2 DIODE CLIPPING and CLAMPING CIRCUITS

Transcription

1 2 DIODE CLIPPING nd CLAMPING CIRCUITS 2.1 Ojectives Understnding the operting principle of diode clipping circuit Understnding the operting principle of clmping circuit Understnding the wveform chnge of diode clipping nd clmping circuits when the is is pplied. 2.2 Bsic Description As you know, diodes cn e used s switches depending on the ising type, reverse of forwrd. The clipping circuit, lso referred to s clipper, clips off some of the portions of the input signl nd uses the clipped signl s the output signl. The clmping circuit or clmper keeps the mplitude of the output signl sme s tht of the input signl except tht the D.C. level (offset) hs een chnged. The clmper through which the input wveform shifts to positive direction is clled positive clmper, otherwise, is clled negtive clmper. Fig. 2.1 Idel Diode Switch Terminlogy 2.2. Clipper Circuits There re two types of clipper circuits, the series nd prllel diode clipping circuits Series Diode Clipping Circuit In these type of circuits, the diode is connected etween the input nd output voltge terminls (Fig 2.2) 10

2 Fig. 2.2 As Fig.2.2 revels, the negtive cycle of the input voltge cn e clipped of y this type of series clippers. Reverse of the diode pins yields to positive cycle clipping circuit s shown in Fig Fig. 2.3 Previous circuits clip the vlues lrger or smller thn zero voltge. This voltge, techniclly clled threshold voltge nd cn e chnged to desired vlue y inserting D.C. voltge source. This is chieved in two different wys. In the first type, the voltge source of E m ( positive or negtive) is connected through output terminls s in Fig Depending on the diode connection (norml 11

3 or reverse), the vlues smller (Fig.2.4.) or greter (Fig.2.4.) thn E m is clipped nd ssigned s E m.. Fig Note tht if E m is negtive, ( where the voltge source is reversely connected) gin the vlues smller or lrger thn this negtive vlue is clipped, do not get confused. In the second type of thresholded series clipping, the voltge source is pplied etween the input nd output terminls, series with the diode. This time, the clipped vlues re ssigned to zero nd the net output voltge equls to the difference etween the input nd threshold vlues.(if E m is negtive, then E 0 = E E m = E + E m ) Fig

4 Prllel Diode Clipping Circuit In this type of clippers, the diode is connected etween output terminls. The on/off stte of diode directly ffects the output voltge. These type of clippers my lso hve non-zero threshold voltge y ddition of voltge series with diode. Following figures illustrte the clipping process. Fig. 2.6 Zero Threshold Prllel Clippers Fig. 2.7 Thresholded Prllel Clippers 13

5 2.2. Clmper Circuits Clmper Circuits, or riefly clmpers re used to chnge the D.C. level of signl to desired vlue.( Fig 2.8 ). Fig 2.8 Being different from clippers, clmping circuits uses cpcitor nd diode connection. When diode is in its on stte, the output voltge equls to diode drop voltge (idelly zero) plus the voltge source, if ny. Now let us exmine the clmping process for the circuit in Fig Fig 2.9 Typicl Clmping Circuit As you know, this circuit, in fct, is series R-C circuit. The resistnce of diode ( severl ohms ove its drop voltge) nd the smll cpcitnce yield to smll time-constnt for this circuit. This mens tht the cpcitor will rpidly e chrged if ny input voltge, tht is enough to swtich on the diode, is pplied. The diode will conduct during the positive cycle of the input signl (Fig. 2.10) nd output voltge will e idelly zero ( in prctice this voltge equls ~0.6 V). Fig Diode conducts during positive cycle Note tht during positive cycle the cpcitor is rpidly chrged in inverse polrity with the input voltge. After trnsition to negtive cycle, the diode ecomes to its off stte. In this cse, the output voltge equls to the sum of the input voltge nd the voltge cross the terminls of the cpcitor which hve the sme polrity with ech other.(fig 2.11) 14

6 E 0 = - ( E i + E c ) Fig Diode is switched off during negtive cycle The resulting signl fter complete cycle is shown elow. Fig By this process, the input signl is shifted to negtive D.C. vlue (its mximum vlue is idelly zero) without ny chnge in its mplitude idelly. There exist gin modified versions of this circuit inwhich threshold vlue is inserted for clmping. Following figures illustrte these modifictions nd resulting outputs. 15

7 Fig.2.13 Fig

8 2.3 Experiment Equipments 1. KL- 200 Liner Circuit L. Device 2. Experiment Module: KL Experiment Instruments: Oscilloscope, Multimeter 4. Connection cles nd short-circuit clips 2.4 Procedures Procedure 1: Series Diode Clipping Circuit ( 1 ) Locte lock of module KL ( 2 ) Insert short-circuit clips refering to Fig Fig ( 3 ) Using oscilloscope, djust function genertor to 10 V p-p ( 7.07 V rms), 1kHz Sine wve. Mke good djustment since this signl is the common input signl tht will e used during whole experiment. ( 4 ) Adjust oscilloscope divisions until you hve cler view of input signl. 17

9 ( 5 ) Disconnect function genertor output from oscilloscope nd pply this to TP2. ( 6 ) Exmine the output signl y connecting the second chnnel of oscilloscope to TP3. Record the plot on Grph 2.1. ( 7 ) Turn off ll ctive devices, nd reconfigure the short-circuit clips refering to Fig ( 8 ) Only chnge the genertor output from TP2 to TP1. ( 9 ) Agin exmine the output wveform nd plot output wveform on Grph 2.1. Grph

10 Procedure 2: Thresholded Series Diode Clipping Circuit In this procedure, threshold vlue is dded to the previous circuit lyout. This is chieved y sustitution of lower short-circuit clip with voltge source. ( 1 ) Turn off ll ctive devices, nd connect short-circuit clip nd voltge source ( + 5 V DC) y refering to Fig Fig ( 2 ) Record the plot of output voltge on Grph 2.2. (on Pg. 25) ( 3 ) Turn off ll ctive devices, nd reconfigure short-circuit clips refering to Fig ( 4 ) Plot output wveform on Grph 2.2. Turn off ll ctive devices. Now you will pply negtive threshold vlue to the clipper circuit. ( 5 ) Refering to Fig.2.17-, reconfigure short circuit clips nd sustitute +5V DC source with -5 V DC Source. Do not directly reverse the terminls of + 5 V source, this will cuse short circuit!!! 19

11 Fig ( 6 ) Oserve nd plot the output wveform on Grph 2.2.c ( 7 ) Turn off ll ctive devices gin nd rerrnge short circuit clip refering to Fig ( 8 ) Oserve nd plot output voltge on Grph 2.2.d 20

12 c d Grph 2.2 Procedure 3: Prllel Diode Clipping Circuit ( 1 ) Locte lock c of module KL ( 2 ) Refer to Fig nd rrnge short circuit clips. 21

13 Fig ( 3 ) Oserve output voltge on TP2 nd plot on Grph 2.3. ( 4 ) Turn off ll ctive devices nd rerrnge short circuit clips y refering to Fig ( 5 ) Oserve output voltge on TP2 nd plot on Grph 2.3. Grph

14 Procedure 4 : Diode Clmping Circuit ( 1 ) Now locte lock e. ( 2 ) Arrnge clips ccording to Fig Fig ( 3 ) Oserve nd plot OUT voltge on Grph 2.4. ( 4 ) Turn off ll ctive devices nd rerrnge circuit in Fig ( 5 ) Agin plot OUT voltge on Grph

15 Grph Conclusion In this experiment you hve lerned two min types of diode circuits. Clippers Clmpers Although the clippers re lso clssified into series nd prllel clipping circuits, oth circuits re sed on the sme principle. In other words, the design of oth circuits utilizes the chrcteristics of diode tht will e forwrd turned on nd will reversely turned off. Clmpers cn e used to chnge the DC level of n input signl. 24