[Diy_efi] A 2N2222A can handle up to 50mA

[Bevan Weiss]

> An even simpler and cheaper solution is one of the following:
>
> MPSA27 (TO-92)
> MPSA28 (TO-92)
> NTE 46 (TO-92)
>
> Those are 500ma Darlingtons at about 14 cents a piece in bulk.  They have
> a gain of 10,000.  Base current is then unimportant.

Base current doesn't become unimportant with this gain, that means that an
Ic of 500mA will see a base current of 50uA.  Now this may seem pretty low,
but it means that you can only drive 8 of these from a standard digital
source (assuming source current max = 400uA typical).  A FET is my preferred
way of interfacing any digital signals... it has an incredibly low leakage,
and a very fast turn on time (depending only on gate capacitence and drive
resistance).

> Digikey doesn't have any of the above in stock, but they do have the
MPSA63,
> it's rated for max continuous collector current of 1.2A and has a gain
> between 5,000 and 10,000.  It's also 26 cents for 1, 19.8 for 25, and
13.73
> at 100.

If it's a DIY thing, then price doesn't play as big a role as it would in
OEM decisions.  The better design decisions can be made without compromise.
If you're dealing with digital devices (which use voltage levels for
signalling) then it makes sense to use a voltage sensing device as the
switch.

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