PUSH-PULL SWITCH CIRCUIT AND SOFT SWITCH THREE TRANSISTOR PUSH-PULL FORWARD CONVERTER

摘要

A push-pull switch circuit (20) and a soft switch three transistor push-pull forward converter, the push-pull switch circuit comprising a first switch transistor (Q1), a second switch transistor (Q2), a third switch transistor (Q3), and a transformer (TS1), a drain electrode of the first switch transistor and a drain electrode of the second switch transistor respectively being connected to the two ends of a primary side winding of the transformer, a source electrode of the first switch transistor and a source electrode of the second switch transistor both being grounded (GND), a gate electrode of the first switch transistor and a gate electrode of the second switch transistor being used for accessing two PWM pulse signals (Q1_PWM and Q2_PWM) with opposite phases, a drain electrode of the third switch transistor being used for accessing a direct current, a source electrode of the third switch transistor being connected to a middle tap of the primary side winding of the transformer, and a gate electrode of the third switch transistor being used for accessing a PWM pulse signal (Q3_PWM) having an adjustable duty ratio; the output voltage of a secondary side winding of the transformer is adjusted by means of adjusting the duty ratio of the PWM pulse signal of the gate electrode of the third switch transistor. The present push-pull circuit is suitable for multiple input voltages, can reduce the voltage stress on the switch transistors, and can prevent the transformer from spiking.