# Precision Full Wave Rectifier Circuit

The use of Operational amplifiers can improve the performance of a wide variety of signal processing circuits. In rectifier circuits, the voltage drop that occurs with an ordinary semiconductor rectifier can be eliminated to give precision rectification.

The below shown circuit is the precision full wave rectifier. It consists of following sections:

1. Precision half-wave rectifier
2. Inverting summing amplifier

The input voltage Vin is applied to one terminal of the summing amplifier along with resistor R3 and to the input of the precision rectifier. The output of precision rectifier is applied to another terminal of summing amplifier. The precision half-wave rectifier circuit uses an inverting amplifier configuration.

Related Products: Bridge RectifierCurrent Regulator

When the input signal Vin is positive, Op-Amp output terminal is negative, Diode D1 is reverse biased and D2 Diode is forward biased, the circuit is

Vb = -(R2/R1) * Vin

In the circuit, R1 and R2 have been chosen such that R2 = 2R1.
So the voltage at Vb = -2Vin.

Thus during the positive half cycle of the rectified voltage Vb is applied to terminal B of the inverting summing amplifier is -2Vin.

The voltage at terminal A is Va = +Vin. The output from the summing circuit with R3=R4=R5 is Vo = – (Va+Vb). Hence Vo = -(Vin – 2Vin) = +Vin. So during the negative half cycle of the input, the Op-Amp output terminal goes positive, causing D2 to be reverse biased. Without D1 in the circuit, the Op-Amp output would be saturated in the positive direction. However, the positive voltage at the Op-Amp output forward biases the D1. This tends to pull the Op-Amp inverting terminal in a positive direction. But, such a move would cause the Op-Amp output to go negative. So, the output settles at the voltage close to ground level. So to be clear, the negative half-cycle is clipped off. That is Vb=0 and Va = -Vin. Totally the Vo will be  Vo = -(-Vin+0) = +Vin.

It is seen that the output is a full wave rectified version of the input voltage. A Precision full-wave rectifier is also known as absolute value circuit. This means the circuit output is the absolute value of the input voltage regardless of polarity.

If you any doubt about the circuit please drop it in comments we will respond you.;

• pallavi

Sir , Why here you used 5K ohm register. I mean gain of 1st opamp is 2, do we really need this amplification. can we use unity gain opamp here instead.

• Mihai

Also, the common from V2…V5(12V power supplies_batteries) should be tied to GROUND(GND)!

• Borja Ardilla

Hi, may you want to review the circuit, R2 should be placed between the negative input of U1 and the anode of D2. Otherwise it will not accurately rectify the input wave.

You can perform a quick simulation and check it.

Regards,

Borja

Dear sir.

How many types of LED avalible and in general what resistance should be used for using them in mains (230volts 50Hz

• Oreleon

Hello, can you recommend the best op-amps and diodes for this circuit please?

Thank you.

• Srihari Rao

Hi sam
This circuit is also referred to as super diode circuit. Because it behaves like a ideal diode. This precision rectifiers are used in high precision signal processing.
And that 12v supply can be given to both the Op-Amps with single 12v battery.

You are always welcome.

• Sam Star

hello
it’s not really clear, but it seems like there are 4 x 12V batteries in this circuit!!
also, what are the practical applications that require the use of a circuit with 2 ICs for rectification? I mean, is it really worth the trouble and complexity?

many thanks 🙂

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