Applications of Operational Amplifiers in Tamil
- The ordinary diodes cannot rectify voltages below the cut-in-voltage of the diode.
- A circuit which can act as an ideal diode or precision signal–processing rectifier circuit for rectifying voltages which are below the level of cut-in voltage of the diode can be designed by placing the diode in the feedback loop of an op-amp.
- It is a single diode arrangement and functions as a non-inverting precision half– wave rectifier circuit.
- If V1 in the circuit is positive, the op-amp output VOA also becomes positive. Then the closed loop condition is achieved for the op-amp and the output voltage V0 = Vi.
- When Vi < 0, the voltage V0A becomes negative and the diode is reverse biased. The loop is then broken and the output V0 = 0.
Precision Diodes Applications
Half wave rectifier
- The below circuit is non-saturating half wave precision rectifier.
- When Vi > 0V, the voltage at the inverting input becomes positive, forcing the output VOA to go negative.
- This results in forward biasing the diode D1 and the op-amp output drops only by ≈ 0.7V below the inverting input voltage.
- Diode D2 becomes reverse biased. The output voltage V0 is zero when the input is positive.
- When Vi > 0, the op-amp output VOA becomes positive, forward biasing the diode D2 and reverse biasing the diode D1. The circuit then acts like an inverting amplifier circuit with a non- linear diode in the forward path. The gain of the circuit is unity when Rf = Ri.
Half Wave Rectifier
The circuit operation can mathematically be expressed as
The voltage VoA at the op amp output is
The advantages of half wave rectifier is a precision half wave rectifier and it is a non saturating.
Full wave Rectifier
The first part of the Full wave circuit is a half wave rectifier circuit. The second part of the circuit is an inverting amplifier.
Full Wave Rectifier
- For positive input voltage Vi > 0V and assuming that RF =Ri = R, the output voltage VOA = Vi. The voltage V0 appears as (-) input to the summing op-amp circuit formed by A2, The gain for the input V‘0 is R/(R/2)
- The input Vi also appears as an input to the summing amplifier. Then, the net output is
V0 = -Vi -2V0= -Vi -2(-Vi) = Vi.
- Since Vi > 0V, V0 will be positive, with its input output characteristics in first quadrant. For negative input Vi < 0V, the output V‘0 of the first part of rectifier circuit is zero. Thus, one input of the summing circuit has a value of zero. However, Vi is also applied as an input to the summer circuit formed by the op-amp A2.
- The gain for this input id (-R/R) = -1, and hence the output is V0 = -Vi. Since Vi is negative, V0 will be inverted and will thus be positive. This corresponds to the second quadrant of the circuit.
To summarize the operation of the circuit,
- Peak detector detects and holds the most positive value of attained by the input signal prior to the time when the switch is closed.
- Clipping circuit is a wave-shaping circuit, and is used to either remove or clip a portion of the applied wave in order to control the shape of the output waveform.
- One of the most basic clipping circuit is the half-wave rectifier.
- A half-wave rectifier clips either the negative half cycle or the positive half cycle of an alternating waveform, and allows to pass only one half cycle.
- Clipping circuits are also referred to as voltage limiters, amplitude selectors, or slicers.
- Clippers are used to eliminate amplitude noise or to fabricate new waveforms from an existing signal.
- A clamping circuit is used to place either the positive or negative peak of a signal at a desired level.
- The dc component is simply added or subtracted to/from the input signal.
- The clamper is also referred to as an IC restorer and ac signal level shifter.
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