Version 4
SHEET 1 3768 1236
WIRE 528 -32 384 -32
WIRE 976 -32 528 -32
WIRE 384 32 384 -32
WIRE 384 144 384 112
WIRE 528 192 528 -32
WIRE 976 320 976 -32
WIRE 672 400 384 400
WIRE 704 400 672 400
WIRE 800 400 768 400
WIRE 896 400 800 400
WIRE 928 400 896 400
WIRE 528 480 528 272
WIRE 800 496 800 400
WIRE 800 496 768 496
WIRE 896 512 896 400
WIRE 672 544 672 400
WIRE 704 544 672 544
WIRE 352 560 -96 560
WIRE 384 560 384 400
WIRE 384 560 352 560
WIRE 480 560 384 560
WIRE -96 592 -96 560
WIRE -96 720 -96 672
WIRE 528 720 528 576
WIRE 528 720 -96 720
WIRE 576 720 528 720
WIRE 768 720 768 592
WIRE 768 720 576 720
WIRE 896 720 896 592
WIRE 896 720 768 720
WIRE 976 720 976 416
WIRE 976 720 896 720
WIRE 528 800 528 720
WIRE 528 976 528 880
FLAG 384 144 0
FLAG 528 976 0
FLAG 352 560 in
FLAG 576 720 out
SYMBOL voltage 384 16 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 500
SYMBOL voltage -96 576 R0
WINDOW 123 24 132 Left 2
WINDOW 39 24 44 Left 2
WINDOW 3 24 72 Left 2
SYMATTR Value ""
SYMATTR InstName V2
SYMBOL res 512 784 R0
SYMATTR InstName R4
SYMATTR Value {Rload}
SYMBOL res 512 176 R0
SYMATTR InstName R1
SYMATTR Value 2k
SYMBOL nmos 928 320 R0
SYMATTR InstName M3
SYMATTR Value STP8NM60
SYMBOL res 880 496 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL nmos 480 480 R0
SYMATTR InstName M1
SYMATTR Value STP8NM60
SYMBOL diode 704 416 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL pnp 704 592 M180
SYMATTR InstName Q2
SYMATTR Value 2N3906
TEXT 584 904 Left 2 !.param Rload=2k
TEXT 584 936 Left 2 !.step param Rload list  2k 4k 10k 20k
TEXT -48 632 Left 2 !.dc V2 4 8 .01