CONTROL OF A STARTUP CIRCUIT USING A FEEDBACK PIN OF A PWM CONTROLLER INTEGRATED CIRCUIT CHIP

摘要

A power supply includes a control transistor that controls a primary winding of a transformer to induce current on a secondary winding of the transformer to generate an output voltage. A pulse width modulation (PWM) controller integrated circuit (IC) chip drives the control transistor through a gate pin. The PWM controller IC chip has a feedback pin that receives a feedback signal indicative of the output voltage. A high voltage (HV) startup transistor is controlled through the feedback pin. The HV startup transistor turns ON during startup to generate a supply voltage from current received from the input voltage of the power supply. The HV startup transistor turns OFF when the supply voltage reaches a startup voltage level that is sufficient to start the switching operation of the control transistor and thereby receive operating current from an auxiliary winding of the transformer.

主权项

1. An integrated circuit (IC) chip comprising:
a gate pin that is configured to output a control signal for driving a control transistor of a switching mode power supply; a current sense pin that is configured to receive a current sense signal indicative of a current through the control transistor; a feedback pin that is configured to receive a feedback signal that is indicative of an output voltage of the switching mode power supply and is configured to be connected to a control terminal of a high voltage (HV) startup transistor that is external to the IC chip; and a pulse width modulator that is configured to generate the control signal that is output at the gate pin to regulate the output voltage by pulse width modulation (PWM) based on the feedback signal and the current sense signal.