>
> >The only value listed is Hfe = 200.
>
> Beta of 200 then.  (I'd design to 100, if I was you :)

From the explanations I've seen it's not a problem.

>
>
> >I think I see what you're saying. The load is a relay coil and when the input
> >is +5, the relay isn't on. Is it still possible that Q2 is conducting but
> >just not enough to trigger the relay?
>
> In this circuit, with two NPNs, it takes a low at the input to turn on the
> relay.

Right. I thought you were saying that there's a situation where Q2 wouldn't
turn off.

> Low in turns off Q1, then the current through Rc has nowhere to go except
> through Q2's base.

Correct, this turns on Q2 and activates the relay. Again I thought you
were talking about Q1 activated and Q2 maybe not going off.


> If Rc isn't small enough, then Q2 may not conduct enough current to pull in
> the relay.

It did no problem. And everything turns off when Q1 is active.

But after reading Bob's suggestion I pulled out Q1 and drove Q2 directly.
It worked fine.

>
> Don't forget that protection diode across the relay!

Of course.

BAJ

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