JP2605397B2 - Startup circuit for multi-output switching power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a starting circuit for a multi-output switching power supply in which a plurality of DC / DC converters are connected in parallel with a DC input power supply.

[Conventional technology]

FIG. 3 shows a conventional multi-output switching power supply of this type.

In FIG. 3, the AC voltage of the commercial AC power supply AC is rectified by a diode bridge rectifier circuit DB to form a smoothing capacitor CO.
To form a DC input power supply PDC, and a primary winding P1 of a transformer T1 and a switching transistor Q1 are connected in series to the DC input power supply PDC. A rectifying / smoothing circuit RS including diodes D3, D4, D5, D6, inductance elements L1, L2 and capacitors C2, C3 is connected to the secondary windings S1, S2 of the transformer T1, respectively, and the secondary winding S1 A series stabilized power supply circuit 3 is connected to the side. Auxiliary winding of transformer T1
A control circuit 1 to which an auxiliary power voltage rectified and smoothed by a diode D1 and a capacitor C1 is supplied to P2,
The control circuit 1 is activated via the activation resistor R1 and controls the switching transistor Q1 to be on / off so that the output voltage V1 on the secondary winding S2 side is constant. A second DC / DC converter is coupled to the DC input power supply PDC in parallel with the first DC / DC converter. This second DC /
The DC converter has a transformer T2 and a primary winding P3 connected to the transformer T2.
And a rectifying / smoothing circuit RS composed of a switching transistor Q2 connected in series with the secondary windings S3 and S4 of the transformer T2 and diodes D7 and D8 and capacitors C4 and C5, respectively.
A control circuit 2 connected to the auxiliary winding P4 of the transformer T2,
The control circuit 2 comprises a starting resistor R2. Reference numeral 4 denotes a series stabilized power supply circuit. The first DC / DC converter is configured as a forward type, and the second DC / DC converter is configured as a flyback type.

In FIG. 3, when the switch S is turned on, the starting resistance R1 is increased.
, The control circuit 1 is activated, whereby the switching transistor Q1 starts the switching operation. A pulse-like voltage is induced on the secondary side of the transformer T1 by turning on / off the switching transistor Q1, and a rectifying / smoothing circuit
The DC output voltage V1 is obtained by RS. The on / off ratio of the switching transistor Q1 is controlled by the control circuit 1 so that the DC output voltage V1 is constant even if the input voltage Vin of the commercial AC power supply AC and the load current I1 on the DC output side fluctuate. In the series stabilizing power supply circuit 3 of the secondary winding S1, since the voltage v2 between the terminals of the capacitor C2 changes depending on the DC output voltage V1, the DC output voltage V2 is stable without changing according to the DC output voltage V1. This is a circuit for obtaining a modified output voltage.

When the switch S is turned on, the second DC / DC converter also starts the switching operation by inputting a start signal to the control circuit 2 via the start resistor R2, so that the switching transistor Q2 starts switching operation. Similarly, stabilized DC output voltages V3 and V4 are obtained.

[Problems to be solved by the invention]

The load to which the DC output voltage is supplied by the above-described multi-output switching power supply device is often required to be supplied with the output voltages V1 to V4 sequentially. However, in the above-described conventional device, when the switch S is turned on, the switching transistors Q1 and Q2 of the first and second DC / DC converters start switching operations almost simultaneously, so that the DC output voltages V1 to V4 rise almost simultaneously. Therefore, there is a disadvantage that a circuit must be added on the load side so that the DC output voltages V1 to V4 are sequentially supplied.
Further, since the starting resistors R1 and R2 are connected to a high-potential DC input power supply, there is a disadvantage that the loss is large and the efficiency of the switching power supply device is reduced.

Accordingly, an object of the present invention is to provide a starting circuit for a multi-output switching power supply device that eliminates the above-described disadvantages of the conventional device and that can set the starting order of a plurality of DC / DC converters and has low power loss due to starting resistance. Is to do.

[Means for solving the problem]

In order to achieve the above object, in the present invention, a primary winding and a switching transistor of a transformer connected in series to a DC input power supply, and a rectifying and smoothing circuit for rectifying and smoothing a secondary output of the transformer And a control circuit that is connected to the auxiliary winding of the transformer, is started via a starting resistor, and controls ON / OFF of the switching transistor so that the output of the rectifying / smoothing circuit becomes constant.
A converter, and a plurality of DCs in parallel with the DC input power supply.
In a multi-output switching power supply unit in which a DC / DC converter is coupled, the control circuit of the DC / DC converters of the second and subsequent stages uses a voltage generated in the auxiliary winding of the transformer of the DC / DC converter of the preceding stage via a starting resistor. It is characterized in that it is activated.

(Operation)

In the multi-output switching power supply according to the present invention, the control circuit of the DC / DC converters of the second and subsequent stages includes
Since it is started via the starting resistor by the voltage which generates the auxiliary winding of the transformer of the C / DC converter, the DC / DC converter of the former stage is started after the DC / DC converter of the former stage is started, and the DC input is started. Multiple DC / DCs connected in parallel to the power supply
The starting order of the converters can be determined.

〔Example〕

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the present invention.
In the figure, the same components as those of the conventional device shown in FIG.

The difference between the conventional example shown in FIG. 3 and FIG.
The starting resistor R2 of the control circuit 2 of the second DC / DC converter applies the voltage generated in the auxiliary winding P2 of the first DC / DC converter to the point Va of the DC voltage source rectified and smoothed by the diode D1 and the capacitor C1. It is a connected point. Also, the first DC
R10 and Zener diode ZD10 between the DC output voltage terminals of the rectification and smoothing circuit RS on the secondary winding S2 side of the DC / DC converter
A series circuit of the photocoupler PC10 and the light emitting diode of the photocoupler PC10 is connected, and a transistor T1 controlled by a phototransistor of the photocoupler PC10 is provided in the series stabilizing power supply circuit 3 on the secondary winding S1 side. A series circuit of a resistor R11, a Zener diode ZD11 and a light emitting diode of a photocoupler PC11 is connected between the DC output voltage terminals on the secondary winding S4 side of the DC converter, and a series stabilized power supply circuit 4 on the secondary winding S3 side is connected. Is provided with a transistor T2 controlled by the phototransistor of the photocoupler PC11.

Now, when the switch S is turned on at time t0 shown in FIG. 2, a start signal is first supplied to the control circuit 1 via the start resistor R1, and the switching transistor Q1 starts switching operation, and the secondary winding S2 side The DC output voltage V1 rectified and smoothed by the rectifying / smoothing circuit RS is output. When the DC output voltage V1 reaches the Zener voltage Za of the Zener diode ZD10, the photocoupler PC10 is turned on and the series stabilized power supply circuit 3 starts operating, whereby the DC output voltage V2 on the secondary winding S1 side is changed to DC. It rises after the output voltage V1 rises. The switching transistor Q1 of the first DC / DC converter starts the switching operation and the DC output voltages V1, V
After 2 rises, the pulse-like voltage generated in the auxiliary winding P2 of the transformer T1 is rectified by the diode D1 and smoothed by the capacitor C1. An activation signal is supplied to the control circuit 2 via the activation resistor R2 by the auxiliary voltage generated in the auxiliary winding P2, and the switching transistor Q2 starts switching operation. As a result, the DC output voltages V3 and V4 are sequentially output from the second DC / DC converter.

Here, assuming that the DC voltage generated in the auxiliary winding P2 is 10 V, the DC input voltage (PDC) of the conventional device is almost equal to 100 V when the input voltage of the commercial AC power supply AC is 100 V. Since the voltage is 140 V, the power loss due to the starting resistor R2 in the conventional device can be reduced to approximately 1/10.

〔The invention's effect〕

As described above, according to the present invention, a primary winding and a switching transistor of a transformer connected in series to a DC input power supply, and a rectifying and smoothing circuit for rectifying and smoothing a secondary output of the transformer, A control circuit connected to the auxiliary winding of the transformer and started via a starting resistor and controlled to turn on and off the switching transistor so that the output of the rectifying / smoothing circuit becomes constant. In a multi-output switching power supply device in which a plurality of DC / DC converters are coupled in parallel to the DC input power supply, a control circuit of the DC / DC converters of the second and subsequent stages includes an auxiliary for a transformer of the DC / DC converter of the preceding stage DC / DC in a multi-output switching power supply unit is configured so that it is started via a starting resistor by the voltage generated in the winding.
An advantage that the efficiency of the multi-output switching power supply device can be improved because the starting order of the converters can be set to determine the order in which the DC output voltage rises, and the power loss due to the starting resistance can be reduced. Having.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a multi-output switching power supply device showing an embodiment of the present invention, and FIG. 2 is a waveform diagram of a main part of FIG.
FIG. 3 is a circuit diagram of a conventional multi-output switching power supply. PDC: DC input power supply, T1, T2: transformer, Q1, Q2: switching transistor, RS: rectifying / smoothing circuit, R1, R2: starting resistance, P1, P2: auxiliary winding, 1, 2: control circuit.

Claims (1)

(57) [Claims] 1. A primary winding and a switching transistor of a transformer connected in series to a DC input power supply, a rectifying and smoothing circuit for rectifying and smoothing a secondary output of the transformer, and an auxiliary winding of the transformer. A DC / DC converter comprising a control circuit connected to a line and activated via a starting resistor and controlled to turn on and off the switching transistor so that the output of the rectifying / smoothing circuit becomes constant. In a multi-output switching power supply device in which a plurality of DC / DC converters are coupled in parallel,
A starting circuit for a multi-output switching power supply device, wherein a control circuit of the converter is started via a starting resistor by a voltage generated in an auxiliary winding of a transformer of a DC / DC converter in a preceding stage.