JPH07322610A - Power supply device - Google Patents

Abstract

PURPOSE:To provide an inexpensive circuit by turning on/off a switching power supply from the output side. CONSTITUTION:The device consists of a switching element Q2 connected to the control terminal of a switching element Q1 for converting power, a photocoupler PC1 (light reception side) connected to the control terminal of the switching element Q2, a resistor R1 connected serially to the photo coupler PC1 and a DC voltage power supply VIN, a resistor R5 connected serial to the photocoupler PC1 (light emitting side), and a control switch Sl connected serially to the photo coupler PC1. Then, by closing the control switch S1, an output voltage V0 can be stabilized to an extremely small value and the operation of the switching power supply is turned on and off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit in a switching type power supply device for controlling an output voltage to be kept low by an external signal or the like.

[0002]

2. Description of the Related Art Conventionally, a switching type power supply device has been used as a power supply device for various electronic devices.
FIG. 2 is a circuit diagram of a conventional switching type power supply device in which the power supply operation is controlled to be turned on and off from the output side (secondary side). In FIG. 2, the photocoupler PC1 (light receiving side) is connected to the control terminal of the switching element Q2 connected to the control terminal of the power conversion switching element Q1, and the photocoupler PC1 is driven by another DC power source V _EXT . This is done by the connected current limiting resistor R5. Current limiting resistor R5 connected to output side DC power supply V _EXT , photo coupler P
It is composed of C1 (light emitting side) and a control switch S1. When the control switch S1 is closed, a current flows from the output side DC power supply to the photocoupler PC1 (light emitting side), the signal is transmitted to the photocoupler PC1 (light receiving side), and the photocoupler PC1 becomes conductive, thereby switching element Q2. Is driven, the switching element Q1 for power conversion is turned off, and the output voltage becomes zero as shown in FIG.

[0003]

However, when the power conversion switching element Q1 is on / off controlled from the output side, the controlled output V0 is used as a driving power source for the signal transmitting photocoupler PC1 (light emitting side). A separate DC power supply V _EXT is required. The present invention does not use a DC power supply V _EXT different from the controlled output as shown in FIG.
It is an object of the present invention to provide an output voltage drop control circuit that sets a switching type power supply device to a low output voltage by an external signal.

[0004]

Therefore, according to the present invention,
Output voltage drop control circuit for switching power supply
Is the drive power of the signal transmission photocoupler PC1 (light emitting side).
Separate DC power source V _EXTControlled without using
Attempt to achieve the above objective by supplying from output V0
To do. One end of the controlled output V0 and the other end G
Power limiting resistor R5 and photocoupler PC1 connected between
(Light emitting side), series circuit and power of control switch S1
Connected to the control terminals of conversion switching elements Q1 and Q2.
Photocoupler PC1 (light receiving side) and DC voltage source V
_INComposed of current limiting resistors R1 and R2 connected to
It

C1 is an input smoothing capacitor, 1 is a voltage stabilization control circuit connected to the control terminal of the power conversion switching element, R3 and R4 are resistors for power conversion switching element activation, and D1 is the switching element driving diode. , C2 is a capacitor for driving the switching element, T
Reference numeral 1 is a power conversion transmission transformer, R1 and R2 are current control resistors, D2 is an output rectifying diode, and C3 is an output smoothing capacitor.

[0006]

Since the present invention is configured as described above, it will be described that the output voltage is controlled and held at a low output voltage by opening and closing the switch S1 in the steps from the following.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given below with reference to FIG. By closing the control switch S1 (control switch by an external signal or an active element such as a transistor), a current flows through the photocoupler PC1 (light emitting side), and the signal is transmitted to the photocoupler PC1 (light receiving side). The transmitted signal turns on the switching element Q2 connected to the control terminal of the power conversion switching element Q1. When the switching element Q2 turns on, the power conversion switching element Q1 turns off and the output voltage V0 decreases. When the output voltage V0 decreases, the current flowing through the photocoupler PC1 (light emitting side) decreases, and the switching element Q1
2 is turned off, and power conversion switching element Q1
However, it is turned on and the output voltage V0 rises to a low holding level as shown in the closed state of the control switch S1 of FIG. When the output voltage V0 rises, as long as the control switch S1 is closed, the above steps (1) to (5) are repeated. As a result, the output voltage V0 is almost stabilized to a voltage required to operate the photocoupler PC1 (light emitting side), The output voltage is extremely low as shown in FIG. Further, by opening the control switch S1, the current flowing through the photocoupler PC1 (on the light emitting side) disappears, and the output voltage set in advance by the control circuit 1 is restored.

Generally, 3V, 5V, 12V, 24V or the like is used as a power supply voltage for driving an electronic circuit. According to the invention, when the control switch S1 is closed,
The output voltage V0 is stabilized at an extremely low voltage, the electronic circuit connected to the power supply output terminal cannot operate, and as a result, the operation can be ON / OFF controlled. In addition,
It is needless to say that a control switch which operates by an external signal or an active element such as a transistor can be used as the control switch S1 in the above-described embodiment, and can be appropriately selected.

[0009]

According to the present invention, it is possible to perform on / off control of the switching power supply from the output side with a simple circuit without the need of using another drive DC power supply. In addition, since another drive DC power supply is not used for the control circuit, it is effective in cost reduction and power saving.

[Brief description of drawings]

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

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

FIG. 3 is an explanatory diagram of a relationship between a state of a control switch S1 and an output voltage V0 in a conventional power supply device.

FIG. 4 is an explanatory diagram of a relationship between a state of a control switch S1 and an output voltage V0 in the power supply device of the present invention.

[Explanation of symbols]

C1 input smoothing capacitor Q1 power conversion switching element (a transistor is used in the figure, but the same applies to FET, SCR, IGBT, etc.) 1 voltage stabilization control circuit connected to the control terminal of Q1 R3 for Q1 startup Resistor R4 Q1 drive resistor D1 Q1 drive diode C2 Q1 drive capacitor T1 Power conversion transmission transformer Q2 Switching element connected to the control terminal of Q1 PC1 Photo coupler R1 Current limiting resistor R2 Current limiting resistor D2 Output rectifying diode C3 Output smoothing capacitor R5 Current limiting resistor S1 Control switch

Claims (1)

[Claims] 1. A transformer in which a primary winding is connected to a DC voltage power source via a power conversion switching element that is on / off controlled at a predetermined frequency, and a rectifying / smoothing means provided on the secondary side of the transformer. A switching power supply circuit having a power conversion switching element which is connected to one end of the primary winding and whose control terminal is a voltage obtained in the auxiliary winding of the transformer and a control circuit. It is connected so as to be controlled by a photocoupler (light receiving side) connected in the direction in which the current of the voltage dividing resistor connected to the other end flows out, and is also connected to the control terminal of the conversion switching element. A switching element, a secondary winding of the transformer, a rectifying diode and a smoothing capacitor, and a current limiting resistor connected between one end and the other end of the output end and an external signal. Alternatively, a power supply device having an output voltage drop control circuit according to an external signal, which is a series circuit with a photocoupler (light emitting side) connected in a direction in which a current flows due to conduction of a switch element for on / off control.