Hi Neil!


In this configuration the current stops early, as others pointed out,
and is recirculated through the power supply
I prefer a different method, that is adding the Zener diode in series
with the regular diode used in the standard configuration, but with the
reverse polarity. In this configuration the transistor sees a peak
voltage that is the sum of the power supply voltage plus the voltage
drop from both diodes, so you must choose a transistor with a higher
Vce. I prefer this method because the current recirculates only through
the coil itself.

There is a third method, which uses a power resistor in series with the
regular freewheeling diode. You may choose the resistance and power of
the resistor to tailor the behavior of your inductor. Some calculations
required.


Cheers,

Isaac


Em 13/10/2015 18:02, Neil escreveu:
> Anyone here a pro on these?  Specifically...
>
> I usually see regular diodes across the inductive load itself, but I=20
> notice the LM1949 fuel injector driver puts a zener across the switching=
=20
> transistor.  Makes sense to protect the transistor, but wondering if=20
> this was just for the ease of putting it internally to the controller,=20
> or if there's something other better about this arrangement.
>
> Secondarily, how does one calculate the value for these?  I can=20
> calculate an estimate of the energy held in coil once energized, but=20
> with the field collapses, what determines the voltage and current=20
> produced?  It should be the resistance of the load, but that would be a=20
> diode in this case.
>
> My end goal here is to determine how to calculate the correct size=20
> protection diode.
>
> Cheers,
> -Neil.
>



--=20
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