Tuning Inductor-Input Filters

Inductor-input power supply filter effectiveness can be increased by connecting a capacitor in parallel with the input inductor that has a capacitive reactance equal to the inductor's inductive reactance at the fundamental ripple frequency. The ripple-filtering improvement occurs because the capacitor and inductor form a high-impedance parallel-resonant circuit in series with the rectifier output current. Even without use of a high Q inductor a fundamental ripple-filtering-improvement of about 3 to 1 can be achieved by this means when filtering the output of a single-phase, full-wave rectifier. ©2004 Martek International All rights reserved.

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