| 摘要 |
A switching mode power supply which controls power source supplied to electronic equipment, which is designed to protect a circuit against an overvoltage through a power line of coil or overcurrent on the occurrence of short-circuit of power line. The switching mode power supply of the present invention comprises a switching transformer for receiving DC voltage to a primary coil from a rectifier, and inducing respective different predetermined voltages into a plurality of coils on the secondary and third side of respective different turns ratio, an error detection and feedback for inputting the voltage VA of a coil with the highest turns ratio of a plurality of the coils and detecting voltage errors, a switching output for outputting a control signal so as to switch a switching transformer, a current sensor for sensing a current signal transmitted from the switching output, a pulse width modulation controller for inputting a voltage error fed back from the error detection and feedback and an output current from the current sensor and a voltage of the third coil, and outputting pulse width modulation signal which duty cycle is modulated in accordance with these input signals to the switching output, and an overvoltage and overcurrent protection circuit for detecting whether an overvoltage from a plurality of the coils occur, whether an undervoltage from a plurality of the coils occur or not, and continuously stopping an operation of pulse width modulation controller when detecting the overvoltage or the undervoltage.
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