1. Gii thiu v Mosfet Mosfet l Transistor hiu ng trng ( Metal Oxide Semiconductor Field Effect Transistor ) l mt Transistor c bit c cu to v hot ng khc vi Transistor thng thng m ta bit, Mosfet c nguyn tc hot ng da trn hiu ng t trng to ra dng in, l linh kin c tr khng u vo ln thch hn cho khuych i cc ngun tn hiu yu, Mosfet c s dng nhiu trong cc mch ngun Monitor, ngun my tnh .

Transistor hiu ng trng Mosfet 2. Cu to v k hiu ca Mosfet.

K hiu v s chn tng ng gia Mosfet v Transistor * Cu to ca Mosfet.

Cu to ca Mosfet ngc Knh N G : Gate gi l cc cng S : Source gi l cc ngun D : Drain gi l cc mng Mosfet kn N c hai ming bn dn loi P t trn nn bn dn N, gia hai lp P-N c cch in bi lp SiO2 hai ming bn dn P c ni ra thnh cc D v cc S, nn bn dn N c ni vi lp mng mng trn sau c du ra thnh cc G. Mosfet c in tr gia cc G vi cc S v gia cc G vi cc D l v cng ln , cn in tr gia cc D v cc S ph thuc vo in p chnh lch gia cc G v cc S ( UGS ) Khi in p UGS = 0 th in tr RDS rt ln, khi in p UGS > 0 => do hiu ng t trng lm cho in tr RDS gim, in p UGS cng ln th in tr RDS cng nh. 3. Nguyn tc hot ng ca Mosfet Mch in th nghim.

Mch th nghim s hot ng ca Mosfet Th nghim : Cp ngun mt chiu UD qua mt bng n D vo hai cc D v S ca Mosfet Q (Phn cc thun cho Mosfet ngc) ta thy bng n khng sng ngha l khng c dng in i qua cc DS khi chn G khng c cp in. Khi cng tc K1 ng, ngun UG cp vo hai cc GS lm in p UGS > 0V => n Q1 dn => bng n D sng. Khi cng tc K1 ngt, in p tch trn t C1 (t gm) vn duy tr cho n Q dn => chng t khng c dng in i qua cc GS. Khi cng tc K2 ng, in p tch trn t C1 gim bng 0 => UGS= 0V => n tt => T thc nghim trn ta thy rng : in p t vo chn G khng to ra dng GS nh trong Transistor thng thng m in p ny ch to ra t trng => lm cho in tr RDS gim xung .