how to calculate the average diode current peak, and average valude of diode current in full wave rectifier with capcaitor filter parallel with resistor
In my opinion, the average value of diode current= Io
with Vo=2vm/pi
Io=Vo/R
how about the peak value?
Ipeak=Irms*sqr(2)=Io*sqr(2)?
any idea?

 

First of all take a look at the schematic of a full-wave rectifier with capacitor filter here, under the "output smoothing" section: http://en.wikipedia.org/wiki/Full_wave_rectifier

Keep in mind that the diodes are not constantly conducting, even inside ther half-period. They conduct only to charge the capacitor when its voltage drops below the desired output voltage. That threshold depends on the load current consumption, \(I_{\tiny{L}}\). The followin image depict quite well the current spikes that travel throught the diode: http://www.electro-tech-online.com/...d1243090102-diode-ripple-source-rectifier.jpg

I will give you the formulas straight away, as I havent found them fully explained in bibliography anyway, and I don't think one should caclulate them in any other way other that geometrical approximation:

\(I_{\tiny{DAV}}=I_{\tiny{L}}\cdot \left(1+\pi \sqrt{\frac{V_p}{2 V_r}} \right) \\
I_{\tiny{DMAX}}=I_{\tiny{L}} \cdot \left(1+ 2 \pi \sqrt{\frac{V_p}{2 V_r}} \right)\)
where \(V_p\ (not\ V_{pp})\ and \ V_r\) are input voltage amplitude and output ripple respectively.