JPH0622554A - Power supply circuit - Google Patents

Abstract

PURPOSE:To protect a circuit element when an abnormal voltage is inputted, in a power circuit from which a stabilized dc voltage is obtained from an ac voltage or a dc voltage. CONSTITUTION:Between a rectifier circuit 3 and a smoothing capacitor 13, a protective circuit composed of a switching element, a constant voltage diode, a resistor, and a capacitor is inserted. When a normal voltage is inputted, the switching element 4 is turned ON and a power circuit operates normally. When an abnormal voltage is inputted, however, the protective circuit works and the switching element 4 is turned OFF. Since the switching element 4 of the protective circuit is turned OFF when an abnormal voltage is inputted and the power circuit is opened, the destruction of the circuit can be avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for obtaining a stabilized DC voltage from an AC voltage or a DC voltage.

[0002]

2. Description of the Related Art FIGS. 4 (a), (b) and 5 (a)
In (b), 1 is an AC voltage source, 2 is a fuse, 3 is a rectifier circuit, 13 is a smoothing capacitor for absorbing ripple of the output voltage, and 14 is a constant voltage diode. Further, in FIGS. 4B and 5B, reference numeral 15 is a DC voltage source.

A conventional power supply circuit is shown in FIG.
As shown in FIG. 5B, some measures are not taken against abnormal voltage input, but as shown in FIGS. 1
When 00v is a normal input voltage and a voltage of 200v is erroneously input), a constant voltage diode 14 that conducts is inserted in parallel with the smoothing capacitor 13, and this constant voltage diode 14 is connected when an abnormal voltage is input. Short it,
There was something that melted the fuse.

[0004]

If no measures are taken against abnormal voltage input as in the example shown in FIG. 4, there is a risk that the explosion-proof valve of the smoothing capacitor will open and electrolyte will flow out. .

Further, in the switching power supply, if the switching element breaks down due to the breakdown voltage exceeding the explosion-proof valve of the smoothing capacitor, the fuse is blown, and if the rectifying element is included, the rectifying element is broken.

In FIG. 5, although the explosion-proof valve of the smoothing capacitor is not opened, the constant voltage diode is broken or the fuse is blown. Further, in the case of having a rectifying element, the rectifying element was destroyed.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a power supply circuit having a protection circuit for preventing destruction at the time of input of an abnormal voltage.

[0008]

In order to solve the above problems, the power supply circuit of the present invention is provided with a protection circuit at the time of abnormal voltage input, which is composed of a switching element, a constant voltage diode, a resistor and a capacitor. is there.

[0009]

With the above-mentioned structure, the operation will be described below. When a normal voltage is input, the switching element is ON and the power supply circuit operates normally. However, when an abnormal voltage is input, the switching circuit is turned off by the function of the protection circuit, which consists of the constant voltage diode, resistor, and capacitor, and the power supply circuit is opened, so it does not operate and prevents the circuit from being destroyed. You can

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a power supply circuit according to the first embodiment of the present invention. In FIG. 1, especially when an abnormal voltage is input (when 100v is a normal input voltage, the
The circuit diagram of the protection circuit for preventing the destruction of the circuit element when the voltage of 00v is applied is shown in detail.

In FIG. 1, 1 is an AC voltage source, 2 is a fuse, and 3 is a rectifying circuit composed of a diode bridge. The AC voltage source 1 is connected to the rectifier circuit 3 via a fuse 2. Reference numeral 13 is a smoothing capacitor for absorbing the ripple of the output voltage. A protection circuit is provided between the rectifier circuit 3 and the smoothing capacitor 13 to prevent damage to circuit elements when an abnormal voltage is input.

Next, the protection circuit will be described. 4 is a switching element, 8 is a base resistor connected to the base of the switching element 4, and 5 is ON / OFF of the switching element 4.
Switching element for controlling OFF, 6 is a switching element for controlling ON / OFF of the switching element 5, 7
Is a base resistor connected to the base of the switching element 5.

The part to be described next is a circuit for controlling ON / OFF of the switching element 6 by the value of the input voltage. Reference numerals 9 and 10 are resistors for dividing the input voltage. Reference numeral 11 is a capacitor for smoothing the voltage generated across the resistor 10 to direct current. Reference numeral 12 is a constant voltage diode which is turned on when the input voltage is excessive and turns on the switching element 6. The constant voltage diode 12 turns on / off the switching element 6 by the voltage of the capacitor 11.
F

With the above configuration, the operation will be described below. The AC input voltage applied by the AC voltage source 1 is
It is converted into direct current by the rectifier circuit 3, divided by the resistors 9 and 10, and smoothed by the capacitor 11. Therefore, the voltage of the resistor 10 becomes direct current.

At this time, if the input voltage is normal (a voltage of 100 V is applied), the DC voltage of the resistor 10 is the voltage across the constant voltage diode 12 and the V of the switching element 6.
The voltage is lower than BE (base-emitter voltage), the switching element 6 is turned off, and a current flows through the base resistor 7 to the base of the switching element 5. Therefore, the switching element 5 is turned on, and a current flows through the base resistor 8 and the switching element 5.

Since the switching element 5 is turned on and the flowing current becomes the base current of the switching element 4, the switching element 4 is turned on, the power supply circuit operates normally, and the load device (DC conversion circuit or AC conversion circuit) is operated. Power to the circuit) normally.

Abnormal input voltage (200v higher than normal)
Voltage), the DC voltage of the resistor 10 becomes higher than the VBE of the constant voltage diode 12 and the switching element 6 and the switching element 6 is turned on, so that the VBE of the switching element 5 becomes 0.7 V or more. Since the switching element 5 is turned off, the switching element 4 does not pass the base current and is turned off.

As a result, the power supply circuit is opened by the switching element 4 when an abnormal voltage is input, and the power supply circuit can be prevented from being destroyed.

FIG. 2 is a block diagram of a power supply circuit according to the second embodiment of the present invention. Reference numeral 15 is a DC voltage source, and this embodiment is an example in which the input voltage is DC. Since the structure of the protection circuit for preventing the destruction of the circuit element when an abnormal voltage is input is the same as the structure of the protection circuit in the previous embodiment, detailed description is omitted.

Although the PNP transistor is used as the switching element 4 in the above embodiments, a circuit configuration to which a semiconductor switch such as an NPN transistor thyristor is applied may be used.

FIG. 3 is a block diagram of a power supply circuit according to the third embodiment of the present invention. Reference numeral 16 is a switching relay, 17 is a switching element for controlling ON / OFF of the switching relay 16, and 18 is a switching element 1.
7 is a collector resistor connected to the collector of 7.

The circuit for turning on / off the switching element 17 in response to the input voltage has the same structure as that of the previous embodiment. That is, 19 and 20 are resistors for dividing the input voltage. Reference numeral 21 is a capacitor for smoothing the voltage generated across the resistor 20 into a direct current. 22 is turned on when the input voltage is excessively high to turn on / off the switching element 17.
It is a constant voltage diode for turning off. Reference numeral 23 is a constant voltage diode.

With the above configuration, the operation will be described below. The AC input voltage applied by the AC voltage source 1 is
The voltage is divided by the resistors 19 and 20 via the diode bridge 2 and smoothed by the capacitor 21. Therefore, the voltage of the resistor 20 becomes direct current. At this time, if the input voltage is normal, the DC voltage of the resistor 20 is lower than VBE (base-emitter voltage) of the constant voltage diode 22 and the switching element 17, and the switching element 17 is turned off.
Therefore, a current flows through the coil 16a of the switching relay 16 through the collector resistor 18, the contact piece 16b becomes conductive, and power is normally supplied to the load device (DC conversion circuit or AC conversion circuit). Supply. Thus, if the input voltage is normal, the power supply circuit operates normally.

Abnormal input voltage (200v higher than normal)
DC voltage of the resistor 10 is higher than the VBE of the constant voltage diode 22 and the switching element 17, and the switching element 17 is turned on. Therefore, the rectified voltage is applied only to the resistor 18, and the switching is performed. The voltage is no longer applied to the coil 16a of the relay 16 for use. Therefore, the current of the coil 16a is cut off, the contact piece 16b becomes non-conductive, the energy supply to the smoothing capacitor 13 is cut off, and the power supply to the load device is stopped.

[0026]

As described above, the present invention comprises a switching element, a constant voltage diode, a resistor and a capacitor.
With the configuration provided with the protection circuit for the abnormal voltage input, when the abnormal voltage is input, the switching element of the protection circuit is turned off and the power supply circuit is opened, so that the circuit can be prevented from being destroyed.

[Brief description of drawings]

FIG. 1 is a block diagram of a power supply circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a power supply circuit according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a power supply circuit according to a third embodiment of the present invention.

FIG. 4 is a block diagram of a conventional power supply circuit.

FIG. 5 is a block diagram of a conventional power supply circuit.

[Explanation of symbols]

 1 AC voltage source 2 Fuse 3 Rectifier circuit 4 Switching element 5 Switching element 6 Switching element 9 Voltage dividing resistor 10 Voltage dividing resistor 11 Capacitor 12 Constant voltage diode 13 Smoothing capacitor

Claims (1)

[Claims] 1. A power supply circuit which is a capacitor input type rectification system having a diode bridge, a smoothing capacitor for rectifying and smoothing an AC voltage, or a smoothing capacitor for smoothing a DC voltage, and having a protection circuit against an abnormal voltage input.