just cap couple the logic signal makes an easy fail safe DF limiter m
LED boost from a uP pin
Dec 17, 2017
24 Replies
Well, don't do that.
John Larkin Highland Technology, Inc
lunatic fringe electronics
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
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
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
I feel old. I read this thread and think: "ULN2003". :)
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