Which driver do I use?

Other Hardware LEDs and Multiplexing
1

Hi,

I'm looking for an LED driver for a project. I need to power IR LEDs (48 currently, around 300 eventually) and pulse them at 38kHz. I'm sure there's a good driver for this but after talking with a representative at Maxim and searching this and other forums, I'm still not sure which to use. Any advice would be appreciated.

Thanks in advance,
Kevin

2

Which LEDs? Maybe all you need is to make strings of LEDs, connect the strings in parallel, and then sink current with good N-channel MOSFET, like AOI514 at digikey.com

What do you have for a voltage source? 12? 15? 24? The higher it is, the more LEDs you can have in series and the less current you will need.

What are you doing that they need to be pulsed at 38 KHz?

3

I'm making a touch screen overlay. It just uses sensors opposing LEDs to read touch locations.

I've changed the LEDs a few times in search of what's best. I still don't know but I think they'll just need to be low viewing angle These, in particular, (QED123) are low viewing angle but otherwise pretty standard. There's a 1.7V forward drop and 20mA through them should be fine.

The problem is, IDEALLY, it would be able to run off of a 5V source, which would make most of them need to be in parallel. I figure some sort of scanning/polling thing might need to happen (another reason I thought a driver might help, since I think there are some that do that).

What do you think? Am I hoping for too much with the 5V source idea? If so, I could trade up to a higher voltage, I would just prefer not to.

4

You do not want all your LEDs on at the same time because no matter what your viewing angle of your LED they will interfere with other sensors. Therefore you need some sort of port expander to drive them. Something like a number of latches or a shift register.
To have 48 LEDs in such a system is silly to have 300 is more than silly.

5

You might want to look at this project of mine which started life as an overlay touch screen.
http://www.thebox.myzen.co.uk/Hardware/The_Sound_Square.html

6

Okay, I think I can figure that out and give it a shot. Also, I'll look into that project and get back to you soon-ish if I need any more assistance.

Thanks a lot for the advice!