An ideal source has its negative terminal on ground

PHYSICS · Multi-part · Fermi University Physics · Electronics, Instrumentation & Communication · Circuit foundations and passive networks · Sensors, detectors and experimental instrumentation

Electronics for Measurement, Ch The resistive network: two laws, one equivalent and the loading error

Problem

An ideal

12.0\,\mathrm{V}

source has its negative terminal on ground.

R_1 = 100\,\Omega

runs from its positive terminal to node

A

R_2 = 100\,\Omega

from

A

to ground,

R_3 = 150\,\Omega

from

A

to node

B

, and

R_4 = 200\,\Omega

from

B

to ground. The output terminals are

B

and ground. ((a)) Taking

A

and

B

as the unknown nodes, find the open-circuit voltage at

B

. Then find the short-circuit current from

B

to ground, and hence

R_{\rm th}

. ((b)) Find

V_{\rm th}

and

R_{\rm th}

a second way: replace everything to the left of

R_3

by its Thevenin equivalent at

A

, then carry that equivalent on through

R_3

and

R_4

. Check

R_{\rm th}

by source suppression as well. ((c)) A

900\,\Omega

load is proposed across the output. Predict the voltage across it and its loading error, and find the smallest load resistance that keeps the error under one per cent. ((d)) With the

900\,\Omega

load in place, find the power dissipated in

R_1

, and choose the smallest rating from

0.25

0.5

1

and

2\,\mathrm{W}

that leaves a factor of two in hand.

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