JPH08289539A - Switching power supply system - Google Patents

Abstract

PURPOSE: To eliminate a sense of incompatibity in operation by adding a simple circuit which detects a turn-off of the AC input and then stops the operation of a switching device by force and thereby getting the stop of operation or display of a load-side equipment such as a personal computer nearly synchronized with the turn-off of the input. CONSTITUTION: A switching power supply system is provided with a forward converter which is constituted of a switching device which obtains the main output from AC input of an AC power supply and other devices and a ringing choke converter which is constituted of a switching device which obtains the auxiliary power output from the power supply and other devices. In this switching power system, an off-state time detecting circuit 17 is added. The off-state time detecting circuit 17 stops operation of the switching devices by force immediately after it detects the turn-off of the AC input. An output off- state time is set by a capacitor 19 and resistors 21, 22 of the off-state time detecting circuit 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device, and more particularly to an AC input / DC multiple output type switching power supply device for use in a personal computer or the like.

[0002]

2. Description of the Related Art Conventionally, this type of switching power supply device generally has a structure shown in FIG. An AC voltage is input from an AC power supply 1 and rectified and smoothed by a rectifier circuit 2 and a smoothing capacitor 3 to obtain a DC input voltage. The main power supply circuit that obtains the main output is
In the forward converter, the DC input voltage is ON / OFF controlled by the switching element 4 and converted into a pulse having a predetermined voltage via the transformer 5. Next, the secondary side diodes 6 and 7 and the smoothing circuit 8 are rectified and smoothed to obtain a DC main output. The voltage of this main output is fed back to the primary side by the photocoupler 16, compared with the reference voltage by the control circuit 9, and the on / off time of the switching element 4 is controlled by the difference to obtain a stable main output.

The auxiliary power supply circuit for obtaining the output of the auxiliary power supply is a ringing choke converter whose circuit is simple and drives the self-excited oscillation circuit 10 and the switching element 11. After being transformed by the transformer 12, the secondary side diode 13,
It is rectified by the condenser 14, and the dropper 15 stably obtains the auxiliary power output.

[0004]

As described above, in the conventional switching power supply device, the main output and the auxiliary power supply output are configured by different circuits, and when the AC input is cut off, the output voltage fall order There are no regulatory factors, and it is undefined. Further, when the AC input is cut off, the output continues while the electric charge remains in the smoothing capacitor on the input side. When used as a personal computer, the auxiliary power output is used for the display, etc., so if it does not turn off faster than the main output and the AC input is cut off particularly quickly, the operation will stop and the display will disappear. There is a problem in that a feeling of discomfort in operation is generated.

[0005]

SUMMARY OF THE INVENTION A switching power supply device of the present invention is a main power supply circuit using a switching system in which an AC power supply is input and a DC main power supply for supplying power to a main circuit of a personal computer is output. A switching power supply device comprising an auxiliary power supply circuit using a switching system for inputting a power supply and outputting a DC auxiliary power supply for supplying power to a display unit of the personal computer, etc., and an AC input when the AC power supply is turned off. It is provided with a circuit for detecting the fall of the voltage and forcibly stopping the switching operation of the auxiliary power supply circuit.

[0006]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of the present embodiment.

The AC voltage from the AC power supply 1 is converted into a DC voltage by the rectifier circuit 2 and the capacitor 3, and a switching element 4, a transformer 5, diodes 6, 7, a smoothing circuit 8, a photo coupler 16, which constitute a forward converter, The main output is obtained by transforming with the control circuit 9.

Further, the same DC voltage is transformed by the switching element 11, the transformer 12, the diode 13, the capacitor 14, the self-excited oscillating circuit 10 and the dropper 15 which form a ringing choke converter to obtain an auxiliary power output. The off-time detection circuit 17 detects interruption of the AC input and forcibly stops the operation of the switching element 11 of the ringing choke converter.

Next, the operation of the off time detection circuit 17 will be described. The off-time detection circuit 17 half-wave rectifies the AC input from the AC power supply 1 with the diode 18, the capacitor 19, and the resistors 20 to 22, and the transistor 2
Turn on 3. When the transistor 23 is turned on, the base potential of the transistor 26 becomes 0V and the transistor 26 is turned off. Since the transistor 26 is off, the switching element 11 of the auxiliary power supply connected to the collector continues to operate under the control of the self-excited oscillation circuit 10.

When the AC input from the AC power supply 1 is cut off, after the electric charge of the capacitor 19 is discharged by the resistors 21 and 22, the base potential of the transistor 23 becomes OV and the transistor 23 is turned off. Transistor 23
Is turned off, the transistor 26 is turned on to forcibly set the base potential of the switching element 11 to 0 V to stop the switching operation of the auxiliary power supply. Therefore, the output of the auxiliary power supply quickly falls to 0V. The time from the interruption of the AC input power supply 1 to the turning off of the auxiliary power supply at this time is determined by the time constants of the capacitor 19, the resistor 21, and the resistor 22.

[0011]

As described above, in the switching power supply device of the present invention, the time from the interruption of the AC input to the turning off of the auxiliary power supply output can be shortened to an arbitrary time.
When used in a device such as a personal computer, turning off the AC input power supply and operation of the device side and stop of display etc. are substantially synchronized, and there is an effect of preventing malfunction and eliminating discomfort in operation. Further, since the output off time can be arbitrarily set by the time constant of the capacitor and the resistor, there is an effect that the output off time can be adjusted to be most suitable for the device used.

[Brief description of drawings]

FIG. 1 shows a block diagram of one embodiment of the present invention.

FIG. 2 shows a block diagram of a conventional example.

[Explanation of symbols]

 1 AC power supply 2 Rectifier circuit 3 Smoothing capacitor 4,11 Switching element 5,12 Transformer 6,7,13,18 Diode 8 Smoothing circuit 9 Control circuit 10 Self-excited oscillation circuit 14 Capacitor 15 Dropper 16 Photocoupler 17 Off-time detection circuit 19 Capacitor 20, 21, 22, 24, 25 Resistor 23, 26 Transistor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H02M 7/06 8726-5H H02M 7/06 A

Claims (1)

[Claims] 1. A main power supply circuit using a switching system for inputting an AC power supply to output a DC main power supply for supplying power to a main circuit of a personal computer; and a display unit of the personal computer for inputting the AC power supply. In a switching power supply device provided with a switching power supply circuit using a switching method for outputting a DC auxiliary power supply for supplying power to the above, the auxiliary power supply circuit detects a fall of an AC input voltage when the input of the AC power supply is turned off. A switching power supply device comprising a circuit for forcibly stopping the switching operation of the above.