mạch lọc

Chng7

Mch lc in

Tm tt L thuyt

Mch lc in l mt mng bn cc thc hin bin i ph ca tn hiu theo mt quy lut ton hc no. Mch lc thng dng tht l mch lc thun khng LC. Mch lc LC li chia thnh loi k v loi m.L thuyt mch lc thun khng thng xut pht t MBC hnh hnh 7.1a). nhn c cng thc c dng ton hc thun tin, ngi ta k hiu tr khng nhnh ngang l , nhnh dc l 2Z2. T mch lc hnh 7.1a) to ra mch loc i xng hnh Thnh 7.1b) v lc i xng hnh ( hnh 7.1c). L thuyt chung lc thun khng xy dng cho mch hnh 7.1a) xut pht t cng thc hng s truyn c tnh gC ca MBC

(7.1) T (7.1) tm c iu kin c lc l Z1v Z2 phi khc tnh.

Trng hp tch tng tr hai nhnh l mt hng th lc l lc loi k. Lc

Z1Z2=R02=K2=const. (7.2) Trong c th nguyn ca in tr, gi l in tr danh nh ca mch lc, k hiu l R0 hoc K.

Trong cng thc 7.1 th gC/2 l hng s truyn c tnh ca mch lc hnh hnh 7.1a) , thng gi l mt na t lc. Mc lin thng hai na t c mt t hnh T hoc (, c hng s truyn c tnh l gC.

+Lc thng thp (hay lc tn s thp) loi K c nhnh ngang l in cm, nhnh dc l in dung nh hnh 7.2. (di thng 0((C, di chn (C(() Cc cng thc tnh cc thng s ca mch lc thng thp:

in tr danh nh: (7.2) Tn s ct: (7.3) H s suy gim c tnh trong di chn:

(7.4) H s pha c tnh: Trong di thng:] (7.5) Trong di chn: bC = (.

Tng tr c tnh: (7.6) Ch : Mch lc c tng tr c tnh ph thuc vo tn s nn ni chung l khng th m bo HHPT. V vy nh ngha mt cch tng i trong cac bi tp s gii l: ch HHPT l ch ti thun tr Rt=R0. S mt ho hp ph ti c c trng bi h s ti: (7.7)+Lc thng cao (hay lc tn s cao) loi K c nhnh ngang l in dung, nhnh dc l in cm nh hnh 7.3. (di thng (C( (, di chn 0 ( (C ) Cc cng thc tnh cc thng s ca mch lc thng cao:

in tr danh nh: (7.8)

Tn s ct: (7.9) H s suy gim c tnh trong di chn:

(7.10) H s pha c tnh: Trong di thng:] (7.12) Trong di chn: bC = -(.

Tng tr c tnh: (7.13) +Lc thng di(hay lc di thng) loi K c nhnh ngang l khung cng hng ni tip, nhnh dc l khung cng hng song song, hai nhnh c cng tn s cng hng (0 (Hnh 7.4). (di thng (C1((C2, di chn 0 ( (C1, (C2 ( ( )

Cc cng thc tnh cc thng s ca mch lc thng di loi k:

in tr danh nh: (7.14)

Tn s ct:

(7.15) Di thng: ((=(C2-(C1= (7.16) Tn s trung tm (7.17) H s suy gim c tnh trong di chn:

(7.18) (7.19) (7.20) H s pha c tnh: bc= (7.21) Tng tr c tnh: (7.22) +Lc chn di (hay lc chn di hay lc di chn) loi K c nhnh ngang l khung cng hng song song, nhnh dc l khung cng hng ni tip hnh 7.5 (di thng 0((C1 v (C2((, di chn (C1((C2). Cc cng thc tnh cc thng s ca mch lc chn di loi K:

in tr danh nh: (7.23)

Tn s ct (ging lc thng di) :

(7.24) Di chn: ((=(C2-(C1= (7.25) Tn s trung tm (7.26) H s suy gim c tnh trong di chn: (7.27)

(7.28) H s pha c tnh: bc= (7.29) Tng tr c tnh: (7.30) Lc loi M:

Kt cu ni tip (hnh 7.6a)

(7.31) Kt cu song song (hnh 7.6b)

(7.32) Cc tham s:

(7.33) Tn s ct gi nguyn cc cng thc nh lc loi k.

Tn s t bin ca aC (tn s ((, ti aC= () =0 (7.34) Suy gim c tnh trong di chn: (7.35) Pha c tnh trong di thng: (7.36) Tng tr c tnh:

(7.37) (7.38) Mch lc RC.

Lc RC thng thp (hnh 7.7) Tn s ct: (7.39) H s suy gim c tnh:

(7.40)

(7.41.) Ti tn s ct shaC=2,2, tc aC=1,53 nepe

Ghp hai na t hnh 7.7a) c mt t lc hnh T hnh 7.7b) hoc mt t lc hnh ( hnh 7.7c). t lc hnh ( s dng s t tn hao nng lng hn t lc hnh T v dng hnhT i qua hai in tr mc ni tip. Lc RC thng cao (hnh 7.8) Tn s ct: (7.42) H s suy gim c tnh: (7.43) Khi (7.44)

Ti tn s ct shaC=2,2, tc aC=1,53 nepe.

Ghp hai na t hnh 7.8a) c mt t lc hnh T hnh 7.8b) hoc mt t lc hnh ( hnh 7.8c). Mc lin thng mt t lc thng thp v mt t lc thng cao c lc RC thng di.

bi tp

7.1.Mch lc thng thp c tn s ct l 15Khz, in tr ti 500(. Hy xc nh:

a) Cc thng s vt l ca mch lc.

b) V s hnh , hnh T v hnh ( ca mch lc, in trn hnh v tr s cc thng s vt l ca mch. c) H s suy gim c tnh tn s 10 Khz, 20 Khz v 25 Khz.

d) H s pha c tnh tn s 5 Khz, 10 Khz v 20 Khz.

e) Tng tr c tnh tn s 5 Khz, 10 Khz.

7.2. Mch lc thng thp tn s ct fC=12 Khz.

a) tn s no th h s suy gim c tnh t 2,172 nepe?

b) tn s no th h s pha c tnh t 90,20?

7.3.Mch lc thng thp loi k c tn s ct 8 Khz. Hy xc nh h s suy gim c tnh tn s 12 Khz v 18 Khz, h s pha c tnh tn s 2,5 Khz v 6 Khz.

7.4.Mch lc thng thp c tn s ct l 500 Hz, in tr ti 600(. Hy xc nh:

a) Cc thng s vt l ca mch lc.

b) V s hnh , hnh T v hnh ( ca mch lc, in trn hnh v tr s cc thng s vt l ca mch. c) H s suy gim c tnh tn s 1000 Hz v 1500 hz.

d) H s pha c tnh tn s 120 Hz v 320 Hz.

e) Tng tr c tnh tn s 120 Hz v 320 Hz.

7.5. t lc thng thp hnh T c in tr danh nh l 450 (, tn s ct 1200 Hz.

a) Xc nh cc thng s vt l ca t lc.

b) tn s no th h s suy gim c tnh ca t lc l 2,585 nepe?

c) tn s va tm c mun c h s suy gim c tnh l 7,755 nepe th phi kt cu mch lc nh th no?

d) Tnh h s suy gim c tnh ca mch lc va kt cu tn s 2000 Hz.

7.6. t lc thng thp hnh T c in tr danh nh l 450 (, tn s ct 1200 Hz. Hy xc nh:

a) Tng tr c tnh tn s 250 Hz.

b) tn s no th tng tr c tnh ca t lc l 320 (?

c) Nu in tr ti l 520 ( th nn kt cu t lc nh th no m bo phi hp tr khng vi ti? Khi tn s no s c phi hp tr khng hon ton?

7.7. t lc thng thp hnh ( c in tr danh nh l 450 (, tn s ct l 1500 Hz.Hy xc nh:

a) tn s no th tng tr c tnh ca mch lc l 600( b) tn s no th h s pha c tnh c tr s 1,46 rad.

7.8.Cho mch lc hnh 7.9.Hy xc nh:

a) Tn s ct ca mch lc. b) in tr danh nh R0 ca mch lc.

c) H s suy gim c tnh tn s 2000 Hz v 2500 hz.

d) H s pha c tnh tn s 500 Hz v 920 Hz.

e) Tng tr c tnh tn s 500 Hz

f) V mch lc hnh ( tng ng v in tr s cc thng s mch trn hnh .

7.9.Cho mch lc hnh 7.10.Hy xc nh:

a) Tn s ct ca mch lc. b) in tr danh nh R0 ca mch lc.

c) H s suy gim c tnh tn s 4000 Hz v 6 000 hz.

d) H s pha c tnh tn s 1000 Hz v 1800 Hz.

e) Tng tr c tnh tn s 500 Hz

f) V t lc hnh T v hnh ( tng ng ; in tr s cc thng s mch trn hnh .

7.10.Cho mch lc hnh 7.11.Hy xc nh:

a) Tn s ct ca mch lc. b) in tr danh nh R0 ca mch lc.

c) H s suy gim c tnh tn s 1000 Hz v 2500 hz.

d) H s pha c tnh tn s 350 Hz v 1200 Hz.

e) Tng tr c tnh tn s 250 Hz

f) V hnh T tng ng v in tr s cc thng s mch trn hnh .

7.11. Mch lc thng cao c tn s ct l 800 Hz,in tr ti 250(.Hy xc nh:

a) Cc thng s vt l ca mch lc.

b) V s hnh , hnh T v hnh ( ca mch lc, in trn hnh v tr s cc thng s vt l ca mch. c) H s suy gim c tnh tn s 150 Hz, 500 Hz v 1000 Hz.

d) H s pha c tnh tn s 250 Hz, 1000 Hz v 1500 Hz.

e) Tng tr c tnh tn s 1200 Hz.

7.12. Mch lc thng cao c tn s ct l 500 Hz.

a) tn s no th h s suy gim c tnh c tnh ca mch lc t 3 nepe.b) tn s no th h s pha c tnh c tr s -1,46 rad.

7.13. Mch lc thng cao c tn s ct l 200 Hz.

a) tn s no th h s suy gim c tnh c tnh ca mch lc t 35,86 dB.b) tn s no th h s pha c tnh c tr s - 600.

7.14.Cho mch lc hnh 7.12.Hy xc nh:

a) Tn s ct ca mch lc. b) in tr danh nh R0 ca mch lc.

c) H s suy gim c tnh tn s 90 Hz v 180 hz.

d) H s pha c tnh tn s 100 Hz v 320Hz.

e) Tng tr c tnh tn s 300 Hz

f) V mch lc hnh T tng ng v in tr s cc thng s mch trn hnh .

7.15. Cho mch lc hnh 7.13. Hy xc nh:

a) Tn s ct ca mch lc. b) in tr danh nh R0 ca mch lc.

c) H s suy gim c tnh tn s 200 Hz.

d) tn s no th h s suy gim t 3,5 nepe.

e) tn s no th h s pha c tnh c tr s l - 700f) V mch lc hnh T v hnh ( tng ng ; in tr s cc thng trn cc hnh .

7.16. Mch lc thng di loi k c tn s ct fC1=8 Khz, fC2= 12,5 Hz, in tr ti 850 (. Hy xc nh:

a) Cc thng s vt l ca mch lc.

b) V s hnh , hnh T v hnh ( ca mch lc, in trn hnh v tr

s cc thng s vt l ca mch. c) H s suy gim c tnh cc tn s 5 Khz v 20 Kz.

d) H s pha c tnh cc tn s 5 Kz, 9 Khz, 11,111 Khz v 20 Khz.

e) Tng tr c tnh cc tn s 9 Khz v 11,111 Khz

7.17. Cho mch lc hnh 7.14.

a) y l mch lc loi g,ti sao?

b) V s hnh hnh ( tng ng ca mch lc v in trn tr s cc thng s vt l ca mch lc trn .c) Tnh h s suy gim c tnh cc tn s 4,5 Khz v 16,082 Kz.

d) H s pha c tnh cc tn s 4 Kz, 7,5 Khz, 9,65 Khz v 18,092Khz.

e) Tng tr c tnh cc tn s 7,5 Khz v 9,65 Khz.

7.18. Mch lc di chn loi k c in tr danh nh l 1000 (, cc tn s ct l 6,25 Khz v 10,24 Khz.a) Cc thng s vt l ca mch lc.

b) V s hnh , hnh T v hnh ( ca mch lc, in trn hnh v tr s cc thng s vt l ca mch. c) V nh tnh dng c tnh bin tn s aC v pha tn s bC (theo l thuyt). d) Tnh h s suy gim c tnh cc tn s 7,5 Khz v 8,533 Kz.

e) Tnh h s pha c tnh cc tn s 4 Kz; 7,5Khz; 8,533 Khz v 16 Khz.

7.19. Mch lc thng thp loi m hnh T c m=0,5; kt cu ni tip, c to t mch lc loi K tng ng c in tr danh nh R0 =1000(, tn s ct fC=1Khz

a) Tnh cc thng s vt l ca mch lc

b) V s mch lc v in tr s cc thng s mch trn s . c) Tnh tn s t bin (( ca c tnh bin tn s (tn s c aC ( ( ) d) Tnh suy gim c tnh tn s 1100 Hz v 1160 Hz

7.20. Mch lc thng thp loi m hnh T c m=0,5, kt cu song song, c to t mch lc loi K tng ng c in tr danh nh R0 =1000(, tn s ct fC=1000 Hz

a) Tnh cc thng s vt l ca mch lc

b) V mch lc v in tr s cc thng s mch trn s

c) Tnh tn s t bin (( ca c tnh bin tn s (tn s c aC ( ( ) d) Tnh suy gim c tnh tn s 1100 Hz v 1160 Hz

7.21. Vi mch lc hnh 7.15

a) y l lc loi no?Ti sao?

b) Tnh tn s ct ca mch lc.

c) tnh h s suy gim aC ca mch lc in vo bng 7.1, t v th tng ng. (Nn lp trnh tnh theo cng thc 7.40). Bng 7.1

( rad/s0102030405060708090100

aC nepe

7.22. Cho mch lc hnh 7.16

a) y l mch lc loi no,ti sao?

b) Xc nh cc tn s ct ca mch lc.

c) Tnh h s suy gim aC ca mch lc in vo bng 7.2, t v th tng ng.

Bng 7.2

(rad/s0255075100125150175200225250275300

aCnepe

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Hnh 7.3

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