QUASI-RESONANT HALF-BRIDGE CONVERTER AND CONTROL METHOD THEREOF

摘要

A quasi-resonant half-bridge converter includes a switch unit including first and second switches that are coupled in series, a capacitor unit coupled to the switch unit in parallel, a rectifier unit, an output capacitor, and a transformer coupled to the aforesaid components. The first and second switches are respectively controlled using first and second control signals that have a constant frequency. Duty cycles of the first and second control signals may be adjusted based upon a DC output voltage across the output capacitor for promoting conversion efficiency of the converter when operating at light load.

主权项

1. A quasi-resonant half-bridge converter adapted to receive a direct-current (DC) input voltage and to output a DC output voltage to a load, said quasi-resonant half-bridge converter comprising:
a switch unit disposed to receive the DC input voltage, and including a first switch and a second switch that are electrically coupled in series, each of said first switch and said second switch having a body diode and a parasitic capacitor electrically coupled in parallel, being disposed to receive a respective one of a first control signal and a second control signal, and being configured to make or break electrical connection in response to the respective one of the first and second control signals; a capacitor unit electrically coupled to said switch unit in parallel, and including a first capacitor and a second capacitor electrically coupled in series; a transformer including a first winding disposed at a primary side, and a second winding and a third winding that are electrically coupled in series at a secondary side, each of said first, second and third windings having a polarity terminal and a non-polarity terminal, said polarity terminal of said third winding being electrically coupled to said non-polarity terminal of said second winding, said polarity terminal of said first winding being electrically coupled to a common node of said first switch and said second switch of said switch unit, said non-polarity terminal of said first winding being electrically coupled to a common node of said first capacitor and said second capacitor of said capacitor unit; a rectifier unit electrically coupled to said second and third windings in parallel between said polarity terminal of said second winding and said non-polarity terminal of said third winding, and including a third switch and a fourth switch electrically coupled to each other; an output capacitor electrically coupled between a common node of said second and third windings, and a common node of said third and fourth switches, and disposed to be electrically coupled to the load in parallel, said output capacitor having a DC output voltage across two terminals thereof; and a control circuit electrically coupled to said first and second switches of said switch unit, receiving the DC output voltage, and configured to generate, based upon the DC output voltage, the first and second control signals that have the same constant frequency, and to respectively adjust, based upon the DC output voltage, duty cycles of the first and second control signals such that a respective one of said first and second switches makes electrical connection when a voltage thereacross is close to zero.