Uninterruptable off-line, isolated flyback topology switch-mode power

Abstract

An all-ranging DC output uninterruptible switched mode power supply (SMPS) of off-line flyback topology is capable of operating with an input voltage between 90 v AC and 270 v AC and an input frequency range of 40 Hz-70 Hz for operation throughout the world. Provided with a battery backup, the SMPS gives DC output without interruption even during AC power failures. The battery and the regulated AC main's supply outlet are connected through an 'OR' connection comprising Shortsky rectifier diodes. A pulse width modulator whose conductive duty cycle is responsive to the condition of a voltage, Vcc, provides a reference voltage. An isolated flyback converter includes MOSFET transistor switch and power transformer. The power transformer stores energy in its primary winding when transistor is conductive and transfers energy to the secondary winding when transistor is nonconductive. The pulse width modulator controls the conduction of the transistor. A snubber circuit allows slow decay of current in the power transformer. An opto-coupler acts as a feedback or the pulse width modulator. Inductor is used for storing energy and transferring energy to the negative voltage regulator when control IC, is off, to provide -12 v at the output of negative voltage regulator.