Switching power supply apparatus

• US 20050162874A1
• Filed: 03/03/2004
• Published: 07/28/2005
• Est. Priority Date: 03/28/2003
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Umetsu, Koji
• Granted Patent: US 7,035,121 B2
• Time in Patent Office: Days
• US Class Current: 363/37
• CPC Class Codes: H02J 7/0068 Battery or charger load switching, e.g. concurrent charging and load supply H02J7/0013 takes precedence
• CPC Class Codes: H02M 1/0006 Arrangements for supplying an adequate voltage to the control circuit of converters
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

An AC power supply supplied from an outlet 11 is rectified by a rectifying circuit 13 through an input filter 12. The rectified power is supplied to a primary winding N1 of a transformer 14. A controlling circuit 19 has a switching device Q1 that controls on/off at predetermined timing. An FB signal that represents a power state of a load circuit 15 is supplied to the controlling circuit 19 through a transistor Q2. A comparator 20 compares a rectified voltage V3 of a tertiary winding of the transformer with a reference voltage REF3 and outputs an error signal. With the error signal, the transistor Q2 is controlled. Thus, the voltage for the controlling circuit supplied from the tertiary winding can be prevented from lowering against abrupt load variation. In addition, the output voltage Vo can be prevented from largely varying.

Claims

1. A switching power supply apparatus, having:

a rectifying circuit for converting an AC voltage into a DC voltage;

a switching device for intermittently turning on and off the DC voltage obtained from the rectifying circuit through a primary winding of a transformer;

a secondary winding and a tertiary winding for inducing powers in accordance with the turning on and off operations of the switching device;

power converting means for rectifying and smoothening the power that is output from the secondary winding and supplying the rectified and smoothened power to a load circuit on the secondary side;

control signal detecting means for driving the power obtained from the tertiary winding with the rectified and smoothened DC voltage and controlling the power supplied from the secondary winding to the load circuit for predetermined voltage and current; and

a controlling circuit having an oscillating portion and a PWM modulating portion for controlling an ON period of the switching device in accordance with a control signal detected by the detecting means so that the power supplied on the secondary side becomes a predetermined value, the switching power supply apparatus comprises;

comparing means for comparing the DC voltage obtained form the tertiary winding with a reference voltage; and

a circuit for supplying a control signal of the detecting means to the controlling circuit,

wherein the DC voltage of the tertiary winding is designated to equal to or higher than the minimum operation voltage of the controlling circuit,

wherein when the load circuit is abruptly turned off, the oscillation stops, and

wherein when the DC voltage becomes equal to or lower than the minimum operation voltage, the oscillation stop state of the controlling circuit is cancelled in accordance with a signal that is output from the comparing means.

2. The switching power supply apparatus as set forth in claim 1,

wherein a pulse width control is performed so that when the load circuit is in a standby state and the switching device oscillates at a low frequency lower than a basic frequency, if the voltage supplied to the controlling circuit becomes equal to or lower than the minimum operation voltage, the operation stop state of the controlling circuit is cancelled, the switching frequency is raised from the low frequency corresponding to the voltage lowered from the minimum operation voltage to the basic frequency, and when the switching frequency becomes the basic frequency, the ON period of the switching device is increased.

3. The switching power supply apparatus as set forth in claim 2,

wherein the pulse width control is configured to cause the ON period of the switching pulses in the standby state of the load circuit so that when the input DC voltage is high, the pulse width decreases and when the DC voltage is low, the pulse width increases.