Zero voltage switching asymmetrical half-bridge converter topology

Abstract

This paper describes a buck derived isolated DC/DC converter topology that includes a half-bridge of switching devices which are asymmetrically controlled so that the top and bottom switches are opened at mutually exclusive times. The center-tap of this half-bridge is connected to the primary winding of the isolation transformer along with a series connection of a small resonant inductor and half-bridge of capacitors. The secondary winding of the isolation transformer is connected via a blocking capacitor to a single output rectification diode and an inductor-capacitor (LC) low pass filter to provide a regulated output. Additionally a voltage clamping circuit which includes an active switch, that may also be connected to the output filter inductor, can be added across the output rectifier to control the voltage across the output rectifier diode and recover the energy stored in the resonant inductor and leakage inductance of the isolation transformer. This converter topology has been shown to provide zero voltage switching of the half-bridge of switching devices over a wide load range and zero current switching of the output rectification device. This topology has been incorporated into 1.5 kW and 2 kW switch-mode rectifiers for telecom applications with 24 Volt and 48 Volt outputs.