# How does this precision rectifier work

Discussion in 'Homework Help' started by nyasha, Mar 26, 2011.

1. ### nyasha Thread Starter Active Member

Mar 23, 2009
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If someone is applying let us say +2 volts to the input of this rectifier, how would it behave ? Am l correct to assume that D1 and D2 are always turned off ?

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2. ### Ron H AAC Fanatic!

Apr 14, 2005
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There is an error in the circuit. D1 needs to be removed.
If the op amp output's low level can go to nearly 0V, it will work as a precision full wave rectifier.

Apr 20, 2004
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4. ### Ron H AAC Fanatic!

Apr 14, 2005
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Sorry, I didn't even consider a half wave rectifier. I was thinking of a full wave rectifier, with a single positive supply, and an op amp whose output can (nearly) reach the negative rail.
As I said, with those conditions, it will function as a full wave rectifier if D1 is removed.

5. ### nyasha Thread Starter Active Member

Mar 23, 2009
90
1
So how does it work ? For instance if a 1V is applied at the waveform

6. ### Ron H AAC Fanatic!

Apr 14, 2005
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First, let me say that you will not have a chance of understanding this if you do not understand basic op amp feedback theory.
When the input swings above 0V, the op amp output goes low until D1 conducts, keeping node A at 0V (virtual GND). D2 is reverse biased, so Vo will be at the same voltage as node A, i.e., 0V.
When the input swings below 0V, the op amp output goes high until D2 conducts, again keeping node A at virtual GND. D1 is now reverse biased. All of the input current flows from the output node to the input, and since node A is 0V, Vo=-Vi.
You therefore have a half wave rectifier.