... kớch dn t Vcc qua Q2->Q4-> mass, Vce/Q4 =25 V, lỳc ú, BJT Q4 s c kớch dn, o ỏp trờn BJT Q4, ta c Vbe/Q2=0.72V,Vce/Q2=0V=>BJT Q2 dn bóo hũa Q2 dn bóo hũa s to dũng t Vcc qua Q2=>ng c=>Q5=>mass S ... NEXTCOD1: JB COL2,NEXTCOD2 JNB COL2,$ SETB KEY INC VAL RET NEXTCOD2: EXIT2: JB COL3,EXIT2 JNB COL3,$ SETB KEY INC VAL INC VAL RET CLR KEY RET DOI_MA: E1: CJNE A,#11,E2 MOV A,#0 RET E2: RET KIEM_TRA: ... D R D I= E E V R E E 0,7 R = I =0 -Diot Zenner : R1 2 R2 1 VCC Iz = VR2 R2 = V1 VR1 R2 = Vz R2 + trờn : V1 l in ỏp mt chiu cha n nh V2 l in ỏp ly trờn ti n nh BJT : BIPOLAR JUNCTION TRANSISTOR...