25 Volt LED?

  I was curious if anyone knew of a vendor who makes/sells high voltage
LEDs.  I have a 25 volt power supply, and for various reasons don't
want to step down the voltage to ~12 volts with a voltage regulator.

If it helps, or makes a difference, I'm looking for an IR led with a
wavelength of about 830 nanometers, but would like to hear of any
suggestions that people have for LED vendors.

Thanks,

Holden
hbonwit04 at yahooDOTcom

 On 25 Aug 2004 08:48:13 -0700, hbonwit04@yahoo.com (Holden Bonwit)
wrote:


All IR led's have about the same inherent voltage drop, 1.2 volts or
so. Just add a series resistor.

John

 www.LEDtronics.com  We had been using a 24 VAC version for 15
years now.

Holden Bonwit wrote:

 

Seriously, even if such a high voltage LED existed, you would need to
current regulate, since the forward drop will change with temperature.
Ideally, you need to get an LED with drive electronics built in. 25v units
are quite common, since trucks use nominally 24v electronics, and many now
use LED rear lights, and instrument panel lights like this. Many are made
by SLi http://www.sli-ml.com/led.htm , and Agilent, but these companies
rarely do IR LEDs, so it does make a large difference that this is the
frequency band needed.
You don't say what sort of brightness you require.
Remember also, that you can series connect several LED's, and minimise the
resistance that has to be used. So (for instance), you could series
connect perhaps 9 IR LEDs, and then have perhaps a 25R resistor to limit
the current (you would need to check the typical forward voltage at the
rated current, but normally this is about 2.4v, for the AIGaAs/GaAS
Technology normally used at this frequency). This would be for a 100mA
rated LED, like the QLD-830-100S.
Some of the LED manufacturers do offer small switch mode drive modules
that will cover this voltage range.

Best Wishes

 Quantum physics dictates that LED voltage is related to wavelength -- about
1.8 volts for red, 3.6 volts for blue, 4 volts for ultraviolet (the white
ones are ultraviolet plus a phosphor).

All LEDs require current-limiting resistors.  There are no 12-volt LEDs
either; LED lamps that run on 12 volts have the resistors built in.