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[ high (>20KV) back EMF suppression ]

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texane:
Hi,

I am working on a project where I load capa then discharge them rapidly
in a coil using a MOSFET to produce a high magnetic field. To be efficient, one
constraint is to make the field as short (in time) as possible. Thus, di/dt is
very high, and the back EMF can reach up to 20kV... and I did not find any
'flyback' diode that can handle such a voltage. I found some monster diodes
that can handle 6kV, but they burned up during the first test ... :/

I try to change the switching MOSFET by an IBGT, but same problem as
above.

Maybe there are some well known techniques to address this issue, and your
help would be very appreciated :)

Cheers,

Fabien.

Psi:
Maybe look at TVS diodes or MOVs

TerminalJack505:
Your diode will try to clamp the voltage at about a volt so the problem is really the current.  More precisely, the power that's dissipated by the diode.

You can try a diode with a higher power rating.

And/or you can clamp at a higher voltage by putting several diodes in series.  This will spread the power dissipation equally across the diodes. 

A small value resistor in series with the diode is another option.  This will limit the current but raise the voltage.

BravoV:

--- Quote from: TerminalJack505 on April 03, 2012, 09:01:18 am ---And/or you can clamp at a higher voltage by putting several diodes in series.  This will spread the power dissipation equally across the diodes. 

A small value resistor in series with the diode is another option.  This will limit the current but raise the voltage.

--- End quote ---

Will a series of diodes also increase the total break down voltage proportionally ?

TerminalJack505:

--- Quote from: BravoV on April 03, 2012, 09:10:39 am ---
--- Quote from: TerminalJack505 on April 03, 2012, 09:01:18 am ---And/or you can clamp at a higher voltage by putting several diodes in series.  This will spread the power dissipation equally across the diodes. 

A small value resistor in series with the diode is another option.  This will limit the current but raise the voltage.

--- End quote ---

Will a series of diodes also increase the total break down voltage proportionally ?

--- End quote ---

As in the reverse breakdown?  That I don't know.

It shouldn't problem in this particular case, though.

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