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Design of a Power Supply Using Fly-Back Converter

Abstract

The fly-back converter is used in both AC/DC and DC/DC conversion with galvanic isolation between the input and outputs. More precisely, the fly-back converter is a buck boost converter with the inductor split to form a transformer, so that the voltage ratios are multiplied with an additional advantage of isolation. In the on-state the energy is transferred from the input voltage source to the transformer while the output capacitor supplies energy to the output load. In the off-state, the energy is transferred from the transformer to the output load and the output capacitor. By controlling the duty ratio of switch used in the primary of transformer a variable DC supply of zero to a designed maximum value is obtained. The switching signal is provided by programming a micro controller which provides a pulse width modulation. The control circuit is isolated using a optocoupler. A fly-back transformer is designed to meet the output requirement. In this project the aim is to design a pure DC supply that can be varied in the limit 0V to 44V from a fixed supply voltage of 12V, which is AC or DC. Thus DC output below 12V which is buck operation and DC output obtained above 12V which is boost operation is obtained. The variable voltage is obtained by adjusting the duty ratio of gate pulse of a MOSFET, which is connected to the primary of a fly-back transformer. The duty ratio is varied using a potentiometer.

Karthika V L, Nimmy Sara George

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