larryd:
Yes, must point out that there is a Vce drop that raises the power expended in the transistor.
Not saturating the transistor makes it switch off faster (Google "Baker clamp" for background info),
and you can drive it with less base current (use 1k base resistor).
Downside is that the power that the current limiting resistor took is now dissipated in the transistor.
But that should not be a problem with intermittent use.
You could always use a second IR LED (two in series).
Leo..
The important point would be to identify to ‘new people’ there is heat dissipation in the transistor with this kind of application.
Obviously, for low current applications this may not be an issue.
For higher power situations, heat does become an issue, example: higher power LEDs using a constant current source for operation.
“ You could always use a second IR LED (two in series).”
If there is head room, this is a good addition in a common emitter cct. too.
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