LED operation changing

I tried

If this is a non-yellowish green, or color varies noticeably with current (lime green at low current and slightly whitish or slightly bluish-whitish green or otherwise less yellowish at higher current), or it's plenty bright at just a few milliamps, then the chip chemistry is probably InGaN. Voltage drop is typically close to 3.5V at full current and close to 3V at a few mA. Such LEDs are often, probably normally static sensitive.

- Don Klipstein ( snipped-for-privacy@misty.com)

Oh yes the resistance is correct and they are not burning out, just changing the level at which they will fire.

Thanks

Don, you are correct in the chemestry. Maybe I am not driving them hard enough to reliable light. Not sure what you mean by static sensitive....like touch, make spark and burn out? So far none have actually burned out.

I am going to try lowering the series resistor or cranking up the ps some more.

Many thanks

Sounds like your 6.5V switching supply is on the fritz.

You real sure that resistor is 1K and not, say, 100 ohms?

Best regards, Spehro Pefhany

Touch one lead when the other is connected to something else and while failing to comply with the usual static procedures can cause this trouble. Such LEDs with such damage usually do not completely die but show a threshold of current required to glow - in my experience, usually a few milliamps.

The amount of static electricity needed to cause such damage often does not cause any audible/visible sparks.

- Don Klipstein ( snipped-for-privacy@misty.com)

What I uderstand Don to be saying s that if you reverse bias the LEDs at a voltage the causes the diodes to break down - usually something like 5V IIRR - these particular LEDs can be degraded and permanently damaged, and need more current to produce the same amont of light when subsequently forward-biased.

Static electricity can do this kind of damage, or a dodgy power supply.

Thanks folks, I understand what you are saying and let me add that there are red and yellow leds of the same series that are in the circuit that are not at all affected like the green. I am going to do some bench testing this morning and see if I can come up with a solution.

many thanks

Just for my edification, try putting a number in series at a reasonable forward current and let us know what the outputs look like.

Oops I really didn't mean they were wired in series, just that the leds are of the same mfg model series.

But further testing shows interesting...When I boost up the ps to

So it appears that indeed, static charges may be to blame here.

I might clarify here what hese units are. They are a red, yellow, green led with switches mounted on a stainless steel single gang electric cover in a medical clinic as room status indicators. The area is of course all carpeted and static could well be the culprit here.

Thanks folks for all the input.

Don, Thanks, you are correct, see my post further down. Now I just have ot come up with a replacement led. Interesting in that it appears that the red and yellow do not have the same static sensitivity.

Buy them a jug of Downy fabric softener and a schpritzer. Dilute the Downy about 4:1 in water, and mist the carpet. Or, have them spring for antistatic carpet.

Good Luck! Rich

Remember back in '80 when GTE gave all their techs nice nylon windbreakers with the company logo on them... to all the guy working in the new electronic COs!

Next rule was not to wear them at work!

Charlie

The guy that told me about the Downy trick thought he was so clever - he said, "Or, any ol' anionic surfactant." ;-)

Cheers! Rich