"Philip Pemberton" wrote in message news: snipped-for-privacy@dsl.pipex.com...
Hi.
Those transistors are not Darlington connected. (But I have never heard of a "complementary Darlington", so maybe you're right.)
I suspect a current setting or limiting resistor is missing somewhere. Either the emitter or collector of the PNP must have a resistor in series, otherwise the NPN base current is poorly determined and likely too high.
If the circuit was really as you've drawn it, then there would be a contest between the zener being over-driven and the NPN base being over-driven. There must be a another resistor.
I think the zener orientation you've drawn is correct. I'm not sure why the designer chooses to dissipate the stored energy from the solenoid in the transistor rather than simply grounding the zener and dissipating it there. Is it a small zener and a larger NPN? Maybe the NPN had to be large anyway to carry the necessary current, and that connection allowed a smaller zener to be used.