JPH0210468Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a load drive circuit that drives a load such as an actuator in response to an output signal from a microcomputer, and particularly relates to a load drive circuit that has a series redundant system and a self-diagnosis function.

In recent years, with the rapid development of microcomputers, there is a tendency for various devices to be controlled by microcomputers. In this case, since the output signal current of the microcomputer is extremely small, this signal cannot be used as it is to drive a load such as an actuator. 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 shot or disconnected for some reason, problems such as incorrect control or damage to other electrical components may occur. Therefore, in a control system using such a microcomputer, it is important to take measures to drive the load by shorting the power transistor and to constantly monitor the drive system.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a load driving circuit having a series redundant system and a self-diagnosis function.

In order to achieve these objectives, the present invention connects two power transistors for driving loads in series, uses a microcomputer to drive each power transistor in a partially different mode, and also Self-diagnosis is performed by monitoring the potential at the connection point with the load. Hereinafter, the load driving circuit according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a load driving circuit according to the present invention. In the figure, Q ₁ and Q ₂ are power transistors connected in series between the power supply V _CC and ground via a load Z _L , and R ₁ is connected in parallel to the series body of power transistors Q ₁ and Q ₂ . The high-resistance pull-up resistor M is a microcomputer that outputs active “L” control signals A ₁ , A ₂ .
It is composed of output ports P ₁ and P ₂ that send out the diagnostic signal B, and an input port P ₃ that takes in the diagnostic signal B. IN ₁ is the output port of microcomputer M
An inverter that inverts the control signal A ₁ generated at P ₁ , Q ₃ is connected between the power supply V _CC and ground through a resistor R ₂ , and the output of the inverter IN ₁ is connected to a resistor.
A transistor whose base input is via _R3 , and the power transistor _Q1 is connected by supplying the output of this transistor _Q3 via a resistor _R5 .
is driving. IN ₂ is an inverter that inverts the control signal A ₂ generated at the output port P ₂ of the microcomputer M, and Q ₄ is connected between the power supply V _CC and ground via a resistor R ₆ , and the output of the inverter IN ₂ . is a transistor whose base input is via a resistor _R7 , and the power transistor _Q2 is driven by supplying the output of this transistor _Q4 via a resistor _R8 . ZD is a Zener diode connected between the connection point K of the transistor Q ₂ and the load Z _L and the ground, and converts the potential at the K point to a TTL level and extracts it. _D1 ,
_D2 is a diode provided to absorb the noise contained in the output of the Zener diode ZD taken out via the resistor _R9 , and the diode _D1 is connected between the power supply +V and one end of the resistor _R9 . diode D ₂ is connected with reverse polarity between one end of resistor R ₉ and ground. IN ₃ converts the K point potential to TTL using Zener diode ZD.
This inverter supplies a diagnostic signal B with inverted polarity to the input port _P3 of the microcomputer M by inputting the level-converted signal via the resistor _R9 .

In the load drive circuit configured in this way,
When the power supply V _CC is supplied during normal operation, the current supplied through the high resistance pull-up resistor R ₁ is the load Z _L
Since the voltage at point K is grounded through the ground, the potential at point K becomes approximately ground potential. Therefore, inverter IN ₃
Since the input signal of the microcomputer M becomes "L" and an "H" signal is supplied to the input port _P3 of the microcomputer M, the microcomputer M
determines whether the load drive system is normal by determining whether the diagnostic signal B is "H" when the control signals A ₁ and A ₂ are "H".

Next, when _diagnosing the load drive system, as _{shown in FIG} .
A control signal A ₁ is generated, and the control signal A 1 is output from the output port P ₂ for the period T ₁ as shown in FIG. 2b.
The period denoted by time t ₁ - _{t 2} and time t ₃ - _{t 4} is part of
A control signal _A2 which becomes "L" only at _T2 is generated. The control signal A ₁ generated in this way,
After A ₂ is inverted in each inverter IN ₁ and IN ₂ , it is supplied to the bases of transistors Q ₃ and Q ₄ , and transistors Q ₃ and Q ₄ are turned on during periods T ₁ and T ₂ , respectively. And this transistor Q ₃ ,
The output of Q ₄ is the power transistor Q ₁ , Q ₂ respectively
, power transistors Q ₁ and Q ₂ are turned on during periods T ₁ and T ₂ , respectively.

In this case, if transistors Q ₁ and Q ₂ are normal, the potential at point K will be raised to approximately the power supply potential only during the period t ₁ to _{t 2} when both transistors Q ₁ and Q ₂ are turned on. Become. As a result, the diagnostic signal B output from inverter IN ₃ is as shown in Fig. 2c.
As shown in , it becomes "L" only during the period t ₁ to _{t 2} . Therefore, the microcomputer M determines that the diagnostic signal B becomes "L" only during the period when both the control signals A ₁ and A ₂ are "L", thereby controlling the transistors Q ₁ and Q _{2 .} check that it is working properly.

Next, if at least one of the transistors Q ₁ and Q ₂ is disconnected, even if the control signals A ₁ and A ₂ shown in FIG. Along with this, inverter
The output of IN ₃ will continue to be in the "H" state as shown in Figure 2d. Therefore, in the microcomputer M, since the diagnostic signal B is always "H" in all combination modes of the control signals A ₁ and A ₂ , a disconnection occurs in at least one of the power transistors Q ₁ and Q ₂ . Determine whether the

Next, when the transistor _Q1 is shorted, the diagnostic signal B becomes "L" even during the period when only the transistor _Q2 is on, as shown in FIG. 2e between time points _t3 and _t4 . This indicates that a short has occurred in transistor _Q1 .

Next, when the transistor Q ₂ is shorted, the diagnostic signal B remains unchanged even during the period from time t ₂ to _{t 3} when only the transistor Q ₁ is turned on, as shown in FIG.
becomes “L”, which causes the transistor Q ₂
This indicates that a disconnection has occurred.

Furthermore, if the load Z _L is disconnected, the pull-up resistor
Current supplied through R ₁ and transistor
Since the flow path of the current supplied when Q ₁ and Q ₂ are simultaneously turned on is opened, the potential at point K is accordingly raised to the potential of the power supply V _CC . As a result, the diagnostic signal B continues to be in the "L" state, and the microcomputer M outputs the control signals A ₁ ,
Disconnection of the load Z _L is determined from the "H" state of the diagnostic signal B when _A2 is "H". If the microcomputer M determines an abnormality in the load drive system in this way, it stops generating the control signals A ₁ and A ₂ to prevent malfunction.

In this case, the two power transistors Q ₁ and Q ₂ that switch the load current are connected in series to form a series redundant system, so the probability that the two transistors Q ₁ and Q ₂ will be fired at the same time is The control signal A 1 becomes extremely low, and as an abnormality is detected, the control signal A ₁ ,
By setting _A2 to "H", erroneous drive of the load, which is an important problem, is reliably prevented.

In addition, in the above diagnostic mode, the control signals A ₁ ,
The period during which the “L” signal of A ₂ overlaps must be set to a time range in which load Z _L does not operate _;
When driving, the control signals A ₁ and A ₂ are simultaneously “L”
This is done by lengthening the period. Also,
This diagnostic mode may be performed at the same time with some conditioning applied to the control signals A ₁ and A ₂ during actual load driving.

As explained above, in the load drive circuit according to the present invention, in order to configure a redundant system by connecting two power transistors in series,
Erroneous driving due to shorting of the power transistor is reliably prevented. In addition, by changing the combination of drive conditions for these two power transistors and identifying potential changes applied to the load in relation to the drive signal, the load drive circuit can be self-diagnosed. It has various excellent effects such as being able to perform fail control.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a load driving circuit according to the present invention, and FIGS. 2 a to 2 f are operation waveform diagrams of various parts of the circuit shown in FIG. 1. Q ₁ to _{Q 4} ... Transistor, M ... Microcomputer, IN ₁ to IN ₃ ... Inverter, Z _L ...
Load, ZD... Zener diode, D ₁ , D ₂ ...
Diode, _R1 to _R9 ...Resistance.

Claims (1)

[Scope of utility model registration request] two power transistors connected in series to a current path for driving a load, a high resistance pull-up resistor connected in parallel to the series body of the two power transistors, and each of the power transistors separated from each other. and a microcomputer that uses as a monitoring input the potential at a connection point between the power transistor and the load, and in the load drive mode, the microcomputer controls the two
By controlling the two power transistors to turn on at the same time and driving the two power transistors while changing the combination of turning on in the diagnostic mode, the monitoring input is equal to or higher than the set value only when the two power transistors are controlled to turn on at the same time. A load driving circuit characterized in that a load driving circuit is determined to be normal when the voltage rises to .