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Discussion Starter · #1 ·
I was wondering if someone could answer a question of mine about rectifiers. If you had a single phase, full wave bridge rectifier with a load of say 1k ohms attached and you paralleled another 1k ohm load(decreasing overall resistance), how would this affect the Vavg and % ripple at the load disregarding any additional cap or choke filters, Thank you?
 

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I was wondering if someone could answer a question of mine about rectifiers. If you had a single phase, full wave bridge rectifier with a load of say 1k ohms attached and you paralleled another 1k ohm load(decreasing overall resistance), how would this affect the Vavg and % ripple at the load disregarding any additional cap or choke filters, Thank you?
Well with a DC full wave rectifier the caps and chokes are the ones who control your ripple the resistor is only your load. And as far as % of Voltage the output is the output of your power supply same voltage your paralleled resistors is what it is voltage stays the same.
 

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Well with a DC full wave rectifier the caps and chokes are the ones who control your ripple the resistor is only your load. And as far as % of Voltage the output is the output of your power supply same voltage your paralleled resistors is what it is voltage stays the same.
Some sort of missing punctuation there, but as I read it, he is right. Ripple and average voltage across the resistors would be unaffected if the only load is pure resistance.
 

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Discussion Starter · #5 ·
Thanks for the replies everyone. I'm just doing my 4th year schooling and got a little information mixed up, straightened away now, thanks again.
 

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Assuming the capacitor was not over sized to begin with, ripple will increase with load.

The capacitor is there as a storage device. It charges as during the leading edge of the sine wave and will discharge into the load on the falling edge. Ripple will depend on the size of the load. If the capacitor is of sufficient size, you may not notice a significant difference in ripple when you put the second 1000 ohm resistor in parallel with the first. If the capacitor was not oversize to begin with, then yes. you will see ripple increase.

The following shows he falling edge where the capacitor supplies current. The heavier the load, the more the capacitor will discharge on the falling edge, the greater the ripple and the lower the average voltage.

So yes, the load will effect ripple and average voltage.

 

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I agree that ripple will increase with load. As load increases, the capacitors will discharge faster before the charge cycle tops them back up again. Ripple on a standard 60Hz input will be 120Hz and the average is taken roughly at the median of the upper and lower limit of the ripple waveform. As the ripple magnitude increases, this means that the average voltage will also decrease.

This is roughly what RFGuy was showing above. I thought I'd chime in as I used to design linear power supplies.
 

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Discussion Starter · #14 · (Edited)
My original question was with regards to having no cap or choke filter because I did this lab in school where I measured results slightly different from each other(Vavg and Vrms) when parallel loading up a bridge rectifier from a 1kohm load to another 1kohm load. % ripple ended up changing from 63.6%(first load) to 63.3%(extra load).
 

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Would I be correct in saying the ripple wave is the current wave leading the voltage?
 

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Is your test equipment accurate enough to make reliable measurements of those small differences?

Is this on the secondary of a transformer that the bridge rectifier is on? how big is the transformer? Is there transformer loading occurring? What's the forward voltage drop of the diodes between the 2 loads? Is that changing?
 
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