Version 4
SHEET 1 1032 680
WIRE 224 16 112 16
WIRE 592 16 320 16
WIRE 752 16 592 16
WIRE 944 16 752 16
WIRE 592 80 592 16
WIRE 752 80 752 16
WIRE 480 176 400 176
WIRE 528 176 480 176
WIRE 752 176 752 160
WIRE 752 176 528 176
WIRE -64 192 -64 128
WIRE 112 192 112 16
WIRE 752 192 752 176
WIRE 352 208 352 176
WIRE 480 208 480 176
WIRE 528 208 528 176
WIRE 944 208 944 16
WIRE 400 224 400 176
WIRE 400 224 384 224
WIRE 272 240 272 80
WIRE 320 240 272 240
WIRE 400 256 384 256
WIRE 400 304 400 256
WIRE 480 304 480 272
WIRE 480 304 400 304
WIRE 528 304 528 272
WIRE 528 304 480 304
WIRE 592 304 592 160
WIRE 592 304 528 304
WIRE -64 320 -64 272
WIRE 352 320 352 272
WIRE 752 320 752 272
WIRE 592 352 592 304
WIRE 112 448 112 272
WIRE 592 448 592 416
WIRE 592 448 112 448
WIRE 752 448 752 400
WIRE 752 448 592 448
WIRE 944 448 944 288
WIRE 944 448 752 448
WIRE 592 464 592 448
FLAG 592 464 0
FLAG 592 304 Uref
FLAG 944 16 Uout
FLAG -64 320 0
FLAG -64 128 +UB
FLAG 352 176 +UB
FLAG 352 320 0
SYMBOL voltage 112 176 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12V
SYMBOL npn 224 80 R270
SYMATTR InstName Q1
SYMBOL diode 496 272 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D1
SYMBOL diode 512 208 R0
SYMATTR InstName D2
SYMBOL zener 608 416 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D3
SYMATTR Value BZX84C6V2L
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 576 64 R0
SYMATTR InstName R1
SYMATTR Value 1k
SYMBOL res 736 64 R0
SYMATTR InstName R4a
SYMATTR Value {Rx}
SYMBOL res 736 176 R0
SYMATTR InstName R4b
SYMATTR Value 900
SYMBOL res 736 304 R0
SYMATTR InstName R5
SYMATTR Value 1k
SYMBOL res 928 192 R0
SYMATTR InstName R7
SYMATTR Value 100
SYMBOL voltage -64 176 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 18V
SYMBOL Opamps\\UniversalOpamp2 352 240 M0
SYMATTR InstName U1
TEXT 78 488 Left 2 !.tran 1
TEXT 368 -56 Left 2 !.step param Rx 50 2000 400