Rectifier Circuits: Questions & Answers

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Discussion Overview

The discussion revolves around rectifier circuits, specifically addressing the effects of load resistance on rectified DC voltage and the behavior of smoothing capacitors in relation to AC signals. Participants explore theoretical and practical aspects of rectification, including voltage changes with varying loads and capacitor charging dynamics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether changing load resistance affects the rectified DC voltage, suggesting that current changes should not impact voltage, though they suspect otherwise.
  • Another participant inquires about the complete charging and discharging behavior of capacitors in each AC cycle, regardless of capacitance and frequency.
  • A participant emphasizes the importance of the capacitor discharge plot, noting that the rectifier "ON" time is critical and that excessive charging current can exceed rectifier specifications if the filter capacitor is too large.
  • A later reply shares personal experience with rectifier circuits, noting that they have not encountered issues with inrush current damaging rectifiers, but acknowledges the importance of the discussed point for future designs.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the impact of load resistance on rectified voltage and the behavior of capacitors, indicating that multiple views and questions remain unresolved.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about load resistance effects and the conditions under which capacitors charge and discharge, which are not fully explored.

daredevil
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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.
 
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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.
 
daredevil said:
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.

daredevil said:
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.

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

ripple9.gif
 
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.
 
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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