daft question on LED indicators and high VDC

**EddyCurrent** · 14-10-2014

I didn't think of using a voltage regulator at first, given the OP's requirements, but it's a good idea.

**Binary** · 14-10-2014

If its because the chip i mention is a smd can i say don't be frightened to try just make sure your not using a blow lamp to solder with, I have soldered these i.c.'s using a soldering iron, there are a few ways of removing the solder if you mess up, solder sucker for one, then check by running a stanley blade between the contact legs to make sure no "whiskers of solder is left".
Can i say if you can buy leds at a good price like Meeee. if your using the LED panel light which will have a resistor in using red leds as a zener could be good. Red LEDs have a 2.2 volt drop times this by 10 in series, yes you've got it 22 volts so 20 leds will give you 44 volt drop with your 24 volt panel light also in series your resistor in the panel light current limiting you leds you will have a 68 volt led ...and a lot of additional light ..but no heat
this is food for thought.

**Clive S** · 14-10-2014

I can see that your going to be another valuable member of this forum.

..Clive

**cropwell** · 14-10-2014

Most of the thinking seems based on 20ma current through the LED. It might be worth experimenting with resistor values that give about 5ma and see if the brightness of the LED is acceptable. So then a single series resistor would dissipate less power and could be a cheaper component.
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Just had a play on the breadboard and LED in series with 4 x 4.7k ohm (18.8k) still gives a reasonable light. I tried it on 30v 15v and 5v (5v is probably too dim). I used a standard 3mm red in a clear capsule LED.

**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.