* SPICE netlist
R1 N001 N008 47k
R2 N005 VCC 47k
R3 0 N001 5.6k
R4 0 N005 5.6k
R5 N002 N001 1k
R6 N004 N005 1k
R7 N003 N004 1Meg
R8 0 N002 1Meg
R9 VCC N008 0.1
R10 VCC 0 R=16/time
V3 + 0 12V
R28 VCC N009 10k
R29 N009 0 10k
R30 + N006 R=0.001+10k*time
R31 N006 0 R=10.0001k-(0.001+10k*time)
V1 N008 0 48V
XU1 N002 N004 + - N003 LM324 ;pnba In+)In-)V+)V-)OUT
XU5 N006 N009 + - N007 LM324 ;pnba In+)In-)V+)V-)OUT
Q2 N017 P001 0 0 NPN
Q1 VCC N016 VCC 0 PNP
R37 N017 N016 1k
R38 N007 P001 47k
V4 - 0 -12V
R11 N022 N025 47k
R12 N018 VSS 47k
R13 0 N022 5.6k
R14 0 N018 5.6k
R15 N019 N018 1k
R16 N021 N022 1k
R17 N020 N021 1Meg
R18 0 N019 1Meg
R19 VSS N025 0.1
R20 VSS 0 R=16/time
R23 VSS N026 10k
R24 N026 0 10k
R25 - N023 R=0.001+10k*time
R26 N023 0 R=10.0001k-(0.001+10k*time)
XU2 N019 N021 + - N020 LM324 ;pnba In+)In-)V+)V-)OUT
XU6 N023 N026 + - N024 LM324 ;pnba In+)In-)V+)V-)OUT
R34 N036 N035 1k
R35 N024 P002 47k
V2 N025 0 -48V
Q3 VSS N035 VSS 0 NPN
Q4 N036 P002 0 0 PNP
XU3 N010 N012 + - N012 LM324 ;pnba In+)In-)V+)V-)OUT
R21 N010 0 5.6k
R22 VCC N010 47k
R27 N013 N012 1k
XU4 0 N032 + - N027 LM324 ;pnba In+)In-)V+)V-)OUT
R32 N031 VSS 47k
R33 N032 N031 5.6k
R36 N027 N032 5.6k
R39 N028 N027 1k
XU7 N011 N014 + - N014 LM324 ;pnba In+)In-)V+)V-)OUT
R40 N011 0 5.6k
R41 VCC N011 12k
R42 N015 N014 1k
XU8 0 N034 + - N029 LM324 ;pnba In+)In-)V+)V-)OUT
R43 N033 VSS 12k
R44 N034 N033 5.6k
R45 N029 N034 5.6k
R46 N030 N029 1k
D1 0 N010 TDZV12
D2 0 N011 TDZV12
D3 0 N013 UMZ5_1N
D4 0 N015 UMZ5_1N
D5 N031 0 TDZV12
D6 N033 0 TDZV12
D7 0 N028 UMZ5_1N
D8 0 N030 UMZ5_1N
.tran 0 1 0 0.0001
.param R=10k

* LTspice schematic (.asc)
Version 4
SHEET 1 1824 1216
WIRE -864 -592 -912 -592
WIRE -752 -592 -864 -592
WIRE -624 -592 -752 -592
WIRE -912 -576 -912 -592
WIRE -864 -496 -864 -512
WIRE -720 -496 -864 -496
WIRE -624 -496 -624 -512
WIRE -624 -496 -640 -496
WIRE -624 -480 -624 -496
WIRE -608 -480 -624 -480
WIRE -448 -464 -544 -464
WIRE -608 -448 -624 -448
WIRE -112 -448 -288 -448
WIRE -752 -416 -752 -512
WIRE -720 -416 -752 -416
WIRE -624 -416 -624 -448
WIRE -624 -416 -640 -416
WIRE -864 -400 -864 -496
WIRE -752 -400 -752 -416
WIRE -624 -368 -624 -416
WIRE -544 -368 -544 -464
WIRE -112 -368 -304 -368
WIRE -304 -288 -304 -368
WIRE -256 -288 -304 -288
WIRE -640 -272 -736 -272
WIRE -128 -272 -192 -272
WIRE -864 -256 -864 -320
WIRE -848 -256 -864 -256
WIRE -752 -256 -752 -320
WIRE -752 -256 -768 -256
WIRE -736 -256 -736 -272
WIRE -736 -256 -752 -256
WIRE -640 -256 -640 -272
WIRE -640 -256 -656 -256
WIRE -448 -256 -640 -256
WIRE -256 -256 -304 -256
WIRE -128 -256 -128 -272
WIRE -640 -240 -640 -256
WIRE -448 -240 -448 -256
WIRE -864 -192 -864 -256
WIRE -640 -144 -640 -160
WIRE -304 -144 -304 -256
WIRE -304 -144 -640 -144
WIRE 80 -144 16 -144
WIRE 192 -144 80 -144
WIRE 592 -144 528 -144
WIRE 704 -144 592 -144
WIRE -640 -128 -640 -144
WIRE 272 -128 256 -128
WIRE 304 -128 272 -128
WIRE 400 -128 384 -128
WIRE 784 -128 768 -128
WIRE 816 -128 784 -128
WIRE 912 -128 896 -128
WIRE -704 -112 -704 -192
WIRE -288 -112 -704 -112
WIRE -176 -112 -208 -112
WIRE 192 -112 176 -112
WIRE 704 -112 688 -112
WIRE 176 -80 176 -112
WIRE 272 -80 272 -128
WIRE 272 -80 176 -80
WIRE 688 -80 688 -112
WIRE 784 -80 784 -128
WIRE 784 -80 688 -80
WIRE -80 -64 -80 -112
WIRE 16 -64 16 -80
WIRE 528 -64 528 -80
WIRE -864 -32 -864 -112
WIRE -640 -32 -640 -48
WIRE -640 -32 -864 -32
WIRE -448 -32 -448 -160
WIRE -448 -32 -640 -32
WIRE -384 -32 -448 -32
WIRE -288 -32 -288 -48
WIRE -288 -32 -304 -32
WIRE -224 -32 -240 -32
WIRE -128 -32 -128 -48
WIRE -128 -32 -144 -32
WIRE -864 -16 -864 -32
WIRE -864 32 -912 32
WIRE -752 32 -864 32
WIRE -624 32 -752 32
WIRE -912 48 -912 32
WIRE -752 128 -752 112
WIRE -720 128 -752 128
WIRE -624 128 -624 112
WIRE -624 128 -640 128
WIRE -624 144 -624 128
WIRE -608 144 -624 144
WIRE -448 160 -544 160
WIRE -608 176 -624 176
WIRE -112 176 -288 176
WIRE -864 208 -864 112
WIRE -720 208 -864 208
WIRE -624 208 -624 176
WIRE -624 208 -640 208
WIRE -864 224 -864 208
WIRE -752 224 -752 128
WIRE -624 256 -624 208
WIRE -544 256 -544 160
WIRE -112 256 -304 256
WIRE -304 336 -304 256
WIRE -256 336 -304 336
WIRE -752 352 -752 304
WIRE -640 352 -752 352
WIRE -128 352 -192 352
WIRE -864 368 -864 304
WIRE -848 368 -864 368
WIRE -752 368 -752 352
WIRE -752 368 -768 368
WIRE -640 368 -640 352
WIRE -640 368 -656 368
WIRE -448 368 -640 368
WIRE -256 368 -304 368
WIRE -128 368 -128 352
WIRE -640 384 -640 368
WIRE -448 384 -448 368
WIRE -864 432 -864 368
WIRE 176 448 176 416
WIRE 192 448 176 448
WIRE 672 448 672 416
WIRE 688 448 672 448
WIRE 272 464 256 464
WIRE 304 464 272 464
WIRE 400 464 384 464
WIRE 768 464 752 464
WIRE 800 464 768 464
WIRE 896 464 880 464
WIRE -640 480 -640 464
WIRE -304 480 -304 368
WIRE -304 480 -640 480
WIRE 80 480 80 464
WIRE 80 480 64 480
WIRE 96 480 80 480
WIRE 192 480 176 480
WIRE 576 480 576 464
WIRE 576 480 560 480
WIRE 592 480 576 480
WIRE 688 480 672 480
WIRE -640 496 -640 480
WIRE -704 512 -704 432
WIRE -288 512 -704 512
WIRE -176 512 -208 512
WIRE -80 560 -80 512
WIRE 176 560 176 480
WIRE 272 560 272 464
WIRE 272 560 256 560
WIRE 672 560 672 480
WIRE 768 560 768 464
WIRE 768 560 752 560
WIRE -864 592 -864 512
WIRE -640 592 -640 576
WIRE -640 592 -864 592
WIRE -448 592 -448 464
WIRE -448 592 -640 592
WIRE -864 608 -864 592
FLAG -912 -576 0
FLAG -864 -16 0
FLAG -288 -48 +
FLAG -224 -240 +
FLAG -112 -288 0
FLAG -576 -432 +
FLAG -80 -64 0
FLAG -128 -48 -
FLAG -240 -32 0
FLAG -912 48 0
FLAG -864 608 0
FLAG -112 336 0
FLAG -80 560 0
FLAG -576 128 -
FLAG -224 320 -
FLAG -576 192 +
FLAG -576 -496 -
FLAG -224 384 +
FLAG -224 -304 -
FLAG -288 -448 +
FLAG -288 176 -
FLAG -448 -256 VCC
FLAG -448 368 VSS
FLAG 224 -96 +
FLAG 224 -160 -
FLAG 80 -224 VCC
FLAG 80 -64 0
FLAG 176 416 0
FLAG 224 432 -
FLAG 224 496 +
FLAG -16 480 VSS
FLAG 736 -96 +
FLAG 736 -160 -
FLAG 592 -224 VCC
FLAG 592 -64 0
FLAG 672 416 0
FLAG 720 432 -
FLAG 720 496 +
FLAG 480 480 VSS
FLAG 16 -64 0
FLAG 528 -64 0
FLAG 400 -64 0
FLAG 912 -64 0
FLAG 80 400 0
FLAG 576 400 0
FLAG 400 528 0
FLAG 896 528 0
SYMBOL res -880 -416 R0
SYMATTR InstName R1
SYMATTR Value 47k
SYMBOL res -768 -416 R0
SYMATTR InstName R2
SYMATTR Value 47k
SYMBOL res -880 -608 R0
SYMATTR InstName R3
SYMATTR Value 5.6k
SYMBOL res -768 -608 R0
SYMATTR InstName R4
SYMATTR Value 5.6k
SYMBOL res -624 -512 R90
SYMATTR InstName R5
SYMATTR Value 1k
SYMBOL res -624 -432 R90
SYMATTR InstName R6
SYMATTR Value 1k
SYMBOL res -528 -384 R90
SYMATTR InstName R7
SYMATTR Value 1Meg
SYMBOL res -640 -608 R0
SYMATTR InstName R8
SYMATTR Value 1Meg
SYMBOL res -752 -272 R90
SYMATTR InstName R9
SYMATTR Value 0.1
SYMBOL res -464 -256 R0
SYMATTR InstName R10
SYMATTR Value R=16/time
SYMBOL voltage -288 -32 R90
SYMATTR InstName V3
SYMATTR Value 12V
SYMBOL res -656 -256 R0
SYMATTR InstName R28
SYMATTR Value 10k
SYMBOL res -656 -144 R0
SYMATTR InstName R29
SYMATTR Value 10k
SYMBOL res -128 -464 R0
SYMATTR InstName R30
SYMATTR Value R=0.001+10k*time
SYMBOL res -128 -384 R0
SYMATTR InstName R31
SYMATTR Value R=10.0001k-(0.001+10k*time)
SYMBOL voltage -864 -208 R0
SYMATTR InstName V1
SYMATTR Value 48V
SYMBOL OpAmps\\opamp2 -576 -400 M180
SYMATTR InstName U1
SYMATTR Value LM324
SYMBOL OpAmps\\opamp2 -224 -208 M180
SYMATTR InstName U5
SYMATTR Value LM324
SYMBOL npn -176 -176 M90
SYMATTR InstName Q2
SYMBOL pnp -656 -192 M270
SYMATTR InstName Q1
SYMBOL res -192 -128 R90
SYMATTR InstName R37
SYMATTR Value 1k
SYMBOL res -144 -272 R0
SYMATTR InstName R38
SYMATTR Value 47k
SYMBOL voltage -128 -32 R90
SYMATTR InstName V4
SYMATTR Value -12V
SYMBOL res -880 208 R0
SYMATTR InstName R11
SYMATTR Value 47k
SYMBOL res -768 208 R0
SYMATTR InstName R12
SYMATTR Value 47k
SYMBOL res -880 16 R0
SYMATTR InstName R13
SYMATTR Value 5.6k
SYMBOL res -768 16 R0
SYMATTR InstName R14
SYMATTR Value 5.6k
SYMBOL res -624 112 R90
SYMATTR InstName R15
SYMATTR Value 1k
SYMBOL res -624 192 R90
SYMATTR InstName R16
SYMATTR Value 1k
SYMBOL res -528 240 R90
SYMATTR InstName R17
SYMATTR Value 1Meg
SYMBOL res -640 16 R0
SYMATTR InstName R18
SYMATTR Value 1Meg
SYMBOL res -752 352 R90
SYMATTR InstName R19
SYMATTR Value 0.1
SYMBOL res -464 368 R0
SYMATTR InstName R20
SYMATTR Value R=16/time
SYMBOL res -656 368 R0
SYMATTR InstName R23
SYMATTR Value 10k
SYMBOL res -656 480 R0
SYMATTR InstName R24
SYMATTR Value 10k
SYMBOL res -128 160 R0
SYMATTR InstName R25
SYMATTR Value R=0.001+10k*time
SYMBOL res -128 240 R0
SYMATTR InstName R26
SYMATTR Value R=10.0001k-(0.001+10k*time)
SYMBOL OpAmps\\opamp2 -576 224 M180
SYMATTR InstName U2
SYMATTR Value LM324
SYMBOL OpAmps\\opamp2 -224 416 M180
SYMATTR InstName U6
SYMATTR Value LM324
SYMBOL res -192 496 R90
SYMATTR InstName R34
SYMATTR Value 1k
SYMBOL res -144 352 R0
SYMATTR InstName R35
SYMATTR Value 47k
SYMBOL voltage -864 416 R0
SYMATTR InstName V2
SYMATTR Value -48V
SYMBOL npn -656 432 M270
SYMATTR InstName Q3
SYMBOL pnp -176 448 M90
SYMATTR InstName Q4
SYMBOL OpAmps\\opamp2 224 -64 M180
SYMATTR InstName U3
SYMATTR Value LM324
SYMBOL res 64 -160 R0
SYMATTR InstName R21
SYMATTR Value 5.6k
SYMBOL res 64 -240 R0
SYMATTR InstName R22
SYMATTR Value 47k
SYMBOL res 400 -144 R90
SYMATTR InstName R27
SYMATTR Value 1k
SYMBOL OpAmps\\opamp2 224 528 M180
SYMATTR InstName U4
SYMATTR Value LM324
SYMBOL res 80 464 R90
SYMATTR InstName R32
SYMATTR Value 47k
SYMBOL res 192 464 R90
SYMATTR InstName R33
SYMATTR Value 5.6k
SYMBOL res 272 544 R90
SYMATTR InstName R36
SYMATTR Value 5.6k
SYMBOL res 400 448 R90
SYMATTR InstName R39
SYMATTR Value 1k
SYMBOL OpAmps\\opamp2 736 -64 M180
SYMATTR InstName U7
SYMATTR Value LM324
SYMBOL res 576 -160 R0
SYMATTR InstName R40
SYMATTR Value 5.6k
SYMBOL res 576 -240 R0
SYMATTR InstName R41
SYMATTR Value 12k
SYMBOL res 912 -144 R90
SYMATTR InstName R42
SYMATTR Value 1k
SYMBOL OpAmps\\opamp2 720 528 M180
SYMATTR InstName U8
SYMATTR Value LM324
SYMBOL res 576 464 R90
SYMATTR InstName R43
SYMATTR Value 12k
SYMBOL res 688 464 R90
SYMATTR InstName R44
SYMATTR Value 5.6k
SYMBOL res 768 544 R90
SYMATTR InstName R45
SYMATTR Value 5.6k
SYMBOL res 896 448 R90
SYMATTR InstName R46
SYMATTR Value 1k
SYMBOL zener 32 -80 R180
SYMATTR InstName D1
SYMATTR Value TDZV12
SYMBOL zener 544 -80 R180
SYMATTR InstName D2
SYMATTR Value TDZV12
SYMBOL zener 384 -64 M180
SYMATTR InstName D3
SYMATTR Value UMZ5_1N
SYMBOL zener 896 -64 M180
SYMATTR InstName D4
SYMATTR Value UMZ5_1N
SYMBOL zener 96 464 R180
SYMATTR InstName D5
SYMATTR Value TDZV12
SYMBOL zener 592 464 R180
SYMATTR InstName D6
SYMATTR Value TDZV12
SYMBOL zener 384 528 M180
SYMATTR InstName D7
SYMATTR Value UMZ5_1N
SYMBOL zener 880 528 M180
SYMATTR InstName D8
SYMATTR Value UMZ5_1N