[Open_electroporator] Why a flyback pulser ?

[Nathan McCorkle]

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. 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.

See pg 2 here, this is the thesis boiled down into a journal article:
http://diyhpl.us/~nmz787/pdf/MOSFET-Based_Pulse_Power_Supply_for_Bacterial_Transformation.pdf

He doesn't show the HV source, but doesn't show a switch (I think)
other than the (2) 2SK3748 MOSFETs, which he mentions:
"to overcome the lower voltage ratings of the MOSFET-based
pulse generators, a pulse generator using several MOSFETs in
series to increase the voltage capabilities of the device has been
designed and tested [11]. A similar device was presented in [12],
which showed simulation results on the effects of varying the
load resistance on the output pulse parameters"

in which he cites (11, 12 respectively):
http://diyhpl.us/~nmz787/pdf/Transformerless_Capacitive_Coupling_of_Gate_Signals_for_Series_Operation_of_Power_MOS_Devices.pdf
and
http://diyhpl.us/~nmz787/pdf/Performance_of_Solid-State_High-Voltage_Pulsers_for_Biological_ApplicationsA_Preliminary_Study.pdf


Yeah multiple pulses makes sense, if the low-side can't recharge the
transformer/inductor fast enough, replicate that as a functional block
and tie the outputs together.

On Mon, Nov 11, 2013 at 2:45 PM, John Griessen <john at industromatic.com> wrote:
> On 11/11/2013 01:03 PM, Nathan McCorkle wrote:
>>
>> The HV switch the MOSFET pulser paper used was parallel MOSFETs right?
>
>
> I have not read that yet.
>
> FETs can be put in parallel to get more current ability, and one decides
> bits like that later on in the process.  They get better and better and
> finding buying one is an easy part of this.
>
> Nathan, Do you get the way pulses can add at the bottom of this sketch?
>
> http://ecosensory.com/diybio/flyback-porator-pulser-2.png
>
> The curves are volts out vs. time.  The rising edges are not drawn quite
> right,
> they should be like in that flyback write up fig 15 for the starting rise.
> The fall time will depend on the load -- with a high resistivity load it
> might fall very slowly
> and no need for repeated pulses if wanting a long discharge...  But assuming
> the load
> uses up the charge, (maybe a small inexpensive cap is the reason), then
> the FET can be turned on again to build up stored energy, and on release the
> output
> will go up.  If the load is heavy and the build up time is short it won't
> even reach
> the highest the pulser can go.  That's one way this kind of pulse generator
> can be used
> with feedback -- as  train of pulses to get the volts up enough, and repeat
> as long as wanted.  That way would have light duty parts, but versatile at
> creating pulses long or short, and of a range of voltages.
>
> The voltage pulses would have ups and downs in the long chained together
> pulses,
> but that might even help.  The main thing I guess to keep from killing too
> many cells
> is to keep the voltage from overshooting.
>
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-- 
-Nathan
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