> Just to add some old/new words;
>
> As a LED switcher, a small transistor should not to be seen as a current
> limiter or extra power heatsink, for this job a much lower cost
> resistor is
> recommended, except of course if the supplied voltage is not known, so the
> transistor should be used also as a current limit device.

Actually as long as you need a transistor, the incremental cost of making it
a bigger transistor to handle the power as a current regulator is small.  It
may be cheaper to use a bigger transistor than to add a resistor as a new
component.  Also the bean counters tell us that reducing parts count
improves reliability (though I have my doubts that is a usefull rule).

Doug Butler
Sherpa Engineering

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