JPH11308857A - Switching power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for compulsively discharging an input capacitor, at the cutting off of the input power source of a switching power source using a power factor collection(PFC). SOLUTION: Boosting is performed using a PFC3, and the secondary side of a transformer T1 is supplied with a constant voltage, being switching by an RCC5 or the like. Switching circuits 6 and 7 on the output side are controlled by a single-chip microcomputer 10 or the like, and at waiting of an apparatus for supplying power, the switch circuits 6 and 7 are turned off, and the power is not supplied to loads 8 and 9. When the input power source is cut off in this condition by turning off the switch SW, it follows that it needs a long time for discharging an input capacitor C1, since it is of light load. So, a one- shot multiple valve 11 or the like detects the cycle of the switching having exceeded the specified cycle, and the microcomputer 10 turns on the switch circuit 6 or the like, in accordance with its detection output, and compulsively discharges the voltage of the input capacitor C1 at the cut off of an input power source, with the light load as a stationary load.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a PFC (Power Fa
The present invention relates to a switching power supply device in which an input capacitor is forcibly discharged to rapidly reduce a voltage even when an input power supply of a switching power supply using a circuit is cut off at a light load.

[0002]

2. Description of the Related Art On the input side, a switching power supply device using a PFC comprising a chopper circuit for improving a power factor of input power by performing a boost or the like is frequently used. In a PFC, generally, an input voltage is boosted to a high voltage of about 380 V and input to a switching circuit. On the other hand, a recent electronic device such as a television includes a control unit including a one-chip microcomputer or the like for connecting a power supply for operating a main body in response to an external control signal from a remote controller in a standby state. In many cases, the main body is operated by using. The power supply for such a device is a so-called multi-power supply that supplies a power supply for standby to the control unit and a power supply for operating one or more main units. When the input power supply (so-called main power supply) of such a switching power supply as a multi-power supply is disconnected at a light load such as in a standby state, the impedance between both terminals of the input capacitor used in the switching circuit is high. Since it is left in a state, it takes a long time to discharge. Therefore, the above-described control unit remains in the operating state even when the input power is turned off, which may cause a malfunction. Further, even when the input power is turned off, for example, during maintenance of the device, a high voltage remains inside the device, which may cause a safety problem.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide means for forcibly discharging an input capacitor when an input power supply of a switching power supply using a PFC circuit is cut off. I do.

[0004]

[Means for Solving the Problems] PFC (Power Factor C)
orrection) In a switching power supply device that improves the power factor of input power using a circuit and switches the input side voltage at a duty ratio according to the output voltage to output the output voltage as a predetermined voltage, the switching cycle And a load adding means for applying a load to the output side in accordance with the detection output thereof, and forcibly changing the voltage of the input capacitor when the input power of the switching power supply device is turned off. Discharge.

The switching cycle detecting means comprises a Schmitt circuit for generating an on / off signal corresponding to the switching cycle from a voltage fluctuating at the switching cycle, and a one-shot multivibrator for triggering at the rise or fall of the on / off signal. I do.

[0006] The switching power supply device has a standby output for supplying power during standby of a control unit for controlling a device using the output, and one or more operating power supply outputs for supplying power during operation of the device. And a multi power supply with
The load adding means is configured to connect a power supply during operation.

The control section is a one-chip microcomputer including an MPU or the like, and the load adding means inputs an output signal of the one-shot multivibrator to the one-chip microcomputer and connects the power supply during operation by the signal. Configuration.

A switching power supply that uses a PFC (Power Factor Correction) circuit to improve the power factor of the input power and to switch the input side voltage at a duty ratio according to the output voltage to output the output voltage as a predetermined voltage. In the device, output voltage detecting means for detecting that the output voltage has exceeded a predetermined voltage, and short-circuit means for connecting a short-circuit resistor to the input capacitor according to the detection signal are provided. Is forcibly discharged.

The output voltage detecting means comprises a Zener diode which conducts at a predetermined voltage, and a switching transistor which is turned on by the conduction current.

The short-circuit means is a resistor having one end connected to the input voltage side of the input capacitor and the other end connected to the collector of a second switching transistor which switches by the output of the switching transistor.

A photocoupler comprising a photodiode and a photothyristor is provided between the switching transistor and the second switching transistor, and the output of the switching transistor switches the second phototransistor via the photocoupler. .

The transmission of the switching circuit is controlled by the second switching transistor.

A predetermined voltage detected by the output voltage detecting means is set within a safe voltage range of the switching power supply, the input capacitor is forcibly discharged, and overvoltage protection of the switching power supply is performed.

The resistor used for the short-circuit means is a thermistor whose resistance value decreases with temperature.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic circuit diagram of one embodiment of a switching power supply according to the present invention. A commercial power input from a power connector 1 is rectified by a diode matrix 2 via a switch SW, and a PF according to the related art is rectified.
Input to C circuit 3. In the PFC circuit 3, the rectified voltage is supplied to the coil L1, and the output side is switched by a transistor Tr1 such as an FET to boost the voltage. The output is rectified by a diode D1 and an input capacitor C1 to approximately 380 V
Voltage of the order. Switching is performed by the transistor Tr1 by controlling the supply of power from the voltage dividing resistors R1 and R2 and the control IC 4 that controls the voltage from the winding L4 of the transformer T1 with the voltage rectified by the diode D5 and the capacitor C4. An input voltage is supplied to a winding L2 of a transformer T1, and the other end is connected to a switching transistor Tr2, Tr2.
RCC (ringing choke converter) consisting of 3 grades
By switching at 5, a secondary voltage is induced in the other winding of the transformer T1. The voltage from windings L5 and L6 is
The power is rectified by the diodes D6 and D7 and the capacitors C5 and C6, and supplied to the loads 8 and 9 of the equipment to which the power is supplied by the power supply device through the switch circuits 6 and 7. That is, in this example, there are two operating power supplies. The RCC performs switching with the output voltage of the winding L3 as usual, and the phototransistor T on the secondary side of the photocoupler 6.
The duty ratio and cycle of the switching are controlled by r4. The primary side of the photocoupler 6 divides the output of the winding L7 by a diode D8 and a voltage rectified by a capacitor C7 by resistors R9 and R10 to shunt a regulator S1.
The current of 0 is controlled, and the current of the photodiode D9 of the photocoupler 6 is controlled by the current. In this way, a constant voltage is supplied to each output of the transformer T1.

The output-side switch circuits 6 and 7 are controlled by a one-chip microcomputer 10 or the like composed of an MPU or the like. No power is supplied. If the switch SW is turned off and the input power is turned off in this state, it takes a long time to discharge the input capacitor C1 because the load is light. Therefore, switching cycle detecting means for detecting that the switching cycle has exceeded a predetermined cycle, and load adding means for applying a load to the output side in accordance with the detected output are provided, and the input power is supplied when the switching power supply is turned off. The voltage of the capacitor is forcibly discharged.

As the switching cycle detecting means, for example, the following can be considered. The output voltage of the winding L7 that supplies the standby voltage is made into a pulsating current by the diode D11, and is input to the operational amplifier OP1 that constitutes a Schmitt circuit that slices with the voltage divided by the resistors R9 and R10. An output signal that turns on and off with a proportional period is obtained. The one-shot multivibrator 11 is triggered by the rise or fall of the on / off signal.
The time constant of the one-shot multivibrator 11 is a constant voltage output when the period of the triggering on / off signal is a period in a steady state when the switch SW is on, and when the period becomes longer than the period, the on / off signal is output. Set to output. With such a configuration, when the output of the one-shot multivibrator 11 becomes an on / off signal, it is possible to detect that the switching cycle exceeds a predetermined cycle.

In this embodiment, the following can be considered as the load adding means. The output of the one-shot multivibrator 11 is input to the one-chip microcomputer 10, and whether or not the output becomes an on-off signal is monitored. When the output becomes an on-off signal, the switch circuits 6 and / or 7 are turned on. , Loads 8 and 9 are connected. As a result, a load is applied to the switching power supply device, and the load changes from a light load to a load during operation. The above operation in this case is summarized as follows. First, it is assumed that the switch SW is turned off at a light load. When the voltage supplied to the RCC starts to decrease, the duty ratio of switching in the RCC increases, and the cycle becomes longer. When this cycle becomes longer than the time constant of the one-shot multivibrator 11, the output becomes a constant voltage from an on-off signal. This is detected by the one-chip microcomputer 10, and the switch circuits 6 and 7 are turned on to change the load from a light load to a steady load. As a result, the electric charge charged in the input capacitor C1 is immediately discharged.

FIG. 2 is a schematic circuit diagram of another embodiment of the switching power supply according to the present invention. The configuration and operation as a switching power supply are the same as described above. However, in the figure, only one output power supply is shown. In this embodiment, an output voltage detecting means for detecting that the output voltage has exceeded a predetermined voltage, and a short-circuit means for connecting a short-circuit resistor to an input capacitor according to the detection signal are provided to cut off the input power of the switching power supply device. Sometimes, the voltage of the input capacitor is forcibly discharged.

Specifically, for example, the following configuration is adopted. The output voltage detecting means includes a Zener diode D21 that conducts at a predetermined voltage, a switching transistor Tr21 that is turned on by the conduction current, and the like. The short-circuit means for connecting a short-circuit resistor to the input capacitor is:
One end is connected to the input voltage side of the input capacitor C1, and the other end is a resistor R25 connected to the collector of a second switching transistor Tr22 that switches with the output of the switching transistor Tr21. Switching transistor Tr21 and second switching transistor T
A photocoupler 21 including a photodiode D22 and a photothyristor D23 is provided between the photocoupler 21 and the output of the switching transistor Tr21.
In this configuration, the second switching transistor Tr22 is switched via the switch, so that the ground level is separated. The collector of the second switching transistor Tr22 has an RCC switching transistor Tr
The base of the second switching transistor Tr22 is connected, and the transmission of the switching circuit is controlled by the second switching transistor Tr22. When the second switching transistor Tr22 is on, the transmission is stopped.

In such a configuration, the following operation is performed. When the switch SW of the input power supply is turned off, the input capacitor C1 starts discharging, and the input voltage V0 decreases. As a result, the base voltage of Tr2 connected by the resistor R4 decreases, and the base current also decreases. On the other hand, the output voltage V1
By controlling the photocoupler 6 controlled by the above, the switching duty ratio of Tr2 becomes large and the cycle becomes long so that the base current of Tr2 is kept constant. But,
Since the base voltage of Tr2 keeps decreasing, there is a limit in keeping the base current constant. As a result, the output voltage V1 cannot be maintained at a constant voltage, and the output voltage V1 increases.
When the output voltage V1 rises and the Zener diode D21 connected by the protection resistor R22 exceeds the Zener voltage, it conducts and turns on the switching transistor Tr21. When the switching transistor Tr21 is turned on, the photodiode D22 of the photocoupler 21 emits light, and the photothyristor D23 becomes conductive. The current of the photothyristor D23 becomes a base current of the second switching transistor Tr22 through the resistor R24, and the transistor Tr22 is turned on. As a result, the input voltage V0 is short-circuited to the reference voltage by the resistor 25, the input capacitor C1 is forcibly discharged, and the transmission of Tr2 is stopped.

By setting the Zener voltage of the Zener diode D22 within the safe voltage range of the output voltage V1 of the switching power supply, the input capacitor C1 is forcibly discharged when the input power is turned off, as described above. In addition, overvoltage protection of the switching power supply device can be performed. The resistor R25 for short-circuiting the input capacitor C1 maintains a high resistance in a steady state,
As a thermistor having low resistance when short-circuited by Tr22, power loss when operating as the overvoltage protection circuit can be reduced.

[0023]

The power factor of input power is improved by using a PFC (Power Factor Correction) circuit, and the output voltage is output as a predetermined voltage by switching the input side voltage at a duty ratio corresponding to the output voltage. In a switching power supply, a switching cycle detecting means for detecting that the switching cycle exceeds a predetermined cycle, and a load adding means for applying a load to an output side in accordance with the detected output are provided. By forcibly discharging the voltage of the input capacitor at the time of disconnection, even when the input power supply is disconnected at a light load, safety is ensured because the input power supply is immediately discharged.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of one embodiment of a switching power supply according to the present invention.

FIG. 2 is a schematic circuit diagram of another embodiment of the switching power supply according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 input outlet 2 diode matrix 3 PFC (Power Factor Correction) circuit 4 control IC 5 RCC (ringing choke converter) 6, 7 switch circuit 8, 9 load 10 one-chip microcomputer 11 one-shot multivibrator R1 to R10 resistors C1 to C7 Capacitor Tr1 to Tr4 Transistor D1 to D10 Diode T1 Transformer L1 to L6 Winding OP1 Operational amplifier 21 Photocoupler R21 to R26 Resistance C21, C22 Capacitor Tr21, Tr22 Transistor D21, D22 Diode D23 Photothyristor V0 Input voltage V1 Output voltage

Claims (11)

[Claims] An output voltage is output as a predetermined voltage by improving a power factor of input power using a PFC (Power Factor Correction) circuit and switching an input side voltage at a duty ratio according to the output voltage. In a switching power supply, a switching cycle detecting means for detecting that the switching cycle exceeds a predetermined cycle, and a load adding means for applying a load to an output side in accordance with the detected output are provided. A switching power supply device characterized in that a voltage of an input capacitor is forcibly discharged when disconnected. 2. The switching cycle detecting means according to claim 1, wherein said switching cycle detecting means generates an on / off signal corresponding to said switching cycle from a voltage fluctuating at said switching cycle, and a one-shot multivibrator for triggering at a rise or fall of said on / off signal. The switching power supply device according to claim 1, wherein the switching power supply device comprises: The switching power supply device includes a standby output for supplying power during standby of a control unit that controls the device using the output, and a power supply for supplying power during operation of the device.
3. The switching power supply according to claim 2, wherein the power supply is a multi-power supply having two or more operation power supply outputs, and the load adding means is connected to a power supply during operation. 4. The control unit is a one-chip microcomputer including an MPU or the like, and the load adding unit inputs an output signal of the one-shot multivibrator to the one-chip microcomputer, and uses the signal to turn on the power supply during operation. The switching power supply according to claim 3, wherein the switching power supply is connected. 5. An output voltage is output as a predetermined voltage by improving a power factor of input power using a PFC (Power Factor Correction) circuit and switching an input side voltage at a duty ratio according to the output voltage. In a switching power supply, an output voltage detecting means for detecting that an output voltage exceeds a predetermined voltage, and a short-circuit means for connecting a short-circuit resistor to an input capacitor according to the detection signal are provided. A switching power supply device for forcibly discharging a voltage of an input capacitor. 6. The switching power supply according to claim 5, wherein said output voltage detecting means comprises a Zener diode which conducts at a predetermined voltage and a switching transistor which is turned on by the conduction current. 7. The short-circuit means is a resistor having one end connected to the input voltage side of the input capacitor and the other end connected to the collector of a second switching transistor that switches at the output of the switching transistor. The switching power supply device according to claim 6, wherein 8. A configuration in which a photocoupler including a photodiode and a photothyristor is provided between the switching transistor and the second switching transistor, and an output of the switching transistor switches the second phototransistor via the photocoupler. The switching power supply device according to claim 7, wherein 9. The switching power supply according to claim 7, wherein said second switching transistor controls transmission of said switching circuit. 10. A predetermined voltage detected by the output voltage detecting means is set within a safe voltage range of the switching power supply device, and the input capacitor is forcibly discharged.
6. The switching power supply device according to claim 5, wherein overvoltage protection of the switching power supply device is performed. 11. The switching power supply according to claim 7, wherein the resistance used for the short-circuit means is a thermistor whose resistance value decreases with temperature.