JP2001333579A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit structure which can reduce waiting power in a switching power supply which turns off a voltage to be supplied to the output side with a switching element to reduce power consumption in the output side. SOLUTION: In the switching power supply for stably supplying a DC voltage obtained through rectifying operation to a secondary side circuit of a switching power supply transformer T by turning on/off a switching element Q1 with a switching IC IC1 on the primary side, a switching element SW2 is connected between a diode D1 connected to an auxiliary coil of the switching power supply transformer T and the switching IC IC1.

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 for reducing power consumption at an output by turning off a power supply for receiving a standby signal and supplying the output to a switching element. The present invention relates to a switching power supply capable of reducing power consumption.

[0002]

2. Description of the Related Art FIG. 2 has been proposed as this type of switching power supply. In FIG. 2, the power supply on the output side can be reduced by turning off the voltage supplied to the output from the secondary winding P3 of the transformer in response to the standby signal by the switch element SW1, but the primary side switching IC
The loss due to IC1 and switching element Q1 could not be reduced, and there was a limit to the reduction in standby power.

[0003]

The conventional means for reducing the power consumption on the output side by turning off the voltage supplied to the output side by the switching element SW1 as described above has a limit in reducing the standby power. An alternative means for reducing standby power has been required.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems. In the present invention, the voltage supplied to the output side after receiving the standby signal is turned off by the switch element SW1, and the auxiliary winding of the transformer around the switching IC IC1. V from line P2
It is an object of the present invention to provide a switching power supply in which the supply of the CC voltage is turned off by a switch element SW2 and the switching IC IC1 and the switching element Q1 are shifted from continuous oscillation to intermittent oscillation, whereby power consumption during standby can be significantly reduced. . That is, in the switching power supply that stably supplies the DC voltage obtained by rectification to the secondary circuit of the switching power supply transformer T by turning on / off the switching element Q1 with the switching IC IC1 on the primary side. A switching power supply characterized in that a switching element SW2 is connected between a diode D2 connected to an auxiliary winding P2 of a switching power supply transformer T and a switching IC IC1.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a switching element SW2 (hereinafter referred to as SW2) is connected between a diode D2 connected to an auxiliary winding P2 of a switching power supply transformer T and a switching IC IC1 (hereinafter referred to as IC2). (Abbreviated). When the standby signal is transmitted to SW2, as shown in FIG. 3, SW2 is turned off, the supply of the voltage from the auxiliary winding P2 of the transformer is cut off, the VCC voltage decreases, and the voltage drops to the operation stop voltage of IC1. IC1 and switching element Q1 (hereinafter abbreviated as Q1) are turned off. IC
After one off, the VCC voltage rises with a time constant determined by the starting resistor R1 and the smoothing capacitor C2, and the IC1 and Q1 are turned on again. This operation is repeated during the OFF period of SW2, and the intermittent oscillation state is set. Thus, the switching IC I
By shifting C1 from continuous oscillation to intermittent oscillation,
Power consumption during standby can be reduced.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram of a switching power supply according to an embodiment of the present invention, where T is a switching power supply transformer for transmitting energy stored in a primary side to a secondary side, P1 is a primary main winding, P2 is an auxiliary winding on the VCC terminal side of IC1, P3 is a secondary winding, and Q1 is a MOS.
A switching element such as an FET, IC1 is a switching IC for driving the switching element Q1, R1 is a starting resistance of the IC1, D2 is a rectifier diode of a P2 winding voltage, and C2
Is a smoothing capacitor of the P2 winding voltage, D3 is a rectifier diode of the P3 winding voltage, C3 is a smoothing capacitor of the P3 winding voltage, SW1 is a switch element for turning off the supply voltage from the secondary winding P3, and SW2 is This is a switch element for turning off the supply voltage from the auxiliary winding P2. The difference from the conventional switching power supply is that the switch element SW2 is connected to the diode D2 on the auxiliary winding P2 side, and this circuit configuration can significantly reduce the power consumption during standby.

After turning on the power, the input voltage rectified and smoothed by the diode D1 and the capacitor C1 is applied to the starting resistor R1, the smoothing capacitor C2 is charged, and the smoothing capacitor C2 is charged.
When the voltage between both ends reaches the activation voltage of IC1, IC1 is activated. Here, if SW2 is on, IC
After the start-up, the auxiliary winding P of the transformer is connected to the VCC terminal of IC1.
2, the voltage is supplied from IC2 and IC1 and Q1 continuously oscillate.

Here, when a standby signal is transmitted to SW2,
As shown in FIG. 3, when the switch SW2 is turned off, the supply of the voltage from the auxiliary winding P2 of the transformer is cut off, and the VCC voltage decreases to the operation stop voltage of the IC1, the IC1 and the switching element Q1 are turned off. Become. After IC1 is turned off, the VCC voltage rises with a time constant determined by the starting resistor R1 and the smoothing capacitor C2, and IC1 and Q1 are turned on again. This operation is repeated during the OFF period of SW2, and the intermittent oscillation state is set. In this state, the output voltage on the secondary side fluctuates due to intermittent oscillation, but does not affect the output side because SW1 is off. FIG. 3 shows the relationship between the VCC voltage and the oscillation waveform of Q1.
Since the loss of IC1 and the switching loss of Q1 are reduced during the off-time of W2, that is, the off-time (T1) of IC1, the standby power can be significantly improved.

[Conventional Example] Next, FIG. 4 shows the relationship between the VCC voltage and the oscillation waveform of Q1 according to the conventional example of FIG. 2 in which the switching element SW2 is not connected to the auxiliary winding P2.
In FIG. 4, the intermittent oscillation as in the embodiment by SW2 is not performed, and the IC1 and Q1 are always in the ON state, so that the standby power is not sufficiently reduced. Comparison of the standby power value (W) between the above embodiment and the conventional example shows the following [Table 1].
It can be seen that in the example, it is reduced to 20% of the conventional example.

[0010]

[Table 1]

[0011]

As described above, the switching element SW2 is connected between the diode on the auxiliary winding side of the switching power supply transformer and the switching IC, and the standby signal is transmitted, whereby the switching IC and the switching element are switched. Intermittent oscillation can be performed, and power consumption during standby can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a switching power supply according to the present invention.

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

FIG. 3 shows a switching IC IC1 according to the circuit of FIG.
3 is an oscillation timing chart of the Vcc voltage and the switching element Q1.

FIG. 4 is a timing chart by the circuit of FIG. 2;

[Explanation of symbols]

 C1 Smoothing capacitor (for power supply input smoothing) C2 Smoothing capacitor (for P2 winding voltage smoothing) C3 Smoothing capacitor (for P3 winding voltage smoothing) D1 Diode (for power supply input rectification) D2 Diode (for P2 winding voltage rectification) D3 Diode (P3 winding voltage rectification) IC1 Switching IC Q1 Switching element T Switching power transformer P1 Primary main winding P2 Auxiliary winding P3 Secondary winding R1 Start-up resistor VCC IC1 input voltage I0 output current V0 output voltage R0 output Load resistance SW1 Switch element SW2 Switch element T1 Off time of IC1

Claims (1)

[Claims] 1. A switching power supply for stably supplying a DC voltage obtained by rectification to a secondary circuit of a switching power supply transformer by turning on / off a switching element by a switching IC on a primary side. A switching power supply comprising a switching element connected between a diode connected to an auxiliary winding of a switching power supply transformer and a switching IC.