Characteristics of BJT-2

Transcription

1 PLEASE S HP://ENGNEERS.N/ ENGNEERS- ONSULANS LEURE NOES SERES ELERONS ENGNEERNG 1 YEAR UPU haractristics of J-2 Output haractristics for ommon Emittr configuration: h output charactristic for transistor is a graph btwn output currnt and output voltag on th basis of diffrnt input currnt. n common Emittr configuration th output currnt is and output voltag is E and input currnt is. So output charactristics for common mittr will b a graph btwn and E on th basis of diffrnt valus of. For pnp transistor to work in activ rgion mittr junction should b forward bias and collctor junction should b rvrs bias. For mittr junction forward bias E should b ngativ, and to mak collctor junction rvrs biasd th voltag should b ngativ as wll as gratr than E in magnitud i.. > E. Hr w hav to apply E in input sid and E on output sid. On applying KL btwn trminals of J w can find rlation btwn voltags. E + - E =0 E = + E From quation E = + E, w can s that, if E is ngativ (to mak mittr junction of pnp forward bias thn to rvrs bias th collctor junction of pnp transistor E should b ngativ. Suppos for Si (pnp transistor, E = -0.7, thn to mak ngativ and gratr than E (i v th E should b at last gratr than 1.4 in magnitud and with ngativ sign. i.. E = or E >1.4 Mans E can b 1.41, and so on hrfor w can say that to mak pnp (Si transistor in activ rgion E should b ngativ and gratr than 1.4 in magnitud. Similarly to mak a Si (pnp transistor in saturation rgion th mittr junction and collctor junction both should b forward bias. Mans E should b ngativ and to mak positiv and smallr in magnitud than E (i.. magnitud. Suppos E = -0.7 (for mittr junction Forward bias So for = + and lowr than E in magnitud [From E = + E = E E < E, E should b always ngativ and lowr than E in Pag 1

2 PLEASE S HP://ENGNEERS.N/ ENGNEERS- ONSULANS LEURE NOES SERES ELERONS ENGNEERNG 1 YEAR UPU = -0.7 E] E can not b positiv. hat mans for pnp transistor in common mittr cas to b in saturation rgion E should b ngativ and should b positiv and lowr than E in magnitud. And to mak this, E will b always ngativ. So finally w can say to mak a pnp transistor in activ or saturation or in cut off E will b always ngativ. Similarly for npn transistor it will b always positiv. So to draw an output charactristics graph for pnp transistors btwn and E only ngativ valus of E will b usd. As w hav discussd for pnp common mittr transistor should b function of E and mans = f (, E. W know (1 / from common bas configuration. E O y using E = + and E = + E ( O (1 ( E E / (1 O (1 ( E E / 1 ( O O (1 (1 ( E E / ( E E / Hr w can s = f (, E, ( 1 O EO 1 EO mans curnt btwn collcor and mittr whn bas is opn. So gnral quation of J in common mittr configuration will b EO (1 ( E E / charactristics of J in common mittr configuration. Activ Rgion:, his quation can b usd to draw Pag 2

3 PLEASE S HP://ENGNEERS.N/ ENGNEERS- ONSULANS LEURE NOES SERES ELERONS ENGNEERNG 1 YEAR UPU For activ rgion mittr junction should b forward bias and collctor junction should b rvrs biasd so will b prsnt in th quation and rspct to1, and quation for activ rgion will b = EO ( So graph of will b dpndnt on and E both, bcaus on E (From bas width modulation (Mans on incrasing E E E / will b nglctd with will b incrasd and as w know varis from 0.92 to 0.99, for variation of from 0.92 to 0.99, = 11. 5, = 99, So for 0.92 to 0.99, varis fro 11.5 to 99. So variation in with rspct to E is fastr than variation in. So slop of graph in common mittr will b gratr than common bas in activ rgion. Saturation rgion: Figur-1(Activ rgion For J to b in saturation rgion mittr junction should b forward bias and collctor junction should also b forward biasd. For PNP transistor E and both should b ngativ and < E is rquird for pnp in saturation rgion. For this E will b always ngativ and Pag 3

4 PLEASE S HP://ENGNEERS.N/ ENGNEERS- ONSULANS LEURE NOES SERES ELERONS ENGNEERNG 1 YEAR UPU E < E.Du to mittr junction forward bias will b availabl in th quation and ( E ( E E E / / will b much gratr than 1, so 1 will b nglctd with rspct to and currnt quation for pnp transistor in saturation rgion will b ( ( E E /. From this quation it is conform that variation EO in E is dominating ovr variation in on valus of. So will b approximatly dpndnt on E xponntially and indpndnt of and E. hat mans is saturatd with rspct to so this rgion is calld saturation rgion Figur-2(Saturation rgion hrfor w can say that in saturation rgion of output charactristics of common mittr configuration, is saturatd with rspct to input currnt and also E. ut off Rgion: n cut off rgion mittr junction is rvrs biasd and collctor junction is also rvrs biasd. So E and both should b applid in such a mannr that can rvrs bias th mittr junction and collctor junction rspctivly. For pnp, E should b positiv and should b ngativ. So in currnt quation Pag 4

5 PLEASE S HP://ENGNEERS.N/ ENGNEERS- ONSULANS LEURE NOES SERES ELERONS ENGNEERNG 1 YEAR UPU = 0, and ( E E / So currnt quation for cut off rgion will b = EO will b nglctd with rspct ot 1. So w can say is cut off from & E, so this biasing condition will b calld cut off rgion and graph will b as shown in figur-3. Figur-3(ut off rgion From abov discussion it is conform that output charactristics graph will b always for ngativ E (for pnp. Activ, saturation and cut off rgion will b on right sid of vrtical,, axis. h slop of th graph will b gratr than slop of graph in common bas cas. Mans variation in with rspct E will b gratr than variation in with rspct (in common bas as shown in fig. Pag 5

6 PLEASE S HP://ENGNEERS.N/ ENGNEERS- ONSULANS LEURE NOES SERES ELERONS ENGNEERNG 1 YEAR UPU Figur-4 (Output charactristics of common mittr pnp transistor Pag 6