VII. MACH TAO XUNG VUONG
www.Beenvn.comdan di~n kh6ng bang nhau Khi mai cap di~n se co mot Transistor diin di~n
dan di~n kh6ng bang nhau. Khi mai cap di~n se co mot Transistor diin di~n
m1.lnh han va m¢t Transistor dan di~n yeu han. Nha tac d.,lflg cua m1.lch h6i tiep duang lir C I ve BI va tit C2 ve B2 se lam cho Transistor da.n di~n m1.lnh han tien dAn den tr~ng thai bao hoa, Transistor dAn di~n yeu han tien dan den ngung dan.
Gii thiet TI dan di¢n m1.lnh han, tl,l CI duqc n1.lp di~n qua Re2 Him cho dong IBI tang cao nen TI tien den tr~ng thai b~o hoa.
Khi T, tien den tr~ng thai bao hoa lam cho lei tang cao va Vel ;::::< O,2V, tl,l C2 phong di~n qua T, va R h2. Khi tl,l C2 phong di~n, di~n ap am tren tl,l C2 dua vao cL!C ~ lam Transistor T2 nglffig dan. Thai gian ngung dan cua T2 chfnh la thai gian phong cua C2 qua Rh2.
Sau khi C2 phong xong, c,!c B2 11.li duqc ph:!n qrc nha Rh2 nen T2 dan bao hoa, lam cho VC2 ;::::< O,2V. Dieu nay lam cho tl,l C I phong di~n qua Rhl va di~n ap am tren C I dLIa ve TI lam cho TI ngung dan. Luc do tl,l C2 11.li duqc n~p di9n qua Rei lam cho dong IB2 tang cao va T2 tien t61 tf1.lng tha.i bao hoa nhanh.
Thai gian ngung dan cua TI chinh Ia thai glan tl,l CI phong di~n qua Rhl •
Sau khi t1:l C I ph6ng xong, cl!c B, l1.li duqc phan qlC nha R"I nen Transistor TI 11.li tfa ve tr<;tng thai dan bao hoa, nhu tf<.tng thai gia thiet ban dau. V~l qua ldnh nay duqc l~p di l~p l<;li m¢t cach tuAn hoan.
* D1.lng tin hi~u:
Xet Cl!C RI' khi TI bao hoa V BI ~ O,BV. Khi TI ngung dan cho tl,l CI phong di~n lam cho cL!C BI co di~n ap am khming - V co va di~n ap am nay giam dan theo ham so' mfi.
Xet cl!c C I, khi TI bao hoa Vel ;::::< O,2V. Khi TI ngung dan V CI ;::::< +V ce. D<;tng song tin hi~u ra 6 qrc C Ia d1.lng song vuong.
Tuang tl! khi xet cL!c B2 va Cb d<.tng song tfn hi~u 6 hai cl!c nay gio'ng v61 d1.lng s6ng tin hi¢u 6 CL!C BI va Cl!C C1 nhung dao pha nhau.
Chu ky cua tin hi~u xung vuong la: T=tl+t2
Trong do, tl la thai gian t1:l C I ph6ng di~n qua R"I tir di~n ap -V ce len::::; OV. VI tl,l CI ph6ng di¢n tu -Vee len nguon +Vee nen di~n ap tuc thm cua tl,l (lay muc -Vee lam g6c) la: VCI(t) = 2 Vee .exp(-t/RBI.C I).
Thai gian t) d~ t':l C I phong di~n qua R"I tu -V cclen OV cho biJi cong thuc: V cc = 2 V cc .exp(-tIJRRI·C I)·
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Suy ra: exp(t,iR".C,): 2
:> t,/ (RBI' C,): In 2
=:) tl= RBI- CI·ln 2;::; 0,69 RBI" C1
Tuang tty, thOi gian t2 de t~ C2 ph6ng di¢n qua RB2 ltT -V cc l~n OV Ia:
t2 ;;::< 0,69 RB2 " C2 VB' a,8V -Vee c, V +V cc VIP a,8V -Vee Vel +Vcc
Hinh 4.17. DCfng tin hi¢u mqch dao dqng da hili
Chu ky dao d<)ng hi:
T:::: tl + t2 = 0,69 (RBI' C] + Ra2-Cz)
t
t
t
t
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Trong m<.teh da hai d6i xung co: RBI = RB2 = RB va CI = C2 = C Khi do ehu ky dao d¢ng la:
T = 2. 0,69 . R,. C Tan s6 dao d(yng eua xung vuong 1a:
f = Iff = 1/0,69 (R". C, + R". C,) Neu la m;:teh da hai d6i xung thi: (adsbygoogle = window.adsbygoogle || []).push({});
f= Iff= 1/l,4R,C
2. Mach tao xung vuong dung Ie
Sau day ta se khao sat m¢t trong cae m;:tch dao d¢ng t<.to xung vu6ng la dao d¢ng tich thoat.
M,!-ch dao d¢ng tich thoat dung ffi'!-ch khueeh d,!-i thu~t toan d~ cho ra tin
hi~u vuong co sO do nhu sau:
* So do mach: R + Vee + - Vee R, R,
Hinh 4.18. Mqch dao dqng ticll tlwat dllng Ie
So do co hai m'.lch hoi tiep tir dau fa ve hai dau vaa. 01u phan ap RC hoi tiep ve dau vao dao In-, cau pharr ap RI - R2 hoi tiep ve dau vaa thu~rr 1/.
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De giilj thich nguyen ly cua m~ch, ta gia Slr tl.1 C chua fi<;l.P di~n va m~ch khuech d;;ti thu~t toan dang b tf~ng thai bao hoa duong, Vo = +Vcc. Luc nay, cUu phan ap R)-R2 dua di~n up duang ve d<i.u vaa thu~n I ~ yoi mue di~n ap la:
V • = + V C'" Rl = V ,
In "R[+R2 i
(V,,: > OV)
Trang khi do, dau vao dao I ~ co di¢n lip lang dan len tir av, di¢n ap tang do
tl.1 C n'olp qua R thea quy lu~t ham mil vai cae hang so thai gian T = RC.
Khi tl.) fi<;lP va co Von' < Vin+ thl m<;lch khucch d~i thU11 toan van 6 tr~ng
theE bao hoa duong. Khi tl.1 C n<;tp den mue di9fi ap Vin ' > V,/ thl m~ch
khuech d;:ti thu~t toan d6i thanh tf<;lng th,ii baa hoa am, dau fa co Vo = - Vcr:_ Luc nay, du pha.n ap Rl-R2 dua di¢n ap am ve dau vao thu~n 1,,- voi mue di¢n ap 13.:
(Vi,: < OV)
Trang khi d6, b dau VaG dao In" van con dang b mue di~n ap dUC1ng vai tf! s6 Vill -> + Vee. RJ (R , + R2), do tl.1 C con n~p di¢n. Nhu v~y, khueeh d~i thu~t
toan se ehuy~n sang tr~ng thai baa hoa am nhanh, eho qnh xung vuong th~ng dung. TI.1 C bay gio se phong di~n ap duang dang n~p tren tl,l qua di¢n tra R, va teU a dau ra xu6ng mat.
Khi tl,l C phong di¢n lip duong dang co thl VII\+ van b mue di¢n ap am nen khueeh d~i thu~t toan van b tr'!.ng thai baa hoa am. Khi tl.1 C da phong het di¢n ap duang thl se n~p di¢n qua R d~ eo di¢n ap urn dang eo, do diu ra dang b tr~ng thai baa hoa am. Chieu n~p di¢n bay gia nguqe vai ehieu dong
n~p tren.
Khi lI.J C n~p di¢n ap am den mue Vin-< Vi/ (di~n ap dau vao dio nha han di¢n ap dau vao thu~n) thl khueeh d~i thu~t toan l<.ti d6i thanh tr<.tng thai baa hoaduang vadau ra co Vo = +VCco
M~eh tra l'!.i gii thiet ban d<1u vu qua trlnh tren tiep tl.1e dien ra m¢t each tuan hoan.
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