At 04:20 PM 5/27/2006 -0700, you wrote:

>On May 27, 2006, at 3:46 PM, Olin Lathrop wrote:
> >> but the book I got this from claims that this is
> >> equivalent.
> >
> > That's nonsense.  Think about it.  How is a diode from the bottom
> > of the
> > relay to ground going to catch the solenoid current when the
> > transistor
> > turns off?
>
>It seemed odd to me certainly.  My thought was that it was something
>too clever for my newbie level of understanding to make sense of, so
>I just transcribed it literally from the book.

The collector junction was avalanching and absorbing perhaps half of the
total energy stored in the coil.

>Thanks again for helping me through this,

You can swap out the diode, in the current position, for a TVS or beefy
zener, and the circuit will work as-is. For example, a 1.5KE62A (JEDEC
1N6290A) . The solenoid will drop out faster than if you used a (cheaper) 
1N400x across the coil.
If you don't care about the drop-out time, the 1N400x is easier on both
the transistor and the diode.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


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