Version 4
SHEET 1 880 680
WIRE 336 -16 320 -16
WIRE 528 -16 512 -16
WIRE -16 0 -32 0
WIRE 320 0 320 -16
WIRE 512 0 512 -16
WIRE -32 16 -32 0
WIRE 320 96 320 80
WIRE 512 96 512 80
WIRE 416 144 384 144
WIRE 448 144 416 144
WIRE 176 192 160 192
WIRE 160 208 160 192
WIRE 288 240 192 240
WIRE 320 240 320 192
WIRE 320 240 288 240
WIRE 416 240 416 144
WIRE 416 240 320 240
WIRE 512 240 512 192
WIRE 320 272 320 240
WIRE 512 336 512 320
WIRE 160 384 160 272
WIRE 240 384 160 384
WIRE 320 384 320 352
WIRE 320 384 240 384
WIRE 240 416 240 384
WIRE 240 512 240 496
FLAG -32 96 0
FLAG -32 0 VCC
FLAG 160 192 VCC
FLAG 320 -16 VCC
FLAG 512 -16 VCC
FLAG 240 512 0
FLAG 512 336 0
FLAG 288 240 REF
FLAG 240 384 A
SYMBOL voltage -32 0 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value {Vs}
SYMBOL References\\TL431 160 240 R0
SYMATTR InstName U1
SYMBOL res 304 -16 R0
SYMATTR InstName R1
SYMATTR Value 10
SYMBOL pnp 384 192 R180
SYMATTR InstName Q1
SYMATTR Value 2N3906
SYMBOL pnp 448 192 M180
SYMATTR InstName Q2
SYMATTR Value 2N3906
SYMBOL res 304 256 R0
SYMATTR InstName R2
SYMATTR Value 250
SYMBOL res 224 400 R0
SYMATTR InstName R3
SYMATTR Value 150
SYMBOL res 496 -16 R0
SYMATTR InstName R4
SYMATTR Value 10
SYMBOL res 496 224 R0
SYMATTR InstName R5
SYMATTR Value {RL}
TEXT 352 464 Left 0 !.op
TEXT 352 496 Left 0 !.step param RL 1 1k 10
TEXT 352 528 Left 0 !.step param Vs 5 12 1