> BTW Tom, I'd recommend ZTX transistors for driving IR LEDs.
> They switch faster and better and more current than other common
> types (eg TO92 like BCxxx or 2Nxxxx). Their higher current rating
> means a low value series R can be used eg 1 or 2 ohms for good
> range, but watch the wattage dissipated by the IR LED

Jinx has got a bit religious over Zetex transistors over time. That 
said, they do make some very nice products. Do take car to read the 
data sheet very carefully to ensure you are really getting what you 
expected.

They make some of the nicest small moderate power transistors around. 
Their E-line package is TO92 size but has far better thermal 
characteristics. Good for a watt in free air as I recall. They have 
some E-Line transistors with simultaneous ratings of 1A, current gain 
in the hundreds and commendable Vsat (tenths of a volt range). You pay 
quite a  premium price for these.

If you want small transistors for switching moderate power that are 
not quite as good as Zetex's best, but still far better than most and 
far cheaper, look at BC337 / BC327. 500 mA (or slightly more for some 
makers). Beta in the hundreds (depending on current) and OK Vsat. Can 
be 10 or 20 times cheaper than top Zetex parts. Pd not as good.


        RM

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