A series-pass regulator uses an npn emitter-follower pass device controlled by an…

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

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Problem

A series-pass regulator uses an npn emitter-follower pass device controlled by an error amplifier whose loop gain has DC value

T_0 = 800

and a single dominant pole at

f_p = 40\,\mathrm{Hz}

, so

T(j\omega) = T_0/(1 + jf/f_p)

. The pass device's small-signal output resistance is

r_e = V_T/I_L

, with

V_T = 25.9\,\mathrm{mV}

300\,\mathrm{K}

, and the load current is

I_L = 50\,\mathrm{mA}

. ((a)) Find the regulator's output impedance at DC. ((b)) Find its output impedance at

f = 200\,\mathrm{Hz}

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