Bipolar Junction Transistors BJT ECE 442 Power Electronics 1 BJT Cross SectionsECE 442 Power Electronics 2 Common Emitter NPN Transistor.
Reverse bias the CBJForward bias the BEJECE 442 Power Electronics 3 Input Characteristics Plot IB as f VBE VCE .
As VCE increases more VBE required toturn the BE on so that Looks like a pnjunction volt ampere.
characteristic ECE 442 Power Electronics 4 Output Characteristics Plot IC as f VCE IB Cutoff region off .
both BE and BCreverse biased Active region BE Forward biased BC Reverse biased.
Saturation region on both BE and BCforward biasedECE 442 Power Electronics 5 Transfer Characteristics.
ECE 442 Power Electronics 6 Large Signal Model of a BJTKCL IE IC IB F hFE IC IBIC FIB ICEO.
IE IB 1 F ICEOIE IB 1 F IE IC 1 1 F IE IC F 1 FECE 442 Power Electronics 7.
I E I B I C F hFE I C F I B I CEOI E I B 1 F I CEO I B F 1 1 F 1.
I E I C 1 I C F FI C F I E F F F 1 1 F.
ECE 442 Power Electronics 8 Transistor Operating PointVB VBEI C VCE VCC I C RC.
ECE 442 Power Electronics 9 DC Load LineECE 442 Power Electronics 10 BJT Transistor SwitchVB VBE.
VCE VCC I C RCVCE VCB VBEVCB VCE VBEECE 442 Power Electronics 11 BJT Transistor Switch continued .
VCC VCE VCC VBEI CM ECE 442 Power Electronics 12 BJT in SaturationVCC VCE sat .
forced ECE 442 Power Electronics 13 Model with Current GainECE 442 Power Electronics 14 Miller Effect.
ECE 442 Power Electronics 15 Miller Effect continued iout Ccb vbe vce Ccb vbe Avbe iout Ccb 1 A vbe Ccb 1 A vbe Ccb Ccb 1 A .
ECE 442 Power Electronics 16 Miller Effect continued Miller Capacitance CMiller Ccb 1 A since A is usually negative phase inversion the Miller capacitance can be much greater.
than the capacitance Ccb This capacitance must charge up to thebase emitter forward bias voltage causinga delay time before any collector currentECE 442 Power Electronics 17.
Saturating a BJT Normally apply more base current thanneeded to saturate the transistor This results in charges being stored in thebase region.
To calculate the extra charge saturatingcharge determine the emitter currentI e I B ODF I BS I BS I BS ODF 1 ECE 442 Power Electronics 18 The Saturating Charge.
The saturating charge QsQs s I e s I BS ODF 1 storage time constant of thetransistorECE 442 Power Electronics 19.
Transistor Switching TimesECE 442 Power Electronics 20 Switching Times turn on Input voltage rises from 0 to V1 Base current rises to IB1.
Collector current begins to rise after thedelay time td Collector current rises to steady state value This rise time tr allows the Millercapacitance to charge to V1.
turn on time ton td trECE 442 Power Electronics 21 Switching Times turn off Input voltage changes from V1 to V2 Base current changes to IB2.
Base current remains at IB2 until the Millercapacitance discharges to zero storage Base current falls to zero as Millercapacitance charges to V2 fall time tf turn off time toff ts tf.
ECE 442 Power Electronics 22 Charge Storage in Saturated BJTsCharge storage in the Base Charge Profile during turn offECE 442 Power Electronics 23 Example 4 2.
ECE 442 Power Electronics 24 Waveforms for the Transistor SwitchVCC 250 VVBE sat 3 VVCS sat 2 V.
ICS 100 Atd 0 5 str 1 sts 5 stf 3 s.
fs 10 kHzECE 442 Power Electronics 25duty cycle k 50 ECE 442 Power Electronics 26 Power Loss due to IC for ton td tr.
During the delay time 0 t td Instantaneous Power LossPc t vCE iC VCC I CEOPc t 250V 3mA 0 75W Average Power Loss.
1 VCC I CEOPd Pc t dt dt VCC I CEO f s tdPd 250V 3mA 10kHz 0 5 s 3 75mWECE 442 Power Electronics 27 During the rise time 0 t tr.
Pc t vCE ic t I CSPc t VCC Vce sat VCC t tr trdPc t Vce sat VCC I CS t I CS.
t VCC Vce sat VCC dt tr tr tr trPc t Pmax t tm2 VCC Vce sat ECE 442 Power Electronics 28.
1 s 250V tm 0 504 s2 250V 2V 4 VCC VCE sat 250V 100 A .
Pmax 6300W4 250V 2V ECE 442 Power Electronics 29 Average Power during rise time1 VCC VCE sat VCC .
Pr Pc t dt f s I CS tr T 0 2 3 250V 2V 250V Pr 10kHz 100 A 1 s 2 3 .
Pr 42 33WECE 442 Power Electronics 30 Total Power Loss during turn onPon Pd PrPon 0 00375 42 33 42 33375W.
Pon 42 33WECE 442 Power Electronics 31 ECE 442 Power Electronics 32 Power Loss duringthe Conduction Period.
0 t tnic t I CS 100 AvCE t VCE sat 2VPc t ic vCE 100 A 2V 200WPn Pc t dt VCE sat I CS f s dt VCE sat I CS f s tn.
Pn 2V 100 A 10kHz 48 5 s 97WECE 442 Power Electronics 33 ECE 442 Power Electronics 34 Power Loss during turn offStorage time.
0 t tsic t I CS 100 AvCE t VCE sat 2VPc t vCE ic VCE sat I CS 2V 100 A Pc t 200W.
Ps Pc t dt VCE sat I CS f s dt VCE sat I CS f s tsPs 2V 100 A 10kHz 5 s 10WECE 442 Power Electronics 35 ECE 442 Power Electronics 36 Power Loss during Fall time.
0 t t fic t I CS 1 I CEO 0 tf vCE t CC t I CEO 0 t t .
Pc t vCE ic VCC I CS 1 t f t f dPc t VCC I CS 1 t t 1 0dt tf t f t f .
t f 3 sPc t Pm t 1 5 sVCC I CS 250V 100 A Pm 6250WECE 442 Power Electronics 37.
Power Loss during Fall time continued 1 VCC I CS t f f sPf Pc t dt 250V 100 A 3 s 10kHz Pf 125W.
VCC t f Poff Ps Pf I CS f s tsVCE sat Poff 10 125 135WECE 442 Power Electronics 38 ECE 442 Power Electronics 39.
Power Loss during the off time0 t tovCE t VCCic t I CEOPc t vCE iC VCC I CEO 250V 3mA 0 75W.
Po VCC I CEO dt VCC I CEO f s toPo 250V 3mA 10kHz 50 5 3 s Po 0 315WECE 442 Power Electronics 40 The total average power losses.
PT Pon Pn Poff PoPT 42 33 97 135 0 315PT 274 65WECE 442 Power Electronics 41 Instantaneous Power for Example 4 2.
ECE 442 Power Electronics 42 BJT Switch with an Inductive LoadECE 442 Power Electronics 43 Load LinesECE 442 Power Electronics 44.
Arial Arial Narrow Default Design MathType 5.0 Equation Bipolar Junction Transistors (BJT) BJT Cross-Sections Common-Emitter NPN Transistor Input Characteristics Output Characteristics Transfer Characteristics Large-Signal Model of a BJT Slide 8 Transistor Operating Point DC Load Line BJT Transistor Switch BJT Transistor Switch (continued) BJT ...

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