P 3.3-5 The model of a cable and load resistor connected to a source is shown in

Figure P 3.3-5. Determine the appropriate cable resistance, R, so that the output voltage, v_o, remains between 9 V and 13 V when the source voltage, v_s, varies between 20 V and 28 V. The cable resistance can only assume integer values in the range 20 < R < 100 Ω.

Figure P 3.3-5.

This is a series circuit. So the voltage division gives us

Solve for R

Consider the two voltage limits, so low voltage limit

High Voltage limit

So now, check values. Use a low R as 58 Ω and a high R as 61 Ω, see if the voltages remain in the limits.

R = 58 V

R = 61 V

A cable with R between will result in an output voltage of

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This page last updated on January 17, 2019