JP2002315336A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of variations in a plurality of secondary-side output voltages due to load variations occurring in a control circuit for a switching power supply, though feedback control is performed by using one of the secondary-side output voltages with a photocoupler. SOLUTION: A switching power supply device is provided which subjects the secondary-side output voltages to constant-voltage control, by fitting a voltage detection circuit to each of a plurality of secondary windings provided on the secondary side, feeding them back collectively to the primary side and performing feedback control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flyback type switching power supply used for an indoor unit and an outdoor unit of an air conditioner, for example.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram of a switching power supply device showing a conventional embodiment. 2, one end of a primary winding 2a of a transformer 2 is connected to + of a DC power supply, the other end is connected to a collector of the switching element 4, and an emitter of the switching element 4 is connected to-of the DC power supply. .
The base of the switching element 4 is connected to an oscillation control circuit 110 including the photocoupler 6.

At one end of the secondary winding 2b of the transformer 2,
The anode of the diode 8 is connected, and the other end of the secondary winding 2b is connected to the secondary-side ground of the transformer 2. The cathode of the diode 8 is connected to the + side of the smoothing capacitor 20, the other end of the capacitor 20 is connected to the ground, and both ends of the capacitor 20 become the secondary-side constant voltage output V1. From the cathode of the diode 8,
The voltage dividing resistors 32 and 34 are connected in series, the other end is connected to the ground, and the connection between the voltage dividing resistors 32 and 34 is connected to the reference of the shunt regulator 14. A current limiting resistor 30 is connected to the cathode of the rectifying diode 8, and the other end of the resistor 30 is connected to the anode of the photodiode 6a of the photocoupler 6, and
The cathode of 6a is connected to the cathode of the shunt regulator 14, and the anode of the shunt regulator 14 is connected to the ground. The above voltage dividing resistors 32, 34 and resistor 30,
The photodiode 6a of the photocoupler 6 and the shunt regulator 14 constitute a voltage detection circuit 100.

At one end of the secondary winding 2c of the transformer 2,
The anode of the diode 10 is connected, and the other end of the secondary winding 2c is connected to the secondary-side ground of the transformer 2. The cathode of the diode 10 is connected to the + side of the smoothing capacitor 22, the other end of the capacitor 22 is connected to the ground, and both ends of the capacitor 22 become the constant voltage output V2 on the secondary side.

The anode of a diode 12 is connected to one end of the secondary winding 2d of the transformer 2, and the other end of the secondary winding 2d is connected to the ground on the secondary side of the transformer 2. The cathode of the diode 12 is connected to the + side of the smoothing capacitor 24, the other end of the capacitor 24 is connected to the ground, and both ends of the capacitor 24 become the constant voltage output V3 on the secondary side.

Next, the operation of the circuit will be described. FIG.
In, the primary side circuit includes a primary winding 2a of the transformer 2, a switching element 4, and an oscillation control circuit 110.
The oscillation control circuit 110 may be of a self-excited type or a separately-excited type, and the driving and control of the switching element 4 are performed by turning the oscillation control circuit 110 on and off. When DC power is input to the primary winding 2a, the switching element 4 is turned on by an ON / OFF signal of the oscillation control circuit 110.
Starts an on / off switching operation. A pulse voltage is applied to the primary winding 2a by the switching operation, and when the primary winding 2a is turned off, the secondary windings 2b to 2b.
An ON voltage proportional to the number of turns of the coil of the transformer 2 is supplied to 2d, and ON and OFF voltages are thereafter output in the same manner as the primary voltage. In addition, the voltage is a rectifying diode
Rectified constant voltage outputs V1 to V3 are output via 8, 10, 12 and the smoothing capacitors 20, 22, 24.

When the DC voltage output to V1 rises,
The voltage from the connection between the voltage dividing resistors 32 and 34 is detected by the reference of the shunt regulator 14, and when the voltage exceeds a certain arbitrary voltage, the shunt regulator 14 is turned on,
The photodiode 6a of the photocoupler 6 turns on. In response to the ON optical signal of the photodiode 6a,
The phototransistor 6b turns on and the oscillation control circuit
110 controls the ON width and the OFF width of the switching element 4, and the rise of the voltage of the constant voltage outputs V1 to V3 generated in the secondary windings 2b to 2d stops and falls.

The constant voltage output V1 of the secondary winding 2b of the transformer 2
Falls, the voltage at the connection between the voltage-dividing resistors 32 and 34 also falls. When the voltage drops below an arbitrary voltage, the shunt regulator 14 turns off, and the photodiode 6a of the photocoupler 6 turns off. By turning off the photodiode 6a, the optical signal sent to the phototransistor 6b is cut, the operation of the phototransistor 6b is also turned off, and the oscillation control circuit 110 controls the on-width and off-width of the switching element 4. Then, the voltage generated in the secondary winding 2b rises, and the shunt regulator 14 is turned on, whereby the oscillation of the switching element 4 is controlled as described above. By performing the ON / OFF operation of the shunt regulator 14, the stabilized constant voltage output V1 is maintained.

[0009]

In the switching operation by the control circuit, the voltage of the secondary winding 2b is detected and fed back to the oscillation control circuit 110, so that the constant voltage output V1 of the secondary winding 2b is Although the voltage fluctuation due to the load fluctuation hardly occurs, the constant voltage outputs V2 and V3, to which the voltage detection circuit 100 is not connected, cause the voltage fluctuation due to the load fluctuation of the constant voltage output V1 or the constant voltage outputs V2 and V3.
However, there is a problem that a stabilized voltage cannot be obtained when the load changes.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and provides a stabilized high-precision DC voltage for all of the constant voltage outputs V1 to V3 by providing a simple voltage detection circuit. An object of the present invention is to provide a highly reliable and inexpensive switching power supply device capable of supplying a voltage.

[0011]

According to the present invention, a transformer 2 comprising a primary winding 2a, a secondary winding 2b having a plurality of arbitrary connecting portions, and a primary winding 2 are provided.
a is the switching element 4 to which the oscillation control circuit 110 is connected.
And a first voltage detection circuit 102 in one of the secondary windings 2b.
And second voltage detection circuits 104 and 106 each composed of a voltage-dividing resistor and a diode in the other secondary windings. The first voltage detection circuit 102 and the second voltage detection circuit 10
A switching power supply device is provided, wherein the switching power supply device includes a voltage detection unit connected to the first and second voltage detection circuits and feedback-controlled from the first voltage detection circuit to the switching element of the primary winding.

[0012]

FIG. 1 is a circuit diagram of a switching power supply according to an embodiment of the present invention. In FIG. 1, one end of a primary winding 2a of a transformer 2 is connected to + of a DC power supply, and the other end is connected to a collector of a switching element 4,
The emitter of the switching element 4 is connected to-of the DC power supply. The base of the switching element 4 is connected to an oscillation control circuit 110 including the photocoupler 6.

At one end of the secondary winding 2b of the transformer 2,
The anode of the diode 8 is connected, and the other end of the secondary winding 2b is connected to the secondary-side ground of the transformer 2. The cathode of the diode 8 is connected to the + side of the smoothing capacitor 20, the other end of the capacitor 20 is connected to the ground, and both ends of the capacitor 20 become the secondary-side constant voltage output V1. From the cathode of the diode 8,
The voltage dividing resistors 32 and 34 are connected in series, and the other end is connected to the ground. Also, the cathode of the rectifying diode 8
The current limiting resistor 44 is connected, the other end of the resistor 44 is connected to the cathode of the photodiode 6a of the photocoupler 6, and the anode of the photodiode 6a is connected to the connection between the voltage dividing resistors 32 and 34. You. The photodiode
The cathode of 6a is connected to the cathode of the Zener diode 26, and the anode of the Zener diode 26 is connected to the ground. The photodiode 6a and the Zener diode 26 constitute a voltage detecting unit 108. further,
The voltage dividing resistors 32 and 34, the resistor 44, the photodiode 6a of the photocoupler 6, and the zener diode 26 constitute a first voltage detection circuit 102.

The anode of a diode 10 is connected to one end of the secondary winding 2c of the transformer 2, and the other end of the secondary winding 2c is connected to the ground on the secondary side of the transformer 2. The positive electrode of the smoothing capacitor 22 is connected to the cathode of the diode 10, the other end of the capacitor 22 is connected to the ground, and both ends of the capacitor 22 become the secondary side constant voltage output V2. From the cathode of the rectifying diode 10, voltage dividing resistors 36 and 38 are connected in series, the other end is connected to the ground, and the connection of the voltage dividing resistors 36 and 38 is connected to the anode of the diode 16. I have.

The anode of a diode 12 is connected to one end of the secondary winding 2d of the transformer 2, and the other end of the secondary winding 2d is connected to the ground on the secondary side of the transformer 2. The cathode of the diode 12 is connected to the + side of the smoothing capacitor 24, the other end of the capacitor 24 is connected to the ground, and both ends of the capacitor 24 become the constant voltage output V3 on the secondary side. From the cathode of the diode 12, voltage dividing resistors 40 and 42 are connected in series, the other end is connected to the ground, and the connection of the voltage dividing resistors 40 and 42 is connected to the anode of the diode 18. The cathode of the diode 16 and the cathode of the diode 18 are connected to the connection of the voltage dividing resistors 32 and 34, respectively.

Next, the operation of this circuit will be described. FIG.
In the circuit on the primary side, the primary winding 2a of the transformer 2,
It comprises a switching element 4 and an oscillation control circuit 110. The oscillation control circuit 110 may be of a self-excited type or a separately-excited type, and the driving and control of the switching element 4 are performed by turning the oscillation control circuit 110 on and off.
When DC power is applied to the primary circuit, the switching element 4 starts an on / off switching operation in response to an on / off signal of the oscillation control circuit 110. The primary winding
2a, a pulse voltage is applied by the switching operation, and when the primary winding 2a is turned off, an on-voltage proportional to the number of coil turns of the transformer 2 is supplied to the secondary windings 2b to 2d,
Thereafter, ON and OFF voltages are output in the same manner as the primary voltage. Further, the voltage is rectified via rectifying diodes 8, 10, 12 and smoothing capacitors 20, 22, 24, and constant voltage outputs V1 to V3 are output.

The DC voltages output to the constant voltage outputs V2 and V3 are passed through second detection circuits 104 and 106 together with the voltages of the voltage dividing resistors 32 and 34 of the first voltage detection circuit 102 of V1.
It is supplied to the anode of the photodiode 6a. The diodes 16 and 18 in the second detection circuits 104 and 106 are provided to prevent a backflow of current to the DC outputs V2 and V3. On the other hand, in the Zener diode 26, the voltage from the constant voltage output V1 is always applied to the Zener voltage VZ via the current limiting resistor 44. When a voltage equal to or higher than the sum of the forward voltage VF of the photodiode 6a and the zener voltage VZ, that is, VF + VZ, is applied to the anode of the photodiode 6a, the photodiode 6a turns on. Upon receiving the ON optical signal of the photodiode 6a, the phototransistor 6b is turned on, the oscillation control circuit 110 controls the ON width and the OFF width of the switching element 4, and applies the secondary windings 2b to 2d. The rise of the generated constant voltage outputs V1 to V3 stops and falls.

Next, when the constant voltage outputs V1 to V3 of the secondary windings 2b to 2d of the transformer 2 drop and the voltage of the anode of the photodiode 6a becomes equal to or lower than VF + VZ, the photodiode 6a is turned off. Operation. When the photodiode 6a turns off, the phototransistor 6b
The optical signal to be sent is cut off, the operation of the phototransistor 6b is also turned off, the oscillation control circuit 110 controls the ON width and the OFF width of the switching element 4, and the voltage generated in the secondary windings 2b to 2d is reduced. As a result, the oscillation of the switching element 4 is controlled as described above by turning on the photodiode 6a. ON of the photodiode 6a,
By performing the OFF operation, the stabilized constant voltage outputs V1 to V3 are held.

Next, each voltage value of the above-described circuit will be described as an embodiment. In the circuit of FIG. 1, the input DC power supply is DC 140 V obtained by rectifying AC 100 V with a diode.
Power is supplied. The constant voltage output V1
12V 700mA, V2 30V 100mA, V
3 is set so that a load of 24 V and 20 mA is connected thereto, and the Zener voltage V
Z is set to 5 to 6V, and the forward voltage VF at the anode of the photodiode 6a is 1V. The output voltage of each load is 6 to 7 V which is the sum of the forward voltage VF of the photodiode 6a and the zener voltage VZ of the zener diode 26, that is, VF + VZ, by the voltage dividing resistors 32 and 34, 36 and 38, and 40 and 42. Thus, the respective resistance constants are set. The constant setting of the resistor can be set by different loads V1 to V3, and a stable power supply can be achieved. Further, the first voltage detection circuit 102 includes the voltage detection circuit 1 shown in FIG.
Even if it is replaced with 00, the same effect can be obtained.

This time, for the three DC outputs, the secondary windings 2b to 2d
Although the control method was described, although not shown,
It is needless to say that two outputs of DC can be used from the two windings of the secondary windings 2b and 2C, and more than four outputs of DC can be realized by adding a circuit of the secondary winding 2C. In this case, an independent secondary winding was described. However, although not shown, a plurality of secondary-side windings are provided by tapping one winding to provide a plurality of DC outputs. Can also be achieved.

[0021]

As described above, in the conventional example, the voltage detection circuit is provided for one output voltage on the secondary side, and the detected voltage is feedback-controlled by the photocoupler. Even if there are a plurality of windings on the side, by setting the constant of the voltage dividing resistor in the voltage detection circuit, the feedback control with higher accuracy than the conventional embodiment is performed even for the voltage output to each winding. Thus, highly reliable and stabilized control can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a switching power supply device showing an embodiment of the present invention.

FIG. 2 is a circuit diagram of a switching power supply device showing a conventional embodiment.

[Explanation of symbols]

 In the drawings, the same reference numerals indicate the same or corresponding parts. 2 Transformer 2a Primary winding 2b to 2d Secondary winding 4 Switching element 6 Photocoupler 6a Photodiode 6b Phototransistor 8, 10, 12, 16, 18 Diode 14 Shunt regulator 20, 22, 24 Capacitor 26 Zener diode 30, 44 Resistance 32, 34, 36, 38, 40, 42 Voltage dividing resistor 100 Voltage detection circuit 102 First voltage detection circuit 104, 106 Second voltage detection circuit 108 Voltage detection unit 110 Oscillation control circuit

Claims (2)

[Claims] 1. A transformer comprising a primary winding, a secondary winding having a plurality of arbitrary connecting portions, a switching element having an oscillation control circuit connected to an end of the primary winding, and a plurality of secondary windings. One of the windings includes a first voltage detection circuit, and the other secondary winding includes a plurality of second voltage detection circuits each including a voltage dividing resistor and a diode. The circuit and the plurality of second voltage detection circuits are connected, and the first
A switching power supply device comprising a voltage detection unit that performs feedback control of the voltage detection circuit to the switching element of the primary winding. 2. The switching power supply device according to claim 1, wherein said secondary winding comprises an arbitrary connection portion formed by tapping, said connection portion comprising a rectifying diode, a smoothing capacitor, and a voltage detection circuit.