Part3 - KHUECH AI CONG SUAT AM TAN (KCSAT) Chng 3 : I. Cac...

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13 Cc i i i i L Vcc R L Ns Np E C R E R1 R2 ri Chöông 3 : KHUEÁCH ÑAÏI COÂNG SUAÁT AÂM TAÀN (KÑCSAÂT) I. Caùc lôùp khueách ñaïi vaø hieäu suaát : * Ñaëc ñieåm cuûa cheá ñoä A : tín hieäu toàn taïi trong caû chu kyø. + Öu : meùo phi tuyeán nh±. +Khuyeát : hieäu suaát thaáp : aùp bieán laø taûi duøng R laø taûi duøng : % 50 : % 25 A A η * Ñaëc ñieåm cuûa cheá ñoä B : tín hieäu ch± toàn taïi trong nöûa chu kyø. + Öu : hieäu suaát cao : η B 78,5 % + Khuyeát : meùo phi tuyeán lôùn Caùch khaéc phuïc : maéc ñaåy-keùo ñeå giaûm meùo phi tuyeán. II. Boä khueách ñaïi coâng suaát aâm taàn ñôn duøng bieán aùp : Maïch laøm vieäc ôû cheá ñoä lôùp A. Heä soá gheùp bieán aùp : N = s p L C N N V V = (1) V C = NV L (1') Ni C = -i L (2) L L C C i V N Ni V - = = -NR L (3) ' 2 L L C C R R N i V = = - (4) : Ñieän trôû taûi phaûn aùnh töø thöù caáp veà sô caáp. * Coâng suaát nguoàn cung caáp moät chieàu laø : P CC = P S = V CC .I CQ (W) (5) * Coâng suaát xoay chieàu ñöôïc cung caáp treân R L (hay coøn goïi laø coâng suaát höõu ích treân taûi) :
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14 P L = 2 1 ' 2 2 2 . 2 1 . ) ( 2 1 . L Cm L Cm L Lm R I R NI R I = = * Hieäu suaát : CC L P P = η (7) * Coâng suaát tieâu taùn cöïc ñaïi treân collector : P C = P CC – P L = I CQ .V CC - 2 1 ' 2 L cm R I (8) Caùc coâng thöùc (5), (6), (7), (8) ñuùng cho moïi tröôøng hôïp. ÔÛ ñieàu kieän tín hieäu cöïc ñaïi (soùng ra max-swing) ta coù : L CC L CC CQ cm R N V R V I I 2 ' max = = = (9) V CEQ = V CC – I CQ R E V CC (10) (do R E raát nhoû) Khi ñoù : + P max CC = V CC ' L CC R V = L CC R N V 2 2 (5’) + P max L = L CC L CC L L CC R N V R V R R V 2 2 ' 2 ' 2 ' 2 1 2 1 . 2 1 = = (6’) + η max = max max CC L P P = 0,5 = 50 % (7’) + P max C = P CC = L CC R N V 2 2 khi P L = 0 V CE C i cmax =2I CQ 0 Q DCLL (-1/R DC ) V CC V CEQ I CQ ADCLL (-1/R AC ) 0 I Cm I Cmax P L P C P CC P Lmax
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15 + L CC L CC C R N V P P P 2 2 2 1 max max min = - = (8’) (Ñeå choïn transistor ngöôøi ta duøng chA soá phaåm chaát : 2 max max = L C P P Ví duï : W P W P L C 2 4 max max = = ) III) BOÂ KHUEÁCH ÑAÏI COÂNG SUAÁT AÂM TAÀN ÑAÅY KEÙO LÔÙP B: o Boä khueách ñaïi coâng suaát aâm taàn ñaåy keùo lôùp B duøng bieán aùp : Nguyeân lyù hoaït ñoäng : + 2 1 T > 0 Q 1 daãn : i C1 0; Q 2 taét : i C2 = 0. + 2 1 T < 0 Q 1 taét : i C1 = 0; Q 2 daãn : i C2 0. + Trong caû hai nöûa chu kyø doøng chaûy trong bieán aùp ra ngöôïc chieàu vôùi nhau neân ta coù : i L = N(i C2 – i C1 ) keát quaû ta thu ñöôïc daïng soùng sine nhö hình veõ.
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Part3 - KHUECH AI CONG SUAT AM TAN (KCSAT) Chng 3 : I. Cac...

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