Phase staggered full-bridge converter with soft-pwm switching

Abstract

A full-bridge converter 10 is provided which performs soft switching based on pulse width modulated switching signals. The, converter 10 includes a primary side 12 and a secondary side 14 interconnected through a transformer 13. The primary side 12 includes a power source connected in parallel with leading and trailing legs 20 and 22, respectively. The leading leg 20 includes first and second switching transistors Q1 and Q2 connected in series, while the trailing leg 22 includes third and fourth switching transistors Q3 and Q4 connected in series. The switching transistors Q1-Q4 each include parasitic diodes D1-D4 and parasitic capacitances C1-C4. A control circuit 15 generates pulse width modulated (PWM) switching signals applied to gates G1-G4 of the transistors Q1-Q4. The control circuit 15 simultaneously turns on transistors Q1 and Q3 during a first energy transfer stage and simultaneously turns on transistors Q2 and Q4 during a second energy transfer stage. Control circuit 15 varies the time during which transistors Q3 and Q4 are turned on during the first and second energy transfer stages to maintain a desired minimum output voltage. The control circuit 15 provides a free-wheeling stage and transition stages between the energy transfer stages to effect soft switching through the use of PWM switching signals.