JPH0817534B2 - Load drive circuit with protection circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a protection circuit for various electronic devices such as automobile control equipment, OA equipment, and audio equipment, and particularly drives a plunger solenoid, a relay switch, and the like. The present invention relates to a circuit technology suitable for being applied to a semiconductor integrated circuit having a power output circuit for achieving the above.

[Conventional technology]

In recent years, electronic technology using a microcomputer has become indispensable for improving the performance and safety of automobiles, and integrated computerization is progressing.

Since each control system using a microcomputer can achieve higher performance than conventional analog control circuits,
It has come to be used in a wide range of devices. Therefore, the driver circuit, which is the interface between the microcomputer and various actuators (solenoids, relays, stepping motors, LEDs (light emitting diodes), heaters), has moved to monolithic ICs, resulting in low cost, miniaturization, and multi-functionality. It is becoming more and more important as it is becoming increasingly popular.

When performing electronic control of the automobile, the most important things are establishment of safety and accurate control, and whichever is missing leads to an accident.

The electronic control of automobiles is described in "Nikkei Electronics" (1978, No. 1-23, publisher Nikkei McGraw-Hill, pp60-81).

The present inventors have studied improvement of safety of electronic control and accurate control. The following is not a known technique, but a technique examined by the present inventors,
The outline is as follows.

FIG. 3 shows an example of gasoline control in the automobile 20, in which 1 is a microcomputer (CPU), 2 is an electronic device (IC), and the solenoid valve 3 is controlled to control the engine from the gasoline tank 4 (GAS). 5 (ENGINE) controls the amount of gasoline supplied.

The solenoid valve 3 is controlled by an output circuit (transistor Q ₁ ) as shown in FIG. Transistor Q ₁
A control signal Vc is supplied to the base of the solenoid valve 3, the energization of the coil L that drives the solenoid valve 3 is controlled, and the solenoid valve 3 is controlled.
It controls the amount of gasoline. The control IC2 has a load short-circuit protection function (the output end is battery power Vcc
It is necessary to add a protection function such as a function of making the output transistor non-operation when connected to the.

However, in order to add this protection function to the above electronic device, the inventors of the present invention have clarified that the following problems are involved.

[Problems to be solved by the invention]

In automobiles, signal transmission lines and the like have a considerably large stray capacity. The stray capacity C ₁ is connected as shown by the dotted line in FIG. 4 when viewed from the output terminal.

Therefore, when viewed from the output terminal, the load is not only inductive but also capacitive. In normal operation, when the output transistor Q ₁ is turned on / off in response to the input signal V _IN , a counter electromotive voltage is generated by the coil, and this voltage charges the stray capacity C ₁ and the output end voltage is not instantaneous. However, it may be held at a high potential with a certain short time width. An example of a protection circuit that detects an abnormal voltage level at the output terminal and protects the output transistor Q ₁ is "Analog Integrated Circuit" issued on February 1, 1982, the 4th edition of the issue, Publisher Modern Science Company, pp218-230. )
However, in the method of simply detecting an abnormal voltage at the output terminal and protecting the output transistor Q _{1 in the} event of an abnormality,
A capacitor C having a certain amount of capacitance as described above
When the drive circuit is driven, the voltage generated due to the capacitance is mistakenly recognized as an abnormal voltage, and the output transistor is shut down, so that the normal load driving operation becomes impossible. On the other hand, if the overvoltage protection function is not provided, a large current will flow to the output transistor when the output terminal and the power supply are short-circuited, resulting in element destruction.

[Means for solving problems]

The following is a brief description of the outline of the typical invention disclosed in the present application.

That is, it is distinguished whether the voltage abnormality generated at the output end is a transient abnormality caused by the parasitic capacitance in a normal driving state or a serious abnormality such as a load short circuit. Therefore, when the input signal is first applied instead of turning on the voltage protect circuit all the time, the drive transistor is turned on according to this timing, and the voltage protect circuit is operated by delaying a predetermined time from the input application timing. Let

[Action]

If the voltage abnormality is transient due to the parasitic capacitance in the normal driving state as described above, after τ has elapsed since the driving transistor was turned on, the output terminal voltage is charged in the parasitic capacitance C ₁ . It should be at a low level because the drive transistor discharges the electric charge that had been stored, and even if the abnormality detection circuit of the voltage protection circuit is activated after τ, the output terminal is at a normal level. The protection circuit does not turn on. Therefore, the load can be driven normally in accordance with the input V _IN .

On the other hand, if the Vcc line is short-circuited to the output terminal, the output terminal is in an overvoltage applied state after τ has elapsed and overvoltage protection is activated to turn off the drive transistor. At this time, the drive transistor is turned on for τ period after the input V _IN is applied, but if τ is made sufficiently small, the amount of energy flowing through the drive transistor during this period is small and the drive transistor (element) is not destroyed. .

〔Example〕

Reference numeral 11 is a microcomputer, and the output signal Va drives the plunger drive circuit 12a of the electronic device 12. It is assumed that the load coil L ₁ is a plunger coil and is used for gasoline control of an automobile.

C is a stray capacity that appears along with the wiring, and is interposed between each output terminal and the ground line. The drive circuits 12a to 12d have the same circuit configuration, and drive the indicator light La, the resistance Rp, the relay coil Ly, etc., which are loads provided for each purpose, by the input signals Vb to Vd.

In addition to the voltage protection function 32 (voltage protection circuit), the driver 12 (which has been integrated into an IC) has a current protection circuit 31.
A (current protection circuit) is also provided and can protect against both overvoltage and overcurrent. MAX current I ₁ as shown in this way more Fig. 5 the two protection function
And the MAX voltage V ₁ can be set to define the ASO (safe operating area), thus providing complete protection.

The current protection circuit 31 shown in FIG. 1 converts the current flowing in the transistor Q11 into a voltage by the resistor R1 and detects it, compares it with a preset voltage Vref by a comparator, and compares the transistor Q12 with the output of the comparator. Control. When an overcurrent flows, the transistor Q12 is turned on and the base current of the transistor Q11 is extracted to turn off the transistor Q11, thereby protecting the transistor Q11 against the overcurrent.

The point of the present invention is to obtain a drive circuit to which an overvoltage protection function is added while enabling a certain capacity drive, so the overvoltage protection will be described below. The protection circuit delays the input signal by τ, delay circuit 22, inverter 23, comparison AND circuit 24, NOR gate 25
The waveform of each part is as shown in FIG.

As can be understood from FIG. 2, during normal operation, even if some capacitance is parasitic, the drive signal V ₅ of the drive transistor Q ₁₁ is generated corresponding to the input V _IN , and the drive transistor is driven.

When a load short circuit occurs and an overvoltage abnormality occurs, the drive signal V ₅ is generated only during the τ period after the input of V _IN , and the drive transistor turns on only during this period, but τ is small, so the drive transistor Q ₁₁ is protected. Done.

 The following effects are obtained in this embodiment.

(1) Even if an abnormality occurs, the output transistor can be protected because it is turned on only for a minute time τ. or,
Capacitive loads below a predetermined value can be driven.

(2) Since the on time of the output transistor is determined by the above (1), the effect of protecting the output transistor can be obtained.

(3) Detecting an abnormality in the output current of the output transistor,
By making the output transistor inoperative, the effect of protecting the output transistor when an abnormal current occurs can be obtained.

(4) Due to the above (1) to (3), it is possible to obtain the effect that the reliability of the electronic device including the output transistor is improved.

Although the invention made by the present inventor has been specifically described above based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, the output transistor Q ₁₁ may be replaced with a push-pull circuit.

The reference power supply circuit 13 is formed outside the IC, but may be inside the IC.

In the above description, the case where the invention made mainly by the present inventors is applied to electronic control of an automobile, which is a field of application which is the background of the invention, is not limited thereto and is applied to all power ICs. You can

〔The invention's effect〕

Overvoltage protection can also be performed on a drive circuit that needs to drive a capacitive load to some extent.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an IC drive device to which the present invention is applied, FIG. 2 is a waveform diagram explaining the circuit operation of the protection circuit shown in FIG. 1, and FIG. An explanatory view showing an example of gasoline control of an automobile examined prior to the invention, FIG. 4 is a circuit diagram of an electronic device used for the control, and FIG. 5 is a characteristic of a transistor showing a safe operation area of the electronic device. It shows a figure. 11 …… Microcomputer, 12 …… Electronic device, 21,23
...... Phase inversion circuit, 22 …… Delay circuit, 24 …… And gate, 25 …… No gate, 31 …… Current protection circuit, Q ₁₁ , Q ₁₂
…… Transistor, L ₁ …… Coil, C …… Capacitor,
V _{1 to} V ₆ ... Voltage level.

Claims (1)

[Claims] 1. A first bipolar transistor having an inductive load connected to drive between its collector and a power supply, a signal obtained by delaying a control signal for a predetermined time τ, and the first bipolar transistor.
Generating a first signal which is a logical product of the output signal of the collector of the bipolar transistor and a second signal which is the inverted control signal, and generating a logical sum circuit of the first and second signals. A voltage protection circuit for driving the base of the first bipolar transistor with a signal, a comparator for comparing the value of the current flowing through the first bipolar transistor with a predetermined level, and the base of which is controlled by the comparator and its collector A current protection circuit having a second bipolar transistor connected to the base of the first bipolar transistor, and a load drive circuit with a protection circuit.