At 12:33 PM 2/11/01 -0500, you wrote:
o ground, would fix that.
>
>I think I see what you're saying. The load is a relay coil

You need a diode or a zener (reverse biased) across the coil, in that case.
The zener should have a lower breakdown voltage than Vceo for the transistor,
at the relay operating current.

> 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?

It isn't supposed to be on, it's supposed to be *off*. For saturated
operation,
keep Ic/Ib in around the range 10-20, as a rule of thumb. Pick the resistors
to assure that. There's no problem about the Q2 turning on if you keep Q1
saturated when it's on, the Vce(sat) will be maybe 100mV if you pick the
resistors reasonably.

If you want it to be *on* when the input is on, use a PNP Q2 transistor to
drive
the relay (emitter to +24, series base resistor to collector of Q1, and a base
to emitter resistor of about the same value. The relay goes to ground, as does
one end of the paralleled diode.

Hope this helps..

Best regards,

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