On 11 Apr 2006 10:53:04 -0700, "BW" wrote:
--- Here's the LTSPICE circuit file for a circuit that works:
Version 4 SHEET 1 1308 680 WIRE -848 416 -848 352 WIRE -848 560 -848 496 WIRE -736 352 -848 352 WIRE -736 416 -736 352 WIRE -736 560 -848 560 WIRE -736 560 -736 496 WIRE -672 352 -736 352 WIRE -544 352 -592 352 WIRE -480 -160 -480 -208 WIRE -480 -32 -480 -80 WIRE -480 304 -480 -32 WIRE -480 560 -736 560 WIRE -480 560 -480 400 WIRE -432 -32 -480 -32 WIRE -304 -32 -352 -32 WIRE -240 -208 -480 -208 WIRE -240 -80 -240 -208 WIRE -240 48 -240 16 WIRE -240 176 -240 128 WIRE -240 320 -240 176 WIRE -240 560 -480 560 WIRE -240 560 -240 384 WIRE -176 176 -240 176 WIRE -16 176 -96 176 WIRE -16 176 -16 -896 WIRE -16 320 -16 176 WIRE -16 560 -240 560 WIRE -16 560 -16 400 WIRE 96 -736 96 -928 WIRE 96 336 96 144 WIRE 144 -928 96 -928 WIRE 144 -896 -16 -896 WIRE 144 144 96 144 WIRE 144 176 -16 176 WIRE 176 -944 176 -1280 WIRE 176 -512 176 -880 WIRE 176 -208 -240 -208 WIRE 176 128 176 -208 WIRE 176 560 -16 560 WIRE 176 560 176 192 WIRE 272 -912 208 -912 WIRE 272 160 208 160 WIRE 432 -912 352 -912 WIRE 432 160 352 160 WIRE 496 -960 496 -1008 WIRE 496 -736 96 -736 WIRE 496 -736 496 -864 WIRE 496 -688 496 -736 WIRE 496 -512 176 -512 WIRE 496 -512 496 -608 WIRE 496 -464 496 -512 WIRE 496 112 496 64 WIRE 496 336 96 336 WIRE 496 336 496 208 WIRE 496 384 496 336 WIRE 496 560 176 560 WIRE 496 560 496 464 WIRE 496 608 496 560 WIRE 576 -1008 496 -1008 WIRE 576 64 496 64 WIRE 704 -1008 656 -1008 WIRE 704 64 656 64 WIRE 832 -1008 784 -1008 WIRE 832 64 784 64 WIRE 960 -1008 912 -1008 WIRE 960 64 912 64 WIRE 1088 -1008 1040 -1008 WIRE 1088 64 1040 64 WIRE 1248 -1280 176 -1280 WIRE 1248 -1008 1168 -1008 WIRE 1248 -1008 1248 -1280 WIRE 1248 -208 176 -208 WIRE 1248 -208 1248 -1008 WIRE 1248 64 1168 64 WIRE 1248 64 1248 -208 WIRE 1248 304 1248 64 WIRE 1248 560 496 560 WIRE 1248 560 1248 384 FLAG 496 608 0 FLAG 496 -464 0 SYMBOL Opamps\\\\LT1006 176 96 R0 SYMATTR InstName U1 SYMBOL res 368 144 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 2700 SYMBOL res 512 480 R180 WINDOW 0 36 76 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName R2 SYMATTR Value 1 SYMBOL npn 432 112 R0 SYMATTR InstName Q1 SYMATTR Value 2N4401 SYMBOL res 672 48 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R3 SYMATTR Value 8.4 SYMBOL res 800 48 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R4 SYMATTR Value 8.4 SYMBOL res 928 48 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R5 SYMATTR Value 8.4 SYMBOL res 1056 48 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R6 SYMATTR Value 8.4 SYMBOL res 1184 48 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R7 SYMATTR Value 8.4 SYMBOL voltage 1248 288 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res -32 304 R0 SYMATTR InstName R8 SYMATTR Value 240 SYMBOL res -80 160 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R9 SYMATTR Value 2200 SYMBOL res -256 32 R0 SYMATTR InstName R10 SYMATTR Value 3300 SYMBOL pnp -304 16 M180 SYMATTR InstName Q2 SYMATTR Value 2N4403 SYMBOL res -336 -48 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R11 SYMATTR Value 10k SYMBOL res -496 -176 R0 SYMATTR InstName R12 SYMATTR Value 10k SYMBOL References\\\\LT1009 -240 352 R0 SYMATTR InstName U2 SYMBOL npn -544 304 R0 SYMATTR InstName Q3 SYMATTR Value 2N3904 SYMBOL res -752 400 R0 SYMATTR InstName R13 SYMATTR Value 10k SYMBOL voltage -848 400 R0 WINDOW 3 -3 207 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value PULSE(0 5 0 1e-6 1e-6 .001 .01 10) SYMBOL res -576 336 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R14 SYMATTR Value 1k SYMBOL Opamps\\\\LT1006 176 -976 R0 SYMATTR InstName U3 SYMBOL res 368 -928 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R15 SYMATTR Value 2700 SYMBOL res 512 -592 R180 WINDOW 0 36 76 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName R16 SYMATTR Value 1 SYMBOL npn 432 -960 R0 SYMATTR InstName Q4 SYMATTR Value 2N4401 SYMBOL res 672 -1024 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R17 SYMATTR Value 8.4 SYMBOL res 800 -1024 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R18 SYMATTR Value 8.4 SYMBOL res 928 -1024 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R19 SYMATTR Value 8.4 SYMBOL res 1056 -1024 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R20 SYMATTR Value 8.4 SYMBOL res 1184 -1024 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R21 SYMATTR Value 8.4 TEXT -858 648 Left 0 !.tran 0 .1 0
It's basically a switched reference driving (if you want 40 lamps) eight five-lamp constant current drivers.
With 5 lamps dropping 2.1V each that's 10.5 volts out of 12, which gives you 1.5 volt of headroom to play with, which the 2N4401's and current sense resistors soak up nicely.
I've modelled the LEDs as 8.4 ohm resistors, since:
2.1V R = ------- = 8.4 ohms 0.25AI've only shown two drivers and their loads, for convenience, but the other six just connect across the 12V supply, with the + input of all the opamps going to the reference voltage at the junction of R8 and R9.
It simulates beautifully, as you'll see when/if you run it.
Post back if you have any questions. :-)
-- John Fields Professional Circuit Designer