JPH0419948Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to an overvoltage protection device for protecting load circuits of automotive electrical components from excessive power supply voltage.

[Purpose of the invention] An object of the invention is to provide an overvoltage protection device that can prevent the application of overvoltage to a load circuit and can contribute to reducing the ratings of circuit components.

[Summary of the invention] The invention uses a voltage detection unit that determines whether the power supply voltage applied to the input terminal is below a certain value based on the Zener voltage of a Zener diode, and creates a determination signal by turning on and off a transistor. and an output section having a main transistor located between the input end and the output end and an auxiliary transistor that controls turning on and off of this transistor, and a discrimination signal from the voltage detection section to oscillate or stop oscillation, and when oscillation stops, The auxiliary transistor is controlled so that the main transistor of the output section is turned on, and during oscillation, the main transistor is turned on according to the duty ratio of the oscillation output.
It is equipped with an oscillation part that controls the auxiliary transistor to turn off, and allows supply of the power supply voltage to the output terminal if the power supply voltage is below a certain value, and repeats supply and blocking at a predetermined ratio when the power supply voltage exceeds a certain value. It is characterized by the following.

[Embodiment] Figure 1 shows an embodiment of the present invention, which includes a voltage detection unit 11 that detects the power supply voltage applied to the input terminal ti and determines whether it is below a certain value, and In the following cases, it is allowed to be supplied to the output terminal to, and when it exceeds a certain value, the output section 12 repeats supply and block at a predetermined ratio, and the output section 12 oscillates or stops oscillating according to the discrimination signal from the voltage detection section. , an oscillation unit 1 that controls the output unit according to its output level.
3 and a control power supply section 14.

The voltage detection section 11 is a Zener diode.
Connect one end of each of the series circuit of ZD1 and resistors R1 and R2 and the parallel circuit of capacitors C1 and C2 to the input terminal, and ground the other ends, while connecting the connection point of resistors R1 and R2 to the base of transistor Q1. , the emitter of the transistor Q1 is grounded, and the collector is connected to the terminal a of the control power supply section 14 via a resistor R3. The criterion for determining the power supply voltage applied to the input terminal ti is the Zener voltage of the Zener diode ZD1.

The output section 12 has a series circuit of a resistor R4 and an auxiliary transistor Q2 connected between the base of the main transistor Q3 located between the input end ti and the output end to and ground, and a series circuit of a resistor R4 and an auxiliary transistor Q2 connected between the base and emitter of the main transistor Q3. The resistor R5 is connected to the resistor R6 between the base and emitter of the auxiliary transistor Q2, and the output of the oscillation section 13 is received at the base of the auxiliary transistor Q2 via the resistor R7.

The oscillation unit 13 includes NOR gates G1 and G2,
It is an unstable multivibrator composed of a capacitor C3, resistors R8 to R10, and diodes D1 and D2.
When the signal is "H", the oscillation is stopped, and when the signal is "L", the oscillation state is entered.
When the oscillation is stopped, the output level becomes "H", and both transistors Q2 and Q3 of the output section 12 are turned on.

The control power supply section 14 also connects a series circuit of a resistor R11 and a Zener diode ZD2 to an input terminal ti.
Connect this Zener diode between
It has a configuration in which capacitor C4 is connected in parallel with ZD2, resistor R11 and Zener diode.
Terminal a is pulled out from the connection point of ZD2.

In addition, a reverse connection prevention diode D is connected to the ground terminal tg.
3 are connected.

Fig. 2 shows an example of use, in which a power supply is connected to the input terminal ti side of the overvoltage protection device 10 configured as described above, and a load circuit of an automobile electrical component (lamp, light emitting diode, etc.) is connected to the output terminal to side. 20 are connected.

Next, the operation will be described. When a power supply voltage is applied to the input terminal ti and is lower than the Zener voltage of the Zener diode ZD1, no current flows to the base of the transistor Q1, and the transistor Q1 is turned off. Therefore, the NOR gate G of the oscillator 13
The control terminal No. 2 is fixed at H level and oscillation is stopped, and both transistors Q2 and Q3 of the output section 12 are turned on. In other words, the input end
The power supply voltage applied to ti is supplied to the output terminal to.

If the power supply voltage applied to the input terminal ti exceeds the Zener voltage of the Zener diode ZD1, a current flows through the Zener diode ZD1, and the resistor R2
is applied to the base of transistor Q1, turning transistor Q1 on. By turning on the transistor Q1, the level of the control terminal of the NOR gate of the oscillator 13 becomes "L",
It becomes an oscillating state. The duty of oscillation output is resistor R
8 and R9 can be set arbitrarily, and transistors Q2 and Q3 of the output section 12 are turned on and off according to the duty. In other words, while the oscillation output is at level "H", the power supply voltage is allowed to be supplied to the output terminal TO, and while the oscillation output is at level "L", supply of the power supply voltage to the output terminal TO is blocked. control becomes possible.

In the above description, only one load circuit 20 is used, but the present device may be shared by a plurality of load circuits. Further, this device can also be used by being incorporated without being separated.

[Effect] As described above, according to the present invention, it is determined whether the power supply voltage is equal to or higher than a certain value based on the Zener voltage of the Zener diode, and depending on the result, the oscillator is set to oscillate or stop oscillating, The output controls the on/off state of the transistor between the input terminal and the output terminal, so if the power supply voltage is below a certain value, supply to the output terminal is allowed, and if it exceeds a certain value, the duty is turned off. The control repeatedly allows and blocks supply at a predetermined ratio, making it possible to provide appropriate protection against overvoltage while maintaining normal operation. As a result, when designing the load circuit, durability of parts, and case, it is sufficient to use the operating point voltage as a guideline, and miniaturization and cost reduction can be achieved. In particular, even if the power supply is 12V, such as in automotive electrical components, 18V or 24V may be applied during testing, and it also serves as overvoltage protection in such cases. In addition, there are 12V and 24V systems for automotive electrical components, and we can expect devices that can be used with both.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the overvoltage protection device according to the present invention, and FIG. 2 is a block diagram showing an example of its use. 11... Voltage detection section, 12... Output section, 13...
...Oscillation section, 14...Control power supply section, Q1 to Q3...
Transistor, R1-R11... Resistor, C1-C
4... Capacitor, D1-D3... Diode,
ZD1 and ZD2... Zener diode, G1 and G2... Noah gate, ti... input end, to... output end.

Claims (1)

[Scope of utility model registration request] A voltage detection section that determines whether the power supply voltage applied to the input side is below a certain value or not based on the Zener voltage of the Zener diode and creates a determination signal by turning on and off the transistor, and between the input end and the output end. oscillation or oscillation is stopped depending on the determination signal from the output section which has a main transistor located at , and an auxiliary transistor that controls on/off of this transistor, and the voltage detection section, and when the oscillation is stopped, the main transistor of the output section is turned on. and an oscillation section that controls the auxiliary transistor so that the main transistor is turned on and off according to the duty ratio of the oscillation output during oscillation.
An overvoltage protection circuit characterized in that if the power supply voltage is below a certain value, the power supply voltage is allowed to be supplied to the output terminal, and if the power supply voltage exceeds a certain value, it is repeatedly supplied and blocked at a predetermined ratio.