Certainly, an important part of every electronic equipment is the power supply. There are two types of power supplies, linear power supplies and the switch mode power supplies. Linear power supplies have high conducting loss which results in low efficiency. Therefore, application of linear power supplies is usually limited to low power cases which is cost effective to implement. In the switching power supplies, conducting losses are low and this type of power supplies can be used for medium and high power applications too. They operate in high frequencies ( which results in reduced size of magnetic elements such as transformers and output filter inductors. Many circuit topologies are introduced for switching power supplies. For high power applications, Full Bridge (FB) converter has received considerable attention. Usually FB converters are controlled using PWM (Pulse Width Modulation) or PS-PWM (Phase Shift PWM) techniques. The PWM controllers typically operate under hard switching, and the PS-PWM controller operates under soft-switching condition. oft-switching can be achieved by either ZVS (zero voltage switching) or ZCS (zero current switching). In the ZVS-FB-PWM converters, switches operate under zero voltage. Zero voltage at turn-on switching instances is achieved by using the transformer leakage inductor to discharge the output capacitance of switches, thus body diode of switches will conduct before turn-on instant. Zero voltage switching at turn off instant is achieved by applying snubber capacitors for switches. ZVS-FB-PWM is implemented without any extra components. So, it is very attractive for high-frequency applications where power MOSFETs are used as the power switches. However, these converters have several disadvantages. They operate with large circulating current during the freewheeling period which increases the conduction losses. Also, the ZVS range of leading and lagging legs are different. The ZVS range of lagging-leg switches is not wide enough unless the leakage inductance is large. This would cause duty-cycle loss and severe secondary parasitic ringing. Also, in this converter IGBTs are not usually applied for the lagging leg switches because of tailing current losses. If the lagging switches can operate under ZCS turn-off conditions, the leakage inductor can be minimized. So, the transfer of power is maximized and the effective duty cycle can be increased. In the ZVZCS-FB-PWM converters, the basic topology is the same as ZVS-FB-PWM converters with the auxiliary components or an auxiliary circuit being added to minimize freewheeling interval. Key Words Switching Power Supply, Soft Switching, Full Bridge, ZVS-FB-PWM, ZVZCS-FB-PWM, Active Clamp Circuit, Passive Clamp Circuit.