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LM338K equivalent?

sq225917 said:
Don't bother, green are lowest noise. Assuming they're not just in a green lens.
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My understanding was that GaP (Gallium Phosphide) green LEDs were the low noise ones; there are some other materials that can give a green LED, which may not be as quiet.
 
PigletsDad said:
LEDs are photodiodes, so will respond slightly to changes in ambient light. If the light is flickering, like say a fluorescent, this will appear as noise. The photocurrents will be tiny, and if they are biased with a mA or so, will make a negligble difference. Remember, we have chosen an LED because it has low dynamic resistance - the voltage changes very weakly with current. Once you have a lid on, the board should be in the dark anyway!

I can have a go at working out how big the photo-current might be, but it is going to be really small.

To convince yourself, try connecting the LED to a DVM on the most sensitive current scale, and exposing it to ambient light, then blocking the light. I would be amazed if it exceeds a microamp.
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Much thanks PD. I've just done as you suggest and the results are surprising.. Pics to follow
 
Do I care about 40 or so Mv of DC?
just about managed 800uV of AC in direct sunlight!

The reading goes up or down as the sun appears
 
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That's into a very high impedance. It indicates that the noise current is minute: 800uV into 1megaohm ~ c.8nA indicative. And less than 1pW of photovoltaic energy.

Can be ignored I think ;)
 
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