JPH01107659A - Power circuit - Google Patents

Abstract

PURPOSE:To prevent rush current from being generated, by discriminating whether the detection value of DC voltage is more or less than a threshold value, and by short-circuiting a rush-current-proof resistor. CONSTITUTION:So far as a power circuit is concerned, an AC power source 1 is connected to a thyristor 4 and a transistor(Tr) 5 via a diode bridge 2, and a resistor 3 is set in parallel with the thyristor 4 and is connected to a capacitor 7 and a resistor 8, and an inverter unit 11. The collector of the Tr 5 is connected to the gate of the thyristor 4 and an emitter on the light receiving side 6 of a photo-coupler, and a base is connected to the collector of the photo-coupler light-receiving section 6. The power circuit is connected to the cathode of a photo-coupler light-generating section 10 and the GND of the inverter circuit unit 11. When the voltage of the AC current 1 is applied to the diode bridge 2, then the capacitor 7 is charged by the OFF of the thyristor 4, through the resistor 3, and when the charge comes to the Zener voltage of a Zener diode 9, then current flows to the photo-coupler light-generating section 10, and the thyristor 4 is turned ON.

Description

[Detailed description of the invention] The present invention relates to power supply circuits.

[Conventional technology]

In conventional power supply circuits, when the main transistor begins to oscillate, the resistor used to prevent inrush current is shorted using a triac.

Problems to be solved by invention and invention] However, the above-mentioned conventional power supply circuit,
When the main transistor starts to oscillate, the resistor for inrush current prevention is shorted with a triac, so even if the AC power supply is removed, the main transistor will continue to oscillate for several seconds. If AC power is applied during that time, charging current flows to the capacitor through the triac without passing through the inrush current prevention resistor, so there is a drawback that inrush current cannot actually be prevented.

[Means for solving problems]

The power supply circuit of the present invention is a capacitor input type switching power supply, and includes means for detecting a DC voltage after rectification and smoothing of a commercial power supply, and determining whether the detected value is above a threshold value or not.
and means for short-circuiting a resistor for preventing inrush current based on the determination.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

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

In the power supply circuit shown in the first factor, the AC power supply 1 is connected to the AC terminal of the diode bridge 2, and the DC 7 node terminal of the diode bridge 2 is connected to the 7 node terminal of the thyristor 4.
node and the emitter of transistor 5. The resistor 3 is connected in parallel to the seventh node and the cathode of the thyristor, and is connected to the capacitor 7, the resistor 8, and the input of the inverter circuit 11. The collector of the transistor 5 is connected to the gate of the thyristor 4 and the light receiving side 6 of the optical coupler 7.
The base is connected to the emitter of the photocoupler 6.
connected to the collector. The DC cathode terminal of the diode bridge 2 is connected to the other end of the capacitor 7, the cathode of the photocoupler light emitting unit 100, and the G of the inverter circuit 11.
Connected to ND. The anode of the photocoupler light emitting unit 10 is connected to the 7th node of the Zener diode 9, and the cathode of the Zener diode 9 is connected to the other end of the resistor 8.

Initially, since the voltage across the capacitor 7 is Ov, no current flows through the photocoupler light emitting section 10. Therefore,
The photocoupler light receiving section 6 remains open, and the transistor 5 also remains open. Therefore, since no trigger is applied to the gate of thyristor 4, thyristor 4 is also open.

Now, when the voltage of the AC power supply 1 is applied to the diode bridge 2, the capacitor 7 is charged through the resistor 3 because the thyristor 4 is open as described above. When the capacitor 7 is charged, the voltage across the capacitor 7 begins to increase, and when it reaches the Zener voltage v2 of the Zener diode 9, current begins to flow through the resistor 8 to the photocoupler light emitting section 10.

As a result, the photocoupler light emitting section 6 is turned on, the transistor 5 is also turned on, a trigger is applied to the gate of the thyristor 4, the thyristor 4 is turned on, and both ends of the resistor 3 are shorted.

In addition, when the voltage of AC power supply 1 is removed, capacitor 7
The voltage across is consumed by the inverter circuit 11,
begins to decrease. At this time, when the voltage across the capacitor 70 falls below the Zener voltage v2 of the Zener diode 9, the photocoupler light receiving section 6 is turned off, and the thyristor 4 is also turned off.
When the voltage of the AC power source 1 is removed, the holding current stops flowing and the AC power source 1 is turned off.

Therefore, when AC power is applied next time, the capacitor 7 starts to be charged through the resistor 3.

Furthermore, if AC power is applied before the voltage across the capacitor 7 drops below the Zener voltage v2 of the Zener diode due to removal of the AC power, the capacitor 7 will still have enough charge to resist the voltage. , does not charge through resistor 3, but the charging current is small.

In the above embodiment, a Zener diode is used as an example of a detection means, but this is not limited to a Zener diode, and a circuit such as a comparator can be used to detect a DC voltage after smoothing. There may be.

Further, in the above-described embodiment, a circuit that combines the light emitting part and the light receiving part of a photocoupler is shown as an example of the determination means, but this may be a logic circuit that transmits the result of a comparator.

Furthermore, in the above-described embodiments, a triac was shown as an example of the short-circuit means, but this may also be a relay circuit operated by the output of a logic circuit.

〔Effect of the invention〕 .

The power supply circuit of the present invention, in a capacitor input type switching power supply, includes means for detecting a DC voltage after rectification and smoothing of a commercial power supply, means for determining whether the detected value is above or below a threshold value, and a means for determining whether the detected value is above or below a threshold value. Providing means for shorting the inrush current prevention resistor has the effect that inrush current can be prevented in any case by appropriately selecting a threshold value.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. 1...AC power supply, 2...Diode bridge, 3.8...Resistor, 4...Triac, 5...PNP type transistor ,6・
...Photocoupler light receiving section, 7...Capacitor, 9...Zena diode, 10...
...Photocoupler light receiving section, 11...Inverter circuit. Agent Patent Attorney Oto Uchihara

Claims (1)

[Claims] a detection means for detecting a rectified and smoothed DC voltage of an AC power supply and outputting a detected value; a judgment means for outputting a judgment result as to whether the detected value is above or below a threshold; and a means for preventing inrush current based on the judgment result. short-circuiting means for short-circuiting a resistor for use in a power supply circuit.