* SPICE netlist
Q1 N032 N032 SF 0 NPN 2
R1 SF V- 8k9
R5 N033 N039 10k6
Q2 N026 N032 N033 0 NPN
Q3 N027 N032 N034 0 NPN
R6 N034 N039 10k6
R9 N027 N026 77k9
R8 N020 N026 8k
R10 N021 N027 8k
Q4 N010 N014 N020 0 NPN
Q5 N011 N015 N021 0 NPN
R15 N035 N040 10k6
Q8 N028 N032 N035 0 NPN
Q9 N029 N032 N036 0 NPN
R16 N036 N040 10k6
R19 N029 N028 77k9
R18 N022 N028 8k
R20 N023 N029 8k
Q10 N012 N016 N022 0 NPN
Q11 N013 N017 N023 0 NPN
R25 N037 N041 10k6
Q16 N030 N032 N037 0 NPN
Q17 N031 N032 N038 0 NPN
R26 N038 N041 10k6
R29 N031 N030 77k9
R28 N024 N030 8k
R30 N025 N031 8k
Q18 N008 N018 N024 0 NPN
Q19 N009 N019 N025 0 NPN
Q6 N002 N002 N005 0 NPN
Q7 N002 N002 N004 0 NPN
Q12 N001 N004 N006 0 NPN
Q13 N003 N005 N006 0 NPN
Q14 N001 N005 N007 0 NPN
Q15 N003 N004 N007 0 NPN
R33 N008 V+ 6k
R32 N008 N003 2k
R35 N001 N009 2k
V+ V+ 0 {Vs}
V- 0 V- {Vs}
Vx X1 0 10
Vz Z2 0 10
R2 Zener N032 18k7
V1 Zener V- 7.7
R34 V+ N009 6k
G1 0 Y2 N003 N001 100
D1 Y2 0 lim
R3 N002 V+ 8k
C1 Y2 0 100n Rser=30m Rpar=35
R4 N039 V- 2k7
R14 N040 V- 2k7
R24 N041 V- 2k7
R7 N014 X1 10k
R11 N015 0 10k
R17 N016 0 10k
R21 N017 Y2 10k
R27 N018 0 10k
R31 N019 Z2 10k
R12 N005 N010 0k5
R13 N004 N011 0k5
R22 N006 N012 0k5
R23 N007 N013 0k5
.op
.param Vs=20

* LTspice schematic (.asc)
Version 4
SHEET 1 1776 992
WIRE -840 -32 -840 -64
WIRE -840 352 -888 352
WIRE -840 352 -840 48
WIRE -792 -64 -840 -64
WIRE -760 -464 -888 -464
WIRE -760 -64 -792 -64
WIRE -760 -32 -760 -64
WIRE -760 80 -760 48
WIRE -760 96 -760 80
WIRE -760 192 -888 192
WIRE -760 224 -760 192
WIRE -760 352 -840 352
WIRE -760 352 -760 304
WIRE -664 80 -760 80
WIRE -664 144 -696 144
WIRE -664 144 -664 80
WIRE -632 16 -648 16
WIRE -600 -464 -680 -464
WIRE -600 -400 -600 -464
WIRE -600 -96 -600 -144
WIRE -600 16 -632 16
WIRE -600 16 -600 -16
WIRE -600 464 -616 464
WIRE -584 -400 -600 -400
WIRE -584 -144 -600 -144
WIRE -584 80 -664 80
WIRE -520 -464 -600 -464
WIRE -520 -448 -520 -464
WIRE -520 -336 -520 -352
WIRE -520 -288 -520 -336
WIRE -520 -192 -520 -208
WIRE -520 -80 -520 -96
WIRE -520 16 -520 0
WIRE -520 32 -520 16
WIRE -520 144 -520 128
WIRE -520 240 -520 224
WIRE -504 464 -520 464
WIRE -472 16 -520 16
WIRE -440 240 -520 240
WIRE -440 256 -440 240
WIRE -440 352 -760 352
WIRE -440 352 -440 336
WIRE -360 -464 -520 -464
WIRE -360 -448 -360 -464
WIRE -360 -304 -360 -352
WIRE -360 -288 -360 -304
WIRE -360 -192 -360 -208
WIRE -360 -80 -360 -96
WIRE -360 16 -392 16
WIRE -360 16 -360 0
WIRE -360 32 -360 16
WIRE -360 144 -360 128
WIRE -360 240 -440 240
WIRE -360 240 -360 224
WIRE -296 80 -584 80
WIRE -280 -464 -360 -464
WIRE -280 -400 -296 -400
WIRE -280 -400 -280 -464
WIRE -280 -144 -296 -144
WIRE -280 -96 -280 -144
WIRE -280 16 -280 -16
WIRE -248 16 -280 16
WIRE -232 16 -248 16
WIRE -200 -304 -360 -304
WIRE -200 -304 -200 -400
WIRE -184 -400 -200 -400
WIRE -152 16 -168 16
WIRE -120 -448 -120 -496
WIRE -120 -96 -120 -144
WIRE -120 16 -152 16
WIRE -120 16 -120 -16
WIRE -104 -144 -120 -144
WIRE -104 80 -296 80
WIRE -104 464 -120 464
WIRE -40 -448 -40 -464
WIRE -40 -352 -120 -352
WIRE -40 -288 -40 -352
WIRE -40 -192 -40 -208
WIRE -40 -80 -40 -96
WIRE -40 16 -40 0
WIRE -40 32 -40 16
WIRE -40 144 -40 128
WIRE -40 240 -40 224
WIRE -8 464 -24 464
WIRE -8 496 -8 464
WIRE 8 16 -40 16
WIRE 8 464 -8 464
WIRE 40 -400 24 -400
WIRE 40 -336 -520 -336
WIRE 40 -336 40 -400
WIRE 40 240 -40 240
WIRE 40 256 40 240
WIRE 40 352 -440 352
WIRE 40 352 40 336
WIRE 56 -400 40 -400
WIRE 104 464 88 464
WIRE 120 -496 -120 -496
WIRE 120 -448 120 -496
WIRE 120 -288 120 -352
WIRE 120 -192 120 -208
WIRE 120 -80 120 -96
WIRE 120 16 88 16
WIRE 120 16 120 0
WIRE 120 32 120 16
WIRE 120 144 120 128
WIRE 120 240 40 240
WIRE 120 240 120 224
WIRE 184 80 -104 80
WIRE 200 -464 -40 -464
WIRE 200 -448 200 -464
WIRE 200 -352 120 -352
WIRE 200 -144 184 -144
WIRE 200 -96 200 -144
WIRE 200 16 200 -16
WIRE 232 16 200 16
WIRE 248 16 232 16
WIRE 248 384 248 16
WIRE 280 -400 264 -400
WIRE 280 -304 -200 -304
WIRE 280 -304 280 -400
WIRE 328 16 312 16
WIRE 360 -96 360 -144
WIRE 360 16 328 16
WIRE 360 16 360 -16
WIRE 376 -144 360 -144
WIRE 376 80 184 80
WIRE 392 -464 200 -464
WIRE 392 -368 392 -464
WIRE 392 -304 392 -368
WIRE 392 -208 392 -224
WIRE 424 -496 120 -496
WIRE 424 -400 424 -496
WIRE 440 -208 392 -208
WIRE 440 -192 440 -208
WIRE 440 -80 440 -96
WIRE 440 16 440 0
WIRE 440 32 440 16
WIRE 440 144 440 128
WIRE 440 240 440 224
WIRE 488 -304 488 -320
WIRE 488 -208 440 -208
WIRE 488 -208 488 -224
WIRE 488 16 440 16
WIRE 520 -320 488 -320
WIRE 520 240 440 240
WIRE 520 256 520 240
WIRE 520 352 40 352
WIRE 520 352 520 336
WIRE 552 -320 520 -320
WIRE 552 -304 552 -320
WIRE 552 -208 552 -224
WIRE 600 -208 552 -208
WIRE 600 -192 600 -208
WIRE 600 -80 600 -96
WIRE 600 16 568 16
WIRE 600 16 600 0
WIRE 600 32 600 16
WIRE 600 144 600 128
WIRE 600 240 520 240
WIRE 600 240 600 224
WIRE 600 464 584 464
WIRE 648 -400 424 -400
WIRE 648 -304 648 -400
WIRE 648 -208 600 -208
WIRE 648 -208 648 -224
WIRE 664 -464 648 -464
WIRE 664 80 376 80
WIRE 680 -368 392 -368
WIRE 680 -144 664 -144
WIRE 680 -96 680 -144
WIRE 680 16 680 -16
WIRE 696 464 680 464
WIRE 712 -400 648 -400
WIRE 712 -352 680 -368
WIRE 712 16 680 16
WIRE 728 16 712 16
WIRE 760 -464 744 -464
WIRE 760 -416 760 -464
WIRE 760 -320 744 -320
WIRE 760 -320 760 -336
WIRE 776 -320 760 -320
WIRE 840 -464 760 -464
WIRE 840 -320 840 -464
WIRE 840 384 248 384
WIRE 840 384 840 -320
WIRE 888 -464 840 -464
FLAG -888 -464 V+
IOPIN -512 -96 In
FLAG -888 352 V-
IOPIN -512 720 In
FLAG -632 16 X1
FLAG -248 16 X2
FLAG -152 16 Y1
FLAG 232 16 Y2
FLAG 328 16 Z1
FLAG 712 16 Z2
FLAG 888 -464 Out
IOPIN 1264 -96 Out
FLAG -168 16 0
FLAG 312 16 0
FLAG -232 16 0
FLAG -8 496 0
FLAG 104 464 V+
IOPIN 480 832 In
FLAG -120 464 V-
IOPIN 256 832 In
FLAG -616 464 X1
FLAG 696 464 Z2
FLAG -504 464 0
FLAG 584 464 0
FLAG -888 192 SF
IOPIN -512 560 In
FLAG 744 -320 0
FLAG 520 -320 V+
FLAG 648 -464 0
FLAG -792 -64 Zener
SYMBOL npn -696 96 M0
SYMATTR InstName Q1
SYMATTR Value NPN 2
SYMBOL res -776 208 R0
SYMATTR InstName R1
SYMATTR Value 8k9
SYMBOL res -536 128 R0
SYMATTR InstName R5
SYMATTR Value 10k6
SYMBOL npn -584 32 R0
SYMATTR InstName Q2
SYMBOL npn -296 32 M0
SYMATTR InstName Q3
SYMBOL res -376 128 R0
SYMATTR InstName R6
SYMATTR Value 10k6
SYMBOL res -376 0 R90
SYMATTR InstName R9
SYMATTR Value 77k9
SYMBOL res -536 -96 R0
SYMATTR InstName R8
SYMATTR Value 8k
SYMBOL res -376 -96 R0
SYMATTR InstName R10
SYMATTR Value 8k
SYMBOL npn -584 -192 R0
SYMATTR InstName Q4
SYMBOL npn -296 -192 M0
SYMATTR InstName Q5
SYMBOL res -56 128 R0
SYMATTR InstName R15
SYMATTR Value 10k6
SYMBOL npn -104 32 R0
SYMATTR InstName Q8
SYMBOL npn 184 32 M0
SYMATTR InstName Q9
SYMBOL res 104 128 R0
SYMATTR InstName R16
SYMATTR Value 10k6
SYMBOL res 104 0 R90
SYMATTR InstName R19
SYMATTR Value 77k9
SYMBOL res -56 -96 R0
SYMATTR InstName R18
SYMATTR Value 8k
SYMBOL res 104 -96 R0
SYMATTR InstName R20
SYMATTR Value 8k
SYMBOL npn -104 -192 R0
SYMATTR InstName Q10
SYMBOL npn 184 -192 M0
SYMATTR InstName Q11
SYMBOL res 424 128 R0
SYMATTR InstName R25
SYMATTR Value 10k6
SYMBOL npn 376 32 R0
SYMATTR InstName Q16
SYMBOL npn 664 32 M0
SYMATTR InstName Q17
SYMBOL res 584 128 R0
SYMATTR InstName R26
SYMATTR Value 10k6
SYMBOL res 584 0 R90
SYMATTR InstName R29
SYMATTR Value 77k9
SYMBOL res 424 -96 R0
SYMATTR InstName R28
SYMATTR Value 8k
SYMBOL res 584 -96 R0
SYMATTR InstName R30
SYMATTR Value 8k
SYMBOL npn 376 -192 R0
SYMATTR InstName Q18
SYMBOL npn 664 -192 M0
SYMATTR InstName Q19
SYMBOL npn -584 -448 R0
SYMATTR InstName Q6
SYMBOL npn -296 -448 M0
SYMATTR InstName Q7
SYMBOL npn -184 -448 R0
SYMATTR InstName Q12
SYMBOL npn 24 -448 M0
SYMATTR InstName Q13
SYMBOL npn 56 -448 R0
SYMATTR InstName Q14
SYMBOL npn 264 -448 M0
SYMATTR InstName Q15
SYMBOL res 504 -208 R180
SYMATTR InstName R33
SYMATTR Value 6k
SYMBOL res 408 -208 R180
SYMATTR InstName R32
SYMATTR Value 2k
SYMBOL res 632 -320 R0
SYMATTR InstName R35
SYMATTR Value 2k
SYMBOL voltage 104 464 R90
SYMATTR InstName V+
SYMATTR Value {Vs}
SYMBOL voltage -8 464 R90
SYMATTR InstName V-
SYMATTR Value {Vs}
SYMBOL voltage -616 464 M90
SYMATTR InstName Vx
SYMATTR Value 10
SYMBOL voltage 696 464 R90
SYMATTR InstName Vz
SYMATTR Value 10
SYMBOL res -776 -48 R0
SYMATTR InstName R2
SYMATTR Value 18k7
SYMBOL voltage -840 -48 M0
SYMATTR InstName V1
SYMATTR Value 7.7
SYMBOL res 536 -320 R0
SYMATTR InstName R34
SYMATTR Value 6k
SYMBOL g2 760 -432 R0
SYMATTR InstName G1
SYMATTR Value 100
SYMBOL Misc\\xvaristor 760 -480 R90
SYMATTR InstName D1
SYMATTR Value lim
SYMATTR Prefix D
SYMBOL res -664 -480 R90
SYMATTR InstName R3
SYMATTR Value 8k
SYMBOL cap 840 -336 R90
SYMATTR InstName C1
SYMATTR Value 100n
SYMATTR SpiceLine Rser=30m Rpar=35
SYMBOL res -456 240 R0
SYMATTR InstName R4
SYMATTR Value 2k7
SYMBOL res 24 240 R0
SYMATTR InstName R14
SYMATTR Value 2k7
SYMBOL res 504 240 R0
SYMATTR InstName R24
SYMATTR Value 2k7
SYMBOL res -616 -112 R0
SYMATTR InstName R7
SYMATTR Value 10k
SYMBOL res -296 -112 R0
SYMATTR InstName R11
SYMATTR Value 10k
SYMBOL res -136 -112 R0
SYMATTR InstName R17
SYMATTR Value 10k
SYMBOL res 184 -112 R0
SYMATTR InstName R21
SYMATTR Value 10k
SYMBOL res 344 -112 R0
SYMATTR InstName R27
SYMATTR Value 10k
SYMBOL res 664 -112 R0
SYMATTR InstName R31
SYMATTR Value 10k
SYMBOL res -536 -304 R0
SYMATTR InstName R12
SYMATTR Value 0k5
SYMBOL res -376 -304 R0
SYMATTR InstName R13
SYMATTR Value 0k5
SYMBOL res -56 -304 R0
SYMATTR InstName R22
SYMATTR Value 0k5
SYMBOL res 104 -304 R0
SYMATTR InstName R23
SYMATTR Value 0k5