Page 86 - Rashid, Power Electronics Handbook

M. Godoy Simo˜es
72
72 M. Godoy Simo ˜e s

FIGURE 5.23 BJT buck chopper.
by the control voltage statement ðV Þ. The listing that follows
G
plots the instantaneous load current ðI Þ, the input current
O
ðI Þ, the diode voltage ðV Þ, the output voltage ðV Þ and
C
S
D
FIGURE 5.22 Ebers-Moll transistor model. calculates the Fourier coef®cients of the input current ðI Þ.
S
This listing for the careful reader as it provides more details
As an example, the model parameters for the 2N2222A NPN and enhancements that are useful when SPICE is chosen for
transistor are given in what follows: simulations as shown below.
.MODEL Q2N222A NPN (IS=14.34F XTI=3
EG=1.11 VAF=74.03 BF=255.9 5.7 BJT Applications
NE=1.307 ISE=14.34F IKF=.2847 XTB=1.5
BR=6.092 NC=2 ISC=0 IKR=0
Bipolar junction power transistors are applied to a variety of
RC=1 CJC=7.306P MJC=.3416 VJC=.75 FC=.5
power electronic functions, switching mode power supplies, dc
CJE=22.01P MJE=.377
motor inverters, PWM inverters [5], and many other functions
VJE=.75 TR=46.91N TF=4.11.1P ITF=.6
too numerous to name. To conclude, three applications are
VTF=1.7 XTF=3 RB=10)
illustrated.
Figure 5.23 shows a BJT buck chopper. The dc input voltage A ¯yback converter is given in Fig. 5.24. The switching
is 12 V, load resistance R is 5 O, ®lter inductance L is 145:8 mH transistor is required to withstand peak collector voltage at
and the ®lter capacitance C is 200 mF. The chopping frequency turn-off and peak collector currents at turn-on. In order to
is 25 kHz and the duty cycle of the chopper is 42% as indicated limit the collector voltage to a safe value, the duty cycle must

*SOURCE
VS 1 0 DC 12V
VY 1 2 DC 0V ;Voltage source to measure input current
VG 7 3 PULSE 0V 30V 0.1NS 0/Ins 16.7US 4OUS)
*CIRCUIT
RB 7 6 250 ;Transistor base resistance
R 5 0 5
L 3 4 145.8UH
C 5 0 200UF IC=3V ;Initial voltage
VX 4 5 DC 0V ;Source to inductor current
DM 0 3 DMOD ;Freewheeling diode
.MODEL DMOD D(IS=2.22E-15 BV=1200V DJO=O TT=O)
Q1 2 6 3 3 2N6546 ;BJT switch
.MODEL 2N6546 NPN (IS=6.83E-14 BF=13 CJE=1PF CJC=607.3PF TF=26.5NS)
*ANALYSIS
.TRAN 2US 2.1MS 2MS UIC ;Transient analysis
.PROBE ;Graphics post-processor
.OPTIONS ABSTOL=1.OON RELTOL=0.01 VNTOL=0.1 ITL5=40000
.FOUR 25KHZ I(VY) ;Fourier analysis
.END