JPH10248256A - Switching power-supply apparatus with electricity-saving function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a switching power-supply apparatus which lowers standby electric power. SOLUTION: In a switching power supply which comprises a standby circuit and which is provided with an electricity-saving function, a light-emitting element at a photocoupler 102 is connected in series with a first switching element 104 which is set in an on-state when a standby signal is received, a Zener diode 103 is connected across an output terminal 4 which supplies electric power to a load circuit and the light-emitting element at the photocoupler 102, a series circuit which comprises a second switching element 105 and a diode 106 is connected across the output terminal 4 which supples the electric power to the load circuit and an output terminal 5 which supplies electric power to the standby circuit, the control electrode of the second switching element is connected to the output terminal of the first switching element 104, and the light- emitting element at the photocoupler 102 is connected in parallel with a soft- start capacitor 101. Thereby, a power consumption in a standby operation is lowered.

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, and more particularly to a switching power supply having a power saving function.

[0002]

2. Description of the Related Art As a conventional switching power supply technology with a power saving function, there is a power down system as shown in FIG.

In the circuit shown in FIG. 3, a photocoupler 11 is used for feedback for constant voltage control, and the output voltage is controlled by a Zener diode 12 while a standby signal is not input.

If the breakdown voltage of another Zener diode 13 is selected to be lower than the other, a standby signal is input, and when the switching element 14 is turned on, the output voltage is controlled by the Zener diode 13; Although the output voltage decreases, the voltage of the winding that has supplied power to the load circuit 9 is applied to the output terminal 4 that supplies power to the standby circuit 14 via the switch element 15. This voltage can be made necessary and sufficient for the standby circuit if the voltage of the Zener diode 13 is appropriately selected.

On the other hand, since the loss due to the snubber circuit and the bleeder resistance decreases as the output voltage decreases, power consumption during standby can be reduced.

Such a conventional switching power supply device with a power saving function has an effect of saving power, but oscillates continuously, and the power required to operate the power supply device itself is less than the required power. Has the disadvantage that it cannot be reduced.

An object of the present invention is to provide a switching power supply having a power saving function which can further improve the power saving effect by adding a small number of components.

[0007]

In the power loss during standby, the power consumed by the main switch element and the circuit driving the main switch element, which is the power required for the power supply device itself to operate, is included in the total power consumption. Accounted for a high percentage.

Therefore, attention has been paid to the fact that the average power consumption is reduced by intermittently operating the main switch element and its drive circuit. For example, in a switching power supply having a maximum output of 100 W, higher efficiency is obtained when the average output is set to 0.5 W by intermittent oscillation of a duty ratio of 10% of 5 W rather than to continuously output 0.5 W. can get.

The disadvantage of the intermittent oscillation that a transformer is likely to generate a harsh sound and the disadvantage that another oscillation circuit is required for the intermittent oscillation are solved by using a soft start circuit.

Many switching power supply control circuits employ a soft start method in which a capacitor is charged and a switching duty ratio is increased in accordance with an increase in the voltage of the capacitor.

Therefore, when a standby signal is input, the duty ratio is made zero by forcibly discharging the soft-start capacitor to stop the oscillation and reduce the output voltage, and the output voltage is reduced to a preset value. When the voltage drops, the discharge is stopped, the duty ratio is increased, and oscillation is started. When the output voltage reaches the set voltage, the soft-start capacitor is discharged again to stop the oscillation. By repeating this, the output voltage is lowered and at the same time, the intermittent oscillation is performed.

The output voltage of the switching power supply with a power saving function includes a relatively low voltage supplied to the standby circuit and a relatively high voltage supplied to the load circuit. A voltage required for the standby circuit is secured by attaching a switching circuit for supplying the standby circuit to the standby circuit.

[0013]

When a standby signal is input, the first switch element is turned on, and current flows through the light emitting element of the photocoupler until the voltage supplied to the load circuit drops to the voltage set by the Zener diode. The device remains on during that time, and switching stops. When the voltage decreases and the current of the photocoupler light emitting element stops, the photocoupler light receiving element is opened and the voltage across the soft start capacitor starts to increase.

When the voltage across the soft start capacitor rises from zero, switching starts, and the pulse width gradually increases from zero.

By the start of switching, the output voltage starts to rise again. When the output voltage approaches the breakdown voltage of the Zener diode, a slight current starts to flow through the photocoupler light-emitting element, so that the voltage across the photocoupler light-receiving element also starts to decrease.

Since the voltage across the soft-start capacitor also starts to decrease, the switching duty ratio gradually decreases.

As described above, since the change in the duty ratio starts from zero and stops at zero, the sound emitted from the transformer is small and hardly perceived by human ears.

Since the rising speed and the falling speed of the output voltage depend on the capacity of the soft start capacitor, the capacity of the output capacitor, and the current consumption of the standby circuit, the frequency of the intermittent transmission can be reduced by adjusting the combination thereof. Decided.

That is, it is not necessary to separately provide an oscillation circuit for intermittent oscillation.

[0020]

FIG. 1 is a circuit diagram showing a switching power supply unit according to an embodiment of the present invention and a load side supplied with power by the switching power supply unit.

In FIG. 1, when a standby signal is input to the terminal 7 from the standby circuit, the first switch element 104 is turned on, and the Zener diode 103 having a breakdown voltage lower than the voltage supplied to the load circuit 9 is supplied to the first switch element 104. A current flows, and the photocoupler 102 is turned on. Then, the voltage across the soft start capacitor 101 of the oscillation control circuit drops to almost zero, and the switching of the MOSFET 1 stops. On the other hand, the output voltage starts to decrease due to the stop of switching, and the voltage supplied to the standby circuit 10 also decreases.
Since the second switch element 105 is turned on, the voltage supplied to the load circuit 9 is also supplied to the standby circuit 14.

When the output voltage further decreases and approaches the breakdown voltage of the Zener diode 103, the current of the light emitting element of the photocoupler 102 decreases, so that the voltage across the light receiving element slightly increases, and at the same time, the voltage across the soft start capacitor 101. Also rises slightly and switching starts.

FIG. 2 shows waveforms when a change in the voltage of the terminal 4 for supplying power to the load circuit and a change in the drain current of the MOSFET 1 when the standby signal is input to the terminal 7 are observed on the same time axis. Is shown.

In FIG. 2, when the output voltage increases, the switching stops, and when the output voltage decreases, the switching starts. In addition, since the switching duty ratios immediately before the stop and immediately before the start are close to zero, the MOSFET 1
Are also close to zero.

Since a ripple appears in the output voltage in synchronization with the frequency of the intermittent oscillation, a constant voltage IC is connected before the standby circuit to remove the ripple.

In FIG. 2, the peak value of the current of the MOSFET 1 has reached a value corresponding to power sufficiently larger than the power required for the standby circuit, and the switching is performed in a state of high efficiency. As a result, power consumption is reduced.

[0027]

According to the present invention, the power consumption during standby can be reduced by adding a small number of components.
In addition, the problem of transformer noise, which easily causes intermittent oscillation, was solved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a voltage current waveform of each part of the circuit diagram shown in FIG.

FIG. 3 is a circuit diagram showing a conventional system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 MOSFET 2 Transformer 3 Oscillation control circuit 4, 5, 6 Output terminal 7 Standby signal input terminal 8 Constant voltage IC regulator 9 Load circuit 10 Standby circuit 11 Photocoupler 12, 13 Zener diode 14, 15 Switch element 101 Soft start capacitor 102 Photo Coupler 103 Zener diode 104 First switch element 105 Second switch element

Claims (1)

[Claims] 1. A switching power supply device for supplying power to a load circuit and a standby circuit, wherein a soft start circuit of a method of increasing a duty ratio from zero by raising a voltage between both ends of a capacitor by constant current charging at a start of startup,
A first switch element that is turned on when a standby signal is received from the standby circuit, an output terminal whose light-receiving element is connected in parallel to a capacitor of the soft start circuit, and a light-emitting element that supplies power; A photocoupler connected in series between one switch element, a zener diode inserted in series with the light emitting element of the photocoupler, an output terminal for supplying power to circuits other than the standby circuit, and the standby circuit. A second switch element connected between an output terminal for supplying power and a control electrode connected to an output terminal of the first switch element; and supplying power to the standby circuit of the second switch element. A switching power supply with a power saving function, wherein a diode inserted in series is added to the output terminal side of the switching power supply.