[Open_electroporator] flyback pulser parts, sketch, pulse shaping ideas

[John Griessen]

On 11/10/2013 04:35 PM, Nathan McCorkle wrote:
> possible that a fast discharging square wave pulse will
>>become a slow exponentially decaying pulse with a long tail.

that's the reason I am searching for good flyback transformers.
It will take some looking at specs, but then you have freedom
to make a shaped pulse from several circuits in parallel, (and fired close in time),
OR'd together by microwave diodes.  With just one diode and one
flyback transformer pulser you can still pulse it again and again to keep the volts up
for a while.

The volts out of a flyback depend on how long you run the low volts in and let
current increase.  So then anything goes -- a little time sequence programming
and you get a pulse with a peak of X after a rise time, and then a decay time similar
to the rise time.  That rise and fall can be chosen by sizing the L's and C's.

With diode switching, as in this sketch:  http://ecosensory.com/diybio/flyback-porator-pulser-1.png

with just one flyback pulser circuit, you can generate a long pulse of a controlled voltage
by switching the transistor again and again so current pumps up to a high voltage again and again.

The first pulse of the transistor will get you a controlled voltage and maybe for one or two more,
and then some feedback will be needed to keep it in control...by measuring it and acting on a divided
down voltage related linearly to the HV that we cannot touch or be close to.
That path is not through a well insulated transformer, but through the
divide down resistor and so is a danger.  Opto isolating is a good way to keep safe from HV reaching back
to a USB cable and wreaking havoc.  The feedback is analog though, so maybe that
means another microcontroller just to do feedback control, send a turn off time pulse back
through and opto coupler transistor LED pair.  Or, just keep it simpler and limit the input
low voltage current pumping pulses to 3 then stop and let all reset back to known zero volts.

John

PS  Where's that other EE MLP mentioned?  The list members are still just you, me and MLP
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