Isolated feedback for off-line switching power supplies with primary-side control

Abstract

Safety regulations require galvanic isolation between the AC line voltage and the outputs of switch-mode power supplies, making implementation of the feedback-control loop difficult. Four existing schemes for providing feedback information across the isolation barrier are examined. The schemes are identified as opto-couplers, amplitude modulation of the error signal, amplitude modulation of the output voltage, and communication of the drive pulse across the barrier. Each is examined with regard to steady-state and frequency-domain considerations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>