Half Bridge power converter with open or short circuited series auxiliary transformer.

摘要

A power converter for delivering power to a load at a regulated voltage 11 includes a regulating stage receiving an unregulated supply 10 and having a main transformer 18. Switches 16a and 16b are arranged in a half-bridge configuration and connect the transformer primary 17 to the unregulated supply 10 to drive the load via a rectifying stage connected to the transformer secondary 19. The on time of the switches 16a 16b are controlled by a controller 14 to effect the regulation over a range of values of the unregulated supply. An auxiliary transformer 103 has a secondary winding 104 connected in series with the main transformer primary 17 and a primary winding which is selectively driven via a switch 106. A comparator 107 detects a low voltage event within the regulating stage, such as a drop in the intermediate voltage at 10. The primary winding 105 of the auxiliary transformer 103 is unshorted (open) whilst a low voltage event persists and shorted at other times. Shorting occurs by means of switch 106. In the event of a low voltage detected on the regulator input voltage, the series auxiliary transformer provides a voltage acting in series with the primary winding, effectively boosting the supply seen by the primary winding of the main transformer. Hence the useful operating voltage range of the converter is enhanced. The half bridge converter circuit may be used in conjunction with a power factor correction circuit PFC (figure 2). Another embodiment of the invention involves the use of a plurality of auxiliary transformers (figure 4).