Rectifier with cap and zener

Thread Starter

scottfarcuz

Joined Dec 9, 2012
4
Im lost as to how to calculate the Vripple (pk-pk) and Vaverage (Including Vripple) of the attached circuit.

For Vsec I used
75Vrms *sqrt(2) = 106Vpk then divided it by the turns ratio of 5 coming up with 21.21Vpk

For the voltage at the top of the cap I just subtracted the 0.7V drop from the diode leaving me with 20.51Vpk

Any help or links would be very appreciated.
 

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#12

Joined Nov 30, 2010
18,224
It seems you have misunderstood the question. The ripple voltage is at the top of C1. What you have found is the peak voltage of the transformer, and that is a good thing to do.

There are 2 diodes in the path of each wave, so your .7 volts is a wrong belief.

You need to find the amount of (mostly) dc on C1. Then calculate the current of the circuit in the DC section. Then calculate the p-p ripple voltage and describe that combined with the DC voltage on C1.
 

MrChips

Joined Oct 2, 2009
30,706
I don't think anyone would want to help by looking at random equations on a piece of paper.

Show your work in step form with appropriate comments.
 

#12

Joined Nov 30, 2010
18,224
Your third equation is wrong. The 200 ohm resistor doesn't go to ground. It goes to a 6 volt zener so the voltage is 19.8 minus 6.
 

The Electrician

Joined Oct 9, 2007
2,971
You've got wrong units on Vripple2; they should be mV, not mA.

Also, the voltage Vc1 can't be anywhere near 6 volts. It should be more like 19 or so volts.

The current in the transformer secondary consists of very narrow, large amplitude pulses. These large pulses cause a larger voltage drop across the diodes than .7 volts each. This will cause the peak voltage across the capacitor to be somewhat less than it would otherwise be.
 
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