# Rectifier questions

1. Apr 23, 2012

### daredevil

I have some confusions regarding rectifier circuits.

I was wondering does any change happen to the rectified dc voltage if i change the load resistance. I was thinking even if the current change with the change in resistance, there should not be any change in the voltage. But, it seems it is not so..

And how do I calculate the capacitance of the smoothing capacitor I need.

2. Apr 23, 2012

### daredevil

And also, does the capacitor charge up completely and discharge completely in each cycle of AC irrelevant of the capacitance and the frequency of the AC signal..??

Thanks.

3. Apr 24, 2012

### Staff: Mentor

This page at Hyperphysics should help answer your questions:

http://www.google.com/imgres?imgurl...ltage+calculation&hl=en&gbv=2&tbm=isch&itbs=1

4. Apr 24, 2012

### Bob S

The capacitor discharge plot given by berkeman is very important for an additional reason. The rectifier "ON" time per cycle is tON = T - tdis. The peak repetitive rectifier charging current is inversely proportional to this ON time, and can easily exceed the rectifier specs if the filter capacitor is too large.

5. Apr 25, 2012

### NeuronsAtWork

Bob S--
Just had to comment on your comment. It's funny--I've been 'into' electronics and circuit building for more than 40 years, and have constructed numerous power supplies for various items in that time without ever stopping to consider your point of potentially damaging a rectifier due to excess inrush charging a cap. Apparently through sheer luck, or the fact that I tend to over-design stuff, (or perhaps because I typically use inherently current-limited voltage regulators) I've never blown a diode that way. But, it is something I will keep well in mind going forward. Very good info!

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