Full wave rectifier/line regulation

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Discussion Overview

The discussion revolves around the performance of a full wave bridge rectifier with a capacitor in a lab setting, specifically focusing on line regulation and load regulation. Participants are troubleshooting unexpected voltage readings and ripple effects in their circuit setup.

Discussion Character

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

Main Points Raised

  • One participant reports a significantly lower than expected minimum output voltage (2.4V instead of 10.5V) and suspects the rectifier may have stopped functioning properly.
  • Another participant inquires about the calculations used to expect a minimum voltage and the maximum output current targeted.
  • Observations of input capacitor voltage and ripple at maximum output current were suggested as important factors to consider.
  • Participants discuss the specifications of the linear regulator being used, noting that standard regulators require a certain input-to-output voltage differential to maintain regulation.
  • Concerns were raised about the effectiveness of a Zener diode regulator for load regulation, with questions about how expected values were calculated versus observed results.
  • Participants express uncertainty about whether they supplied sufficient current or voltage for the rectifier to operate correctly.
  • Discussion includes the relationship between RMS voltage and peak voltage, with calculations provided for expected peak voltages based on the supplied RMS values.
  • One participant proposes a formula for calculating the DC voltage output but expresses uncertainty about its accuracy.
  • Another participant clarifies that ripple voltage should be subtracted from the peak rectified voltage and suggests using a circuit simulator for further analysis.

Areas of Agreement / Disagreement

Participants express uncertainty and concern about the accuracy of their setup and calculations. There is no consensus on the cause of the low output voltage or the effectiveness of the regulator used, indicating multiple competing views and unresolved issues.

Contextual Notes

Participants mention various assumptions regarding voltage levels, ripple effects, and the characteristics of the components used, but these assumptions remain unresolved within the discussion.

Michaud12
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This is more of a lab then a homework

Ok, so i had a full wave bridge rectifier w/capacitor hooked up to a power regulator. and i was attempting to perform line regulation- and for a Vmin i should have got around 10.5V but i got 2.4V. Why is that? I think the rectifier stopped rectifying but i don't know why. I was advised to use the lowest resister with in the range for my load to get max current. Any ideas what when wrong?
 
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Michaud12 said:
This is more of a lab then a homework

Ok, so i had a full wave bridge rectifier w/capacitor hooked up to a power regulator. and i was attempting to perform line regulation- and for a Vmin i should have got around 10.5V but i got 2.4V. Why is that? I think the rectifier stopped rectifying but i don't know why. I was advised to use the lowest resister with in the range for my load to get max current. Any ideas what when wrong?

Welcome to the PF. What calculations did you use to expect a Vmin of 10.5V? What max output current were you targeting?

Did you observe the input capacitor voltage with an oscilloscope? How much ripple was there at maxiumum output current out of the linear regulator?
 
Im Sorry it was the Load regulation I screwed up.
Yes we did observe with a oscilloscope
For the Load VDC= 12VDC 10ma<IDC< 60ma
Load ripple < 50 mV p-p
AC Supply 12VRMS +/- 10% 60Hz
[PLAIN]http://img207.imageshack.us/img207/4391/loadimax.png
loadmax
[PLAIN]http://img38.imageshack.us/img38/8089/loadimin.png
load min-this is what I expected to be closer to 10.8/.9 Also ripple jumped and is out of the range
with this i got a percentage of over 100 and i know its suppose to be close to 0.
 
Last edited by a moderator:
What linear regulator are you using? What was the input voltage and ripple into the regulator when you were making your measurements with max output current?

Standard linear regulators require an input-to-output voltage differential of about 2.5V over the output voltage, in order to stay in regulation. You can also get "low dropout" linear regulators, which have much lower input-to-output voltage differential requirements.
 
our regulator was made with 2 1n750 zener diodes in series both pointing up Rs and the resistive load. .

Im thinking we must have been out of the range then
 
Michaud12 said:
our regulator was made with 2 1n750 zener diodes in series both pointing up Rs and the resistive load. .

Im thinking we must have been out of the range then

Yeah, you're not going to get good load regulation out of a simple Zener regulator. But you mentioned that you had an expected value of load regulation -- how did you calculate that, and what do you think is different from what you observed in the experiment?
 
ahhhh crap. I am starting to think my group did this whole thing wrong.

Well ok so +/-10% for a max we supplied 12V+10%- 13.2rms
and then for the min 12V-10%-10.9rms

We must not have been supplying enough current/voltage for the rectifier to do its job.
 
Last edited:
isnt that 2.5V dependent on the diodes in the bridge? we used 1N4002's
 
Michaud12 said:
ahhhh crap. I am starting to think my group did this whole thing wrong.

Well ok so +/-10% for a max we supplied 12V+10%- 13.2rms
and then for the min 12V-10%-10.9rms

We must not have been supplying enough current/voltage for the rectifier to do its job.

When you supply 12Vrms, what is the peak voltage (not p-p, just peak)? When you supply 10.9Vrms, what is the peak voltage?

The full wave rectifier will output the peak voltage minus 2 diode drops for each half phase. If there is no load, the output voltage for a 12Vrms input would be what DC voltage? And as there is an output load current, how do you calculate the ripple voltage on your storage cap after the diode bridge?
 
  • #10
peak voltage of 12rms is 12square root of 2 so 16.97V
and with the 10.9rms --> 15.41
 
  • #11
i believe VDC = Vmax-(Vr\2) but I am not sure
 
  • #12
Michaud12 said:
i believe VDC = Vmax-(Vr\2) but I am not sure

Actually the ripple will just subtract from the peak rectified voltage. Do you have access to a circuit simulator (some form of SPICE)? That's the easiest way to see how the voltages act with a full wave bridge rectifier under load.
 

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