Capabilities of switching DC-DC converters have made them an important part of electrical equipment. Some of these capabilities are high efficiency and high power density. In applications where non-isolated, step-down conversion ratio, and high output current with low ripple are required, interleaved buck converter (IBC) has received a lot of attention due to its simple structure and low control complexity. Interleaved buck converter consists of two parallel buck converters, which are controlled out of phase. However, IBC suffers from some disadvantages. In the conventional IBC, the voltage stress of all semiconductor devices are equal to the input voltage, so they suffer from high voltage stress and hence, high voltage devices should be used. High-voltage-rated devices have generally poor characteristics such as high cost, high on-resistance, high forward voltage drop, severe reverse recovery problems, etc. In addition, the converter operates under hard switching condition. Thus, the cost becomes high and the efficiency is low. For higher power density and better dynamics, it is required that the converter operate at higher switching frequencies. However, higher switching frequencies increase the switching losses associated with turn-on, turn-off, and reverse recovery of diodes. Consequently, the efficiency is further reduced. Also, IBC experiences an extremely short duty cycle in the case of high-input and low-output voltage applications. In this thesis, after a short survey on IBC, three new topologies are introduced to overcome the mentioned draw backs of high step down converters. Also, a new interleaved zero-voltage-transition PWM buck converter with one auxiliary switch is proposed to improve IBC efficiency. Moreover, a family of single-switch soft switching PWM converters with single magnetic core is introduced to implement soft switching condition in IBC without using any additional active switch. The presented simulation and experimental results of these topologies confirm to theoretical analysis. Keywords: Buck converter, low switch voltage stress, step-down conversion ratio, ZCT, ZVT
