JP3203521B2 - Load disconnection detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for detecting a disconnection of a load, and can be used, for example, in a driver circuit for driving a solenoid or an electric motor as a load to detect a failure due to the disconnection.

[0002]

2. Description of the Related Art For example, in various on-vehicle electronic devices,
Since the failure of the device adversely affects the driving operation, when a failure occurs, it is desirable to automatically detect the failure and notify the driver that the abnormality has occurred. For this reason, in-vehicle electronic devices often include various abnormality detection circuits.

[0003] By the way, abnormalities that are likely to occur in the on-vehicle electronic device include a solenoid or an electric motor connected to the output of the device.
Short-circuit or disconnection at the point Conventionally, an output stage of a drive circuit is configured as shown in FIG. 2, for example, to detect disconnection of a load. That is, the disconnection detection circuit identifies whether or not the potential difference between one end of the load and the power supply line (Vdd) is equal to or greater than a predetermined value, and detects whether or not the load is disconnected. Further, a resistor Ri is connected in series to the power transistor PT for switching the load, and the current limiting circuit detects a load current based on a voltage drop at the resistor Ri, and detects a short circuit or the like in the load. Prevent overcurrent. The disconnection detection circuit
A voltage between terminals of a series circuit of the resistor Ri and the transistor PT is detected. That is, when the load is normally connected, the potential difference input to the disconnection detection circuit depends on the same voltage as Vdd when PT is off, and on the magnitude of the load current and the resistance value of the resistor Ri when PT is on. The voltage Von (for example, 0.
7V) and when the load is disconnected,
It becomes 0V regardless of off.

[0004]

Actually, in a current limiting circuit and a disconnection detecting circuit as shown in FIG. 2, a potential difference to be detected is applied between a base and an emitter of a transistor.
The magnitude of the potential difference is detected by turning on / off the transistor. However, to turn on the transistor,
Normally, a voltage of about 0.6 V needs to be applied between the base and the emitter. Therefore, in order to reliably determine whether the voltage when the power transistor PT is on is normal (Von) or not (0 V), the voltage Von needs to be sufficiently large (more than 0.6 V). Therefore, the power consumption by the resistor Ri becomes so large that it cannot be ignored, and the power consumption increases with the addition of the disconnection detection function.

Accordingly, an object of the present invention is to provide a disconnection detecting circuit which consumes less power.

[0006]

In order to solve the above-mentioned problems, in the present invention, there is provided an energization control means connected between a load and a power supply for controlling energization of the load; connected in parallel with the energization control means First transistor means; emitter
Second transistor means terminal and the base terminal is connected to the emitter terminal and the base terminal of each of the first transistor means; emitter terminal and base - the scan terminals each second transistor means base - scan terminals and the collector A third transistor connected to the terminal; a constant current source for supplying a constant current to the collector terminal of the second transistor; and a detector for detecting the magnitude of the collector current of the third transistor. .

[0007]

In the disconnection detecting circuit according to the present invention, the first transistor means, the second transistor means, the third transistor means and the constant current source constitute a so-called current mirror circuit. Since the constant current source supplies a predetermined collector current to the second transistor means, the same current tends to flow to the collector of the first transistor means. This current flows through the load connected thereto regardless of the on / off of the conduction control means (for example, a power transistor). However, when the load is disconnected, the collector current of the first transistor means becomes zero.
To the base terminal of the transistor means. That is, the base current of the first transistor means greatly changes depending on whether or not the load is disconnected. This change in current has a large change in the collector current of the third transistor means, and the change is detected by the detection means. That is, the disconnection of the load can be detected by the detecting means.

According to the present invention, whether or not a current can flow through the load is detected by the first transistor means. Therefore, a resistor (Ri in FIG. 2) for detecting the magnitude of the load current is provided. There is no need to connect in series with the load, and power consumption for disconnection detection can be extremely small.

[0009]

FIG. 1 shows a circuit configuration of a power device unit having a disconnection detecting circuit according to an embodiment. Referring to FIG. 1, this power device unit has six terminals 1,
2, 3, 4, 5 and 6 are provided. Terminal 1 is a power supply line to which a DC voltage Vcc (for example, 5 V) is applied.
Is a power supply line to which a DC voltage Vdd (for example, 12 V) is applied, and terminal 3 is connected to an output terminal of the control device. A load 7 (for example, a solenoid or an electric motor) is connected to the terminals 4 and 5. From the terminal 6, an electric signal indicating whether or not the load 7 is disconnected is output.

A power transistor PT is connected between terminals 3 and 4, and a control input terminal (gate) of PT.
Are connected to the terminal 3. Although an FET is used as the power transistor PT in this example, it may be replaced with a general transistor element. A transistor Q2 is connected to the terminals 3 and 4 in parallel with the power transistor PT. Further, the base terminal and the emitter terminal of the transistor Q1 are connected to the base terminal and the emitter terminal of the transistor Q2, respectively. The base terminal and the collector terminal of the transistor Q1 are connected to the emitter terminal and the base terminal of the transistor Q3, respectively.
Terminal is connected. Further, a constant current source CC is connected between the collector terminal of the transistor Q1 and the terminal 5 of the unit. A resistor R1 is connected between the collector terminal of the transistor Q3 and the terminal 5 of the unit,
The collector terminal of Q3 is connected via a resistor R2 to the base terminal of transistor Q4. The transistor Q4 has an emitter terminal connected to the terminal 5 of the unit,
The collector terminal is connected to the terminal 1 of the unit via the resistor R3.
(Vcc), and the collector terminal is further connected to the terminal 6 (disconnection detection output) of the unit.

The transistors Q1 and Q2 form a current mirror circuit. The collector of the transistor Q1 is equal to the current i3 determined by the constant current source CC (Q3
The same current flows if the base current is ignored, and an equivalent current will also flow to the collector of the transistor Q2. This current i5 can flow through the load 7 if the load 7 is normally connected between the terminals 4-5. However, if the load 7 is disconnected or is about to be disconnected and its resistance value is abnormally high,
The current i5 does not flow. However, even when the collector current i5 does not flow through the transistor Q2, the emitter-base voltage of the transistor Q1 is applied between the emitter and the base of the transistor Q2. When the collector current i5 of Q2 decreases, the base current i2 of Q2 increases by the decrease. The base current i1 of the transistor Q1 and the base current i2 of the transistor Q2 flow from the emitter terminal to the collector terminal of the transistor Q3. However, while i1 is almost constant, i2
Greatly changes in accordance with the presence or absence of the disconnection of the load 7, the collector current i4 of the transistor Q3 changes in response to the presence or absence of the disconnection of the load, and the change appears as a change in the voltage between the terminals of the resistor R1. . The voltage between the terminals of the resistor R1 is
Since the voltage is applied to the base terminal of the transistor Q4 via the resistor R2, the collector current of the transistor Q4 changes depending on whether the load 7 is disconnected, and the collector voltage also changes. The collector voltage of Q4 is connected to terminal 6 as a disconnection detection output.
Output from

For example, if the current i3 is 50 [μA], the current amplification factors hfe of the transistors Q1 and Q2 are both 100, and the resistance value of the resistor R1 is 15 [KΩ], when the load 7 is normal, When the current i5 is 50 [μA], i1 and i
2 becomes 0.5 [μA], i4 becomes about 1 [μA], and the voltage (voltage drop) between the terminals of R1 becomes 0.015 [V]. However, when the load 7 is disconnected and the current i5 becomes zero, i1 becomes 0.5 [μA]. [ΜA]
Does not change, but since i2 increases to 50 [μA], i
4 becomes approximately 50.5 [μA], and the voltage between terminals of R1 is 0.76
[V]. The transistor Q4 is turned on / off by the change in the voltage between the terminals of the resistor R1, and the signal level of the disconnection detection output changes. That is, when the load 7 is normal, the transistor Q4 turns off and the signal of the disconnection detection output goes to a high level H (equivalent to Vcc). However, when the load is disconnected, the transistor Q4 turns on and the signal of the disconnection detection output goes to a low level. L
(0 V).

In any case, in this disconnection detection, whether or not the connection of the load 7 is normal is determined by whether or not the collector current i5 of the transistor Q2 flows.
The presence / absence of disconnection can be detected at any time regardless of the on / off state of the power transistor PT, and there is no need to directly detect the large current i7 (or i6) flowing through the load 7, so that it is required for disconnection detection. Power consumption is very small.

In the above embodiment, only the configuration relating to disconnection detection is shown. However, in an actual apparatus, it is desirable to add a protection circuit against load short-circuit and an abnormality detection circuit. When detecting an abnormality related to a load short circuit, for example, as shown in Japanese Patent Application Laid-Open No. 63-187604, it is determined whether or not the load is normal by discriminating the voltage between the terminals of the load when the output transistor is turned on. Can be identified.

[0015]

As described above, according to the present invention, the disconnection of the load can be detected by a circuit with very low power consumption, the circuit configuration is simple, and it is independent of the on / off of the power supply control means (PT). The presence or absence of disconnection can be detected at any time.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing a circuit configuration of a power device unit including a disconnection detection circuit according to an embodiment.

FIG. 2 is a block diagram showing a configuration of an output circuit of a conventional device.

[Explanation of symbols]

 1 to 6: terminal 7: load Q1: transistor (second transistor means) Q2: transistor (first transistor means) Q3: transistor (third transistor means) Q4: transistor (detection means) PT: power transistor (Electrification control means) CC: constant current source R1 to R3: resistor i1 to i7: current

Claims (1)

(57) [Claims] An electric power supply control means connected between a load and a power supply for controlling energization of the load; a first transistor means connected in parallel with the electric power supply control means; an emitter terminal ;
Second transistor means for a base terminal connected to e <br/> emitter terminal and the base terminal of each of the first transistor means; emitter terminal and base - the scan terminals each of the second transistor means base - scan Third transistor means connected to the terminal and the collector terminal; a constant current source for supplying a constant current to the collector terminal of the second transistor means; and detecting means for detecting the magnitude of the collector current of the third transistor means. A load disconnection detection circuit comprising: