Precision full-wave rectifier using operational amplifier

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Precision full-wave rectifier using operational amplifier

Posted Date: 2024-01-13

What is full-wave rectification?

Full-wave rectification refers to the process of converting both the positive and negative half-cycles of an alternating current signal into a unidirectional direct current signal. In a full-wave rectification circuit, each AC cycle is completely converted into a unidirectional DC current, so it is called "full-wave" rectification.

Full-wave rectification usually consists of a bridge rectifier or four unidirectionally powered diodes. In a bridge rectifier, four diodes are arranged in such a way that they rectify both the positive and negative half-cycles of the AC signal simultaneously.

The advantages of full-wave rectification are smaller losses, high efficiency, and reduced output total harmonic distortion. It is used to generate a supply voltage with a small ripple ratio. Full-wave rectifiers are widely used in power circuits that require high precision, ultra-low noise and DC stability, such as precision measurement, medical equipment, wireless communications and high-end audio equipment.

What is the function of precision full wave rectifier

A precision full-wave rectifier is a circuit used to convert alternating current signals into unidirectional direct current signals with high accuracy and low ripple. Its function is to rectify the positive half-cycle and negative half-cycle of the input signal simultaneously to produce a stable DC output signal with low ripple.

The functions of precision full-wave rectifiers are mainly reflected in the following aspects:

1. Effectively utilize all the energy of the input signal: Compared with half-wave rectifiers, precision full-wave rectifiers can convert both the positive and negative half-cycles of the input signal into one-way current, effectively utilizing all the energy in the input signal. . This can improve the efficiency of the rectifier circuit.

2. Reduce output ripple: A precision full-wave rectifier can effectively reduce the ripple of the output signal by adding an additional diode to the rectifier. This is because during the conversion process, when one diode is off, the other diode is on, thereby reducing the ripple amplitude of the output signal.

3. Provide stable DC output: Precision full-wave rectifiers, combined with filter capacitors, can further filter the DC output signal to reduce ripple and provide a more stable DC output. This is very important for application scenarios that require high accuracy and low noise, such as precision measurement, instrumentation, etc.

The precision full-wave rectifier reduces output ripple by simultaneously rectifying the positive and negative half-cycles of the input signal and provides a stable DC output through the filter capacitor. It plays an important role in applications requiring high accuracy, low ripple and stable output.

Precision full-wave rectifier using operational amplifier

In order to make a full-wave precision rectifier circuit, a summing amplifier is added to the output of the half-wave rectifier circuit mentioned earlier. From this point of view, points P1 to P2 are the basic precision rectifier circuit. The configuration of the diodes allows us to The output gets a negative voltage.

Precision full-wave rectifier using operational amplifier

From point P2 to point P3 is the summing amplifier, and the output of the precision rectifier is fed to the summing amplifier through resistor R3. The value of resistor R3 is half the value of R5 or you can say it is R5/2 and this is how we set the gain of 2 times in the op amp.

The input from point P1 is also fed to the summing amplifier with the help of resistor R4, resistors R4 and R5 are responsible for setting the gain of the op amp to 1X.

Since the output at point P2 is fed directly to the summing amplifier with a gain of 2X, this means that the output voltage will be 2 times the input voltage. Assume the input voltage is 2V peak, so we will get 4V peak at the output. At the same time, we feed the input directly to a summing amplifier with a gain of 1X.

Now when the summing circuit happens we get a summed voltage at the output which is (-4V) + (+2V) = -2V and as an op amp at the output. Since the op amp is configured as an inverting amplifier, we will get +2V at the output, which is point P3.

The same happens when negative peaks of the input signal are applied.

The final output waveform of the precision rectifier circuit

The picture above is the final output of the circuit. The blue waveform is the input, the yellow waveform is the output of the half-wave rectifier circuit, and the green waveform is the output of the full-wave rectifier circuit.

Causes of distortion in precision full-wave rectifier circuits

The following reasons may cause distortion in precision full-wave rectifier circuits in practical applications:

1. Nonlinear characteristics: Diodes and other components used in precision full-wave rectification circuits may have nonlinear characteristics, causing the relationship between the output voltage and the input voltage to be not completely linear, thereby introducing distortion.

2. Diode impedance: The rapid switching of a diode between on and off states can result in non-zero dynamic impedance. This introduces varying capacitive and inductive effects, resulting in deformation and distortion of the output waveform.

3. Temperature changes: Temperature changes have a greater impact on precision circuits, especially diodes. Temperature changes may cause the cut-off voltage of the diode to shift, affecting the accuracy and stability of the rectifier circuit.

4. Noise interference: Precision circuits are very sensitive to noise, especially at high gain and low signal-to-noise ratio. Noise can come from the power supply, signal source, or other circuit components, and this noise can propagate into the rectifier circuit and introduce distortion.

5. Input power quality: Precision full-wave rectifier circuits have higher requirements for input power quality. Factors such as input power ripple, amplitude fluctuation, and voltage stability may affect the performance of the rectifier circuit.

In order to reduce distortion, some measures can be taken, such as using high-quality components, optimizing circuit layout, enhancing filter circuits, providing stable power supply, etc. In addition, distortion can be corrected and calibrated, and feedback circuits or digital signal processing techniques can be used to improve the accuracy and stability of the rectifier circuit.

Review Editor: Huang Fei

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