Patent ID: 6980444
Filing Date: 2005-12-27
Classification: H02M,Y02B

Abstract:
1. A switching power supply, comprising: a transformer, a switching element including an input terminal connected to a first primary winding of the transformer and receiving a first direct voltage via the transformer, an output voltage generation circuit connected to a secondary winding of the transformer, and rectifying and smoothing a secondary-side output voltage of the transformer, so that a second direct voltage smaller than an absolute value of the first direct voltage is generated and outputted from the first direct voltage, an output voltage control circuit for stabilizing the output voltage, a control signal transmission circuit for transmitting a signal of the output voltage control circuit to a primary side, a control circuit for controlling an operation of the switching element, and an auxiliary power supply voltage generation circuit connected to an auxiliary winding of the transformer, the auxiliary power supply voltage generation circuit being for generating a primary-side output voltage, and rectifying and smoothing the generated primary-side output voltage, so that an auxiliary power supply voltage for supplying a power supply voltage to the control circuit is generated and outputted, wherein the control circuit comprises: a regulator for generating and supplying a power supply voltage of the control circuit from the first direct voltage and the auxiliary power supply voltage, an oscillator circuit for generating and outputting a switching signal applied to the switching element, a current detection circuit for detecting a current applied to the switching element and outputting the current as an element current detection signal, a feedback signal control circuit for outputting a signal from the control signal transmission circuit as a feedback signal, a comparator for comparing the element current detection signal with the output signal of the feedback signal control circuit, and outputting a comparison signal, a switching signal control circuit for controlling an amount of current and an output of the switching signal according to the comparison signal, a clamping circuit for fixing a maximum value of the element current detection signal, a light load mode detecting comparator for comparing an output voltage of the feedback signal control circuit with an internally set light load reference voltage source, and a feedback voltage detection circuit for detecting an input voltage to the feedback signal control circuit, and outputting a switching stop signal when the input voltage is not lower than a specified voltage, wherein a current peak of the switching element is controlled and an intermittent operation is performed in response to a signal to the feedback signal control circuit, and an operation of the switching element is stopped according to an increase in input voltage to the feedback signal control circuit.