# Full-Wave Bridge Rectifier

Discussion in 'Homework Help' started by gbox, May 18, 2016.

1. ### gbox Thread Starter Member

Dec 29, 2015
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I am trying to understand, why do the Full-Wave Bridge Rectifier turns the negative wave into a positive one.
I get it that when the AC wave is positive is has one direction to go and so does when the AC wave is negative, but why we measure it has positive?

2. ### crutschow Expert

Mar 14, 2008
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5,809
I if you look at the bridge you will see that the diodes are such that whichever side of the AC signal is positive goes to the positive side of the bridge output, and whichever side is negative goes to the bridge negative output.
It works because the AC signal source is not grounded so, in effect, the bridge alternately grounds the negative side of the signal so that the output is always positive.

If the source were grounded than the bridge circuit wouldn't work into a grounded load.

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3. ### gbox Thread Starter Member

Dec 29, 2015
42
0
I can look at the AC as a battery that changes sides, this way if the probe will always read a positive voltage difference?

4. ### wayneh Expert

Sep 9, 2010
15,219
5,568
There are some excellent animations online that show how the current flows as the AC sine wave passes. I can't provide a link right now but you be able to find one if you include "rectifier animation" in your search.

5. ### shteii01 AAC Fanatic!

Feb 19, 2010
4,452
707
You are missing the reference points. When sine wave enters the rectifier, it is referenced to some external reference point. When you look at the sine wave with respect to that external reference, then you have positive half of the sine wave and negative half of the sine wave.

But, the circuit that comes after the rectifier does not use that external reference. It has its own reference point. So whatever comes out of the rectifier and enters the circuit will be positive because it is higher voltage (meaning positive) then the internal reference of the circuit.

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6. ### crutschow Expert

Mar 14, 2008
20,501
5,809
Yes, if you hook a battery up to the bridge input, the bridge output will always be positive, no matter which way the battery is connected.

Last edited: May 19, 2016

May 20, 2015
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