CHAPTER 3 DIODES. NTUEE Electronics L. H. Lu 3-1

Transcription

1 CHAPER 3 OE Chapte Outline 3.1 he eal ioe 3.2 eminal Chaacteistics of Junction ioes 3.3 Moeling the ioe Fowa Chaacteistics 3.4 Opeation in the Reese Beakown Region ene ioes 3.5 Rectifie Cicuits 3.6 Limiting an Clamping Cicuits NUEE Electonics L. H. Lu 3-1

2 3.1 eal ioe eal ioe chaacteistics An ioe is a two-teminal eice: Anoe: the positie teminal Cathoe: the negatie teminal Fowa biase tune on shot Reese biase tune off open Cicuit applications Y = A B C Y = A B C NUEE Electonics L. H. Lu 3-2

3 - chaacteistics of junction ioes 3.2 eminal Chaacteistics of Junction ioes / n ioe cuent: i ( e 1) (satuation cuent): popotional to ioe aea n (ieality facto): between 1 an 2. (themal oltage) 25 m at oom tempeatue he fowa-bias egion, etemine by 0. he eese-bias egion, etemine by 0. he beakown egion, etemine by K Fowa-bias egion he simplifie fowa-bias - elationship: Fo a gien fowa oltage: i e / n Fo a gien fowa cuent: n ln( / ) ue to the exponential - elationship i 0 fo < 0.5 (cut-in oltage) Fully conuction fo 0.6 < < 0.8 on = 0.7 empeatue epenence oubles fo eey 5C ise in tempeatue. olage eceases 2m/C fo a gien cuent. Cuent inceases with tempeatue fo a gien oltage. NUEE Electonics L. H. Lu 3-3

4 Reese-bias egion Reese cuent: eally, the eese cuent is inepenent of eese bias. n eality, eese cuent is lage than an also inceases somewhat with the incease in the eese bias. empeatue epenence: eese cuent oubles fo eey 10C ise in tempeatue. Beakown egion i he knee of the - cue is specifie as beakown oltage K fo ene beakown mechanism. he eese cuent inceases apily with the associate incease in oltage op being ey small. Nomally, the eese cuent is specifie by extenal cicuity to assue the powe issipation within a safe ange (non-estuctie opeation). NUEE Electonics L. H. Lu 3-4

5 Cicuit analysis 3.3 Moeling the ioe Fowa Chaacteistics etemine the ioe cuent an oltage fo cicuit analysis he equation equie fo the analysis: = exp( /n ) oie - chaacteistics = ( )/R Kichhoff loop equation Nee to sole non-linea equations Gaphical analysis Plot the two equations in the same - cooination he staight line is known as loa line. he intesect tis the solution fo an teatie analysis et initial alue = 0 Use = ( )/R to obtain 1 Use = n ln ( / ) to obtain 2 Repeat until it coneges ( 3, 4, 5, 6 ) teations ae neee to sole the nonlinea cicuit NUEE Electonics L. H. Lu 3-5

6 he nee fo api analysis Rapi analysis using simplifie moels fo initial esign. Accuate analysis (iteatie analysis o compute pogam) fo final esign Rapi analysis (): ieal-ioe moel he most simplifie moel an can be use when supply oltage is much highe than the ioe oltage ioe on: = 0 an i > 0 ioe off: i = 0 an < 0 Equialent cicuit moel as an ieal ioe Rapi analysis (): constant-oltage-op moel he most wiely use moel in initial esign an analysis phases ioe on: = 0.7 an i > 0 ioe off: i = 0 an < 0.7 Equialent cicuit moel as an ieal ioe with a 0.7- oltage souce NUEE Electonics L. H. Lu 3-6

7 mall-signal appoximation he ioe is opeate at a c bias point an a small ac signal is supeimpose on the c quantities: Une small-signal conition: / n <<1 associates with c opeating point Q i associates with small signal esponse he ioe exhibits linea - chaacteistics n n n n n e e e e e t i t t / / / )/ ( / ) ( ) ( ) ( i n n t i ) (1 ) ( une small-signal conitions ( 10m) ioe small-signal esistance an conuctance at opeating point Q: he ioe small-signal moel Choose pope c analysis technique o moel to obtain the opeation point Q he small-signal moel is etemine once Q is poie he small-signal moel is use fo cicuit analysis when the ioe is opeating aoun Q NUEE Electonics L. H. Lu 3-7 g n i / i i n g ] [ i i n ] 1/[

8 Cicuit analysis techniques fo total quantities (AC+C) Eliminate all the time aying signals (ac oltage an cuent souces) fo opeation point analysis Use api analysis o accuate analysis to obtain c oltage an cuent at opeating point Q etemine the paametes of small-signal moels fom Q Replace the eices with small-signal moels an eliminate all the c souces Cicuit analysis une small-signal appoximation he complete esponse (ac + c) of the cicuit is obtaine by supeposition of the c an ac components oltage egulato by ioe fowa op A oltage egulato is to poie a constant c oltage egaless changes in loa an powe-supply oltage he fowa-oltage op emains almost constant at 0.7 within a wie cuent ange Multiple ioes in seies to achiee the equie oltage op Bette egulation can be poie fo highe bias cuent an smalle NUEE Electonics L. H. Lu 3-8

9 3.4 Opeation in the Reese Beakown Region ene ioes ymbol an cicuit moel fo the ene ioe n beakown egion, a eese bias ( ) beyon the knee oltage ( K ) leas to a lage eese cuent ( ). he ioe in beakown egion is gien by = 0 + z z he beakown ioe is moele by a oltage souce 0 in seies with an incemental esistance z ncemental oltage esus cuent: = z he simplifie moel is only ali fo > K (knee cuent) Equialent z inceases as eceases ioe types: ioe: only fowa an eese egions ae consiee ene ioe: fowa, eese an beakown egions NUEE Electonics L. H. Lu 3-9

10 esign of the ene shunt egulato Output oltage of the egulato: Line egulation: Loa egulation: Line an loa egulation shoul be minimize L z O R R R R R 0 O R L O R R Fo z << R, line egulation can be minimize by choosing small z Loa egulation can be minimize by choosing small z an lage R hee is an uppe limit on the alue of R to ensue sufficiently high cuent ( z inceases if is too low) R shoul be selecte fom NUEE Electonics L. H. Lu 3-10 max min min 0 min L z R

11 3.5 Rectifie Cicuits Block iagam of a c powe supply C powe supply Geneate a c oltage fom ac powe souces he ac input is a low-fequency lage-signal oltage Powe tansfome tep the line oltage own to equie alue an poies electic isolation ioe ectifie Conets the input sinusoial to a unipola output Can be iie to half-wae an full-wae ectifies Filte Reuces the magnitue aiation fo the ectifie output Equialent to time-aeage opeation of the input waefom oltage Regulato Futhe stabilizes the output to obtain a constant c oltage Can be implemente by ene ioe cicuits NUEE Electonics L. H. Lu 3-11

12 he half-wae ectifie oltage tansfe cue: 0 O 0 0 O 0 Rectifie ioe specifications: Cuent-hanling capability: the lagest cuent the ioe is expecte to conuct. Peak inese oltage (P): the lagest eese oltage the ioe can stan without beakown. P = s (input oltage swing) an the ioe beakown oltage is selecte at least 50% highe. NUEE Electonics L. H. Lu 3-12

13 he full-wae ectifie (cente-tappe tansfome) oltage tansfe cue: 0 0 O 0 O 0 0 O 0 ansfome seconay wining is cente-tappe. Peak inese oltage (P) = 2 s 0. Rectifie output waefom fo both positie an negatie cycles. NUEE Electonics L. H. Lu 3-13

14 Full-wae ectifie (Bige ectifie) oltage tansfe cue: O 2 0 O 2 0 O 2 0 oes not equie a cente-tappe tansfome Highe tun-on oltage (2 0 ). Peak inese oltage (P) = s 0. Most popula ectifie cicuit configuation. NUEE Electonics L. H. Lu 3-14