[Open_electroporator] Why a flyback pulser ?

[John Griessen]

On 11/11/2013 06:14 PM, Nathan McCorkle wrote:
> I think I get the pulse idea, when the magnetic field is no longer
> sustained, it crashes and I believe current/voltage rushes oppositely
> of the charging current.

Sort of, but here's the essence:
Forget the transformer action first -- just call its input side an inductor, L.
The magnetic field stays mostly in the volume of the core material
and stores energy proportional to the current going through the L.
applying a voltage initially yields no  current, and current changes
gradually -- no step change of current -- like a flywheel.
When the voltage across the L is stopped, (FET off),  the current keeps going
the same just after FET off.

after that, the magnetic field, and the proportional current reduces only
as it finds ways to dissipate energy.  If there is no freewheel diode or resistive path
for the only gradually changing current, it goes into the small air capacitance of its own circuit shapes and
The cap shoots to high voltage oscillating or until it arcs.

Since the resistance has gone up when the
> power was cut, the voltage spikes up, something like keeping I in V=IR
> constant when the R has gone almost to infinity. Maybe the polarity
> changing is wrong, but I know the voltage spike can then be channeled
> with diodes and stored into capacitors rated for HV.


I don't like the stacked FETs for HV design.  No safety isolation of HV.
Has a path through failed semiconductors and resistors.  They can fail shorted.