Design and Implementation of SMPS Circuit using PWM Concepts

Abstract

Switched Mode Power Supply (SMPS) is the most prevailing architecture for DC power supply in modern systems, primarily for its capability to handle variable loads. Apart from efficiency the size and weight of the power supplies is becoming a great area of concern for the Power Supply Designers. In this thesis an AC to DC converter SMPS circuit, having a power MOSFET for switching operation and a PWM based Feedback circuit for driving the switching of the MOSFET, is designed and simulated in NI MULTISIM circuit design environment. Further the same circuit is Hardware implemented and tested using NI ELVIS Suite.
In this design the line voltage at 220V/50Hz is taken as input, this voltage is stepped down, rectified and passed through filter capacitor to give an unregulated DC voltage. This unregulated voltage is chopped using a MOSFET switch, driven by PWM feedback signal, to control the output voltage level. An Isolation Transformer is used to isolate the DC output from input supply. The transformer output is again rectified by the high frequency Diode bridge rectifier and is filtered using a capacitor to give the regulated DC output. A Voltage regulator is connected to give the precise voltage output.
The feedback network generates a high frequency PWM signal to drive the MOSFET switch. The dc voltage at the output depends on the width of the switching pulse. The pulse width is varied with the changes in the DC output voltage level, this change in the pulse width cancels the output voltage change and the SMPS output remains constant irrespective of load variations.