JPH0142054Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a failure mode discrimination circuit, and more particularly to a mode discrimination circuit that discriminates between a short circuit in a power transistor and a disconnection in a load in a solenoid drive device.

In recent years, with the rapid development of electronic technology, there is a tendency for various devices to be controlled by microcomputers. In this case, since the output signal of the microcomputer is extremely small, this signal cannot be used as it is to drive a load such as a solenoid. Therefore, in a control system using a microcomputer, a power transistor controlled by the microcomputer is provided, and the output of this power transistor is used to drive a load.

In this case, if the power transistor is short-circuited or the load is disconnected for some reason,
Problems may occur such as incorrect control or damage to other electrical components. Therefore, in a control system using such a microcomputer, a failure mode discrimination circuit is provided that constantly monitors the power transistor and load in series, and switches to fail-safe control as soon as a failure occurs. .

FIG. 1 is a circuit diagram showing an example of a conventionally commonly used failure mode discrimination circuit, particularly when applied to a solenoid drive circuit. In the figure, Q ₁ is a transistor connected between the power supply +V and ground via resistors R ₁ and R ₂ , and has a base input of a control signal A supplied from a microcomputer (not shown). Q ₂ is a power transistor whose base input is the signal at the voltage dividing point of resistors R ₁ and R ₂ , and Z is a solenoid as a load, which is connected between the power supply +V and ground via the power transistor Q ₂ . There is. _R3 is a pull-up resistor connected in parallel to power transistor _Q2 .

In the circuit configured as described above, since the control signal A is normally "L", the transistor _Q1 is turned off, and the power supply +V is connected to the power transistor Q through the resistor _R1 . ₂ , the power transistor Q ₂ is turned off and the solenoid Z remains inactive. In this case, the solenoid Z has its internal resistance r
pull-up resistor with a sufficiently large value for
Because it is connected to the power supply +V via R ₃ ,
If the power transistor _Q2 is off and the solenoid Z is not disconnected, the discrimination signal B taken out from point b becomes "L", indicating normality. Next, when a short-circuit accident occurs in the power transistor _Q2 for some reason, the discrimination signal B output from point b becomes "H", indicating that a failure has occurred. Also, if solenoid Z is disconnected,
Even if the power transistor _Q2 is off, the discrimination signal B output from point b is connected to the pull-up resistor _R3.
It becomes "H" due to the power supplied through the circuit, indicating that a failure has occurred. Therefore, by determining the "H" state of the discrimination signal B during the "L" period of the control signal A, the microcomputer can know that a failure has occurred in the power transistor _Q2 or the solenoid Z, and can detect this. Along with this, the system is switched to fail-safe control.

However, in the circuit configured as described above, the discrimination signal B becomes "H" when the power transistor _Q2 is short-circuited, and also becomes "H" when the solenoid Z as a load is disconnected. Therefore, in the above configuration, the discrimination signal B
A microcomputer that receives as input can only confirm that either a short circuit in the power transistor _Q2 or a disconnection in the solenoid as a load has occurred, but it cannot determine at all which type of failure is occurring. . However, in the case of a short-circuit accident in the power transistor Q ₂ and a disconnection accident in the solenoid Z as a load, the fail-safe control is often completely reversed, and in such cases, there is a problem that reliable fail-safe control cannot be performed. have.

Therefore, the failure mode discrimination circuit according to the present invention is as follows:
It is an object of the present invention to provide a failure mode discrimination circuit that can reliably and easily discriminate between a short circuit of a power transistor provided for driving a load and a disconnection of the load when a failure occurs.

In order to achieve such an objective, the present invention provides that when a discrimination signal indicating a failure is generated, the state of the discrimination signal is determined when the discrimination signal is connected to the other pole side via a resistor. This is to determine the failure mode. EMBODIMENT OF THE INVENTION Hereinafter, the failure mode discrimination circuit according to the present invention will be explained in detail using an embodiment shown in the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the failure mode discrimination circuit according to the present invention, and the same parts as in FIG. 1 are indicated using the same symbols. In the same figure
_Q3 is a transistor connected in parallel through a resistor _R4 , and is turned on by the discrimination control signal C sent from a microcomputer (not shown) when the discrimination signal B is "H". And this resistance
The resistance value of _R4 is set to be sufficiently large with respect to the internal resistance r of the solenoid Z, and sufficiently small with respect to the pull-up resistor _R3 .

In the circuit configured as described above, if a short circuit in the power transistor _Q2 or a disconnection accident in the solenoid Z occurs when the control signal A is at "L", the discrimination signal B becomes "H" as described above. Therefore, the microcomputer (not shown) detects that a failure has occurred from the mismatch between the control signal A and the determination signal B, and shifts to a failure determination mode. When the microcomputer shifts to the discrimination mode, an “H” level discrimination control signal C is generated and the transistor
Supplied on the base of Q ₃ . As a result, transistor _Q3 is turned on by the discrimination control signal C,
This causes point b to be grounded via resistor _R4 . In this case, the value of resistor R ₄ is set to a value sufficiently smaller than the value of pull-up resistor R ₃ as described above, so if transistor Q ₂ is short-circuited, point b will be at the power supply voltage. Accordingly, the discrimination signal B becomes "H". Also,
If the solenoid Z is disconnected, the determination signal B becomes "L" because the point b is grounded by the resistor _R4 . Therefore, the failure mode can be easily determined by identifying the state of the determination signal B in the failure determination mode. In other words, "H" of the discrimination signal B when the discrimination control signal C is "H" indicates a short circuit in the power transistor _Q2 , and "L" of the discrimination signal B indicates a disconnection of the solenoid Z. FIG. 3 shows a flowchart of such failure determination.

Incidentally, as in the conventional case, an open failure of the power transistor _Q2 is determined by detecting the "L" state of the discrimination signal B when the control signal A is "H".

As explained above, the failure mode discrimination circuit according to the present invention is an excellent method that can reliably discriminate between a short circuit of a power transistor and a disconnection of a load in a series body of a power transistor and a load, despite its simple configuration. have an effect.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a conventional failure mode discrimination circuit, Fig. 2 is a circuit diagram showing an embodiment of the failure mode discrimination circuit according to the present invention, and Fig. 3 shows the operation of the circuit shown in Fig. 2. This is a flowchart. Q ₁ , Q ₃ ... transistor, Q ₂ ... power transistor, Z ... solenoid, R ₁ to _{R 4} ... resistance.

Claims (1)

[Scope of utility model registration request] A series body of a power transistor and a load, a pull-up resistor connected in parallel to the power transistor, and a series body of a resistor and a transistor connected in parallel to the load, the resistor being connected in parallel to the pull-up resistor. has a sufficiently small value, and when the power transistor is controlled to turn off, the transistor is turned on to determine whether the power transistor is shorted or the load is shorted depending on the state of the discrimination signal generated from the connection point between the power transistor and the load. A failure mode discriminating circuit characterized by discriminating a disconnection of a wire.