daft question on LED indicators and high VDC

**irving2008** · 15-10-2014

Cropwell has a good point and running the LED at a lower current reduces the heat generated - assuming sufficient brightness.

You can't change the laws of physics - any linear analog solution needs to dissipate 0.88w @ 20mA LED current and using more esoteric devices doesn't change that. The NUD chip is a great solution for driving strings of LEDs and/or where input voltage varies. It's simply overkill for this requirement and adds unnecessary complexity. Incidentally the NUD chip would need 2sq in of copper (the same 40 x 30mm board) to stay within ratings and from the data sheet would run a junction temperature of 113degC and a lead temperature of 46degC due to marginally better thermal characteristics than the diode, but for 10degC difference its not worth the hassle.

@binary. Your assertion that a string of LEDs would generate no heat is wrong. LEDs are around 50% efficient and do generate heat in the junction. They don't emit IR like incandescent bulbs so don't feel hot through radiated heat. But a standard 5mm 2.2v red LED run at 20mA would consume 0.02 x 2.2 = .044W of which 50% is light and 50% is heat. A string of 20 would indeed drop 44v but would still generate 4.4W of heat, the other 4.4W being light energy. But bulky overkill !!!

**EddyCurrent** · 15-10-2014

Re. putting more diodes in series, maybe this is the next trend for control cabinets

http://www.custompcreview.com/review...eview/12513/3/

**dsc** · 15-10-2014

Btw this is the LED I'm using:

http://cpc.farnell.com/apem/q8f3cxxr...56?Ntt=SC09356

**cropwell** · 15-10-2014

Get a grip !!!

Originally Posted by EddyCurrent

Re. putting more diodes in series, maybe this is the next trent for control cabinets

http://www.custompcreview.com/review...eview/12513/3/

Set me thinking though, I have a reel of white smd Led's bought for a job that never happened.

**EddyCurrent** · 15-10-2014

Maybe this thread would be useful ?

http://www.instructables.com/answers...er-dc-voltage/

**cropwell** · 15-10-2014

I have just made and installed a control panel for a glass blower friend. The labels for the modules are fibreglass circuit board. If you put LEDs behind them the lettering shines though beautifully. Next phase of project ??? I might even go full steampunk. maroon and green with gold striping and ornate Ibis carvings in the blank areas of the panels and , of course I would have to change the stainless metric button head screws to whitworth bronze slothead.

The picture btw is a screenshot of an IP camera set up to view the panel from anywhere.

**Binary** · 15-10-2014

Nice work on the furnace control, just for those still not disillusioned with LEDs have a look at http://www.onsemi.com/pub_link/Colla...I45020JZ-D.PDF http://www.onsemi.com/pub_link/Colla...SI45030A-D.PDF and there are versions of this with different current and voltages
I'm still trying to work out how to use a illuminated led as a switch if any one has done this let me know