Alt-BEAM Archive
Message #04358
To: beam@sgiblab.sgi.com
From: Bob Shannon bshannon@tiac.net
Date: Tue, 08 Jun 1999 22:50:02 -0400
Subject: [alt-beam] Re: SE questions not found in the FAQ.
Wilf Rigter wrote:
> Hullo Bob,
>
> The D1 works this way:
>
> Charge when bright, discharge when dark.
>
> When the light is bright the cap starts to charge through the 1N4001 diode.
> This is a 1A diode with a slightly lower Vf (ie at 100ma) than small signal
> diodes like the 1N4148 so maybe a 1N4148 is ok too. When the cap is charged
> above 2V, the voltage will be high enough to turn on the 2N7000 if the
> output of the solar panel drops significantly!
Ahhh, ok, got it, thanks.
> Without feedback the switching will be
> soft and waste power. The D1 will reset when the light level increases.
Really?
Ok, if your claiming the D2 title, I'll present the 'D3'...using 1 NPN
phototransistor, 1 PNP switch
transistor, and one fixed (or variable) resistor.
NPN phototransistor (2 lead or 3) collector, and the emitter of the PNP switch
to V+.
NPN phototransistor emitter to bias resistor (~5.1K) and PNP switch transistor
base.
The other end of the bias resistor connects to ground.
The load is between the PNP collector and ground. If you want to soften the
respose, use a 3 lead
phototransistor with a small cap to ground on the base.
With this circuit there is no diode drop between the cap and solar cell, and
what little leakage there is is only present when there is light (<20 ua).
(sorry for the lack of schematic attached)
> The PM1:
>
> Charge until it reaches the 1381 trigger level then discharge. Reset after
> the 1381 cap (0.47uf) is discharged (very slowly) through the 1381 and
> reversed biased 1N4001.
Ahhh, bingo! to provide the hysteresis, of course.
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