An important aspect of modern power supply design is the need to increase the power density of the power supply since many power applications involve locations in which the size of the power supply relative to its power output is restricted by space considerations. The power train and control circuits in addition to being highly compact must also have high overall efficiency to limit heat creating power dissipation. An illustrative application of a high density power supply is an off-line power supply used to power a laptop computer or similar appliance. Bridge type converters are suitable for such applications since they may be designed to operate resonately, which is an operational mode permitting a very high power density and high power efficiency.
The power switching transistors in a half bridge converter have an applied voltage stress half that of the switching transistors in a push-pull converter of comparable power handling capability. Hence the half bridge converter is especially suitable for high input voltage applications such as power converters powered directly from a rectified AC power line or from a power factor correction boost converter powered off the AC line.
Synchronous rectifiers are used in power supplies requiring high efficiency since they have little loss in operation. Proper drive circuits must be provided to drive the synchronous rectifier devices. Power supplies are often connected in parallel and without proper drive arrangements a synchronous rectifier of a failed power supply may be improperly biased into operation allowing a reverse feed to power into the power supply.