]
An error amplifier 3 compares the reference voltage generated in the reference voltage circuit 4 with the voltage at the node a and drives the drive transistor Q1 by the difference voltage. The voltage at the node a is obtained by dividing the output voltage Vo by the resistors R1 and R2, and its value changes according to the change of the output voltage Vo. By controlling the output transistor Q1 through the transistor Q2 by the output of the error amplifier 3, the output voltage Vo can be held at a predetermined value.
[0004]
The resistor R3 connected between the emitter and the base of the output transistor Q1 is provided to prevent the output transistor Q1 from malfunctioning due to a leakage current at a high temperature of the drive transistor Q2 or the like. For example, when the junction temperature of the transistors constituting the heat protection circuit 5 reaches 150 ° C., the heat protection circuit 5 becomes conductive, and the base voltage of the transistor Q2 is dropped to the ground voltage, so that the transistor Q2 is turned off. As a result, the output transistor Q1 is also turned OFF and the collector current of the transistor Q1 hardly flows. However, if there is no resistor R3, if there is a leak in the drive transistor Q2, the leak current becomes a pseudo drive current of the transistor Q1, and the output transistor The current multiplied by the current amplification factor h _fE by Q1 flows to the collector of the output transistor Q1.
[0005]
However, if the resistor R3 exists, the leakage current flows to the resistor R3 side. If the voltage drop at the resistor R3 due to the leakage current does not reach the base-emitter voltage V _BE of the output transistor Q1, the output transistor Q1 will not conduct, so that malfunction can be prevented even if there is a leak.
[0006]
When a large capacitance is connected to the output side of the output transistor Q1, if the input side voltage is cut off, the output side voltage becomes higher than the input side, and a reverse current I ₁ ′ flows through the resistor R3. The output transistor Q1 causes reverse transistor operation (current flows from the collector to the emitter side). When this reverse transistor operation occurs, the output transistor Q1 may be destroyed. In order to prevent this destruction, the protection diode D inserted with the illustrated polarity is required.
[0007]
[Problems to be solved by the invention]
By the way, a recent DC stabilized power supply circuit having a low current consumption is demanded. As the basis for this, for example, it is possible to cope with the expansion of the operation time of battery-driven devices such as mobile phones and PHS. This low current consumption is very important because it leads to an extension of the standby time of the mobile phone.
[0008]
However, in the above conventional DC stabilized power supply circuit, since the protective resistor R3 for preventing malfunction due to heating is provided, the consumption current I ₁ is
I ₁ = V _BE (Q1) / R3
Has only increased. Here, V _BE (Q1) is the base-emitter voltage of the output transistor Q1.
[0009]
The current I ₁ given by the above equation needs to be about 10 μA at a high temperature. Since I ₁ has a negative temperature characteristic, I ₁ at a normal temperature is about 30 μA. Since the current consumption at no load in the entire DC stabilized power supply circuit is about 150 μA, the ratio occupied by this current I ₁ is large, which causes a large power loss.
[0010]
The present invention has been made in view of these points, and an object of the present invention is to provide a stabilized DC power supply circuit capable of effectively performing the above-described heating protection and reverse withstand voltage protection with a small no-load current.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, the emitter of the PNP output transistor is connected to the power input terminal, the collector is connected to the output terminal, the drive transistor is connected to the base, and the drive transistor is connected via the drive transistor. an output transistor from the power input terminal for preventing the malfunction due to the leakage current of the drive transistor when nonconductive DC stabilized power supply circuit is the drive transistor so as to control on the basis of the voltage information of the output terminal Te A unidirectional conductive element for measuring the leakage current of the drive transistor and a temperature detection circuit are provided on the base side of the output transistor, and the conduction / non-conduction of the unidirectional conductive element is controlled by the output of the temperature detection circuit. In the protection circuit of the stabilized DC power supply circuit, the temperature detection The road characterized in that the junction temperature of the drive transistor to control the unidirectional conductive elements to Hakaro the leakage current of the drive transistor in the above normal temperature.
[0012]
By using a unidirectional conductive element, the current during conduction can be kept small. Further, by using the unidirectional conductive element, a bias current that reversely operates the output transistor does not flow.
[0015]
According to a second aspect of the present invention, in the protection circuit for the DC stabilized power supply circuit according to the first aspect, the reference output voltage from the temperature detection circuit is directly applied to the base, and the threshold value is set according to the temperature rise. The collector output of the first transistor is used to control the conduction / non-conduction of the one highly conductive element, and the collector output of the second transistor is the drive output of the drive transistor. The transistor is used to control conduction / non-conduction of a transistor.
[0016]
According to a third aspect of the present invention, the unidirectional conductive element is a PNP transistor having an emitter connected to the emitter of the output transistor and a collector connected to the base of the transistor.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1 showing the first embodiment of the present invention, the same parts as those in the conventional example of FIG. In the present embodiment, malfunction prevention and reverse breakdown voltage protection due to high temperature leakage are configured by a single circuit (high temperature leak malfunction prevention / reverse breakdown voltage protection circuit) 7. Reference numeral 6 denotes a temperature detection circuit.
[0019]
FIG. 2 specifically shows the heating protection circuit 5 and the high temperature leakage malfunction / reverse breakdown voltage protection circuit 7 in the circuit of FIG. In FIG. 2, the heat protection circuit 5 includes resistors R4 and R5, a PNP transistor Q3, and an NPN transistor Q4.
[0020]
One end of the resistor R4 is connected to the input terminal 1, and the other end is connected to the temperature detection circuit 6. The transistor Q3 has an emitter connected to the input terminal 1, a base connected to the connection node (A) of the temperature detection circuit 6 and the resistor R4, and a collector connected to the ground terminal 8 via the resistor R5.
[0021]
The base of the transistor Q4 is connected to the connection node (B) of the collector of the transistor Q3 and the resistor R5, and the emitter is connected to the ground terminal 8. The collector is connected to the base of the drive transistor Q2.
[0022]
The high-temperature leakage malfunction prevention / reverse withstand voltage protection circuit 7 is composed of a current mirror circuit composed of two PNP transistors Q5 and Q6. The transistor Q5 on the input side of the current mirror circuit has an emitter connected to the input terminal 1 and a base. And the collector are connected to the temperature detection circuit 6.
[0023]
The emitter of the transistor Q6 on the output side of the current mirror circuit is connected to the input terminal 1, and the collector is connected to the base of the output transistor Q1 and the collector of the drive transistor Q2. The base of transistor Q6 is connected to the base of transistor Q5.
[0024]
When the temperature detection voltage in the temperature detection circuit 6 becomes lower than the reference voltage supplied from the reference voltage circuit 4, the temperature detection circuit 6 becomes conductive and the voltage at the node (A) decreases, so that the transistor Q3 is turned on. As a result, the voltage at the node (b) rises and the transistor Q4 is turned on. As a result, the base voltage of the drive transistor Q2 falls to the ground voltage, and the drive transistor Q2 is fixed to the OFF state.
[0025]
At this time, even if a leak current flows through the drive transistor Q2, the leak current does not become the base current of the output transistor Q1. This is because the transistors Q5 and Q6 are separately turned on by the output of the temperature detection circuit 6, so that the leakage current of the drive transistor Q2 flows as the collector current of the transistor Q6 and bypasses the output transistor Q1.
[0026]
At this time, the emitter-collector voltage of the transistor Q6 may be considered to be almost zero. Therefore, no conduction bias is applied between the emitter and base of the output transistor Q1, and the transistor Q1 remains OFF. Thus, the malfunction (ON) of the output transistor Q1 due to the leakage current of the drive transistor Q2 and the like during heating (at high temperature) is prevented.
[0027]
Next, when a large capacity is connected to the load and the input side is cut off, the output transistor Q1 does not reversely operate. That is, at this time, even if the transistor Q6 is OFF or ON, no current flows to reversely operate the transistor Q1. That is, since there is no means (the resistor R5 in FIG. 5) for supplying a current that causes the transistor Q1 to operate in reverse, the transistor Q1 does not perform reverse operation. Therefore, it is not necessary to connect the protective diode D between the emitter and the collector as in the prior art.
[0028]
Next, FIG. 3 specifically shows the temperature detection circuit 6 in the circuit of FIG. Here, the temperature detection circuit 6 includes NPN transistors Q7 and Q8 and a resistor R7. The base of the transistor Q7 is connected to the reference voltage circuit 4, and the reference voltage Vref is applied. The transistor Q8 has a diode configuration in which a collector and a base are coupled, and an emitter thereof is connected to the ground terminal 8 via a resistor R7, and a collector and a base are connected to an emitter of the transistor Q7 and an emitter of the transistor Q9. Yes. Note that a capacitor C is connected to the output terminal 2, and a load 100 is also connected.
[0029]
If the temperature is lower than a predetermined value, the thresholds of transistors Q7 and Q9 (transistor V _F ) do not drop sufficiently, so that transistors Q7 and Q9 cannot be turned on by reference voltage Vref. Therefore, the current mirror circuit (Q5, Q6) is OFF. For this reason, the current I _C does not flow. At this time, if the capacitor C connected to the output terminal 2 is not fully charged, the voltage of the node a is lower than the reference voltage Vref, so that the output of the error amplifier 3 becomes high level and the drive transistor Q2 becomes conductive. As a result, the output transistor Q1 also conducts. Capacitor C is fully charged by the collector current of transistor Q1.
[0030]
When the load 100 connected to the output terminal 2 is in a no-load state, when the capacitor C is fully charged, the output of the error amplifier 3 becomes low level, the drive transistor Q2 is turned off, and the output transistor Q1 is also turned off. Become. In this case, if the temperature is low, it may be considered that no leak current is generated in the drive transistor Q2 or the like. Therefore, the output transistor Q1 does not malfunction.
[0031]
When the load 100 connected to the output terminal 2 operates and a load current flows, the voltage of the capacitor C decreases, so that the drive transistor Q2 is turned on and the output transistor Q1 is also turned on to charge the capacitor C.
[0032]
Next, when the temperature becomes higher than a predetermined value (during heating), the threshold values of the transistors Q7 and Q9 are lowered, and when these transistors Q7 and Q9 are turned ON, the transistor Q3 is turned ON and current flows through the resistor R5. The transistor Q4 is turned ON, and the base of the drive transistor Q2 is clamped to the ground voltage.
[0033]
For this reason, the drive transistor Q2 is turned off, and the output transistor Q1 is also turned off. At this time, a leak current at a high temperature may flow to the drive transistor Q2. However, at this time, since the transistor Q9 is also ON and the current mirror circuit (Q5, Q6) is ON, the current I _C flows from the emitter to the collector of the transistor Q6, which flows to the drive transistor Q2, and cancels the leakage current. To do.
[0034]
The current I _C is smaller than the current flowing in the conventional resistor R3 (see FIG. 5), and does not flow in a steady state (below a predetermined temperature), so that the current consumption can be reduced. Further, temperature detection for operating the high temperature leakage malfunction / reverse breakdown voltage protection circuit 7 (current mirror circuit) is performed by the transistors Q8 and Q9, and temperature detection for operating the overvoltage protection circuit is also performed by the transistors Q8 and Q9. As described above, since the temperature detection circuit is almost shared, the circuit configuration for temperature detection is reduced correspondingly, which contributes to cost reduction.
[0035]
FIG. 4 shows current consumption characteristics in which the horizontal axis represents the transistor junction temperature Tj (° C.) and the vertical axis represents the current flowing through the protection circuit. Here, α is the current consumption characteristic of the conventional example (FIG. 5), and Ia, Ib, and Ic indicate the current consumption flowing in the protection circuit of the embodiment (FIG. 4) of the present invention. From this, it can be seen that the currents Ia, Ib, and Ic in this embodiment can be much smaller than the conventional current α even if they are totaled.
[0036]
【The invention's effect】
As described above, according to the present invention, the current consumption can be significantly reduced as compared with the conventional example, so that the operation time of battery-powered devices such as mobile phones and PHS can be extended. In particular, this low current consumption is very effective because it leads to an extension of the standby time in a mobile phone. Further, by using a unidirectional conductive element, the current during conduction can be easily kept small. In addition, since a bias current that reversely operates the output transistor does not flow by using a unidirectional conductive element, a protection diode is provided between the emitter and collector of the output transistor to prevent reverse operation breakdown as in the prior art. I don't need it.
[0037]
According to the second aspect of the present invention, since one temperature detection circuit is commonly used for temperature detection for unidirectional conductive element control and temperature detection for drive transistor control, a circuit for temperature detection correspondingly. The configuration is reduced and the cost can be reduced. In addition, since the output voltage of the reference voltage circuit is directly applied to the bases of the first and second transistors of the temperature detection circuit, for example, compared with a circuit that is applied via a voltage dividing resistor, for example. Less power consumption during standby.
[0038]
In the invention of claim 3 , since the unidirectional conductive element has an emitter connected to the emitter of the output transistor and a collector connected to the base of the transistor, it is easy to apply a control signal to the base. Since the ON / OFF can be controlled and the current mirror circuit can be configured as a part of the current mirror circuit as described in the embodiment, the current value can be easily controlled.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a protection circuit of a DC-stabilized power supply circuit according to an embodiment of the present invention. FIG. 2 is a circuit configuration diagram specifically showing a part of the protection circuit. FIG. Fig. 4 is a circuit diagram showing a current consumption characteristic with respect to temperature according to a conventional example and the present invention. Fig. 5 is a circuit diagram showing a protection circuit of a conventional DC stabilized power supply circuit.
DESCRIPTION OF SYMBOLS 1 Input terminal 2 Output terminal 3 Error amplifier Q1 Output transistor Q2 Drive transistor 4 Reference voltage circuit 5 Heating protection circuit 6 Temperature detection circuit 7 High temperature leak malfunction prevention / reverse breakdown voltage protection circuit Q5, Q6 Transistor constituting current mirror circuit

Claims (3)

The emitter of the PNP output transistor is connected to the power input terminal, the collector is connected to the output terminal, the drive transistor is connected to the base, and the output transistor is controlled based on the voltage information of the output terminal via the drive transistor. In order to prevent the stabilized DC power supply circuit from malfunctioning due to the leakage current of the drive transistor when the drive transistor is not in operation, the leakage current of the drive transistor is reduced from the power input terminal to the base side of the output transistor. In a protection circuit for a DC-stabilized power supply circuit in which a unidirectional conductive element to be measured and a temperature detection circuit are provided, and conduction / non- conduction of the unidirectional conductive element is controlled by an output of the temperature detection circuit .
A protection circuit for a DC stabilized power supply circuit, wherein the temperature detecting circuit controls the unidirectional conductive element so as to track the leakage current of the drive transistor when the junction temperature of the drive transistor is equal to or higher than room temperature. The temperature detection circuit includes first and second transistors whose reference output voltage from the reference voltage circuit is directly applied to the base and whose threshold value decreases as the temperature rises. The collector output of the first transistor And the collector output of the second transistor is used to control the conduction / non-conduction of the drive transistor. The protection circuit for the DC stabilized power supply circuit according to 1. 3. The DC stable transistor according to claim 1, wherein the unidirectional conductive element is a PNP type transistor having an emitter connected to an emitter of the output transistor and a collector connected to a base of the transistor. Power supply circuit protection circuit.

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