* SPICE netlist
R1 N017 0 .67
C1 N018 0 500p
C2 N015 0 .1
C3 N014 N013 .01
R2 N013 N010 200K
R3 N015 N018 13K
R4 N010 0 20K
R5 N017 N016 1K
MQ1 N004 N012 N017 N017 Si7802DN
R6 N012 N011 12
R7 N006 N010 152K
C4 N006 0 .0022
C5 N007 0 100p
D1 N007 N006 BAT54
C6 N005 0 22
R8 N009 N005 39
D2 N008 N009 BAT54
R9 IN N016 1.32Meg
R10 IN N003 10K
C7 IN N003 470p
L1 N001 0 16 Rser=.05 Rpar=2K
L2 N008 0 18.8 Rser=.1
L3 N004 IN 100 Rser=.05 Rpar=5K
D3 N001 N002 MBRS340
C8 N002 0 3.3 Rser=.1
L4 N002 +20V 1
C9 +20V 0 3.3 Rser=.1
R11 +20V 0 750
V1 IN 0 200
D4 0 N005 BZX84C15L
D5 N004 N003 MURS320
R12 N008 N007 510
R13 IN N005 400K
XU1 N014 N010 N016 N018 0 N011 N005 N015 LT1241 ;pnba COMP)FB)Isense)Rt/Ct)GND)Output)Vcc)Vref
Rload +20V 0 50
.tran 2m
K1 L1 L2 L3 .98

* LTspice schematic (.asc)
Version 4
SHEET 1 1888 832
WIRE -432 -416 -592 -416
WIRE -240 -416 -432 -416
WIRE -16 -416 -240 -416
WIRE 96 -416 -16 -416
WIRE 224 -416 96 -416
WIRE -592 -400 -592 -416
WIRE -16 -384 -16 -416
WIRE 96 -384 96 -416
WIRE -432 -352 -432 -416
WIRE -240 -352 -240 -416
WIRE 224 -352 224 -416
WIRE 288 -352 224 -352
WIRE 432 -352 352 -352
WIRE 560 -352 496 -352
WIRE 608 -352 560 -352
WIRE 736 -352 688 -352
WIRE 832 -352 736 -352
WIRE 944 -352 832 -352
WIRE 288 -336 288 -352
WIRE 352 -336 352 -352
WIRE 560 -336 560 -352
WIRE 736 -336 736 -352
WIRE 832 -336 832 -352
WIRE 944 -336 944 -352
WIRE -592 -304 -592 -320
WIRE -16 -288 -16 -320
WIRE 96 -288 96 -304
WIRE 96 -288 -16 -288
WIRE 96 -256 96 -288
WIRE 288 -240 288 -256
WIRE 288 -240 224 -240
WIRE 352 -240 352 -256
WIRE 560 -240 560 -272
WIRE 560 -240 352 -240
WIRE 736 -240 736 -272
WIRE 736 -240 560 -240
WIRE 832 -240 832 -256
WIRE 832 -240 736 -240
WIRE 944 -240 944 -256
WIRE 944 -240 832 -240
WIRE 944 -224 944 -240
WIRE -432 -192 -432 -272
WIRE -384 -192 -432 -192
WIRE -288 -192 -320 -192
WIRE 96 -176 96 -192
WIRE 224 -176 224 -240
WIRE 224 -176 96 -176
WIRE -832 -128 -928 -128
WIRE -768 -128 -832 -128
WIRE -640 -128 -704 -128
WIRE -560 -128 -640 -128
WIRE 32 -128 -480 -128
WIRE 288 -128 32 -128
WIRE -832 -112 -832 -128
WIRE -640 -112 -640 -128
WIRE 288 -112 288 -128
WIRE -928 -96 -928 -128
WIRE -432 -64 -432 -192
WIRE -208 -64 -432 -64
WIRE -144 -64 -208 -64
WIRE -48 -64 -64 -64
WIRE 32 -64 32 -128
WIRE 32 -64 16 -64
WIRE -208 -48 -208 -64
WIRE -832 -16 -832 -48
WIRE -640 -16 -640 -48
WIRE 288 -16 288 -32
WIRE -432 0 -432 -64
WIRE 96 16 96 -176
WIRE -208 48 -208 16
WIRE -928 64 -928 -16
WIRE -592 64 -928 64
WIRE -144 96 -272 96
WIRE 48 96 -64 96
WIRE -928 128 -928 64
WIRE -832 128 -928 128
WIRE -704 128 -752 128
WIRE -592 128 -640 128
WIRE -928 144 -928 128
WIRE -736 192 -848 192
WIRE -592 192 -736 192
WIRE -848 208 -848 192
WIRE -736 208 -736 192
WIRE -240 224 -240 -272
WIRE -240 224 -272 224
WIRE -144 224 -240 224
WIRE 96 224 96 112
WIRE 96 224 -64 224
WIRE -928 240 -928 224
WIRE 96 240 96 224
WIRE -592 256 -640 256
WIRE -736 288 -736 272
WIRE -848 320 -848 288
WIRE -640 320 -640 256
WIRE -640 320 -848 320
WIRE -848 336 -848 320
WIRE 96 336 96 320
WIRE -432 368 -432 320
WIRE -848 416 -848 400
FLAG 96 336 0
FLAG -848 416 0
FLAG -736 288 0
FLAG -928 240 0
FLAG -432 368 0
FLAG -832 -16 0
FLAG -640 -16 0
FLAG -208 48 0
FLAG 288 -16 0
FLAG -592 -304 0
FLAG -288 -192 0
FLAG 944 -352 +20V
FLAG 944 -224 0
FLAG -592 -416 IN
SYMBOL RES 80 224 R0
SYMATTR InstName R1
SYMATTR Value .67
SYMBOL cap -864 336 R0
SYMATTR InstName C1
SYMATTR Value 500p
SYMBOL cap -752 208 R0
SYMATTR InstName C2
SYMATTR Value .1
SYMBOL cap -640 112 R90
SYMATTR InstName C3
SYMATTR Value .01
SYMBOL res -736 112 R90
SYMATTR InstName R2
SYMATTR Value 200K
SYMBOL res -864 192 R0
SYMATTR InstName R3
SYMATTR Value 13K
SYMBOL res -944 128 R0
SYMATTR InstName R4
SYMATTR Value 20K
SYMBOL res -48 208 R90
SYMATTR InstName R5
SYMATTR Value 1K
SYMBOL NMOS 48 16 R0
SYMATTR InstName Q1
SYMATTR Value Si7802DN
SYMBOL res -48 80 R90
SYMATTR InstName R6
SYMATTR Value 12
SYMBOL res -944 -112 R0
SYMATTR InstName R7
SYMATTR Value 152K
SYMBOL cap -848 -112 R0
SYMATTR InstName C4
SYMATTR Value .0022
SYMBOL cap -656 -112 R0
SYMATTR InstName C5
SYMATTR Value 100p
SYMBOL schottky -704 -144 R90
SYMATTR InstName D1
SYMATTR Value BAT54
SYMBOL cap -224 -48 R0
SYMATTR InstName C6
SYMATTR Value 22
SYMBOL res -48 -80 R90
SYMATTR InstName R8
SYMATTR Value 39
SYMBOL schottky 16 -80 R90
SYMATTR InstName D2
SYMATTR Value BAT54
SYMBOL res -256 -368 R0
SYMATTR InstName R9
SYMATTR Value 1.32Meg
SYMBOL res 80 -400 R0
SYMATTR InstName R10
SYMATTR Value 10K
SYMBOL cap -32 -384 R0
SYMATTR InstName C7
SYMATTR Value 470p
SYMBOL ind2 368 -352 M0
SYMATTR InstName L1
SYMATTR Value 16
SYMATTR SpiceLine Rser=.05 Rpar=2K
SYMBOL ind2 272 -128 R0
SYMATTR InstName L2
SYMATTR Value 18.8
SYMATTR Value2 Rser=.1
SYMBOL ind2 272 -240 M180
SYMATTR InstName L3
SYMATTR Value 100
SYMATTR SpiceLine Rser=.05 Rpar=5K
SYMBOL schottky 432 -368 M90
SYMATTR InstName D3
SYMATTR Value MBRS340
SYMBOL cap 544 -336 R0
SYMATTR InstName C8
SYMATTR Value 3.3
SYMATTR SpiceLine Rser=.1
SYMBOL ind 592 -336 R270
SYMATTR InstName L4
SYMATTR Value 1
SYMBOL polcap 720 -336 R0
SYMATTR InstName C9
SYMATTR Value 3.3
SYMATTR SpiceLine Rser=.1
SYMBOL res 816 -352 R0
SYMATTR InstName R11
SYMATTR Value 750
SYMBOL VOLTAGE -592 -416 R0
SYMATTR InstName V1
SYMATTR Value 200
SYMBOL zener -320 -176 M270
SYMATTR InstName D4
SYMATTR Value BZX84C15L
SYMBOL diode 80 -192 M180
SYMATTR InstName D5
SYMATTR Value MURS320
SYMBOL res -464 -144 R90
SYMATTR InstName R12
SYMATTR Value 510
SYMBOL res -448 -368 R0
SYMATTR InstName R13
SYMATTR Value 400K
SYMBOL PowerProducts\\LT1241 -432 160 R0
SYMATTR InstName U1
SYMBOL res 928 -352 R0
SYMATTR InstName Rload
SYMATTR Value 50