LED Frequency Ranges

Hi.

I once tried to find the same kind of data, and found a SLED (superluminescent diode) with the feature "pulsed operation"

I wrote to the manufacturer to see if they would part with some data as to what that meant, and got a nice reply with some frequency response data. Sorry I cannot lay hands on it. (It was for a one-time job.) But you should be able to retrace that path.

All I remember was that it was much faster than necessary to be considered flat in the 100 KHz to 10 MHz band.

You might see if you can find anything on the diffusion capacitance of GaAs diodes. That relates directly to carrier lifetime which in turn controls emission frequency response since emission is directly related to carrier density/population.

Good luck. You'll need it as I recall.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

Virtually all LEDs have rise/fall times in the range of 10nsec to

1usec. For 100% modulation, the upper limit for LEDs is in the neighborhood of 20MHz for types designed to be modulated (e.g., communications devices at 850nm wavelength). The upper limit is usually just a MHz or less for devices optimized for illumination energy output. It doesn't take much equipment to make your own measurements. Just be sure to use a really small photodiode, a small load impedance, and to keep LED and photodiode far enough apart that you're not looking at capacitive or magnetic coupling between them. You can check for either by blocking the light with an opaque non-metallic object: any light coupling should go away. Paul Mathews

Thanks to both of you - Paul and Larry for the information. At least I now have some clue and something more to go on - which is more than I had when I originally wrote my question. I just wanted to be sure they would modulate to at least 500KHz and from what you are telling me - that should not be a problem.

Best to both of you!

Don H

On 16 Mar 2005 22:29:49 -0800, "LightBoy" wroth:

So far, all the responses have concerned "bare" LEDs. I'll be willing to bet that "white" LEDs, the ones that use a UV LED to excite a white phosphor, will have dramatically slower rise and fall times because of the phosphor.

Jim

I use conventional T1-3/4 LEDs driven by a stiff square 50% 40mA source at

6MHz. You will have no difficulty at 500KHz.

Tom