Importance

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Abstract

A PWM switching power supply of the buck regulator type converts an unfiltered rectified d.c. input voltage into a regulated stepped down d.c. output voltage for use by load circuits. The power supply includes a PWM switching regulator which controls the duty cycle of an N-channel field effect transistor (FET) power switch which has its source connected to a Schottky flyback diode. The flyback diode is connected to an LC output filter which generates the stepped down output voltage. The PWM regulator includes a 555 timer operating in conjunction with an RC timing network in a modulated a stable mode. Timer 555 has an output lead electrically connected to the gate of the FET for switching the FET on/off in response to an output voltage modulating feedback input from a feedback path with the source of the FET serving as the 'ground' for the PWM regulator. The feedback path includes a diode connected in series to a sampling capacitor which supplies a sampled output voltage feedback via a voltage divider and another diode to the 555 timer to allow the regulator circuit to fly with the FET power switch. When the FET is conductive, current flows through the LC output filter charging the capacitor and generating the stepped down d.c. output voltage. When the FET is non-conductive, the current loop is through the flyback diode. A smoothing filter is electrically connected to the FET power switch to smooth the unfiltered rectified d.c. input voltage.

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First Claim