what power supply?

Silent Shrill

Hi,
Need to power 100 Led's. Spec of each as follows:
Forward current 30 ma
Forward voltage 3 - 3.2v

I'm guessing 3amp minimum, but unsure of voltage requirements. Any help appreciated.

PeterTheEighth

What type of LEDs are they? Do they have built in resistors? Each LED will need to have a resistor in series to limit the current passing through it.

KeithTS

Looking at the 3A it's obvious you plan on wiring all 100 in parallel?
That way you'll just need 5V say with current limiting resistors before each LED.

Depending on your use I would suggest wiring them in sets of say 5 LEDs in series and then have each of those sets in parallel.
That way you can use less current and a higfher voltage and will have much more control over what power supply you use. The more in series the more voltage you'll need but the less current and vice versa.

ShRT

Have a look at this for a good hint on layout aswell:

http://led.linear1.org/led.wiz

PeterTheEighth

KeithTS wrote: »

Looking at the 3A it's obvious you plan on wiring all 100 in parallel? That way you'll just need 5V say with current limiting resistors before each LED.

Yeah Keith, I was gonna suggest that as well, but as you know yourself it's a lot of voltage to drop across the resistors, and almost half the power wasted.

How about getting something like a 19V laptop power supply. Then have them in batches of 5 LEDs with a series resistor. Might make it a bit more manageable.

+19V -- RESISTOR (4V) -- LED1 (3V) -- LED2(3V) -- LED3(3V) -- LED4(3V) -- LED5(3V) -- GND


Then calculate resistor to limit the current to 30ma
I = 30ma = V/R = 4/R
R= ~133ohms
Power dissipated through resistor = 120mW (so a 1/4 watt resistor will do).

What do you think? I think I'll build one myself.

PeterTheEighth

ShRT wrote: »

Have a look at this for a good hint on layout aswell:

http://led.linear1.org/led.wiz

That IS class. Really good.

Silent Shrill

Thanks for the assistance lads.
All sorted.
I have them in batches of 5. So I'll get a 15v supply. The link to the page with suggested layout was extremely helpful.
because I have 2 different types of Led's, (2 colours from different sources), 2 different sized resistors are needed, but it's no problem, I have plenty of various types here.
Thanks again.

gctest50

loads of driver chips for that craic

32 channels, 3 leds per channel , dimming , Individual Open/Short LED and Overtemperature Fault

13v to 42v input so its not too fussy

http://www.linear.com/product/LT3746

Silent Shrill

gctest50 wrote: »

loads of driver chips for that craic

32 channels, 3 leds per channel , dimming , Individual Open/Short LED and Overtemperature Fault

13v to 42v input so its not too fussy

http://www.linear.com/product/LT3746

Want to do it myself. I could just buy a 100, 2 colour led unit with power supply, switches, knobs, etc., but I ain't.
And the unit, if purchased, would need to have a certain wave length and luminous intensity. In Ireland the cost would be extravagant. If from the state's, there's post and probably duty to add on.
Makes perfect sense to build it myself for less than €20.

gctest50

Silent Shrill wrote: »

Want to do it myself. I could just buy a 100, 2 colour led unit with power supply, switches, knobs, etc., but I ain't.
And the unit, if purchased, would need to have a certain wave length and luminous intensity.

that yoke above i posted above as an example is just the chip for driving the LEDs