JP2000324818A - Power supply - Google Patents

Abstract

(57) Abstract: Provided is a power supply device capable of confirming an overvoltage protection function without blowing a fuse, and capable of quickly discharging residual charge of a smoothing capacitor after power is cut off. A circuit for detecting and displaying a voltage between both ends of a smoothing capacitor is provided, a load is removed, an input is cut off, a pseudo output overvoltage state is externally generated, and the quality of the overvoltage protection function is checked. Further, an input monitoring circuit 12 and a timer circuit 13 are provided, and after the input is cut off, the short-circuit switch circuit 4 is automatically turned on for a predetermined time to discharge the residual charge of the smoothing capacitor 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply, in which, when an overvoltage of an output voltage is detected, a fuse or the like is forcibly cut to disconnect the power supply from an input to protect a load.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional flyback type switching power supply. In FIG. 2, 1 is a protective fuse, 2 is a diode bridge for input rectification, 3 is an input smoothing capacitor, and 4 is a protective fuse 1 at the time of power failure.
Switch 5 such as a thyristor 16 for blowing off, 5 is a main switching element, 6 is a transformer, 7 is a secondary side rectifying and smoothing circuit composed of a diode and a capacitor, 8 is a control circuit of the main switching element 5, 9 is a constant voltage diode. A circuit 10 serves also to detect abnormal output voltage using a resistor 15, a resistor and a photocoupler, and to drive a switch 4 composed of a transistor and a resistor.

Next, a description will be given of a protection operation in the event of an abnormal output voltage. If a failure or the like occurs in the main switching element 5 or the main switch control circuit 8, the output voltage becomes abnormally high, and the heat of the transformer 6 or the overvoltage may occur in the secondary rectifying / smoothing circuit 7 and the load 10, which is dangerous. Therefore, the short circuit switch circuit 4 and the output overvoltage detection / switch drive circuit 9 are provided.

When the output voltage becomes equal to or higher than the Zener voltage of the constant voltage diode 15 constituting the output overvoltage detection / switch drive circuit 9, the thyristor 16 of the short-circuit switch circuit 4 is turned on, and the input short-circuit current flows. When the current exceeds the fusing current, the protection fuse 1 is blown, the power supply is disconnected from the input, and the output stops.

Usually, when an input is applied, the switching power supply rectifies the commercial power supply voltage, so that the rectified voltage is high, and the smoothing capacitor 3 stabilizes the output voltage and generates self-heating. The capacitance is large to suppress. Therefore, if the impedance of the discharge path of the residual charge of the smoothing capacitor 3 is high in a state where the operation of the switching power supply device is stopped due to the power cutoff, the voltage after rectification keeps a considerably high state for a long time.

[0006]

In the conventional power supply device, when testing the function of output overvoltage protection of the power supply device, an output overvoltage state is simulated, the fuse is blown, and the protection function is confirmed. Fuse must be replaced after test.

After the input is cut off, the capacitor is charged to a high voltage, and depending on how the power supply is handled after the test, there is a risk of an accident such as an electric shock due to residual charge of the capacitor.

According to the present invention, to solve such a problem, it is possible to judge the quality of the output overvoltage protection function without blowing a fuse at the time of a test, and to discharge the residual charge of the smoothing capacitor immediately after the power is turned off. It is an object of the present invention to provide a power supply device capable of performing the above.

[0009]

A circuit capable of generating a pseudo output overvoltage condition externally after an input is cut off and detecting and displaying a voltage between both ends of a smoothing capacitor charged by a switch such as a thyristor is provided. As a result, if the residual charge of the smoothing capacitor is rapidly discharged and the voltage between both ends is rapidly reduced, it can be confirmed that the operation of the output overvoltage protection function is normal. In addition, by providing an input monitoring and timer circuit to automatically turn on the switch for a certain period of time after the input is cut off in the same manner as in the case of the output overvoltage state, the residual charge of the smoothing capacitor is discharged, and the voltage between both ends is reduced. Can be reduced.

[0010]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a circuit for detecting and displaying the voltage between both ends of the capacitor 3 added in the present invention, 12 denotes an input cutoff monitoring circuit using a photocoupler, and 13 denotes a start-up by an output signal of the input cutoff monitoring circuit 12. The timer circuit and the simple power supply circuit 14 are provided with an output overvoltage detection / switch drive circuit 9,
This is a simple power supply circuit that operates the voltage detection / display circuit 11, the monitoring circuit 12, and the timer circuit 13. However,
It is necessary to have a voltage holding time necessary for confirming the operation of the output overvoltage protection function. Further, reference numeral 21 denotes a voltage detector constituting the circuit of the voltage detection display circuit 11, and reference numeral 22 denotes a display circuit comprising an emitting diode and a transistor.

The zener voltage of the constant voltage diode 15 of the output overvoltage detection / switch drive circuit 9 is selected to be higher than the normal output voltage. If the output voltage is normal, the photocoupler connected to the constant voltage diode 15 17 and the transistor 18 are off, and the thyristor 16 of the short-circuit switch circuit 4 is also off. When an abnormality occurs in the power supply device and the output voltage becomes higher than the Zener voltage of the constant voltage diode 15, the photocoupler 17 and the transistor 18 are turned on, and the short-circuit switch circuit 4 is also turned on. The fuse 1 is blown and the input is cut.

When testing the output overvoltage protection function, the load is disconnected and a test voltage source is connected to the output terminal. When the voltage of the test voltage source becomes higher than the Zener voltage immediately after the input is cut off, the photocoupler 17 and the transistor 18 are turned on, and the short-circuit switch circuit 4 is also turned on. Immediately after the input is cut off, the residual charge of the smoothing capacitor 3 is rapidly discharged through the short-circuit switch circuit 4, so that the voltage across the smoothing capacitor 3 drops rapidly.

When the voltage across the smoothing capacitor 3 is normal, the transistors in the voltage detection circuit 21 and the display circuit 22 are turned on, and the light emitting diode in the display circuit 22 emits light. When the voltage between both ends decreases, the transistor in the display circuit 22 turns off and the light emitting diode stops emitting light.

Therefore, a test for confirming the output overvoltage protection function is performed immediately after the input is cut off, and it can be confirmed that the output overvoltage protection function operates normally when the light emission of the light emitting diode disappears. Since the input is cut off, the protection fuse 1 is not blown.

The photocoupler of the monitoring circuit 12 is on when there is an input, but is off when there is no input. At this time, if the timer circuit 13 is started when the input is turned off and the output of the timer circuit 13 is held at the low level for a fixed time, the short-circuit switch circuit 4 is short-circuited for a fixed time immediately after the input is cut off, and the smoothing is performed. The residual charge of the capacitor 3 is discharged, and the voltage between both ends can be reduced.

[0016]

According to the present invention, since the operation test of the output overvoltage protection function can be performed when the input is cut off, the input short circuit does not occur even if the output overvoltage state is generated artificially from the outside. It is possible to check the output overvoltage protection function without fusing.

Further, by causing a short circuit between both ends of the smoothing capacitor for a certain period of time after the input is cut off and discharging the residual charge of the smoothing capacitor, an electric shock accident or the like can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Protective fuse, 2 ... Rectifier circuit, 3 ... Smoothing capacitor, 4 ... Short circuit switch circuit, 5 ... Main switching element,
6 transformer, 7 secondary rectification smoothing circuit, 8 main switch control circuit, 9 output overvoltage detection / switch drive circuit, 1
0: load, 11: voltage detection / display circuit, 12: monitoring circuit, 13: timer circuit, 14: simple power supply circuit, 21:
Voltage detection circuit, 22 ... Display circuit.

Continued on the front page F-term (reference) 5H006 AA04 CA02 CA03 CA12 CA13 CB01 CC02 CC08 DA04 DB01 DC05 FA01 GA04 5H410 CC03 CC09 CC10 DD02 DD09 DD10 EA11 EB04 EB32 EB40 FF03 FF22 FF25 FF28 LL02 LL04 LL18 LL20 5A730 A12AB12A DD04 EE07 FD01 FD11 FF19 FG01 VV03 XX03 XX12 XX23 XX32

Claims (2)

[Claims] 1. A protective fuse, a rectifier circuit, a smoothing capacitor, a switch connected in parallel with the smoothing capacitor and short-circuiting an input when an abnormality occurs to blow the fuse, and an output voltage detecting the switch when an abnormality is detected. A power supply device comprising: a driving circuit; and a circuit for detecting and displaying a voltage between both ends of the smoothing capacitor. 2. The power supply device according to claim 1, further comprising a circuit for turning on said switch for a predetermined time after the input is cut off.