* SPICE netlist
Q1 N001 N002 N003 0 NPN
Q2 N005 N004 N010 0 NPN
Q3 N012 N012 0 0 NPN
Q4 N010 N012 0 0 NPN
R1 N003 N007 68R
R2 N007 N011 300K
Q5 0 N013 N008 0 PNP
Q6 N012 N009 N008 0 PNP
R3 N013 0 6K8
Q7 N002 N006 N007 0 NPN
D1 0 N009 EDZV6_8B
D2 0 N004 EDZV30B
V1 N001 0 400 Rser=50
R4 N006 0 180K
R5 N003 N006 3K
I1 N001 N002 2mA
R9 N007 0 {LOAD_RESISTANCE}
I2 N004 N009 2mA
D3 N002 N005 D
R8 N011 N013 30K
I3 N004 N008 4mA
I4 N001 N004 10mA
D4 N007 N006 D
.tran 10
.step param LOAD_RESISTANCE 50001 1 1000

* LTspice schematic (.asc)
Version 4
SHEET 1 1840 1216
WIRE -136 -608 -920 -608
WIRE 360 -608 -136 -608
WIRE 536 -608 360 -608
WIRE -136 -544 -136 -608
WIRE 360 -544 360 -608
WIRE 536 -464 536 -608
WIRE 328 -416 168 -416
WIRE 360 -416 360 -464
WIRE 360 -416 328 -416
WIRE 472 -416 360 -416
WIRE 168 -336 168 -416
WIRE 536 -304 536 -368
WIRE 536 -304 472 -304
WIRE 600 -304 536 -304
WIRE 472 -240 472 -304
WIRE 600 -224 600 -304
WIRE -136 -176 -136 -464
WIRE -136 -176 -632 -176
WIRE 168 -160 168 -272
WIRE 328 -160 328 -416
WIRE -136 -144 -136 -176
WIRE -136 -144 -520 -144
WIRE -136 -112 -136 -144
WIRE 104 -112 -136 -112
WIRE 424 -112 392 -112
WIRE 472 -112 472 -160
WIRE 472 -112 424 -112
WIRE -920 -64 -920 -608
WIRE -520 -64 -520 -144
WIRE -136 -64 -136 -112
WIRE 424 -64 424 -112
WIRE 600 -48 600 -144
WIRE 920 -48 600 -48
WIRE 328 64 328 -64
WIRE 424 64 424 0
WIRE 424 64 328 64
WIRE 600 64 600 -48
WIRE 600 64 424 64
WIRE -136 80 -136 16
WIRE -136 80 -264 80
WIRE -8 80 -136 80
WIRE 600 112 600 64
WIRE -264 160 -264 80
WIRE -520 208 -520 16
WIRE -328 208 -520 208
WIRE 168 224 168 -64
WIRE 168 224 -136 224
WIRE 600 240 600 192
WIRE 920 240 920 -48
WIRE -264 336 -264 256
WIRE -264 336 -392 336
WIRE -8 336 -8 80
WIRE -632 368 -632 -176
WIRE -520 368 -520 208
WIRE 600 384 600 320
WIRE 600 384 56 384
WIRE -392 400 -392 336
WIRE -136 400 -136 224
WIRE -264 448 -264 336
WIRE -264 448 -328 448
WIRE -200 448 -264 448
WIRE 472 448 472 -112
WIRE 600 448 600 384
WIRE -920 608 -920 16
WIRE -632 608 -632 432
WIRE -632 608 -920 608
WIRE -520 608 -520 432
WIRE -520 608 -632 608
WIRE -392 608 -392 496
WIRE -392 608 -520 608
WIRE -136 608 -136 496
WIRE -136 608 -392 608
WIRE -8 608 -8 432
WIRE -8 608 -136 608
WIRE 168 608 168 496
WIRE 168 608 -8 608
WIRE 472 608 472 528
WIRE 472 608 168 608
WIRE 600 608 600 528
WIRE 600 608 472 608
WIRE 920 608 920 320
WIRE 920 608 600 608
FLAG 168 496 0
SYMBOL npn2 472 -464 R0
SYMATTR InstName Q1
SYMBOL npn2 104 -160 R0
SYMATTR InstName Q2
SYMBOL npn2 -328 400 M0
SYMATTR InstName Q3
SYMBOL npn2 -200 400 R0
SYMATTR InstName Q4
SYMBOL res 584 -240 R0
SYMATTR InstName R1
SYMATTR Value 68R
SYMBOL res 584 96 R0
SYMATTR InstName R2
SYMATTR Value 300K
SYMBOL pnp2 56 432 R180
SYMATTR InstName Q5
SYMBOL pnp2 -328 256 M180
SYMATTR InstName Q6
SYMBOL res 584 432 R0
SYMATTR InstName R3
SYMATTR Value 6K8
SYMBOL npn2 392 -160 M0
SYMATTR InstName Q7
SYMBOL zener -504 432 R180
SYMATTR InstName D1
SYMATTR Value EDZV6_8B
SYMBOL zener -616 432 R180
SYMATTR InstName D2
SYMATTR Value EDZV30B
SYMBOL voltage -920 -80 R0
SYMATTR InstName V1
SYMATTR Value 400
SYMATTR SpiceLine Rser=50
SYMBOL res 456 432 R0
SYMATTR InstName R4
SYMATTR Value 180K
SYMBOL res 456 -256 R0
SYMATTR InstName R5
SYMATTR Value 3K
SYMBOL current 360 -544 R0
SYMATTR InstName I1
SYMATTR Value 2mA
SYMBOL res 904 224 R0
SYMATTR InstName R9
SYMATTR Value {LOAD_RESISTANCE}
SYMBOL current -520 -64 R0
SYMATTR InstName I2
SYMATTR Value 2mA
SYMBOL diode 152 -336 R0
SYMATTR InstName D3
SYMBOL res 584 224 R0
SYMATTR InstName R8
SYMATTR Value 30K
SYMBOL current -136 -64 R0
SYMATTR InstName I3
SYMATTR Value 4mA
SYMBOL current -136 -544 R0
SYMATTR InstName I4
SYMATTR Value 10mA
SYMBOL diode 408 0 M180
SYMATTR InstName D4