signal from coil and back emf......

[Steven Gorkowski]

Simon
Two answers to the question put a zener across the collector to the
emitter pick a zener at ~14v or a bit  higher to snub cemf across the
xsistor  or a diode across the coil is ok but it slows down the injector
because of circulating current through the diode.
Simon Quested wrote:

> Hi All
>
> I'm using a 555 timer set up as a one shot firing an injector. To
> trigger it I want to
> use the negative of the coil. The circuit works great on the bench
> but the once I connect it it fries the input.... I think this is
> because of the back emf from the coil so I put a 12v zener across the
> input.
> Can anyone help me with a filter/clipper to stop this.
>
> Cheers
>
> Simon
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   Simon Quested (E-mail questeds at lincoln.ac.nz)
>   Computer Technician, Silicon Graphics & Windows NT Support
>   Centre for Computing and Biometrics
>   LINCOLN UNIVERSITY OF NEW ZEALAND
>   Phone (64)(03) 3252811 Ext. 8087
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> http://www.lincoln.ac.nz/ccb/techs/simon/default.htm
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> I drive way too fast to worry about cholesterol
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++