JPH0866006A - Protective circuit - Google Patents

Abstract

PURPOSE: To obtain a circuit for protecting a load, connected with the output of a constant voltage regulator, easily and surely through inexpensive circuitry against heating or smoking under an abnormal state where an overvoltage appears at the output of the constant voltage regulator. CONSTITUTION: The protective circuit comprises a plurality of constant voltage regulator circuits 10 being fed with power from a second power supply circuit 8, a plurality of circuit for detecting overvoltage at the output of the constant voltage regulator 10, a circuit being fed with power from a first power supply circuit and latching the output of the overvoltage detecting circuit, and a transistor 22 for short-circuiting the output of the second power supply circuit based on the output from the latch circuit, wherein the fuse 5 for the second power supply circuit 8 is blown out upon detection of overvoltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply protection circuit in which a power supply transformer has two secondary windings, and a power supply circuit of one of the power supply circuits supplies a constant voltage to a plurality of loads. is there.

[0002]

2. Description of the Related Art In recent years, electric appliances generally have a large number of parts such as microcomputers and ICs due to diversification of applications and specifications. To operate these parts, a constant voltage regulator circuit is used for each part. It has a complicated configuration for supplying a corresponding voltage and current.

In addition, safety measures for electric products are defined by safety standards in various countries around the world, and the importance of a protection circuit for preventing heat generation, ignition, etc. due to abnormal voltage of electric products makes the configuration of the device complicated. Along with that, it is increasing.

An example of a conventional power supply protection circuit will be described below with reference to the drawings. FIG. 2 shows a circuit configuration of a conventional power supply protection circuit.

In FIG. 2, the voltage supplied from the AC power supply 1 is converted into each secondary voltage by the power supply transformer 2. First composed of fuse 3 and rectifier circuit 4
The voltage of the power supply circuit 7 is supplied to the load 9 through the smoothing electrolytic capacitor 23.

On the other hand, the voltage of the second power supply circuit 8 composed of the fuse 5 and the rectifying circuit 6 is connected to the constant voltage regulator circuit 10 through the smoothing electrolytic capacitor 24, and after being converted into a required output voltage. , Are supplied to the load 11.

Since the voltage at which the Zener diode 25 conducts is set higher than the output voltage of the constant voltage regulator circuit 10, no voltage is applied to the gate of the thyristor 27 in the normal state. The thyristor 27 does not become conductive.

If an abnormal state occurs in which the output of the constant voltage regulator circuit 10 becomes an overvoltage than the set voltage at which the Zener diode 25 conducts, a voltage is applied to the gate of the thyristor 27 via the Zener diode 25,
The thyristor 27 becomes conductive.

Since the thyristor 27 continues to be in the conductive state once it becomes conductive, a current exceeding the fusing current value flows through the fuse 5 of the second power supply circuit 8 to disconnect the fuse 5 and connect it to the output of the constant voltage regulator circuit 10. The loaded load 11 can be protected from damage such as heat generation and smoke generation due to overvoltage.

[0010]

However, in the conventional protection circuit as described above, the zener diode 25 detects the overvoltage of the constant voltage regulator circuit 10 connected to the second power supply circuit 8 and the thyristor 27 is turned on. Since the fuse 5 of the second power supply circuit 8 is made to be in a state of being cut off and the fuse 5 of the second power supply circuit 8 is cut off, the power supply for cutting off the fuse 5 that cuts off the power supply to the load when the overvoltage state occurs is the second power supply. Since the voltage of the circuit 8 is used, there was concern about the timing and reliability of circuit operation.

When the constant voltage regulator circuit 10 supplies constant voltages of different voltages to a plurality of loads, it is necessary to provide the Zener diode 25 and the resistor 26 for each output terminal of the constant voltage regulator, and the Zener diode is particularly expensive. Therefore, there is a problem that the protection circuit for the power supply becomes expensive.

[0012]

In order to solve the above problems, the protection circuit of the present invention is a power supply transformer having two secondary windings, and a first transformer for rectifying the secondary voltage of these two secondary windings.
And a second rectifying means, a fuse inserted between the second rectifying means and the secondary winding, and a constant voltage for supplying a constant voltage to a plurality of loads from the output voltage of the second rectifying means. A circuit, first control means for shorting the output of the second rectification means when a first control voltage is applied, and the first control means for applying a second control voltage to the first control means. Second control means for applying the control voltage of No. 1 and overvoltage detection means for applying the control voltage to the control terminal of the second control means when an overvoltage of a certain value or more is applied to the load from the constant voltage circuit. And a second voltage from the output voltage of the first rectifying means to the second transistor based on the output of the overvoltage detecting means.
The control voltage is applied.

[0013]

According to the present invention, when the load is applied with an overvoltage of a certain value or more, the overvoltage detection means first causes the second control means to conduct, and after the second control means conducts, Since the control voltage is continuously applied from the first rectifying means to the second control means, the control voltage is continuously applied to the first control means by the output voltage of the second control means, and the second rectification means is applied. The output of the means is continuously shorted to the second
The fuse inserted between the rectifying means and the secondary winding of the power transformer can be cut off, and the load can be reliably protected from damage such as heat generation and smoke generation due to overvoltage.

Further, according to the present invention, even when the constant voltage regulator circuit supplies a constant voltage to a plurality of loads without using an expensive Zener diode, it is possible to provide the overvoltage detecting means according to the number of the loads. Therefore, a protection circuit that reliably protects the load can be manufactured at low cost.

[0015]

Embodiments of the protection circuit of the present invention will be described in detail below with reference to FIG.

FIG. 1 shows a circuit configuration of a power supply protection circuit having a power transformer, a plurality of secondary power supply circuits, a rectifying circuit, a fuse, and a plurality of constant voltage regulator circuits according to an embodiment of the present invention. The same components as those in 2 are given the same numbers.

In FIG. 1, the voltage supplied from the AC power supply 1 is converted into each secondary voltage by the power supply transformer 2. First composed of fuse 3 and rectifier circuit 4
The voltage of the power supply circuit 7 is supplied to the load 9 through the smoothing electrolytic capacitor 23.

On the other hand, the voltage of the second power supply circuit 8 composed of the fuse 5 and the rectifying circuit 6 is connected to the constant voltage regulator circuit 10 through the smoothing electrolytic capacitor 24, and after being converted into a required output voltage. , Loads 11 and 12 are supplied.

The voltage passing through the diode 13 connected to the load 11 is divided by the resistors 14 and 21 so that the transistor 20 (second control means) is turned off during normal operation.

Similarly, diode 1 connected to load 12
The voltage passed through 5 is divided by resistors 16 and 21, and is set so that the transistor 20 is turned off during normal operation.

Thus, the diode 13 and the resistor 14
And resistor 21 (diode 15, resistor 16, resistor 2
1) constitutes the overvoltage detecting means.

Since the transistor 18 is turned off during normal operation by the resistor 17 connected between the base and emitter, the transistor 20 (second control means) and the transistor 22 (first control means) are turned off. It is configured.

The operation of the protection circuit configured as described above will be described below when an abnormal state occurs in which the output of the constant voltage regulator circuit 10 becomes an overvoltage.

First, when an abnormal state occurs in which the output of the constant voltage regulator circuit 10 connected to the load 11 becomes an overvoltage, the voltage passed through the diode 13 connected to the load 11 and divided by the resistor 14 and the resistor 21. Rises, the base voltage of the transistor 20 rises, and the transistor 20 is turned on. As a result, a potential difference is generated between the base and the emitter of the transistor 18 connected to the output of the first power supply circuit 7 formed by the fuse 3 and the rectifier circuit 4, the transistor 18 is turned on, and the resistance 1
The transistor 20 is turned on via the switch 9. That is, the transistor 18 connected to the output of the first power supply circuit 7
Since the latch circuit is constituted by the transistor 20 and the transistor 20, the output of the first power supply circuit 7 is used to fix the transistor 22 in the ON state, and as a result, the fuse 5 of the second power supply circuit 8 is closed. It is possible to break the wire.

Similarly, when an abnormal state occurs in which the output of the constant voltage regulator circuit 10 connected to the load 12 becomes an overvoltage, the diode 15 connected to the load 12 and divided by the resistor 16 and the resistor 21 is used. Since the voltage rises, the base voltage of the transistor 20 rises and the transistor 20 is turned on. The following operation is the same as when an abnormal state occurs in which the output of the constant voltage regulator circuit 10 connected to the load 11 becomes an overvoltage.

[0026]

As described above, according to the present invention, when an overvoltage of a constant value or more is applied to the load from the constant voltage circuit, the overvoltage detecting means first makes the second control means conductive, and
Since the control voltage is continuously applied from the first rectifying means to the second control means after the second control means is turned on,
The control voltage is continuously applied to the control means of the second control means by the output voltage of the second control means, and the output of the second rectifying means is continuously short-circuited so that the second rectifying means and the secondary winding of the power transformer. The fuse inserted between and can be cut, and the load can be surely protected from damage such as heat generation and smoke generation due to overvoltage.

The present invention also provides a first circuit for short-circuiting the output of the second rectifying means to disconnect a fuse inserted between the second rectifying means and the secondary winding of the power transformer.
Since the control voltage of 1 is supplied from the output of the first rectifying means in which no abnormality has occurred, the reliability of the operation of the protection circuit can be enhanced and the load can be reliably protected.

Further, according to the present invention, even when the constant voltage circuit supplies a constant voltage to a plurality of loads without using an expensive Zener diode, it is sufficient to provide the overvoltage detecting means according to the number of the loads, so that it is possible to ensure the reliability. It is possible to realize an inexpensive protection circuit that protects the load.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a protection circuit according to an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a conventional protection circuit.

[Explanation of symbols]

 1 AC power supply 2 Power supply transformer 3,5 Fuse 4,6 Rectifier circuit 7 First power supply circuit 8 Second power supply circuit 9,11,12 Load 10 Constant voltage regulator circuit 13,15 Diode 14,16,17,19, 21 Resistor 18 Transistor 20 Transistor (Second Control Means) 22 Transistor (First Control Means) 23, 24 Electrolytic Capacitor 25 Zener Diode 26 Resistor 27 Thyristor

Claims (1)

[Claims] 1. A power supply transformer having two secondary windings, first and second rectifying means for rectifying a secondary voltage of the two secondary windings, the second rectifying means, and the second rectifying means. A fuse inserted between the secondary winding, a constant voltage circuit that supplies a constant voltage from the output voltage of the second rectifying means to a plurality of loads, and a first control voltage when the first control voltage is applied. Second control means for short-circuiting the output of the second rectifying means, second control means for outputting the first control voltage when the second control voltage is applied, and overvoltage of a certain value or more for the load. An overvoltage detection unit that outputs the second control voltage when
A protection circuit characterized by applying a second control voltage from the first rectifying means to the second control means based on the output of the overvoltage detecting means to disconnect the fuse.