Full wave rectifier/line regulation

  • Thread starter Michaud12
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  • #1
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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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  • #2
berkeman
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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?

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?
 
  • #3
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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 [Broken]
loadmax
[PLAIN]http://img38.imageshack.us/img38/8089/loadimin.png [Broken]
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.
 
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  • #4
berkeman
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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.
 
  • #5
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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
 
  • #6
berkeman
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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?
 
  • #7
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ahhhh crap. im 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.
 
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  • #8
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isnt that 2.5V dependent on the diodes in the bridge? we used 1N4002's
 
  • #9
berkeman
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ahhhh crap. im 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
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peak voltage of 12rms is 12square root of 2 so 16.97V
and with the 10.9rms --> 15.41
 
  • #11
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i beleive VDC = Vmax-(Vr\2) but im not sure
 
  • #12
berkeman
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i beleive VDC = Vmax-(Vr\2) but im 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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