TWI631799B

The invention relates to a system used for providing input under-voltage and overvoltage protection for a power supply convertor. The system used for providing the input under-voltage and overvoltage protection for the power supply convertor comprises a line voltage-line current conversion module, a protection control logic module, a power-on reset and under-voltage lock module, a switch driving module and a power transistor. When the system is about to start, the switch driving module receives one or more test pulses. In a one or more test pulse period, the switch driving module receives a first control signal and combines a first signal and a pulse control PWM signal so as to generate the first control signal to control the transistor so that the system enters into a first mode, and receives a second control signal and combines a second signal and the PWM signal so as to generate the second control signal to control the transistor so that the system enters into the first mode.