ByBhavita Modi

Integrated Circuits and Applications EC 204

A nail clipper or a nail cutter is a perfect introduction to the topic of my presentation.We all are very well familiar with the working of a nail clipper. This will form the base of our discussion.

CONTENTS

• What is an op-amp?

• Clippers

• Positive Clippers

• Negative Clippers

• Practical application of clippers

• Other applications of clippers

• Reference

TOPIC:

CLIPPERS USING OP-AMP741

Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however some integrated or hybrid operational amplifiers with special performance specifications may cost over $100 US in small quantities. Op-amps may be packaged as components, or used as elements of more complex integrated circuits.

We will discuss the application of op-amp as a clipper.

What is an op-amp?

In electronics, a clipper is a device designed to prevent the output of a circuit from exceeding a predetermined voltage level without distorting the remaining part of the applied waveform.A clipper circuit is known as a wave shaping circuit. Waveshaping circuits are commonly used in digital computers and communicationsuch as TV and FM receiver. Waveshaping technique include clipping and clamping.

In op-amp clipper circuits a rectifier diode may be used to clip off a certain portion of the input signal to obtain a desired o/p waveform. The diode works as an ideal diode (switch) because when ON ,the voltage drop across the diode is divided by the open loop gain of the op-amp. When OFF(reverse biased) , the diode is an open circuit.

CLIPPERS

POSITIVE CLIPPERSCircuit that removes positive parts of the input signal can be formed by using anop-amp with a rectifier diode. The clipping level is determined by the reference voltage Vref,which should be less than the i/p range of the op-amp (Vref < Vin). The output voltage has theportions of the positive half cycles above Vref clipped off.

The circuit works as follows:

During the positive half cycle of the input, the diode D1 conducts only until Vin = Vref. This happens because when Vin <Vref , the output volts V0 of the op-amp becomes negative to device D1 into conduction when D1 conducts it closes feedback loop and op-amp operates as a voltage follower ,i.e., Output V0 follows input until Vin = Vref.When Vin > Vref => the V0 becomes +ve to derive D1 into off. It opens the feedback loop and op-amp operates open loop. When Vin drops below Vref (Vin<Vref) the o/p of the op-amp V0 again becomes –ve to device D1 into conduction. It closed the f/b. (o/p follows the i/p). Thus diode D1 is on for Vin<Vref (o/p follows the i/p) and D1 is off for Vin>Vref. The op-amp alternates between open loop (off) and closed loop operation as the D1 is turned off and on respectively. For this reason the op-amp used must be high speed and preferably compensated for unity gain.

PRACTICAL OUTPUT

NEGATIVE CLIPPERS

The positive clipper is converted into a negative clipper by simply reversing diode D1 and changing the polarity of Vref voltage. The negative clipper clips off the negative parts of the input signal below the reference voltage.

The circuit works as follows:

Diode D1 conducts -> when Vin > -Vref and therefore during this period o/p volt V0 follows the i/p volt Vin. The –Ve portion of the output volt below –Vref is clipped off because (D1 is off) Vin<-Vref. If –Vref is changed to –Vref by connecting the potentiometer Rp to the +Vcc, the V0 below +Vref will be clipped off. The diode D1 must be on for Vin > Vref and off for Vin.

PRACTICAL OUTPUT

A PRACTICAL APPLICATION OF CLIPPER CIRCUITS

Clipper prevents over driving radio transmitter by voice peaks.

A practical application of a clipper is to prevent an amplified speech signal from overdriving a radio transmitter in above figure. Over driving the transmitter generates spurious radio signals which causes interference with other stations. The clipper is a protective measure. A sine wave may be squared up by overdriving a clipper.

Another clipper application is the protection of exposed inputs of integrated circuits. For example, CMOS IC's use 0V and +5 V. Analog amplifiers might use ±12V for the V1 and V2 sources.

Clippers find several applications, such as :

•They are frequently used for the separation of synchronizing signals from the composite picture signals.

•The excessive noise spikes above a certain level can be limited or clipped in FM transmitters by using the series clippers.

•For the generation of new waveforms or shaping the existing waveform, clippers  are used.

•The typical application of diode clipper is for the protection of transistor from transients, as a freewheeling diode connected in parallel across the inductive load.

•Frequently used half wave rectifier in power supply kits is a typical example of a  clipper. It clips either positive or negative half wave of the input.

•Clippers can be used as voltage limiters and amplitude selectors.

REFERENCES:• Op-Amps and linear integrated circuits

by Ramakant A. Gayakwad

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