JPS631321A - Overvoltage protective circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is interposed between a TL source and a load to cut off momentary overvoltage of the TL source. ! The present invention relates to an S voltage protection circuit, and particularly to an overvoltage protection circuit that can obtain good cutoff characteristics without requiring a large-capacity impedance element.

[Prior Art] Conventionally, as this type of overvoltage protection circuit, as shown in FIG.

A configuration in which a circuit consisting of a coil 3 and a capacitor 4 is inserted is known.

In a circuit with such a configuration, when the power supply 1 is turned ON-OFF by a switch (not shown), an instantaneous overvoltage will occur at this switching time, but due to the inductance of the coil 3 and the capacity of the capacitor 4, The instantaneous overvoltage is cut off by the time constant determined by , so that the load 2 can be protected from the overvoltage.

[Problems to be solved] However, as mentioned above, in the conventional overvoltage protection circuit, the inductance of the coil 3 and the capacitor 4
There was a problem in that unless the capacitance of the impedance element, that is, the capacitance of the impedance element, was considerably large, sufficient breaking characteristics could not be obtained.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an overvoltage protection circuit that can obtain sufficient cutoff characteristics without using a large-capacity impedance element.

[Means for solving problems] In order to achieve the above object, the present invention provides first and second
Terminal and load side cylinder 1. an overvoltage protection circuit that is inserted between a power source and a load to block instantaneous overvoltage of a distributed power source, one end of which is connected to the first terminal on the power source side, and the other end of which is is connected to a series circuit including a resistor and a capacitor connected to the second terminal on the power supply side and the second terminal on the load side, and one end is connected to the midpoint of the connection between the resistor and the capacitor in the series circuit, and is O<
A Zener diode selected such that IVl l<IV+I (IV+1 is the specified voltage value of the power supply and load),
a light emitting element having one end connected to the other end of the Zener diode and the other end connected to the power supply side second terminal and the load side second terminal; and one end connected to the Ml source side first terminal; The photocoupler includes a photocoupler including a light receiving element whose other end is connected to the load-side first terminal.

[Example] An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of the overvoltage protection circuit according to this embodiment, FIG. 2 is a circuit diagram showing the configuration of another embodiment, and FIG.
Figures (a) and (b) are characteristic diagrams for explaining the operation of the embodiment shown in Figure 1.

In FIG. 1, the overvoltage protection circuit of this embodiment is constructed between a power supply 1, such as a DC/DC conversion power supply, which has an output terminal of a positive potential element 1 and an output terminal of a ground potential G, and a load 2. This is an example of a configuration inserted into the . That is, the overvoltage protection circuit of this embodiment has a first terminal 5 on the power supply side and a second terminal 6 on the power supply side.
It has a load side first terminal 7 and a load side second terminal 8. One end of the circuit in which the resistor 9 and the capacitor 10 are connected in series is connected to the power supply side first terminal 5, and the other end is connected to the power supply side second terminal 6 and the load side second terminal 8. The cathode terminal of the Zener diode 11 is connected to the midpoint between the resistor 9 and the capacitor 10, and its 7 node terminal is connected to the light emitting diode 12a of the photocoupler 12, which is composed of a light emitting diode 12a as a light emitting element and a phototransistor 12b as a light receiving element. connected to the anode terminal of the The cathode terminal of this light emitting diode 12a is connected to the power supply +I! It is connected to the second terminal 6 and the load side second terminal 8. The collector terminal of the phototransistor 12b is connected to the power supply side first terminal 5, and the emitter terminal is connected to the load side first terminal 7. Here, the Zener diode 11 used has a Zener voltage Vl selected such that o<vl<v. Therefore, when the potential across the Zener diode 11 becomes V1 or higher, the Zener diode 11 is turned ON, and when the source 1 is OFF (7), that is, when there is no potential difference between terminals 5 and 6, the light emitting diode 12a is turned OFF. It is what it is.

Next, the operation of this embodiment configured as described above will be explained. That is, when the power supply 1 is switched from ON to OFF, the voltage between the terminals 5 and 6 generally becomes instantaneous at time t1, as shown in FIG.
2, a normal voltage +V1 is generated. Here, the instantaneous overvoltage (section E in FIG. 3(a)) is blocked by a direct voltage circuit including a resistor 9 and a capacitor 10.

Since the Zener diode 11 remains OFF and therefore the photocoupler 12 also maintains the OFF state of 7g, the load 2
No voltage is applied to.

Next, when the normal voltage 10v1 appears at the terminal 5 at time t2, the voltage generated on the cathode side of the Zener diode 11 becomes a time-responsive value due to the time constant determined by the resistance value of the resistor 9 and the capacitance of the capacitor 10. , changes exponentially from 0 to 10M+, but the Zener diode 11
When the voltage generated on the cathode side reaches vl, the Zener diode 11 is turned on, the first light emitting diode 12a is turned on, and the photocoupler 12 is also turned on. Therefore, as shown in FIG. 3(b), the normal voltage v1 is applied to the load 2 at time t3. Here 11-12
is the time delay due to the above time constant.

As described above, according to this embodiment, the Zener diode 11
．． Since the photocoupler 12 can detect momentary overvoltage and cut it off, the resistor 9. Sufficient cutoff characteristics can be obtained without increasing the capacitance of the capacitor 10.

FIG. 2 is a configuration diagram showing an example of application to an i source 13 having an output terminal with a negative potential -vl and an output terminal with a ground potential G. Here, a Zener diode 11, a photocoupler 1
The polarity of 2 is connected oppositely to that in FIG. 1, and the operation, characteristics, etc. of 1 are the same as in FIG.

[Effects of the Invention] As detailed above, in the present invention, voltage fluctuations in the power supply are detected and cut off by a Zener diode and a photocoupler, so a large-capacity impedance element is not required. This has the effect of providing sufficient blocking properties.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram for explaining one implementation of the overvoltage protection circuit according to the present invention, and FIG. 4 is a circuit diagram showing a conventional example. 1.13: Power supply 2: Load 5: TL power supply side first terminal 6: Power supply side second terminal 7: Load side first terminal 8: Load side second terminal 9: Resistor 1
0: Capacitor 11: Zener diode 12: Photocoupler

Claims (1)

[Claims] In an overvoltage protection circuit that has first and second terminals on the power supply side and first and second terminals on the load side, and is inserted between the power supply and the load to cut off momentary overvoltage of the power supply, one end is a series circuit including a resistor and a capacitor connected to the first terminal on the power supply side and whose other end is connected to the second terminal on the power supply side and the second terminal on the load side; and one end of the resistor and the capacitor in the series circuit. and a Zener diode whose Zener voltage V_l is selected to be 0<|V_Z|<|V_1|, and whose one end is connected to the other end of the Zener diode and whose other end is connected to the power supply side. A photocoupler comprising a second terminal and a light emitting element connected to the load side second terminal, and a light receiving element whose one end is connected to the power supply side first terminal and the other end is connected to the load side first terminal. An overvoltage protection circuit characterized by comprising: