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

[Brian Dessent]

Perry Harrington wrote:

> 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.

Not to feed the flames but remember that a darlington has terrible
saturation voltages.  Look at the datasheet:

http://www.fairchildsemi.com/ds/MP/MPSA64.pdf

(that is the mpsa64, but the mpsa63 datasheet refers to this one for the
characterizations.)

1.2A is the absolute maximum Ic.  If you look at the graph of Vce(sat)
vs. Ic, you'll see that at 1A, Vce(sat) is about 1.6V, and that's at a
beta of 1000, let alone your suggestion of 5000 or 10000.  1.6W
dissipated through a to-92?  In an automotive environment?  You've got
to be kidding me, that's over twice the rated max.  Even at Ic=500mA,
you're still dissipating about 550mW which is marginal for to-92.  

Why nickel and dime?  Get a FET for $1 and never worry about heat
dissipation.  I don't think the OP was building these in bulk and so the
cost of $0.26 vs a dollar or so matters little.

Brian

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