A converter regulating its output draws from a bus through an input filter with

PHYSICS · Multi-part · Fermi University Physics · Electronics, Instrumentation & Communication · Circuit foundations and passive networks · Semiconductor devices and analogue circuits

Inside the Instrument, Ch References, regulators and switching converters

Problem

A converter regulating its output draws

15\,\mathrm{W}

from a

24\,\mathrm{V}

bus through an

LC

input filter with

L = 47\,\mu\mathrm{H}

C = 10\,\mu\mathrm{F}

and

30\,\mathrm{m}\Omega

of total series loss. ((a)) Find the converter's incremental input resistance

r_{\rm in}

. ((b)) Find the filter's characteristic impedance

Z_0

, its resonant frequency, its quality factor and its undamped peak output impedance. Does it meet the rule

|Z_f| \le |r_{\rm in}|/2

? ((c)) The text damped a

Z_0 = 1\,\Omega

filter with a leg

C_d = 4C

R_d \approx 0.6\,\Omega

, bringing its peak to about

0.8\,\Omega

. With the small series loss neglected, filter and leg depend on frequency only through

\omega\sqrt{LC}

and on impedance only through

Z_0

, for a fixed ratio

C_d/C

. Scale that leg to this filter: give

C_d

R_d

and the damped peak, and say whether the rule is now met. ((d)) Find the power a bare resistor equal to

R_d

would dissipate across the filter capacitor, and say what the blocking capacitor

C_d

prevents.

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