Darren Gibbs wrote:
> The NTE261 data sheet says:
>
> Collector Current = 5A continuous and 8A peak
> Collector Emitter Voltage = 100V

So that's OK as long as your relays draw less than 5A at the maximum supply
voltage.

> Small-Signal Current Gain     Ic = 3A, Ie = 4V, f=1MHz
> (not sure if this is what you mean by gain specs)

That shows the parameters at which they were going to give you the gain, but
not the gain itself.  That is probably on the next line, which you didn't
show.  Also, 4V doesn't make sense for Ie.  You probably didn't copy
something correctly.

In any case, I was trying to see if your transistor was being given enough
base drive.  How much current do the relays draw at your maximum supply
voltage?  For starters until you can report the real current gain, figure
such a power transistor needs a base current of 1/15 the maximum collector
current.  If your relays draw 5A, then that means you need 335mA of base
current.  Also note the power dissipation.  Even at Vce of 500mV that is
still 2.5W.  A free standing TO-220 isn't going to take that for long, and
Vce is likely between 1V and 1.5V at maximum current.


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