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Power-Factor-Slide11

This page shows how boost converters work. The boost converter is in the class of non-isolated, indirect transfer converters. There’s no galvanic isolation input to output, and the energy transfer is indirect. The power switch stores energy in the inductor during the Ton portion of the switching cycle, then the inductor “flies back” and transfers energy to the bus capacitor. During the switch T1-on interval, a linearly increasing current flows through the boost inductor L1. The inductor stores energy determined by the inductance and the total volt-seconds, that is the product of voltage and time across the inductor. In this interval, the output capacitor supplies load current. During the T1-off interval, the voltage on the inductor L1 flips as the inductor returns the applied volt-seconds and transfers energy through the boost rectifier diode D1 into the output capacitor and the load. Vout is determined by the ratio of T-on to T-off and the input voltage, averaged over an AC line cycle. In practice, the size of the output capacitor is made large and the PFC regulator loop has a zero gain crossover point below the AC line frequency.

PTM Published on: 2011-09-02