JPH07337012A - Multi-output switching power supply circuit - Google Patents

Abstract

PURPOSE:To realize a multi-output switching power supply circuit by connecting a sub-output circuit for rectifying/smoothing a positive voltage in parallel with a sub-output circuit for rectifying/smoothing a negative voltage and taking out positive and negative voltages from one secondary winding. CONSTITUTION:A reset circuit comprising a main switch 12, a capacitor 15, and an auxiliary switch 13 is connected with the primary winding of a transformer 60. A sub-output circuit 30 for rectifying/smoothing the positive voltage induced in the secondary winding of the transformer 60 is connected in parallel with a sub-circuit 30 for rectifying/smoothing the negative voltage induced in the secondary winding of the transformer 60 so that positive and negative voltages can be taken out from one secondary winding. This circuitry realizes a multi-output switching power supply circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-output switching power supply circuit suitable as a power supply for computers and the like.

[0002]

2. Description of the Related Art A conventional example of a multi-output switching power supply circuit of this type is shown in FIG. In the figure, 10 is a converter,
20 is a main output circuit, 30 is a secondary output circuit, 40 is a transformer, and 50 is a feedback circuit. The transformer 40 has a primary winding n
1, a secondary winding n2 for the main output circuit 20, and a pair of secondary windings n31 and n32 for the secondary output circuit 30. The feedback circuit 50 is composed of an error amplifier 51 for detecting an error of the output voltage + V of the main output circuit 20, an insulating photo coupler 52, and a PWM (pulse width modulation) control circuit 53.

In the converter 10, a DC power source 11 is connected to the primary winding n1 of the transformer 40. 1
2 and 13 are switches, each of which is a field effect transistor. The switch 12 is driven by the output of the PWM control circuit 53. The switch 13 is the PWM control circuit 5
It is controlled via the auxiliary transformer 14 which is controlled by the output of No. 3. Reference numeral 15 is a snubber capacitor. The switch 12 is directly connected to the switch 12, and the switch 13 is connected to the primary winding n1 of the transformer 40 via the capacitor 15. A parasitic diode 16 is connected to the switch 13. The switch 13, the capacitor 15, and the parasitic diode 16 constitute a transformer / reset circuit.

In the main output circuit 20, 21 is a saturable inductor, 22 is a rectifying diode, 23 is a freewheeling diode, 24 is a choke coil, and 25 is an output smoothing capacitor. One end of the secondary winding n2 for the main output circuit 20 is connected to the output terminal 26 via the saturable inductor 21, the rectifying diode 22, and the choke coil 24. The other end of the secondary winding n2 is connected to the output terminal 27, and the output terminal 27 is connected to the common potential point COM.
A freewheeling diode 23 and a capacitor 25 are connected to both ends of the choke coil 24. The output terminals 26 and 27 are connected to the input terminal of the error amplifier 51 that constitutes the feedback circuit, and the output terminal of the error amplifier 51 is connected to the PWM control circuit 53 via the photocoupler 52.

In the secondary output circuit 30, the secondary windings n31 and n32 of the transformer 40 are connected in series, and the connection point is connected to the common potential point COM. 31 and 31a are saturable inductors, 32 and 32a are rectifying diodes,
33 and 33a are return diodes, 34 and 34a are choke coils, 35 and 35a are smoothing capacitors, and 36 and 3
6a is a post regulator for regulating the output voltage of the slave output circuit, and 37 and 37a are output smoothing capacitors. The saturable inductor 31, the rectifying diode 32, the free wheeling diode 33, the choke coil 34, the smoothing capacitor 35, the post regulator 36, and the output smoothing capacitor 37 constitute a circuit for obtaining the DC output voltage + V2, and the saturable inductor 31a, The rectifying diode 32a, the free wheeling diode 33a, the choke coil 34a, the smoothing capacitor 35a, the post regulator 36a, and the output smoothing capacitor 37a constitute a circuit for obtaining the DC output voltage -V2.

In such a configuration, the converter 10
When the switch 12 configuring the above is directly conducted, and the switch 13 is alternately conducted by the output of the PWM control circuit 53 via the auxiliary transformer 14, the voltage Vi of the DC power supply 11 is turned on / off. A voltage is induced in each of the secondary winding n2 of the main output circuit 20 and the secondary windings n31, n32 of the slave output circuit 30. Main output circuit 2
The voltage induced in the secondary winding n2 of 0 is the saturable inductor 2
It is converted into a DC voltage + V through the diode 1, the diodes 22 and 23, the choke coil 24, and the smoothing capacitor 25, and taken out from the terminals 26 and 27. The extracted DC voltage + V is applied to the error amplifier 51 that constitutes the feedback circuit 50 and compared with the reference voltage, and the error voltage is applied to the PWM control circuit 53 via the photocoupler 52.
The pulse width of the PWM control circuit 53 is modulated in accordance with the applied error voltage, and the switch 1 is switched in accordance with the pulse width.
On and off of 2 and 13 are controlled. As a result, the DC voltage + V taken out from the main output circuit 20 is controlled to a constant value.

In such a state, the slave output circuit 30
The voltage induced in the secondary winding n31 of the saturable inductor 3
1, a positive DC voltage represented by + V2 is taken out from the output terminal 38 through the diodes 32, 33, the choke coil 34, and the smoothing capacitors 35, 37 as a reference. On the other hand, the secondary winding n of the slave output circuit 30
The voltage induced in 32 is taken as a negative DC voltage -V2 from the output terminal 38a with reference to the common potential point COM through the saturable inductor 31a, the diodes 32a and 33a, the choke coil 34a, and the smoothing capacitors 35a and 36a.

A multi-output switching power supply having such a structure has been conventionally used, but in order to obtain positive and negative outputs in the secondary output circuit 30, the transformer 40 has a pair of secondary windings for secondary output. Requires lines n31,32. In such a case, (1) the transformer 40 becomes large, which hinders downsizing and cost reduction of the power supply device. (2) If the size of the transformer 40 is limited, the loss of the transformer becomes large, and the efficiency of the power supply is lowered. (3) When the main switch is made to perform zero voltage switching, a saturable inductor is required for each output, and the number of parts increases. There is a problem such as. Further, when the output voltage of the secondary output is small, such a configuration is disadvantageous in size.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an object thereof is to realize a small-sized, low-priced, multi-output switching power supply circuit.

[0010]

The present invention comprises a main switch connected to the primary winding of a transformer, and a reset circuit composed of a capacitor and an auxiliary switch, and turns the main switch and the auxiliary switch on and off alternately. Did PW
In the M control type multi-output switching power supply circuit,
A secondary output circuit that rectifies and smoothes a positive voltage induced in the secondary winding wound around the transformer; and a secondary output circuit that rectifies and smoothes a negative voltage induced in the secondary winding. Then
The dual output circuits are connected in parallel so that two outputs of positive voltage and negative voltage are taken out from one secondary winding.

[0011]

In the present invention as described above, two outputs of the positive voltage and the negative voltage are taken out from one secondary winding of the main transformer.

[0012]

The present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention. Note that, in FIG. 1, the same parts as those in FIG. 3 are denoted by the same reference numerals as those in FIG. In FIG. 1, 6
Reference numeral 0 denotes a transformer, which includes a primary winding n61, a secondary winding n62 of the main output circuit 20, and a secondary winding n63 of the slave output circuit 30.
Has become That is, in the transformer 40 in the conventional multi-output switching power supply circuit shown in FIG. 3, the secondary winding of the secondary output circuit 30 includes two windings n31 and n32, but in the present invention, this is n63. It is one. In addition, the saturable inductor 31a becomes unnecessary,
The number of parts has been reduced. The cathode pole of the rectifying diode 32 a in the slave output circuit 30 is connected to the anode pole of the diode 32.

In the switching power supply circuit having such a configuration, similarly to the circuit of FIG. 3, the output voltage + V of the main output circuit 20 is input to the error amplifier 51, and the PWM control circuit 53 driven by the output of this error amplifier. The switches 12 and 13 forming the converter 10 are alternately turned on by the output of
By turning off, the output voltage of the main output circuit 20 + V
Is controlled to a constant value. Switches 12 and 1
3 is provided with an appropriate dead time so as not to be turned on at the same time. The reset of the transformer 60 is performed as follows.

That is, the main switch 12 and the auxiliary switch 13
Is turned on and off in reverse phase, so the main switch 12
During the off period, the exciting current resonates with the main inductance of the transformer 60 and the capacitor 15 to discharge the capacitor 15, and the flowing direction of the exciting current is reversed. In this way, since the exciting current commutates, the magnetic flux in the transformer 60 is reset. If the capacitor 15 has a sufficiently large capacitance value, the voltage V across the capacitor 15
s has a substantially constant value in one switching cycle.
Therefore, the input voltage Vi is added to the main inductance during the ON period of the main switch 12, and the capacitor 15 during the OFF period.
The difference between the voltage Vs across V and the input voltage Vi is applied to the main inductance. In the steady period, the voltage-time product applied to the main inductance during the ON period and the OFF period becomes equal, so T
Is the switching cycle and D is the on-duty of the main switch 12, then (Vi-Vs) (1-D) .T = Vi.D) .T (1) holds. Therefore, the voltage applied to the primary winding during the off period of the main switch 12 is (Vi−Vs) = D · Vi / (1−D) (2). In this state, assuming that the voltage induced in the secondary winding n63 of the secondary output circuit 30 is V2, the waveform of this voltage V2 is as shown in FIG.

In FIG. 2, "0" is shown in the steady state.
The area with the level as Sakai is always equal. Therefore, when the positive half-wave indicated by is rectified by the saturable inductor 31, the diodes 32 and 33, and the choke coil 34 that configure the slave output circuit 30 illustrated in FIG. 1, and averaged by the capacitor 35 that configures the smoothing circuit, The averaged voltage | + V2 | is | + V2 | = (Vi / n) × (DT / T) = D · Vi / n (3) On the other hand, the negative half-wave shown in FIG. 2 is rectified by the saturable inductor 31, the diodes 32a and 33a, and the choke coil 34a to form a smoothing circuit.
5a, the averaged voltage | -V2 | is | -V2 | = {D / (1-D)} * (Vi / n) * (1-D) T / T = D.Vi / n … (4). In the equations (3) and (4), n represents the winding ratio of the primary winding n61 and the secondary winding n63 of the transformer 60. As shown by the equations (3) and (4), the average voltages of the positive and negative half waves are equal. Therefore, the common COM is passed through the post regulators 36 and 36a.
+ V which is taken out from the output terminal 38 with reference to
Becomes equal to the voltage −V taken out from the output terminal 38a.

The post regulators 36, 36a
With this, | + V2 | and | -V2 | can be independently controlled by constant voltage, whereby the voltages + V2 and -V2 taken out from the output terminals 38 and 38a can be made asymmetrical. In addition, the saturable inductors 21, 31
Delays the timing of turning on the secondary diode 32 immediately after the main switch is turned on, and the main switch 1
2 is added to enable zero voltage switching. Therefore, when the zero voltage switching is not required, the saturable inductors 21 and 31 may be omitted.

In the above-described embodiments, the case where the reset circuit including the capacitor 15 and the auxiliary switch 13 is added to the forward converter has been described. However, the circuit of the present invention is a flyback system or the like in which all the trans reset circuits are added. It can be applied to converters.

[0018]

According to the present invention, two outputs of positive voltage and negative voltage are taken out from one secondary winding of the main transformer, so that the winding structure of the main transformer is simplified. The number of saturable inductors can be reduced when the main switch is caused to perform zero voltage switching. Therefore, it has a great effect on downsizing and cost reduction of a multi-output switching power supply.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a converter according to the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the converter according to the present invention.

FIG. 3 is a circuit configuration diagram of an example of a conventional converter.

[Explanation of symbols]

 10 converter 11, 12 switch 15 capacitor 20 main output circuit 30 slave output circuit 40 transformer 50 feedback circuit 53 PWM control circuit

Claims (1)

[Claims] 1. A main switch connected to a primary winding of a transformer, and a reset circuit comprising a capacitor and an auxiliary switch, wherein the main switch and the auxiliary switch are alternately turned on.
In a PWM control type multi-output switching power supply circuit that is turned off, a secondary output circuit that rectifies and smoothes a positive voltage induced in a secondary winding wound around the transformer, and the secondary winding And a secondary output circuit for rectifying and smoothing the induced negative voltage,
A multi-output switching power supply circuit characterized in that the two sub-output circuits are connected in parallel to extract two outputs of a positive voltage and a negative voltage from one of the secondary windings.