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Problem with calculation of the smooting capacitor rms current of a diode rectifier

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Newbie level 2
Jul 9, 2015
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Hello everybody,

I'm working on the PSpice-based examples, on the example 1 : "1-Phase Diode Bridge Rectifier".

I have a problem with question 4, which asks to calculate Icap (the rms current though the filter capacitor) as a ratio of the average load current Iload.

For me it is impossible to calculate this as a simple ratio, because the capacitor ripple current is more difficult than this (must take into account the diode conduction time, the frequency, the capacitor value, ...) and I saw some formulas on the web, and they are all complicated !

Does anyone see what does they mean by "calculate Icap (the rms current though the filter capacitor) as a ratio of the average load current Iload" ? Is this determined by varying the resistive load and measure the capacitor RMS current and the average load current, and after determine the ratio by linearizing ? or is it a real calculation with a formula ?

Thank you very much for your help, I post the example with the schematics.


  • Example 1.pdf
    85.2 KB · Views: 64

The problem specification is clearly referring to a SPICE fourier anaylsis performed before teh calculations, in so far I don't understand your problem.

All currents and voltages, including the deferred values like Irms are results of a nonlinear transient analysis and not "calculated" or obtained by a formula.

thanks for answer FvM,

but how do you obtain this ratio if it is not by a calculation ?

Yes, the ratio is a simple calculation. The problem is to determine the RMS current.

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