Precision Amplifier with OPAMP

Thread Starter

alimutlu1

Joined Aug 4, 2017
23
Hi everyone;

I am trying to build rectifier circuit using opamp. And I improve understanding and knowledge about that circuit. Normally I expect to see in output half wave rectified signal but seeing full wave rectified signal. When line is in negative interval, the left side opamp trying to equal input and therefore its output go high and diode is reverse biased, opamp lost feedback control. And I think I see in output only divided line signal. What do you think about that comment and can you clarify me about that circuit maybe in positive and negative line interval? And why the left output opamp output is nearly zero volt in line is positive?
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crutschow

Joined Mar 14, 2008
27,188
When the input is positive, the U1's output negative, which forward biases D2 and allows U1 to act as an inverter.
U1's inverted output is then inverted again by U2, giving a positive output.

When the input is negative, U1's output goes positive which reverse biases D2, so no current flows out of U2 and it has no effect on the signal.
The signal then goes directly to U2, which inverts it to a positive signal.

Thus, no matter the polarity of the input signal, the output signal is always positive, giving a full-wave rectifier.

Below is one of my favorite full-wave precision rectifier circuits, which requires only one power supply, two resistors and and a diode, beside the two op amps.

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