In this thesis, after a survey on isolated and Non isolated PFC converters and their problems, features and a brief review on the applied controllers, some of the applied soft switching methods on Non isolated bridgeless PFC converters are presented. The Non isolated PFC converters can shap the input current of the rectifiers according to the related standards but because of the variable input power of a sinusoidal voltage, there will be some rippels in the output voltage. In isolated converters to reduce the output voltage ripple a storage capacitor can be placed in the converter to save some of the input power and release it during the zero crossing of the sinosidal input voltage. Due to the limited band width of the voltage controller loop of the converter the storage capacitor voltage can increase when the output power decreases. So a stprage capacitor with higher voltage rating should be installed which increases the total cost of the converter. Several approaches are presented to reduce the maximum voltage stress of the bulk capacitor. The approaches are negative magnetic feedback and frequency modulation. In negative magnetic feedbackmethid the converter uses an extera winding to set a part of the bulk capacitor voltage in series with the input inductor to reduce the input current when the bulk capacitor voltage increases. This method increases the converter complexity and its total cost. In frequency modulation method the converter uses a variable frequency controller to control the converter. The controller uses the frequency to control the bulk capacitor voltage and the duty cycle to control the output voltage. With this method the converter does not need any extera components but the controller will be so complex and due to the variable switching frequency the magnetic component design will be more complex. Another way to reduce the bulk capacitor voltage is to locat that in the low voltage side of the isolation transformer which makes the series inductance interval PFC converters. In this family of PFC converters the bulk capacitor voltage is well limited but they can achieve justify; TEXT-INDENT: 0.25in; MARGIN: 0in 0in 0pt; unicode-bidi: embed; DIRECTION: ltr" Then the proposed PFC converters are presented. The first proposed converter is a Zero-Voltage-Switching bridgeless PFC which uses an improved auxiliary circuit to achieve Zero-Voltage-Switching conditions for its main switches and diodes. In this converter all of the resonant current flowes through the auxiliary circuit so there is no extera voltage or current stress on the main switches and diodes, also the auxiliary switch operates in the ZCS conditions so it dos not introduce any switching loss, in addition with that auxiliary circuit the converter Keywords Power factor correction (PFC), Bridgeless PFC, Soft switching, Series inductance interval PFC converters.