The invention relates to a short-circuit and under-
voltage protection method for a 12V120W direct-current power converter. When a
system is powered on and delayed for a period of time,
voltage dividerresistors R21 and R23 are used for detecting the output
voltage; after voltage division, a pin 7 of a low-power-consumption control
chip U5 detects a low level, which means that external
short circuit or
overcurrent occurs; the output of a pin 4 of the low-power-consumption control
chip U5 is changed from a low level to a high level, a
triode Q5 is controlled to be conducted, an optocoupler primary side
diode is conducted, and a
secondary side triode is conducted; a COMP pin of a power supply conversion
chip UC3845 is pulled down, the OUT pin of the UC3845 is controlled to stop outputting a PWM
signal, and then, the whole converter does not output, namely, the power supply converter is in an open-circuit state, and in the state, even if the output continues to maintain a
short circuit phenomenon, the problem that an electric device is damaged does not occur; and the
short circuit is cancelled after the control, the power supply ACC is restarted, and the converter resumes work.