Direct filtering type switching power supply

Abstract

A direct filtering type switching power supply is provided, for an occasion including pulsating direct current, including a filter circuit, a main power stage and an indicating circuit. A direct current input is connected to the filter circuit through the indicating circuit. The filter circuit and the main power stage are connected in parallel. The indicating circuit is formed by connecting a light emitting unit with an inductor in parallel, and make sure that the direction of the direct current input passing through the inductor is opposite to the conducting direction of the light emitting unit. The filter circuit at least includes an electrolytic capacitor. When the electrolytic capacitor is normal, an excitation current of a switching transistor in the main power stage basically does not appear in the inductor, and an LED in the light emitting unit does not emit light. When the Equivalent Series Resistance of the electrolytic capacitor rises greatly, the excitation current of the switching transistor appears in the inductor. Furthermore, when the switching transistor is switched off, the excitation current flowing through the inductor, which cannot be changed abruptly, freewheels through the LED, and drives the LED to emit light, so as to notify a user or a circuit that the electrolytic capacitor may have the risk of complete failure. The LED may also be a light emitter of a photocoupler. The switching power supply is low in cost, has unchanged efficiency and is easy to implement.