초록 ▼

A switching mode power supply apparatus has a low voltage protection circuit with a simple construction. The apparatus is not actuated or have its operation stopped under brown-out conditions where the voltage value of the input is reduced to a predetermined value. The switching mode power supply ap

A switching mode power supply apparatus has a low voltage protection circuit with a simple construction. The apparatus is not actuated or have its operation stopped under brown-out conditions where the voltage value of the input is reduced to a predetermined value. The switching mode power supply apparatus includes a first rectifying and smoothing circuit, an actuating power supply unit having an overvoltage protection circuit, a switching transistor, a switching transformer, a switching transformer, a second rectifying and smoothing circuit, a third rectifying and smoothing circuit, a constant-voltage circuit, a first protection circuit, and a second protection circuit.

대표청구항 ▼

[ What is claimed is:] [1.]1. A switching mode power supply apparatus having a low voltage protection circuit comprising:a first rectifying and smoothing circuit for rectifying and smoothing an input alternating current voltage to output a direct voltage;an actuating power supply unit for receiving

[ What is claimed is:] [1.]1. A switching mode power supply apparatus having a low voltage protection circuit comprising:a first rectifying and smoothing circuit for rectifying and smoothing an input alternating current voltage to output a direct voltage;an actuating power supply unit for receiving the direct voltage from the first rectifying and smoothing circuit and for converting it to a predetermined DC voltage;a PWM controller actuated by the predetermined DC voltage from the actuating power supply unit for outputting a predetermined pulse width modulation waveform, said PWM controller having an overvoltage protection circuit;a switching transistor which is switchedby the output waveform of the PWM controller;a switching transformer having first, second and third coils for accumulating output power of the first rectifying and smoothing circuit, as applied to the first coil, at the second and third coils in accordance with the switching of the switching transistor;a second rectifying and smoothing circuit for rectifying and smoothing a voltage accumulated in the second coil, and for outputting a predetermined DC voltage supplied to a load circuit;a third rectifying and smoothing circuit for rectifying and smoothing a voltage accumulated at the third coil of the switching transformer for outputting another predetermined DC voltage;a constant-voltage circuit for receiving the predetermined DC voltage from the third rectifying and smoothing circuit and for outputting the driving voltage of the PWM controller;a first protection circuit for receiving the direct voltage from the first rectifying and smoothing circuit and for controlling in such a way that the actuating power supply unit is not driven when the value of the direct voltage from the first rectifying and smoothing circuit becomes lower than a pre-determined value; anda second protection circuit for controlling such that, when the input alternating current voltage becomes lower than a pre-determined value, the driving voltage of the PWM controller outputted by the constant voltage circuit is sufficient to operate the overvoltage protection circuit of the PWM controller to thereby stop the operation of the PWM controller.