Re: Real Quick LED Driver Question


"John Fields" <jfields@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:skc943l500a6r6kh3nc6f3mlos98jimth7@xxxxxxxxxx
On 11 May 2007 10:58:40 -0700, Tom <kuhnto@xxxxxxxxx> wrote:

I am trying to drive an LED (2.1Vf, 20mA) from a digital signal
(3.3V). From what I have been able to understand, the logic level
output I am using does not provide enough current to drive an LED
brightly. I have another power souse (7.4V) on board to drive the
LEDs, but I do not know what transistor to use. There are so many
different ones. What would be my best option? Can someone point me
out to a model number?

---
For 20mA, almost anything will work. 2N2222 (PN2222) and 2N3904 are
popular and cheap.


My personal favorite NPN is MPSA06 (TO92), and for higher power PNP I like
MJE170 (TO225). Mostly because I have several hundred of the one and a
couple thousand of the other, among my surplus stock. I design many of my
projects around these and other components I have in bulk, unless I have to
compromise too much on specs.

For driving 8 LEDs (or even relays) it's hard to beat the 18 pin ULN2803
octal darlington driver.

Paul


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