Precision Rectifier 

1. It is basically rectifier circuit, which converts an ac voltage to dc voltage.

2. Then Why it is called as ‘Precision Rectifier’? Because it generates accurate output which is missing in normal rectifier circuit or power-supply rectifier circuit (rectifier circuit using diode).

If you don’t know what is a normal rectifier circuit, please visit the link below and watch the video on ‘Rectifier Circuit Design’.

3. Now we have to understand what we mean by accurate output. If you already watched the video on ‘Rectifier Circuit Design’, you will know from both theoretical and practical analysis, we have observed that for practical diode there is a voltage drop (Vd). It varies from 0.4 V to 0.7 V (approximately). This voltage drop effects the output voltage significantly. Sometimes output voltage increases or decreases from the desired level for this voltage drop. But it is not the case for Precision Rectifier. It generates accurate desired output. Thus, how it got it name.

4. Now we will learn how this rectifier generates accurate output. This rectifier uses ‘Super Diode’. A ‘Super Diode’ is a circuit combination of Op amp and diode. Diode rectifies the input, generates the output and OP amp reduces the voltage drop of diode (Vd) to zero (approximately). Thus, basically it works and generates the accurate output.

For more details on operating principal, theoretical and practical analysis of Precision rectifier, please visit the link below and watch the video on ‘Precision Rectifier Circuit Design’.

5. Another drawback of normal rectifier is it can’t generate output for a very weak signal. If the signal voltage is less than diode’s cut in voltage, the diode will be in cut off mode and no output will be generated. But Precision Rectifier is able to generate output for weak signal because Op amp has a very large gain. So, it can boost a weak signal to a sufficient level where it can drive a diode into forward biased condition.

Circuit Diagram:


Half Wave Precision Rectifier (Circuit Diagram)

Operating principal:


For the circuit Vin is input voltage applied to non inverting terminal of OP AMP. Output is Vout, feedback to inverting terminal of OPAMP. Open loop output is Vo′. Closed loop connection is formed by connecting a diode (D) between Vo′ and Vout. Voltage drop at diode is Vd .R is load resistor.

Condition for diode (D) on → whenever, Vin → Positive; then Vd→Positive; so diode on.
It closes the the feedback loop. V+ = Vin; V- = Vout; Vo′ = A(Vin -Vout), A → Open loop gain of OPAMP. Vo′ - Vd - Vout=0; so, A(Vin - Vout) - Vd - Vout=0; Vout = A(Vin - Vd)/(A+1).
A is very large → A+1 ≈ A and Vd/(A+1) ≈ 0; so, Vout ≈ Vin

Condition for diode (D) off → whenever, Vin→ negative; then Vd → negative;so diode off.
It opens the the feedback loop. So, Vout = 0.

This the operating principal and derivation of Half Wave Precision Rectifier.

For more details on operating principal, theoretical and practical analysis of this rectifier and other Precision rectifiers, please visit the link below and watch the video on ‘Precision Rectifier Circuit Design’.

6. There are also disadvantages for Precision Rectifier. Some of are:
a) If input voltage exceeds power supply voltage of Op amp, the output will be saturated and we will not get accurate output.
b) This circuit has limitations for high frequency signals.

7. Application of Precision Rectifier:
a) Mainly this rectifier is used in instrumentation circuit design.

For more details please visit:
1. Rectifier Circuit Design - YouTube
2. Precision Rectifier Circuit Design - YouTube

For more details on various electronics circuit, please visit: It’s All About Electronics.

Comments

Post a Comment

Popular posts from this blog

Image
Capacitor Charging and Discharging Part 1 A capacitor charging and discharging phenomenon is one of the most important factor in Analog electronics. There are many electronics circuits in which capacitor charging and discharging plays a very important role. It is also one of the most confusing concept in electronics. In this video we will discuss capacitor charging and discharging phenomenon for four different situation: 1. Time enough to fully charge and fully discharge. 2. Time enough to fully charge but not fully discharge. 3. No time to fully charge but time to fully discharge. 4. No time to fully charge or even fully discharge.      This is a basic R-C series circuit. Circuit consists of a DC voltage source, a capacitor an d a resistor. Now let’s start circuit analysis. It’s a series circuit. So, the common element which is same for all three components is current. Same current is flowing through all the three components....
Keep reading
Image
Half Wave Rectifier Circuit Using Op amp Simulation Using LTspice Definition: The half wave rectifier circuit is a rectifier circuit, which converts an ac voltage to dc voltage. These circuits are called half wave rectifier because it generates output of half cycle for input of full cycle. Another half cycle is wasted. Positive half wave rectifier Input and output waveform of positive half wave rectifier Negative half wave rectifier Input and output waveform of negative half wave rectifier Working principal: For both circuit Vin  is input voltage applied to non inverting terminal of OP AMP. Output is Vout,  feedback to inverting terminal of OP AMP. Open loop output is Vo' . Closed loop connection is formed by connecting a diode (D) between Vo'  and Vout . Voltage drop at diode is  Vd. R is load resistor.  For positive half wave rectifier, when Vin is positive diode is forward biased i.e. diode is on, it closes the feedback loo...
Keep reading
Series Inductor Filter Definition: A filter is a device or process that removes some unwanted components or features from a signal. Rectifier filter is an electronic circuit that removes ripple or unwanted AC signal components from the output of a Rectifier. The main question is, “Why we use inductor filter for rectifier circuit?” The reason is, one of the important property of inductor is, it passes the DC signal but blocks the AC signal. Now what is the meaning of that? The reactance of inductor is 𝑋𝐿=𝑗𝑀𝐿 (𝑀→π‘Žπ‘›π‘”π‘’π‘™π‘Žπ‘Ÿ π‘“π‘Ÿπ‘’π‘žπ‘’π‘’π‘›π‘π‘¦, 𝐿→π‘–π‘›π‘‘π‘’π‘π‘‘π‘Žπ‘›π‘π‘’ π‘œπ‘“ π‘–π‘›π‘‘π‘’π‘π‘‘π‘œπ‘Ÿ). For DC signal, 𝑀=0, so, 𝑋𝐿=0 The output of rectifier circuit (without any Filter) is a pulsating DC. Pulsating DC is a DC signal comprises of unwanted AC component known as ripples. So, if we pass this signal through an inductor, it will able to remove ripples from the output and will smooth the output signal. This the reason we use Inductor Filter for Rectifier circui...
Keep reading