Today we are going to learn about the type of Precision rectifier circuits using OP-AMP. We cannot use a diode as an AC voltage rectifier when the voltage is in the low mV range. So this OP-AMP rectifier can have much use in circuits such as filters, various signal measurements, etc. Because it has a low base voltage.
The notable one is the 741 OP-AMP rectifier circuit, which we talk more about down the line. We will also try them on the breadboard because this IC is popular and cheap.
Basic Diode rectifier
But first, let us talk about a normal diode rectifier. They are typically divided into two types: silicon diodes and germanium diodes, with cut-in voltages of 600mV for silicon diodes and 300mV for germanium diodes, respectively.
In which both types of diodes are unable to rectify signals that are lower than their cut-in voltage at all.
We then add an OP-AMP to the diode rectifier circuit to reduce the cut-in voltage of the diode. By using the open-loop gain feature of an OP-AMP, it will be capable of rectifying a signal under 1mV.
Or, in another word, we can say that we manage to make a diode work even more perfectly.
According to the basic principle of the diode, it would only conduct electricity in one direction with no resistance and no voltage across it at all. Which would not work for our use.
But with OP-AMP’s help, the diode will become more useful and more suitable for filtering low-frequency signals.
Let’s first review the pinout and symbols of 741.
Learn 741 op-amp circuits basic with example
Simple Half-wave rectifier using OP-AMP – Super Diode
The circuit below is a non-inverting amplifier circuit that acts as an AC to DC signal half-wave rectifier.
At first glance, we will notice that an input signal comes in through a non-inverting input pin (pin 3), and the output of the circuit is connected to an inverting input pin (pin 2), or, to put it simply, pin 2 is the output.
But I didn’t quite understand, the output is supposed to be a pin 6 instead of the current pin 2. So, we revised the circuit to make it easier to understand.
And next, we are going to make a “super diode.”
This can effectively cancel the forward voltage of the diode, lowering it to a lot less than 600 mV.
The D1 will feedback the signals from the output (pin 6) of the OP-AMP to the inverting input (pin 2).
When the input signal swings into a positive range of about µV (microvolts). The gain of the OP-AMP will cause the output voltage to increase quickly to 600 mV, and D1 will conduct current (receive the forward bias).
This causes the inverting pin to have a similar voltage to the input signal, which is characteristic of the voltage follower circuit, or what is called a buffer.
When the input voltage is negative, D1 will not conduct current (receive the reverse bias). And immediately cutting off the output voltage.
A simple Peak detector circuit
From the simple precision half-wave rectifier or super diode circuit above, we will adapt it into a simple peak voltage detector circuit to determine the maximum voltage level of the input. And maintains that voltage level at the output as well.
The super diode passes only a positive voltage. The capacitor (C) can hold a peak positive voltage for a long time while also releasing it to the output.
Next, let’s look at the experimental circuit.
When the input is in the positive range AC, the C1 will quickly charge up to the maximum voltage through D1.
After passing the maximum voltage, C1 will slowly discharge through R1, which has a resistance of around 1M.
Then, IC2 will be the voltage follower or buffer. Its output will also be a DC voltage.
Precision Half-wave Rectifiers circuit using op-amp
The circuit below is a Half-wave Precision Rectifiers circuit using a 741 OP-AMP. When the AC input voltage is in the negative half, the output of the op-amp will swing to a positive voltage.
The D1 will receive a forward bias. The gain of the op-amp is approximately 1. Because the resistance of D1 while in forward bias is very low.
When the AC input voltage is in the positive half, the output will swing to approximately -600mV, and D2 will get forward bias. On the other hand, D1 will have a reversed bias.
The R3 compensates for the offset voltage of the OP-AMP.
But this circuit has a few limitations. Its speed in particular was quite slow and therefore only suitable for low-frequency signals. Due to the operational process of the op-amp.
Precision Half-wave Rectifier using NE55532
This is a Precision Half-wave Rectifiers circuit that uses a better op-amp than the first one. It is NE5532 or NE5535 OP-AMP. The differences between them are as follows:
- NE5532 is Dual Low-Noise High-Speed Audio Operational Amplifier.
- NE5535 is a Dual High Slew Rate OP-AMP.
The NE5532 will process up to 10kHz with less than 5% distortion.
This circuit is the same as the previous circuit. But I have changed its layout, making it a little different than before.
Precision Full-wave Rectifiers circuit
We know that full-wave rectifier circuits have higher efficiency than half-wave rectifier circuits.
We can create a full-wave rectifier by simply connecting two half-wave rectifier circuits together.
We will replace D1 with the super diode. At the same time, we will use an inverting precision half-wave rectifier instead of the inverting amplifier and D2. Both outputs are connected together to get the precision full-wave rectifier.
The output will still have a pulsating pattern, which is half of the AC wave. We can turn it into a complete DC signal with a filter circuit.
Let’s see the full circuit schematic diagram below to help us understand it more.
When the AC input voltage is in the negative half. It causes the output of IC1 to be positive 600mV because D2 receives forward bias. The inverting input of IC2 also receives some negative half from the input (-Vin) through R4. There will also be feedback from the output going through R5 to pin 2 of IC2 as well.
Causing the output of IC2 to be the same as the input voltage but in only the positive half (+Vin).
Then, when the AC input is in the positive half, the output of IC1 will be negative. Causing D1 to be forward biased or conduct current until the output is 2 times the Vin, or the output is -2Vin.
When this signal flows through IC2, which is an inverting amplifier circuit, the output will be +2Vin.
But at the same time, the positive AC input voltage (+Vin) will also go through R4 to pin 2 of IC2. This causes the output at pin 6 to be -Vin.
Therefore, the sum of the voltages at pin 6 of IC2 will be +2Vin – Vin. Which is equal to +Vin.
So in summary, the output of IC2 will be +Vin, regardless of whether the AC input voltage is Positive or Negative.
All this should be enough for you to implement these precision rectifier circuits using OP-AMP in a case where you are dealing with very low signal levels of approximately mV or µV. But if you want to continue reading further, see Wikipedia and Uottawa for more in-depth details.
In the future, we might bring this circuit into more use, such as in AC millivoltmeters and more. And we hoping to learn more about OP-AMP because they are fascinating in components.
Here are a few related posts you may find helpful, too:
- Dual DC power supply rectifier using 2 terminal transformer
- What is switching power supply vs linear, and how does it work?
- Simple temperature to voltage converter circuit
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7 thoughts on “Precision Full-wave | Half-wave rectifier circuit using OP-AMP”
The circuits shown would be more complete by showing the voltage connections
to the actual op amp ie Pin 8 and Pin 4 , or at least mention why they are not shown
As provided the schematic is presently incomplete.
ben bu tam dalga doğrultucunun çalışacağına inanmıyorum birinci opamp ın girişi ile çıkışı kısa devre
Thank you again. I just update it new.
741 with full wave precision rectifier circuit,Short circuit between input and output of the first op amp…
Oh…You are excellent, so noticed. I am very grateful.
I feel sorry for this mistake. It can cause friends to waste time.
Hi there! Greetings4m India. Circuits presented are very interesting but it appears that there is a problem in the presentation as the flow of the English language sometimes becomes very puzzling. Other than that, keep it up as the circuits are really outstanding. Of we could understand t the corridors better then we could have modified the same to as per our requirements. Than you.
I very much appreciate your visit to our site.
As for my English writing, it is undeniably bad—some parts were even considered unreadable. But in the last few months or so, we have been trying our best to improve our writing.