Edward Cooper wrote:
> I'm finding it hard to search transistors by Vbe ON voltage,

That is basically a diode and is mostly dictated by the semiconductor
material.  Doping levels do have some effect, but the rest is largely an
exponential equation.  Basically silicon diodes are going to have 500-700mV
drop for most "normal" operating uses.

If you really need less, you have to use a different semiconductor material,
like germanium.  Germanium transistors are pretty scarce these days, but
there are probably some specialty ones out there somewhere.  The volumes
will be low, so be prepared to pay several times the price of a similar
silicon transistor.

> basically I need a NPN with a fairly high sensitivity, ie saturates
> at a small voltage on the base.

This really smells like the wrong pre-supposed solution to a problem.  The
right answer is probably to step back and take another look at the problem
you are trying to solve two levels up.


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