ab89

AB89 Diode Clamper

Operating Manual Ver.1.1

An ISO 9001 : 2000 company

94-101, Electronic Complex Pardesipura, Indore- 452010, India Tel : 91-731- 2570301/02, 4211100 Fax: 91- 731- 2555643 e mail : [email protected] Website : www.scientech.bz Toll free : 1800-103-5050

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AB108

Scientech Technologies Pvt. Ltd. 2

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RoHS Compliance

Scientech Products are RoHS Complied. RoHS Directive concerns with the restrictive use of Hazardous substances (Pb, Cd, Cr, Hg, Br compounds) in electric and electronic equipments. Scientech products are “Lead Free” and “Environment Friendly”. It is mandatory that service engineers use lead free solder wire and use the soldering irons upto (25 W) that reach a temperature of 450°C at the tip as the melting temperature of the unleaded solder is higher than the leaded solder.

Diode Clamper AB89

Table of Contents

1. Introduction 4

2. Theory 6 3. Experiments

To study clamper circuits. 10 4. Warranty 12

5. List of Accessories 12

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Introduction AB89 is a compact, ready to use Diode Clamper experiment board. This is useful for students to understand basics of diodes and clamping circuits. It can be used with Scientech Analog Lab ST2612 which has built in DC power supply, AC power supply, function generator, modulation generator, continuity tester, toggle switches, and potentiometer..

List of Boards : Model Name AB01 Diode characteristics (Si, Zener, LED) AB02 Transistor characteristics (CB NPN) AB03 Transistor characteristics (CB PNP) AB04 Transistor characteristics (CE NPN) AB05 Transistor characteristics (CE PNP) AB06 Transistor characteristics (CC NPN) AB07 Transistor characteristics (CC PNP) AB08 FET characteristics AB09 Rectifier Circuits AB10 Wheatstone Bridge AB11 Maxwell’s Bridge AB12 De Sauty’s Bridge AB13 Schering Bridge AB15 Common Emitter Amplifier AB14 Darlington Pair AB16 Common Collector Amplifier AB17 Common Base Amplifier AB18 Cascode Amplifier AB19 RC-Coupled Amplifier AB20 Direct Coupled Amplifier AB21 Class A Amplifier AB22 Class B Amplifier (push pull emitter follower) AB23 Class C Tuned Amplifier AB25 Phase Locked Loop (FM Demodulator & Frequency Divider /

Multiplier) AB28 Multivibrator ( Mono stable / Astable) AB29 F-V and V-F Converter AB30 V-I and I-V Converter AB31 Zener Voltage Regulator AB32 Transistor Series Voltage Regulator AB33 Transistor Shunt Voltage Regulator AB35 DC Ammeter AB39 Instrumentation Amplifier AB41 Differential Amplifier (Transistorized) AB42 Operational Amplifier (Inverting / Non-inverting / Differentiator)

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AB43 Operational Amplifier (Adder/Scalar) AB44 Operational Amplifier (Integrator/ Differentiator) AB45 Schmitt Trigger and Comparator AB49 K Derived Filter AB51 Active filters (Low Pass and High Pass) AB52 Active Band Pass Filter AB54 Tschebyscheff Filter AB56 Fiber Optic Analog Link AB57 Owen’s Bridge AB58 Anderson’s Bridge AB59 Maxwell’s Inductance Bridge AB64 RC – Coupled Amplifier with Feedback AB65 Phase Shift Oscillator AB66 Wien Bridge Oscillators AB67 Colpitt Oscillator AB68 Hartley Oscillator AB80 RLC Series and RLC Parallel Resonance AB82 Thevenin’s and Maximum power Transfer Theorem AB83 Reciprocity and Superposition Theorem AB84 Tellegen’s Theorem AB85 Norton’s theorem AB88 Diode Clipper AB90 Two port network parameter AB91 Optical Transducer (Photovoltaic cell) AB92 Optical Transducer (Photoconductive cell/LDR) AB93 Optical Transducer (Phototransistor) AB96 Temperature Transducer (RTD & IC335) AB97 Temperature Transducer (Thermocouple) AB101 DSB Modulator and Demodulator AB102 SSB Modulator and Demodulator AB106 FM Modulator and Demodulator

………… and many more

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Theory Clampers : A circuit that places either the positive or negative peak of a signal at a desired DC level is known as a clamping circuit or we can say that the clamping network is one that will clamp a signal to a different dc level. Suppose the input signal of a clamping network is a sine wave having a peak to peak value of 10V.The clamper adds the DC component and pushes the signal upwards or downwards according to the configuration .The point should be noted here is that the clamping circuit does not change the peak to peak or r.m.s. value of the waveform. A clamping circuit should not change the peak to peak value of the signal; it should only change the DC level. To do so, a clamping circuit uses a capacitor, together with a diode and a load resistor RL, but it can also employ an independent dc supply to introduce an additional shift .The operation of a clamper is based on the principle that charging time of a capacitor is made very small as compared to its discharging time. In the practical clamping circuit, the magnitude of RL and C must be chosen such that the time constant is large enough to ensure that the voltage across the capacitor does not discharge significantly during the interval the diode is nonconducting . Clamper are classified as-

1. Positive clamper 2. Negative clamper

Positive Clampers :

Positive Clamper

Figure 1 The output of the clamping network is like that the shape of the original signal has not changed; only there is upward shift in the signal. Such a clamper is called a positive clamper. When a positive clamper has a sine wave input, it adds a positive DC voltage to the sine wave. Stated another way, the positive clamper shifts the AC reference level (normally zero) up to a DC level. This means that each point on the sine wave is shifted upward. figure 1 shows the circuit of a positive clamper .The input signal is assumed to be a sine wave with time period T. The clamped output is obtained across RL. The circuit design incorporates two man features. Firstly, the values of C and RL are so selected that time constant τ = CRL is very large. Secondly, RLC time constant is deliberately made much greater than the time period T of the incoming signal.

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How the circuit works ? The capacitor is initially uncharged. On the first negative half cycle of the input signal, the diode is forward biased. Therefore, the diode behaves as a short. At the negative peak of the AC source, the capacitor has fully charged and its voltage is Vm. The charging time constant is very small so that the capacitor will charge to Vm volts very quickly .During this interval, the output voltage is directly across the short circuit. Therefore,

Vout = 0V When the input switches to positive half cycle, the diode is, reverse biased and behaves as an open. Since the discharging time constant is much greater than the time period T of the input signal, the capacitor remains almost fully charged to Vm volts during the off time of the diode. The resulting waveform shown in figure 1 is a positively clamped output that means the input signal has been pushed upward by Vm volts, so that negative peaks fall on the zero level. Ideally, the clamping is less than perfect because the negative peaks have a reference level of 0.7V instead of 0V. Negative Clamper : The output of the clamping network is like that the shape of the original signal has not changed; only it pushes the signal downwards so that the positive peaks fall on the zero level or if we change the polarity of the diode in positive clamper we get the negative clamper. Figure 2 shows the circuit of a negative clamper. The clamped output is taken across RL. Again, the clamping is less than perfect because the positive peaks have a reference level of 0.7V instead of 0V. During the positive half cycle of the input signal, the diode is forward biased. Therefore, the diode behaves as a short. The charging time constant is very small so that the capacitor will charge to V volts very quickly. During this interval the output voltage is directly across the short circuit. Therefore,

Vout = 0V When the input switches to negative half cycle, the diode is reverse biased and behaves as an open .Since the discharging time constant is much greater than the time period of the input signal, the capacitor almost remains fully charged to V volts during the off time of the diode. Applying Kirchhoff’s voltage law to the input loop, we get output amplitude equal to sum of input amplitude and the charged capacitor voltage amplitude. The resulting output waveform shown in figure 2.

Negative Clamper

Figure 2

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Although all the waveforms appearing in figures are sine wave, clamping networks work equally well for square wave. Both positive and negative clampers are widely used in television receivers to change the reference level of video signals. Clampers are widely used in Radar and communication circuits.

Biased Clampers : If we want to clamp input signal with some reference level, use biased clamper circuits. Biased clampers are circuits, which use DC voltage in series with diode. Figure 3 shows the circuits of biased clamper. In figure 3(a) during positive half cycle of the input signal, the diode is forward biased, so it acts as a short. It is clear that

Vout = VA

Where VA is the DC voltage, Vm is the peak input voltage. Applying Kirchhoff’s voltage law to the input loop in figure 3(a), we have

Vm - Vc - VA =0 and

Vc = Vm - VA Where Vc is the voltage across capacitor.

During the negative half cycle of the input signal, the diode is reverse biased and behaves as an open. Now battery or DC voltage has no effect on Vout. Applying Kirchhoff’s voltage law to the outside loop of figure 3(a), we have,

-Vm - VC - Vout =0 and

Vout = - Vm - VC This same procedure follows in an all biased clamper circuits to find the amplitude of output wave.

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(d)

Biased Clamper Circuits Figure 3

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Experiment 1 Objective : To study clamper circuits Equipments Needed : 1. Analog board AB89 2. DC power supplies +5V and -5V from external source or ST2612 Analog Lab. 3. Oscilloscope 4. Function generator

5. 2 mm patch cords Circuit diagram : Circuit used to study different combinations of clamper is shown in figure 4

Figure 4

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Procedure : • Connect +5V and -5V DC power supplies at their indicated position from

external source or ST2612 Analog Lab. 1. Apply sine wave of 1 KHz frequency and amplitude 10Vpp approximately with

zero DC voltage at terminal a. 2. To make the circuit of negative clamper as shown in figure 2, connect 2mm

patch cord between socket b & ground terminal. 3. Put oscilloscope in DC coupling mode and monitor output signal at terminal f

with respect to ground on oscilloscope. 4. To make circuit of positive clamper as shown in figure 1, disconnect 2 mm

patch cord between terminals b & ground and connect between c & ground. 5. Keep the oscilloscope in DC coupling mode and observe output at terminal f

with respect to ground. 6. Next to make circuit of biased clamper as shown in figure 3(a), remove 2 mm

patch cord between terminal c & ground and connect between b & d terminals. 7. Observe output signal at terminal f with respect to ground. 8. Vary the voltage VA to increase the DC voltage from 0 to 5V and observe the

output voltage at terminal f. 9. Observe the level of output DC voltage at TP1. 10. Disconnect 2 mm patch cord between terminal b and d and connect between c &

e terminals, to make biased clamper circuit as shown in figure 3(d). 11. Monitor output signal at terminal f with respect to ground. 12. Vary the voltage VB to decrease the DC voltage from 0 to -5V and observe the

output voltage at terminal f. 13. Observe the level of output DC voltage at TP2. 14. To make the another combination of biased clamper ,as shown in figure 3(b),

remove the 2mm patch cord between terminal c & e and connect between b & e terminals. Observe the effect of adding DC voltage at terminal f.

15. Disconnect 2 mm patch cord between terminal b & e and connect between c & d terminals, to make circuit same as figure 3(c). Observe the effect of adding DC voltage at terminal f.

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Warranty 1. We guarantee the product against all manufacturing defects for 24 months from

the date of sale by us or through our dealers. Consumables like dry cell etc. are not covered under warranty.

2. The guarantee will become void, if

a) The product is not operated as per the instruction given in the operating manual.

b) The agreed payment terms and other conditions of sale are not followed.

c) The customer resells the instrument to another party. d) Any attempt is made to service and modify the instrument.

3. The non-working of the product is to be communicated to us immediately giving full details of the complaints and defects noticed specifically mentioning the type, serial number of the product and date of purchase etc.

4. The repair work will be carried out, provided the product is dispatched securely packed and insured. The transportation charges shall be borne by the customer.

For any Technical Problem Please Contact us at [email protected]

List of Accessories

1. 2mm Patch Cord (Red) 16” ................................................................... 2 Nos. 2. 2mm Patch Cord (Black) 16”................................................................. 3 Nos. 3. 2mm Patch Cord (Blue) 16” .................................................................. 3 Nos. 4. e-Manual.................................................................................................1 No.

Updated 26-06-2009

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