LED boost from a uP pin

just cap couple the logic signal makes an easy fail safe DF limiter m

Reply to
makolber
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Well, don't do that.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

The conduction curve of an LED, or of any diode, has an ohmic component, so you can get away with constant-voltage drive if you're not too picky about the exact current.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

A TL431 makes a nice constant voltage source for multiple red/yellow/green LEDs when driving from a regulated 5 volt supply; serendipitously each time I've tried it the LEDs involved seem to run at the right current to give them appropriate brightness for the application.

That lash-up appears to be quite temperature-stable as well; hit it with a heat gun or cool the LED and '431 with cold spray until they're covered with frost, and I don't notice any change in the apparent intensity

Reply to
bitrex

I feel old. I read this thread and think: "ULN2003". :)

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Reply to
mpm

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