JPH06187056A - Witching power source unit for multiple output - Google Patents

Abstract

PURPOSE:To make continuous resistance possible even at the time of load short-circuiting and to provide a miniaturized switching power source concerning the switching power source unit for supplying power to plural output circuits with one switching circuit. CONSTITUTION:Series regulators 6 and 7 and two of current limit circuits 13-16 are provided for each of respective output circuits 17 and 18, the outputs of series regulators 6 and 7 are limited by one side current limit circuits 13 and 14, and the output of a switching circuit 2 is limited by the other side current limit circuits 15 and 16.

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 device having a plurality of output circuits, each having an overcurrent protection function.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing a configuration of a conventional switching regulator. In FIG. 3A, 1 is a rectifying / smoothing circuit, 2 is a switching circuit, 8 is a current detector, 9 is a current limiting circuit, 10 is a control circuit, T1 is a switching transformer, 21, 22, 23, 24 are respectively Primary, secondary, tertiary and quaternary windings of a switching transformer, 3, 4, 5 are rectifier circuits, C1, C2, C3 are smoothing capacitors, 6, 7
Is a series regulator. Here, the control circuit 10 controls the rectified output voltage of the fourth winding 24 of the switching transformer to be constant. Further, the current detector 8 and the current limiting circuit 9 limit the output current of the switching circuit 2 to a certain value or less. That is, since the current limiting circuit 9 limits the primary input power, for example, the output terminal of the series regulator 6
If a load short circuit occurs between 32a and 32b, most of the power loss will be concentrated on the series regulator 6.

FIG. 3B is a diagram in which current detectors 11 and 12 and current limiting circuits 13 and 14 are added to the configuration of FIG. 3A, and current limiting circuits 13 and 14 are provided in respective output circuits. It is a thing. In this case, the power loss of the series regulator when the load is short-circuited is about 1.2 times the rated output power of each, and the power loss when the load is short-circuited is approximately 0.6 to 0.4 by making the current limiting circuit have a foldback characteristic. You can hold it down.

[0004]

In the configuration of this conventional switching regulator, the input voltage fluctuation is stabilized by the switching circuit on the primary side, and the series regulator only needs to compensate for the load fluctuation and is normally used. The power load on the series regulator in this state can be greatly reduced, so it is possible to make the power supply highly efficient and small, but if it can withstand the power loss when the load is short-circuited, the device will become large and expensive. There was a drawback that said.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a highly efficient and compact switching power supply that can continuously withstand a load short circuit.

[0006]

In order to achieve the above object, the present invention is a switching power supply device for supplying power to a plurality of output circuits by one switching circuit, and a series regulator for each output circuit, Two current limiting circuits are provided, one of which limits the output of the series regulator, and the other of which limits the output of the switching circuit.

[0007]

When a load short circuit occurs in the output circuit, one current limiting circuit of the output circuit limits the output current of the series regulator to a predetermined current. At this time, the other current limiting circuit limits the output of the switching circuit so that the output current becomes a value smaller than the predetermined current.

[0008]

1 shows an embodiment of a multi-output switching power supply device according to the present invention. In FIG. 1, 1 is a rectifying / smoothing circuit, 2 is a switching circuit, 10 is a control circuit, T1 is a switching transformer, and 21, 22, 23, and 24 are primary, secondary, tertiary, and quaternary windings of the switching transformer, respectively. Line 3,
4, 5 are rectifier circuits, C1, C2, C3 are smoothing capacitors, 6 and 7 are series regulators, 11 and 12 are current detectors, 13 and 14 are first current limiting circuits, and 15 and 16 are second currents. It is a limiting circuit.

The operation of the present invention will be described with reference to FIG. Figure 2 shows the series regulator 6 when a load short circuit occurs.
FIG. 6 is a diagram for explaining an input voltage and an output current of the. Figure 2
, I1 is the current limit value of the first current limiting circuit 13, I
2 is a current limit value of the second current limiting circuit 15. When a short circuit occurs, the input voltage does not immediately drop due to the charging charge of the smoothing capacitor C1, the output current of the series regulator is limited by the current limit value I1, and the input voltage and output current of the series regulator are points P1 in FIG. become.
At this time, since the output current exceeds the second current limit value I2, the power supply from the primary switching circuit is restricted to the minimum by the current limit circuit 15. Next, as the charge of the smoothing capacitor C1 is discharged, the input voltage and output current of the series regulator drop from the point P1 to the point P2. When the voltage difference of the series regulator decreases to the saturation voltage, it is limited to the limiting current I2 of the current limiting circuit 15, so that the input voltage and the output current of the series regulator are stable at P3. At this time, the power loss of the series regulator is suppressed to the minimum because the voltage difference is reduced to the saturation voltage.

[0010]

According to the present invention, in a multi-output switching power supply having a series regulator in the secondary output circuit, the power loss of the series regulator can be suppressed to the minimum when the output is short-circuited. (Including) can be made smaller, and a small-sized and inexpensive multi-output switching power supply device can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a multi-output switching power supply device of the present invention.

FIG. 2 is a characteristic diagram for explaining the operation of the above embodiment.

FIG. 3 is a configuration diagram of a conventional multi-output switching power supply device.

[Explanation of symbols]

1 ... Rectifying / smoothing circuit, 2 ... Switching circuit, 10 ... Control circuit, T1 ... Switching transformer, 21, 22, 23, 24 ... Primary and secondary of switching transformer,
3rd and 4th windings, 3, 4, 5 ... Rectifier circuit, C1, C2, C3 ... Smoothing capacitor, 6, 7 ... Series regulator, 11, 12 ... Current detector, 13, 14 ... First current limit Circuit, 15, 16 ... Second current limiting circuit

Claims (1)

[Claims] 1. A switching power supply device for supplying power to a plurality of output circuits by one switching circuit, wherein a series regulator and two current limiting circuits are provided for each output circuit, and one of the current limiting circuits is used. A multi-output switching power supply device characterized by limiting the output of the series regulator and limiting the output of the switching circuit by the other current limiting circuit.