Rapidimprovement inmicroprocessorstechnology has createdmany challenges for their power supplies. With the incrementof microprocessors current requirement, their power consumption hasincreasedand byreducingthe supply voltage,power consumption can be decreased. Therefore, low voltage, high current and high switching frequency(to achieve fast dynamic and high power density) are some of the challenges for the microprocessors power supply.In some devices like laptops, desktop applications and portable products, the voltage regulated modules are used to deliver the effective power to the microprocessors. Usually, these modules use the buck converter with synchronous rectifier due to the low voltage drop of synchronous switch in comparison to the diode. But, with increased current requirement and ripple reductionin the single-phase buck converter, a relatively large output filter inductor is required with excessive increase in the number of output filter capacitors. During the transient period, this large inductor limits the energytransfer speed of the VRM so that the capacitor alone must discharge its stored energy to the load. The filter capacitor must be large enough to maintain the output voltage level. But, due to the space limitation in low voltage high current applications, the inductance and capacitance of the output filter not be increased. Moreover, this structure is not able to provide the requirments of microprocessors and as a result, in processors with higher power, a multiphase interleaved synchronous buck converter is utilized in this method.The size of converters filter components is determined by the switching frequency and to achieve high power density, high switching frequency is required. But withincreasing the switching frequency, switching losses and EMI noiseincreases, which reduces theefficiency of synchronous buck converter. This problem can be solved by providing soft switching condition for switches. Very low operating duty cycle is another problem for the voltage regulatormodule since the output voltage is very low.Due to very small operating duty cycle of the buck converter which is equal to the ratio of the output to input voltage, the regulation period is very short. Consequently, gate drive of the main switch is difficult to realize, switch current level is very high and thus, the efficiency is low.The coupled inductor, series capacitor and non-isolated buck type converters are some solutions for increasing the duty cycle of synchronous buck converter. In this thesis, soft switching synchronous buck converters with extendedduty cycle are studied. Thenthe proposed soft switching converters are presented. Coupled inductor and series capacitor techniques are applied in order to extend the duty cycle. The operating modes of the converters are explained and to verity of theoretical analysis, simulation results for all proposed converters and experimental results for one of the proposed converters are presented. Keywords: 1-voltage regulated module, 2-synchronous buck converter, 3-duty cycle extension, 4-coupled inductors.