Re: Looking for pulse-rated zener.

Fred Bloggs wrote...
>
> Failing availability of the pulse-rated zener, you can always use the
> more common TVS variety by reverse biasing to just below minimum
> withstanding voltage.

>.
>. ------ o----------+---LLLLLLLLL---------+
>. | | |
>. | o--+ | - + |
>. -- | '--|<|-+-----||-------+
>. | | C |
>. | | |
>. | | TVS |
>. | | / |
>. | +-----|>|------+
>. | | / |
>. | | |
>. +-----------------------------+
>. | | |
>. --- | R
>. - | |
>. | |+ |
>. '---||---|>|---'
>. |
>. 100V

But, TVS, Transient Voltage Suppressors, are just pulse-rated zeners.
No complex circuit is needed to use them with the MOSFET and coils.

.. 8A <-- coils
.. ,---UUUUU--UUUUU--- constant-current supply
.. | or supply + ballast R
.. | TVS p6ke150A
.. +-----|<|------ gnd
.. | /
.. |--'
.. ||<-, MOSFET
.. --/\/\--'|--+ fqaA34n20
.. |
.. gnd

This assumes one doesn't simply use the FET's avalanche capability:

.. 8A <-- coils
.. ,---UUUUU--UUUUU--- constant-current supply
.. | or supply + ballast R
.. |--'
.. ||<-, MOSFET
.. --/\/\--'|--+ fqaA34n20
.. |
.. gnd

In fact, with an appropriately-chosen gate resistor, the current
turnoff could be programmed to the desired 1us time, without the
200V + avalanche-voltage for the fqaA34n20 even being reached...
Same circuit as above, different gate-resistor value. :>)


--
Thanks,
- Win
.