JPS604431B2 - voltage detection circuit - Google Patents

Description

Detailed Description of the Invention The present invention relates to a voltage detection circuit with hysteresis characteristics added by using a Zener diode as a reference power source of a voltage comparison circuit, and reduces the number of active elements such as transistors and greatly centralizes the responsibility of each element. The aim is to improve operational reliability, improve performance, and reduce costs by reducing the

As shown in FIG. 1, a conventional voltage detection circuit uses a differential amplifier circuit, but it is not suitable for simple use because it requires a large number of active elements such as transistors. In addition, the detection level is determined by dividing the voltage between 14 and 15 using resistors 8 and 9, but since 14 and 15 also function as a power supply circuit, there may be large load fluctuations or part of the load circuit If a failure occurs, the voltage will fluctuate and the operation of the detection circuit will also become abnormal. Therefore, considering the configuration, there were many causes of unstable operation. In Fig. 1, 1 and 2 are bare transistors for differential increase, 3 is an output transistor, 4 is a constant current transistor for plexus increase, 5 is a constant current Zener diode for differential increase, and 6 is a constant current transistor for differential increase. Resistor for constant current for differential increase, 7 is current limiting resistor of Zener diode 5, 8 and 9 are resistors for setting detection level, 10 is resistor for hysteresis, 11 is diode for backflow prevention, 12 is input terminal, 13 is output It is a terminal.

The present invention eliminates the above-mentioned drawbacks of the prior art, and one embodiment of the present invention will be described below with reference to FIG.

In the figure, 21 is a detection transistor, 22 is a hysteresis transistor, 23 is a Zener diode for detection reference, 24 is a Zener current limiting resistor, 25 is a hysteresis resistor, 26 is a drive resistor for the transistor 22,
27 is an input terminal, and 28 is an output terminal. In the above configuration, when the input voltage of the input terminal 27 becomes higher than the Zener voltage of the Zener diode 23 by V88, the transistor 21 is turned on and the transistor 22 is turned off.

Therefore, the zener current of the zener diode 23 is
, so the zener voltage becomes lower by the drop due to its operating resistance. When the input voltage becomes lower than the reference, the above operation is reversed. FIG. 3 shows another embodiment of the invention.

That is, in the above embodiment, the transistor 22 is
Since this is an emitter-grounded operation and the increase rate is small, it is affected by the load impedance, so this is an improvement on this point. Note that when the load impedance is high, the configuration shown in FIG. 2 is sufficient. Next, to explain the operation, when the input of the input terminal 27 is higher than the zener voltage of the zener diode 23 by VB8, the input detection transistor 21 is activated.
N, the increase transistor 29 is turned on, and the hysteresis transistor 22 is turned off.

Therefore, the current of the Zener diode 23 is reduced by the amount caused by the resistor 25, and the terminal voltage of the Zener diode 23 is also reduced. Therefore, the voltage of the zener diode 23 is b in Fig. 4.
The collector voltage (output voltage) of the transistor 22 has hysteresis with respect to the input waveform a, as shown in c in FIG. FIG. 5 shows yet another embodiment of the present invention, in which the zener current is varied in a parallel manner.

To explain its operation, when the input to the input terminal 27 becomes higher than the zener voltage of the zener diode 23 by V88,
Transistor 21 is turned on, and transistors 29 and 22 are also turned on. Then, the zener current is bypassed through the resistor 25, and the terminal voltage of the zener diode 23 decreases by that amount. The output waveform of the output terminal 28 at this time is obtained by inverting the output waveform c in FIG. 4. As is clear from the above embodiments, the present invention uses only one sensing transistor, so the configuration is simpler and cheaper than using two like a differential amplifier, and the sensing transistor is ON.
Then, the hysteresis transistor reduces the current flowing through the reference Zener diode connected to the emitter of the detection transistor and lowers the reference potential, so even if there is some fluctuation in the input, the detection transistor's ○M can be guaranteed. Extremely stable detection operation can be performed.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional voltage detection circuit, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is a circuit diagram showing another embodiment, and Fig. 4 shows the same operating waveform. FIG. 5 is a circuit diagram showing still another embodiment. 21...Detection transistor, 22...
- Transistor for hysteresis, 23... Zener diode, 26... Resistor for hysteresis. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1 A detection transistor whose base is an input terminal,
A voltage detection circuit comprising a reference Zener diode connected to the emitter of the detection transistor, and a hysteresis transistor that reduces the current flowing through the reference Zener diode when the detection transistor is turned on.