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I'm given a full bridge rectifier circuit with values for power, industance, and RMS input voltage: [P = 380 W, L = 85 uH, Vs = 115 V].

Full Bridge

The question states to 'select' output resistance for a simulation, but I am unsure if it's possible to calculate this. It might be that it is asking to select an arbitrary number.

I'm guessing that it can be calculated using:

$$ R = V_s^2/P = 34.8 \varOmega $$ I am wondering if the voltage drop across the inductor can be omitted at steady state. Is this the correct way one would determine the load resistance?

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Assuming negligible losses in the inductor and rectifier and a low value for C, your calculation is good.

As the source is 115V I'm assuming the frequency is 60Hz, so L has a reactance of 0.032Ω - insignificant compared to R. Assuming silicon diodes with suitable ratings the rectifier should be dropping about 1.4V - again an insignificant amount.

The capacitor is a wild card - if large enough to hold the voltage up between peaks then DC output voltage could get close to 160V, and R might have to be much higher (67Ω?).

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Or you could just read the number on the resistance. It's not the output impedance you are looking for but the value of the load resistor.

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  • \$\begingroup\$ This doesn't seem helpful, it looks like a theory question rather than measuring the value from a physically built circuit. \$\endgroup\$ – PeterJ Jan 20 '15 at 2:19

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