Regulator circuit. subckt ic7231245678910 Complete circuit Type 723 voltage regula Load source x1121087。pam Internal voltage referenc s Power input v922.5 VpP 1374mm x11045678910ic723 927 56 mm Series Pass transistors model mm npn(is=le-12 bf=100 q31411mg3 q41112mq4 r14112.2k Ideal opamp with limiting subckt opamp 1 2 3 45 350 vcc vee +in -in out r4260.075 rd1381e5 r568510 rdi]2 48 le5 r68051 r7910270 Common mode gain Control cards gcm6080 le of del mq3 npn(is=le-9bf30 Differential mode gain gdi6043100 br5 ik 50m) r1601 model mq4 npn(is=le- 6 bf=30 cI60.01 dc vout 1.5.o1 d1 6 1 ideal plot dc i(vout) model ideal d (is=le-6 n,o1) ends opamp FIGURE 13.2 SPICE input listing of regulator circuit shown in Fig. 13.1 by plotting VOUT vS. VOUT/I(VOUT)(using PROBE in this case; see Fig. 13.3). Note that for this circuit, eventhough a current source would seem a more natural choice, a voltage source must be used as a load rather than a current source because the output characteristic curve is multivalued in current. If a current source were used it would not be possible to easily simulate the entire curve. Of course, many other interesting quantities can be plotted; for example, the power dissipated in the pass transistor can be approximated by plotting IC(Q3)*VC(Q3) For these simulations PSPICE was used running on an IBM PC. The simulation took 1 min of CPU time Pitfalls. Convergence problems are sometimes experienced if "difficult" bias conditions are created. An exam- ple of such a condition is if a diode is placed in the circuit backwards, resulting in a large forward bias voltage SPICe will have trouble resolving the current. Another difficult case is if a current source were used instead of ⊥(vout》 vaut/⊥(vout FIGURE 13.3 Output characteristics of regulator circuit using PSPICE. c 2000 by CRC Press LLC© 2000 by CRC Press LLC by plotting VOUT vs. VOUT/I(VOUT) (using PROBE in this case; see Fig. 13.3). Note that for this circuit, eventhough a current source would seem a more natural choice, a voltage source must be used as a load rather than a current source because the output characteristic curve is multivalued in current. If a current source were used it would not be possible to easily simulate the entire curve. Of course, many other interesting quantities can be plotted; for example, the power dissipated in the pass transistor can be approximated by plotting IC(Q3)*VC(Q3). For these simulations PSPICE was used running on an IBM PC. The simulation took < 1 min of CPU time. Pitfalls. Convergence problems are sometimes experienced if “difficult” bias conditions are created. An exam￾ple of such a condition is if a diode is placed in the circuit backwards, resulting in a large forward bias voltage, SPICE will have trouble resolving the current. Another difficult case is if a current source were used instead of FIGURE 13.2 SPICE input listing of regulator circuit shown in Fig. 13.1. FIGURE 13.3 Output characteristics of regulator circuit using PSPICE