Switched-mode power supply unit reducing mains harmonic loading

摘要

Between the relatively small charge capacitor (CN) and a tap (A) on the prim. winding (W1) of the transformer (Tr), a choke (LH) is connected in series with a first diode (DH). The relatively large storage capacitor (CS) across the prim. winding and its switching transistor (T1) is decoupled from the smaller capacitor by a second diode (DN)> This series circuit generates an additional charging current for the larger capacitor which prolongs the current drawn from the mains (UN) during each half-cycle and reduces its amplitude.