On Tue, 11 Oct 2011 16:32:09 -0500, "Dave" wrote:
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..
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Thought I had it with the mini
photocell. Still can't figure out why that one doesn't work. sigh

Dave

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Seems to work nicely after a few resistor value changes.

Also, I guessed at the PV's output voltage as 8V with a 50mA load and
fiddled with R1 (its internal resistance) to get 50mA into D1.

Do you have the open circuit voltage and short circuit current spec's
for the PV?

Here's the sim:

Version 4
SHEET 1 880 680
WIRE -144 -112 -192 -112
WIRE -48 -112 -80 -112
WIRE 64 -112 -48 -112
WIRE 144 -112 64 -112
WIRE 320 -112 224 -112
WIRE 320 -80 320 -112
WIRE 64 -64 64 -112
WIRE -192 -16 -192 -112
WIRE -48 -16 -48 -112
WIRE 320 16 320 -16
WIRE 64 64 64 16
WIRE 144 64 64 64
WIRE 256 64 224 64
WIRE -192 112 -192 64
WIRE -48 112 -48 64
WIRE 64 112 64 64
WIRE -192 240 -192 192
WIRE -48 240 -48 192
WIRE -48 240 -192 240
WIRE 64 240 64 192
WIRE 64 240 -48 240
WIRE 320 240 320 112
WIRE 320 240 64 240
WIRE -192 304 -192 240
FLAG -192 304 0
SYMBOL res 48 -80 R0
SYMATTR InstName R3
SYMATTR Value 4700
SYMBOL npn 256 16 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL LED 304 -80 R0
SYMATTR InstName D2
SYMATTR Value NSCW100
SYMBOL schottky -144 -96 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value 1N5817
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 48 96 R0
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 240 -128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 56
SYMBOL voltage -48 96 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 4.8
SYMBOL voltage 128 64 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 -32 56 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value PULSE(0 4 0 12 12 0 0 1)
SYMBOL voltage -192 96 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(0 8 0 12 12 0 24 1)
SYMBOL res -64 -32 R0
SYMATTR InstName R2
SYMATTR Value .1
SYMBOL res -208 -32 R0
SYMATTR InstName R1
SYMATTR Value 58
TEXT -162 272 Left 2 !.tran 24 startup uic

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JF