S dng ng h vn nngBi 1 : Hng dn s dng ng h vn nng1. Gii thiu v ng
h vn nng ( VOM)ng h vn nng ( VOM ) l thit b o khng th thiu c vi bt
k mt k thut vin in t no, ng h vn nng c 4 chc nng chnh l o in tr, o
in p DC, o in p AC v o dng in.u im ca ng h l o nhanh, kim tra c
nhiu loi linh kin, thy c s phng np ca t in , tuy nhin ng h ny c hn
ch v chnh xc v c tr khng thp khong 20K/Vol do vy khi o vo cc mch
cho dng thp chng b st p.2. Hng dn o in p xoay chiu.S dng ng h vn
nng o p ACKhi o in p xoay chiu ta chuyn thang o v cc thang AC,
thang AC cao hn in p cn o mt nc, V d nu o in p AC220V ta thang AC
250V, nu ta thang thp hn in p cn o th ng h bo kch kim, nu thanh qu
cao th kim bo thiu chnh xc.* Ch ch :Tuyt i khng thang o in tr hay
thang o dng in khi o vo in p xoay chiu => Nu nhm ng h s b hng
ngay lp tc ! nhm thang o dng in, o vongun AC => s hng ng h nhm
thang o in tr, o vo ngun AC=> s hng cc in tr trong ng h* Nu
thang o p DC m o vo ngun AC th kim ng h khng bo , nhng ng h khng nh
hng . thang DC o p AC ng h khng ln kimtuy nhin ng h khng hngBi 2 :
Hng dn o in p mt chiu (DC)1. Hng dn o in p mt chiu DC bng ng h vn
nng.Khi o in p mt chiu DC, ta nh chuyn thang o v thang DC, khi o ta
t que vo cc dng (+) ngun, que en vo cc m (-) ngun, thang o cao hn
in p cn o mt nc. V d nu o p DC 110V ta thang DC 250V, trng hp thang
o thp hn in p cn o => kim bo kch kim, trng hp thang qu cao =>
kim bo thiu chnh xc.Dng ng h vn nng o in p mt chiu DC* Trng hp sai
thang o :Nu ta sai thang o, o p mt chiu nhng ta ng h thang xoay
chiu th ng h s bo sai, thng thng gi tr bo sai cao gp 2 ln gi tr thc
ca in p DC, tuy nhin ng h cng khng b hng . sai thang o khi o in p
mt chiu => bo sai gi tr.* Trng hp nhm thang o Ch ch : Tuyt i
khng nhm ng h vo thang o dng in hoc thang o in tr khi ta o in p mt
chiu (DC) , nu nhm ng h s b hng ngay !!Trng hp nhm thang o dng
inkhi o in p DC => ng h s b hng !Trng hp nhm thang o in tr khi o
inp DC => ng h s b hng cc in tr bn trong!Bi 3 : Hng dn s dng
thang o in tr1. Hng dn o in tr v tr khng. Vi thang o in tr ca ng h
vn nng ta c th o c rt nhiu th. o kim tra gi tr ca in tr o kim tra s
thng mch ca mt on dy dn o kim tra s thng mch ca mt on mch in o kim
tra cc cun dy bin p c thng mch khng o kim tra s phng np ca t in o
kim tra xem t c b d, b chp khng. o kim tra tr khng ca mt mch in o
kim tra i t v bng bn dn.* s dng c cc thang o ny ng h phi c lp 2 Pn
tiu 1,5V bn trong, x dng cc thang o 1Kohm hoc 10Kohm ta phi lp Pin
9V.o in tr : o kim tra in tr bng ng h vn nng o tri s in tr ta thc
hin theo cc bc sau : Bc 1 : thang ng h v cc thang o tr, nu in tr nh
th thang x1 ohm hoc x10 ohm, nu in tr ln th thang x1Kohm hoc
10Kohm. => sau chp hai que o v chnh trit o kim ng h bo v tr 0
ohm. Bc 2 : Chun b o . Bc 3 : t que o vo hai u in tr, c tr s trn
thang o , Gi tr o c = ch s thang o X thang oV d : nu thang x 100
ohm v ch s bo l 27 th gi tr l = 100 x 27 = 2700 ohm = 2,7 K ohm Bc
4 : Nu ta thang o qu cao th kim ch ln mt cht , nh vy c tr s s khng
chnh xc. Bc 5 : Nu ta thang o qu thp , kim ln qu nhiu, v c tr s cng
khng chnh xc. Khi o in tr ta chn thang o sao cho kim bo gn v tr gia
vch ch s s cho chnh xc cao nht.Dng thang in tr o kim tra t in Ta c
th dng thang in tr kim tra phng np v h hng ca t in , khi o t in ,
nu l t gm ta dng thang o x1K ohm hoc 10K ohm, nu l t ho ta dng
thang x 1 ohm hoc x 10 ohm.Dng thang x 1K ohm kim tra t gm Php o t
gm trn cho ta bit : T C1 cn tt => kim phng np khi ta o T C2 b d
=> ln kim nhng khng tr v v tr c T C3 b chp => kim ng h ln = 0
ohm v khng tr v.Dng thang x 10 ohm kim tra t ho trn l php o kim tra
cc t ho, t ho rt t khi b d hoc chp m ch yu l b kh ( gim in dung)
khi o t ho bit chnh xc mc hng ca t ta cn o so snh vi mt t mi c cng
in dung. trn l php o so snh hai t ho cng in dung, trong t C1 l t mi
cn C2 l t c, ta thy t C2 c phng np yu hn t C1 => chng t t C2 b
kh ( gim in dung ) Ch khi o t phng np, ta phi o chiu que o vi ln
xem phng np.Bi 4 : Hng dn o dng in v c ch sHng dn o dng in bng ng h
vn nng. Cch 1 : Dng thang o dng o dng in bng ng h vn nng, ta o ng h
ni tip vi ti tiu th v ch l ch o c dng in nh hn gi tr ca thang o cho
php, ta thc hin theo cc bc sau Bc 1 : t ng h vo thang o dng cao nht
. Bc 2: t que ng h ni tip vi ti, que v chiu dng, que en v chiu m .
Nu kim ln thp qu th gim thang o Nu kim ln kch kim th tng thang o,
nu thang o thang cao nht th ng h khng o c dng in ny. Ch s kim bo s
cho ta bit gi tr dng in .Cch 2 : Dng thang o p DCTa c th o dng in
qua ti bng cch o st p trn in tr hn dng mc ni vi ti, in p o c chia
cho gi tr tr hn dng s cho bit gi tr dng in, phng php ny c th o c cc
dng in ln hn kh nng cho php ca ng h v ng h cmg an ton hn.Cch c tr s
dng in v in p khi o nh th no ? * c gi tr in p AC v DCKhi o in p DC
th ta c gi tr trn vch ch s DCV.A Nu ta thang o 250V th ta c trn vch
c gi tr cao nht l 250, tng t thang 10V th c trn vch c gi tr cao nht
l 10. trng hp thang 1000V nhng khng c vch no ghi cho gi tr 1000 th
c trn vch gi tr Max = 10, gi tr o c nhn vi 100 ln Khi o in p AC th
c gi tr cng tng t. c trn vch AC.10V, nu o thang c gi tr khc th ta
tnh theo t l. V d nu thang 250V th mi ch s ca vch 10 s tng ng vi
25V. Khi o dng in th c gi tr tng t c gi tr khi o in pTrc khi o cn
lu Khng o trong mch, v cc linh kin xung quanh hoc cc in p xung
quanh s gy ra sai s.Nu in p trong mch ln qu s lm hng VOM.Que o phi
tip xc tht tt vi chn linh kin. Nu cn th co nh chn linh kin.Khi o in
tr ln (c hng trm kohm tr ln) th khng ng tay vo que o hay chn linh
kin. in tr ca tay bn s gy sai s.Trc khi o phi chp 2 que o kim tra v
0.-Cn mt ch na:ng bao gi thang o in tr hay thang o dng in khi o vo
in p xoay chiu,nu nhm th chun b sa + o in tr: c 4 mc X1 ng o in tr
=< 500 OmhX10:=< 1000 OmhX100:=< 5000 OmhX1K: =<
100.000 Omh+ o in p xoay chiu:Chn thang o ACV (chn thang o ln hn in
p cn o mt nc)*Ch : nhm thang o in tr, o vo ngun AC cc in tr trong
ng h s hng- thang DC o p AC ng h khng ln kim tuy nhin ng h vn OK +
o in p 1 chiu (DCV): Khi o t que vo cc dng (+) ngun, que en vo cc m
(-) ngun, thang o cao hn in p cn o mt nc*Ch : Cng khng nhm ng h vo
thang o dng in hoc thang o in tr khi ta o in p mt chiu (DC).Nu nhm
th li chun b...-Chn nhm thang o in tr khi o in p DC th cc R bn
trong s hng+ o dng mt chiu DCA : o dng mt chiu cn tnh ton trc da
trn k thut mch (thng ngi ta bit l khong bao nhiu),ri mc ni tip ng h
vo mch.Nu bn khng c nhiu kinh nghim th nn hc t t (sm mun g cng phi
hng mt ln).Ngoi ra cn c mt s loi ng h hin i hn(c th hin th gi tr m
khi o ngc que o m khng s hng ng h,c cc l cm KT tranistor &
t...vn vn & vn vn. y l mt s hiu bit qua ca mnh (c ch no khng ng
cc bn no bit ri sa h)Nhng bit s dng ng h mi l bc u tin ,cn phi bit
thuc tnh,cch o ca linh kin,th mi o c.Lc no rnh mnh s bo cch o v kim
tra nhng linh kin m mnh bit n.Chc thnh cng!By gi th ny,bn mun bit
cch c tr s ng khng? Bn c lm nh sau,ri t suy lun,ch khng trc tip th
kh din t lm:+ o in tr:Trc khi o in tr phi bit cch c vch mu v d bn
kim mt con 4,7KOhm c mu (vng,tm,,nh vng) con ny c sai s 0.1% bn chn
thang o ph hp vi n.Thang o X100 l ph hp ng khng?o v nhn xem trn ng
h kim ng v tr no c logic ph hp vi mc ny.Nu cha ngh ra li ly mt con
in tr khc.Kiu g bn cng tm ra cch c thi +o in p xoay chiu(hnh 2):nhn
khu vc ACV(Alternating current voltage) chn thang 250 kim mt ci
Lioa c vi mc in xoay chiu(100V,110V,220V) o th +o in p 1 chiu(tng
t):chn DCV kim Pin,Acqui...chn thang o ln hn in p bn cn o....+o dng
mt chiu (hnh 1)Tm li c o i ri s bit cch c.Nhng nh phi ng cc qui tc
post ln trcCc ghi nhn khc qua s dng ng h kim (SUNWA YX-360TR)-
thang o in tr, u dng ca ngun pin trong ng h c a ra que o mu en v u
m ca pin c a ra que o mu . Thang o tr s in tr cng nh cho dng ra cng
ln. ng dng cp dng th LED, DIOD bit sng, cc tnh.- Khi thang o VAC o
in p DC, c 2 kh nng xy ra :1/ Kim khng ln2/ Kim ln cao hn so vi tr
s in p tht Gii thch 2 trng hp ny nh sau. thang o VAC, ng h c ni tip
vi 1 diod chn b 1 bn k ca in xoay chiu, o ly in p trung bnh trong
bn k cn li, nhng c tnh ton b li a tr s hiu dng y ra kim ch th. Trng
hp 1, khi t 2 que o sao cho in p DC cn o b diod phn cc nghch th kim
s khng ln. Trng hp 2, khi o 2 u que o, diod phn cc thun cho in p DC
qua y (khng b mt 1 bn k nh in AC) nn khi c b th kim ln cao khong gp
2 ln.- thang o VAC, gi que o mu en l cm (-COM), di que o mu t l cm
(+) sang l cm (OUTPUT) o tn hiu xut m.Chn (OUTPUT) c ni vi chn (+)
qua 1 t nh, t ny ni tip vi mch o VAC nn s loi b DC trong tn hiu hn
hp (AC cng vi DC, hay DC c bin thay i) ly ring ra o tn hiu AC i
xng.1 cht kinh nghimV ng h o kim nh mnh cng c mt ci .Nn mnh cng c
bit cht t v cch dng :+ o ohm :Bn nhp hai que o li v sau chnh bin tr
cho kim ch th v s 0 Sau bn t 2 que o ln 2 chn in tr v o + o Vn :o
AC :Chn thang o ACV (chn thang o ln hn in p cn o mt nc)*Ch : nhm
thang o in tr, o vo ngun AC cc in tr trong ng h s hngO DC : Khi o t
que vo cc dng (+) ngun, que en vo cc m (-) ngun, thang o cao hn in
p cn o mt nc*Ch : Khng nhm ng h vo thang o dng in hoc thang o in tr
khi ta o in p mt chiu (DC). Khng thang o DC o AC . V nh th ng s b h
+ o A : a s cc ng h vn nng u o dc cng dng in rt thp > Do ,khng
dng ng h ny o pin , cquy, My o VOM l Con-Mt nhn vo mch in ca ngi th
in t. My o VOM (o c Volt - Ohm - Milliampere) l mt dng c bt kh ly
thncangi thint, quamyoanngny,chngtabitc cng dng in chy vo - chy ra
trn cc chn ca cc linh kin, bit c mc p cao thp trn cc ng mch. Tuy
nhin, c th khai thc ht cng nng ca loi my o ny, chng ta phi hiu tht
tng tn cu to mch in bn trong ca n. Qua bi vit ny,mong rng Bn s nhn
thy c vai tr rt quan trng ca loi my o thng dng ny. Ch vi mt my o
VOM thi cng cho Bn thm him vo ch su nhtca cc mch in. Bn xem hnh.
Trong bi ny, chng ti tp trung ni v chc nng o Ohm ca my o VOM SUNWA
(YX960TR hay YX-360). Bn xem s mch in: Khi Bn dng VOM chc nng Ohm
k, lc Bn s s dng dng in t ca ngun pin 3V gn trong my o bm dng in
cho qua cc vt o m Bn ang t trn hai dy o. S mch in cho thy dng in t
chy ra trn dy o mu , v chy vo dy o mu en v ri s chy qua in tr thang
o (RTD), y ngi ta t mt volt k c mc o p ti a 3V o mc p xut hin trn
in tr RTD, v ty theo gc lch ca kim trn bng chia vch Ohm, Bn tnh ra
tr s in tr ca vt c o. Mi khi Bn thay i thang o th trong mch in s
cho thay i tr s ca in tr thang o RTH. Chng ta thy (Bn xem hnh). -
thang o Rx1: in tr thang o RTH=20 Ohm- thang o Rx10: in tr thang o
RTH= 200 Ohm.- thang o Rx100 in tr thang o RTH=2K Ohm.- thang o
Rx1K. in tr thang o RTH=20K Ohm. Khi o Ohm Bn c th c kt qu trn 3
vch chia c trn mt my o: - Vch chia LV: Trn vch chia ny, Bn bit c mc
p gim trn vt o t trn 2 dy o.- Vch chia LI: Trn vch chia ny, Bn bit
c mc dng chy qua vt o.- Vch chia Ohm: Trn vch chia ny, Bn xc nh c
sc cn dng ca vt o.
Bn thy, thang o Rx1, nu Bn chm hai dy o li, dng in chy trong mch
s ln nht v bng 150mA (con s ny c ghi trn thang o Rx1).
Bn thy, thang o Rx10, nu Bn chm hai dy o li, dng in chy trong
mch s ln nht v bng 15mA (con s ny c ghi trn thang o Rx10).
Bn thy, thang o Rx100, nu Bn chm hai dy o li, dng in chytrong
mchs lnnht v bng 1.5mA(cons nycghi trn thang o Rx100).
Bn thy, thang o Rx1K, nu Bn chm haidy o li, dng in chytrong mchs
lnnht v bng 150A(consnycghi trn thang o Rx1K).
Qua phn tch trn, chng ta rt ra c cc iu cn nh khi dng loi Ohm k
YX-960TR. l:
iu cn nh 1: Sc p ca in p trn hai dy o ca my o Ohm ny l 3V (do
trong my dng 2 pin 1.5V).iu cn nh 2: Dng in t lun chy ra trn dy v
chy tr vo qua dy en.iu cn nh 3: Khi Bn ly thang o Ohm nh S C DNG
CHY TRN DY O LN V NGC LI.iu cn nh 4: C th xc nh mc p gim trn vt o v
cng dng in t chy qua vt o khi c kt qu trn vch chia LV v LI.iu cn nh
5: Vch chia theo vch Ohm trn in k xc lp theo t s V/I (theo lut
Ohm).iu cn nh 6: Ch thang o Rx10K, in p trn dy o lc ny s l 12V. Dng
Ohm k kim tra cc linh kin c trn my in thoi di ng. Chng ta thy cc
linh kin trn board mch in ca cc my in thoi di ng u rt nh, nh li-ti,
nn trc ht Bn phi cho thay u hai cy o bng hai cy kim may (ly loi kim
may bao ln), Bn xem hnh. Bn gn kim may vo u dy o, loi kim may ny rt
cng v c u kim rt nh nhn nn rt tin dng o cc linh kin nh trn board
mch, nht l o trn cc chn ca cc IC. Dng u kim nh Bn d dng cho u kim
qut qua cc hng chn tm n cc chn cn o.
Khi dng Ohm k KIM TRA CC LINH KIN TRN BOARD MCH IN, BN LUN NH
DNG IN T T CC M CA PIN 3V GN TRONG MY O s bm dng ra trn dy mu , v
sau khi chy qua cc b phn trong mch, dng in t s b ht vo dy o mu en v
chy v cc dng ca pin. Dng in ny khi chy qua in tr thang o s lm lch
kim trn bng chia vch ca mt Volt k. Kt qu o s c c trn 3 vch chia, l
vch chia LV ( bit p c trn hai dy o), LI ( bit dng chy ra chy vo cc
chn ca vt o) v vch chia Ohm ( bit sc cn dng ca mch v vt o). Sau y l
cc th d: Qg o in tr, nhit tr, t in, cun cm. Bn xem hnh: Dng Ohm k o
tr s ca cc in tr. Trc ht, Bn ly thang o Rx1K, chp hai dy o, chnh
kim v ngay vtr 0 Ohm. Khi o, dng in ca ngun pin 3V trong my o s bm
dng ra dy , dng qua in tr Rx=10K tr vo dy en, kim s ln ch ngay vch
s 10, v in tr ang o l 10K. Kt lun: in tr tt. Dng Ohm k o cc nhit
tr. t nhit tr RTH vo hai dy o, dng in chy qua nhit tr, c ktqu trn
vch chia Ohm. 25 C, kim s ch 47K. Bn th lm nng nhit tr RTH, Bn thy
g? Kim trn vch chia Ohm s gim dn, iu ny cho thy nhit tng lm cho ni
tr ca nhit tr gim xung (do Bn ang o l loi nhit tr m). Du hiu ny cho
bit nhit tr tt. Dng Ohm k kim tra tnh r in ca cc t in. Khi o t in
ho hc, Bn nh t cc dng ca t ho phi trn dy en, khi t t ln hai dy o,
dng in t ca ngun pin 3V s cho np dng vo t in, thi im u, dng np rt
mnh, kim bc ln cao, kim s gim dn v v tr v cc khi t np y p (3V). Vic
chn thang o: Nu Bn ly thang o ln, in tr thang o ln,dng chy trn dy o
nh, thi gian t np y s lu hn, kim tr v vtrvccchm. Nu Bnly
thangonh,thigian tnpys nhanh, kim v v cc rt nhanh. Do vy, khi kim
tra cc t in c in dung nh, BN PHI LY THANG O LN KP THY C DNG NP VO
T. KIM LN KHNG V: T CHM. KIM LN V KHNG HT: T R. KIM KHNG LN: T T.
_g o Diode, Led, Led hng ngoi. Diode l mt van in. Khi phn cc thun s
cho dng chy qua. V khiphn cc nghch, diode ng, ct dng. Khi o diode,
nn ly thang o Rx1 c dng chy trn dy o ln. Khio cc linh kin thuc nhm
bn dn Bn c kt qu trn: - Vch chia LV bit diode ghim p my volt (thng
l 1V dng ln, thang o Rx1).- Vch chia LI bit cng dng in chy qua
diode (thng vichc mA). Ch : Trong cc my in thoi di ng, do ngun nui
thp, nn ngita thng dng loi diode Schottky, c im ca diode Schottky l
ghim mc p rt thp ( thang o Rx1, dng ln, mc p ngang diode Schottky
ch gn 0.3V). LED cng l mt diode. (1) Khi phn cc thun s c dng chy
qua Led v Led pht sng. (2) Khi phn cc nghch, Led ng, ct dng v khng
sng. Khi o Led nn ly thang o Rx1 c dng trn dy o ln. Lc ny Bn c kt
qu trn vch chia LV bit Led gi li my Volt v c trn vch chia LI bit
cng dng in ang chy qua Led l bao nhiu. Bn hy th cho i thang o Ohm.
Bn thy g? Khi Bn ly thang o Ohm cng ln, in tr thang o trong mch ln
, dng chy trn dy o lc ny s nh v Led s sng m. Khi Bn o cc linh kin
thuc nhm bn dn, Bn c kt qu trn thang o Ohm khng c nhiu ngha, vcc
linh kin bn dn c tnh phi tuyn tnh, nn tr s Ohm thay i theo cng dng
in, vy mi thang o, Bn s c c mt tr s Ohm khc nhau. O LINH KIN BN DN
BN CH CN BIT MC VOLT GIM TRN VT O (C KT QU TRN LV) V DNG CHY QUA VT
O (C KT QU TRN LI). Kim tra Led hng ngoi, cch o cng tng t nh cch o
cc Led chiu sng. Lc phn cc thun, c dng, kim ln. Khi phn cc nghch,ct
dng, kim khng ln. Vi Led hng ngoi (IR Led), khi c dng chy qua Led,
kim ln, Led pht ra nh sng hng ngoi, mt thng khng th thy c loi nh
sng ny. Led hng ngoi thng c dng trao i d liu vi cc my in thoi khc.
Khi o Led hng ngoi, Bn c kt qu trn vch chia LV ( bit mc ghim p trn
Led), v trn vch chia LI ( bit cng dng in ang chy qua Led). g o
motor rung. kim tra hot ng ca mt motor rung, Bn ly thang o Rx1 c
dng chy trn dy o ln (DNG IN TI A L 150MA). T MOTOR LN HAI DY O.
MOTOR S C CP DNG V S QUAY. LC NY HY C KT QU TRN VCH CHIA LV BIT MC
P TRN MOTOR V C KT QU TRN VCH CHIA LI BIT CNG DNG IN CHY QUA MOTOR.
MOTOR RUNG THNG LM VIC MC DNG 100MA V MC P GIM NGANG MOTOR L 1V.
NUBNKIMTRAMOTORRUNGTHANGORX10,KIMOCLNCHOBITC
DNGCHYQUAMOTOR(MOTORKHNGHMCH),NHNGMOTORKHNGQUAYVDNG LY RA THANG O
RX10, TI A CH C 15MA, KHNG LN LM QUAY CC MOTORRUNG.
THANGORX1,KHIBNOHAIDYO,MOTORRUNGSQUAYNGC CHIU. +g o Loa. Trong cc
loa loi in ng lun c mt cun dy (gi l coil), cun dy gn trn mt mn
rung, Bn dng thang o Rx1 ( ly dng ln), cp dng cho cun dy, cun dy s
tr thnh mt nam chm in, lc ny cun dy s tng tc vi mt nam chm vnh cu
(gn trn loa) v lm rung mn loa, pht ra ting ku rt rt. Du hiu ny cho
bit loa cn tt.Nu Bn th thang o Rx10 dng in trn d o nh hn, m vn cn
nghe loa ku, l loi loa nhy. Tr khng ca loa in thoi thng l 20 Ohm.
Khi o thang Rx1, thy kim ln m mn loa khng rung, cun coil bkt. Cun
coil rt ra khng dnh vo mn loa, loa s ku rt yu. Loa bqu cng sut s b
r. Loa gn khng cht vo v my cng s pht ra ting b r. g o Microphone.
Micro dng ccmyin thoidingthngl micro in dung. Trong micro in dung
lun c mt transistor FET nh. LOIMICRONYCNCPDNGPHNCCMITORACTNHIU.
CHNS (SOURCE) CA FET S CHO LY DNG VO TNG MASSE, DNG CHY RA TRN CHN
DRAIN V CHY V NGUN DNG. DO KHI DNG OHM K KIM TRA MICRO,BN T DY TN
CHN S, DY EN TRN CHN D (CHNG TA BIT, DY ENNIVOCCDNGCAPIN).
LCNYSCDNGCHYQUAKNHDNCA TRANSISTOR FET, KIM S LN. BN HY THI MNH VO
MICRO, LM RUNG MNG TNH IN, NU KIM O C DAO NG NH L MICRO TT. g
oTransistor, quangtransistor, transistor MOSFET. o transistor nh
cc: Transistor nh cc c hai mi ni PN, quen gi l transistor bipolar.
N c 2 loi, transistor NPN v transistor PNP. Bn c th dng mt Ohm k
kim tra cc loi transistor bipolar. Trnh t thng lm l: (1) Hy tm chn
B. Bn ly thang o Rx1, tm o trn hai chn ca transistor, o chiu ny kim
khng ln, ri cho o dy o kim cng khng ln, Bn kt lun haichn ang o l
chn E (Emitter, chn phun dng) v chn C (Collector,chn thu gom dng),
vy chn cn li chnh l chn B (Base, chn nn)ca transistor. (2) Hy kim
tra hai diode ca mi ni B-E vB-C.
TRANSISTORTNGNGNHHAIDIODE,NNVICKIMTRAMTTRANSISTOR TT/XU L KIM TRA
HAI DIODE (B-E V B-C). VI TRANSISTOR NPN, NU DY EN (C TNH HT DNG) T
TRN CHN B, DY (C TNH BM DNG) NM TRN CHN C. KIM PHI LN DO MI NI PHN
CC THUN V DY T TRN CHN E, KIM CNGLN (CNG DO C PHN CC THUN). NGC LI,
T DY TRN CHN B, DY EN O TRN CHN C, RI O QUA CHN E, KIM U S KHNG LN,
V DIODE B PHNCC NGHCH.
Ch : Vi cc transistor loi PNP th kt qu o s ngc li. Ngha l dy
TRNCHNB,DYENTRNCHNE,RITRNCHNC,KIMSLNDO PHN CC THUN V DY EN TRN CHN
B, DY TRN CHN C, RI CHN E,KIM PHI KHNG LN V PHN CC NGHCH. Hnh v trn
cho thy, dy en trn chn B (cho ht dng ra chn B),dy trn chn E (cho bm
dng vo trn chn E), kim ln v lc ny diode B-E ang phn cc thun. Nu t
dy trn chn B, ly dy en t ln chn E, diode phn cc nghch, kim khng ln
v dy en trn chn C, kim cng phi khng ln. (3) Hy xc nh chn E v chn C.
Chng ta bit, minibn dn B-C chu volt nghch cao (thng trn 60V), trong
khi mi ni B-E chu volt nghch thp (thng khong 9V). Do , Bn hy ly
thang o ohm Rx10K, lc ny trn dy o s c 12V (t ngun pin 9V + vi ngun
pin 3V), dng mc p ny o nghch trn mi ni B-C (kim s khng ln) v o
nghch trn mi ni B-E, kim s ln,v sao c khc bit ny? v mi ni B-E chu p
9V b nh thng mc p 12V ca my o. Qua du hiu ny Bn d dng xc nh c chn C
v chn E. (4) Hy xc nh li dng in ca transistor. Bn ly thang o ohm
Rx10, chp hai dy o, chnh kim v vch 0 Ohm. Cm transistor C1815 vo ng
chn C, B, E ca 3 l cm NPN trn my o. Kim ln, Bn c kt qu trn vch chia
HEF. Kim ch 200, c ngha l li dng in ca transistor 2SC1815 l 200 ln
(n c ngha dng in IC chy ra trn chn C ln hn dng in IB chy ra trn chn
B l 200 ln). Tham s HFE cn gi l h s beta ca transistor. Vi
transistor PNP cng lm tng t, cm transistor vo 3 chn C, B, E ca b
chn cm PNP v c kt qu trn vch chia HFE, Bn s bit c li dng in HFE ca
transistor. o quang transistor: Quang transistor l linh kin bn dn 2
chn, chn E cho ly dng (dng chy vo chn E), dng chy ra trn chn C, khi
Bn cho nh sng kch thch vo vng B ca transistor, khi mc sng yu,
transistor dn in yu v khi cng nh sng mnh th quang transistor s dn
in mnh hn. Vy o mt quangtransistor, Bn t quang transistor trn hai
dy o (Bn xem hnh). Khic nh sng rivo quang transistor, n s dn in,
kim s ln,cng sng cng mnh, kim ln cng cao (ngha l dng chy qua
quangtransistor cngln). Tronginthoi di ng, ngi tadng quang
transistor trao i tn hiu bit dng tia sng hng ngoi. o transistor
MOSFET: Transistor MOSFETthngdnglmkhoinbndnngm nhanh, Bn thng gp
loitransistor ny cc b adaptor DC dng np li in cho pin. Cch o loi
transistor MOSFET nh sau: Trong transistor MOSFET dng lm kho in ng
m nhanh thng c thm diode dp in p ngc. Dng in chy vo trn chn Source
v chy ra trn chn Drain, c dng in ny, chn Gate cn c in pdngphncc.
Dokhi dngOhmkokimtraloitransistorny. Trcht, BnhylythangoohmRx1,
othun nghch trn hai chn xc nh diode D v qua s bit c chn Source v
chn Drain. Nu dy nm trn chn Source v dy en trn chn Drain, Bn s
thy:KIM KHNG LN, NGHA L TRONG KNH DN IN LOI P GIA VNG GING SOURCE V
GING DRAIN CHA XUT HIN CC HT IN T DO (BN XEM HNH). LC NY, BN HY CHO
DY EN CHM NH VO CHN GATE,V T LI DY EN TRN CHN DRAIN, BN S THY KIM
LN. V SAO? V BN CHONPINPDNGVOCHNGATEVLCNYTRONGVNGGIAGING SOURCE V
GING DRAIN C HT MANG IN, NN KNH DN IN. g o cc IC. IC (Intergrated
Circuit) l cc mch in tch hp, cu to ca IC c bn l cc cht bn dn, mun
bm c dng in chy qua cc mi nibn dn (vn c ro p l 0.6V) trong cc IC,
Bn phi dng Ohm k loikim (vn c in p trn hai dy o l 3V). Vy kim tra
mt IC, trc ht Bn hy chn mt chn ca IC, cho bm dng vo chn ny (t dy mu
LN CHN IC CHN), V CHO HT DNG RA TRN MT CHN KHC VI DY O MU EN, NU
KIM LN L C DNG, DNG IN NY CHY QUA CU TRC BN TRONG CA IC. DNG PHP O
I CHNG CC MCH IN CNG LOI, CC IC CNG LOI BIT IC ANG KIM TRA TT XU. g
Kim tra bn phm. Th d 1:HYKIMTRAIC MYTNHTHNGQUACCHOOHMTRNCCIM NG CA
MCH IN BN PHM. TRONG CC MY IN THOI DI NG, NGI TA LY NHIU CHN CA IC
MY TNH LPTHNH BNG MA TRN, GM CC HNG (ROW) V CC CT (COLUMN). TRN BNG
MA TRNBNPHMNYGNCCNTNHN,CNGDNGCANLSLMCHMMTHNGVIMTCTVQUADUHIUNYSCIC
MYTNHGIIMTMRANIDUNG CA PHM NHN RI CHO CHP HNH. NGI TA DNG BN PHM
NHP LNHV NHP D LIU VO KHI MY TNH. Bn ly Ohm k chn thang o Rx100, dy
chm vo ng masse (Cho bm dng vo ng masse). By gi cho dy en ln lt chm
vo cc im ng ca ma trn bn phm, kim ln l c dng in chy ra trn mt chn
ca IC. Dng cch kim tra ny, Bn s bit c c h chn bn di IC khng, c t
mch khng. Hy so snh cc kt qu o c, nu thy cc s ohm o c u ging nhau l
mch in bn phm tt. Ghi nhn: Sau khi o ly mu trn mch in bn phm ca my
Nokia 8210, chng ti thy cc im o u c kt qu l 30K. wg Kim tra mn hnh.
Th d 2: Hy kim tra IC my tnh thng qua cch o Ohm trn cc im ng ca mch
in mn hnh. Trong cc my in thoi di ng, ngi ta dng cht tinh th lng to
ra cc nh im sp trn mt mn hnh v dng cc nh im ny in ra cc hnh nh.
Chng ta bit, khi tinh th lng bkch thch, n s che sng v cho ra mt im
en hay mt im mu (R, G, B), khi khng bkch thch th cht tinh th lng
khng che sng, trong sut. Ngi ta ch to chip mch in iu khin mn hnh v
dn chip mch in ny bn di mn hnh (k thut COG). to kt ni gia board mch
in v chip mch in mn hnh, trn board mch in dng cc di tip im hay dng
b ni nhiu dy. Nh vy, mch in mn hnh s c nhiu chn kt nivikhimy tnh,
do Bn c th dng mt Ohm k loi kim c in p trn dy o l 3V kim tra cc ng
mch v kim tra cu trc bn trong ca chip IC. Cch o nh sau: Bn hy ly
Ohm k, ly thang o Rx100, dy t trn ng masse (cho bm dng vo board mch
in qua ng masse). Dy en t trn cc chn ng ca mch in mn hnh ht dng in
ra. Nu kim ln, cho bit c dng in chy vo BN TRONG IC V CHY RA TRN CC
CHN CA IC. NU KIM KHNG LN L C T MCH HAY H CHN. Bn c th dng cch o ny
o ly mu trn cc board mch in ca cc my tt v sau ny dng cc tham s ny
so snh vi cc my h (cch o i chng), v qua tm ra kt lun nhanh v tnh
trng tthay xu ca my. Kt lun: i vi ngi th in t, my o VOM l con mt th
ba ca h, ngi th dng my o ny cng nh dng con mt sng nhn v cc board
mch v thy s vn hnh ca tt c cc b phn trong mch in, h cn thy dng in t
ang chy vo / chy ra trn cc chn ca linh kin, cn thy mc p cao / mc p
thp trn cc ng mch. Hin ny, ngi ta tm ra c 1001 cch s dng loi my o
ny. Khi no c dp chng ta s tr li ti ny. Cho! Ngi son, gio vin dy
ngh: Vng Khnh Hng
