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Transient Voltage Test Circuit help

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I found this basic boost circuit https://www.ladyada.net/library/diyboostcalc.html but in my testing on LTSPice it would take a very long time to charge up a useable cap.. Mind you I'm not sure if I got the PULSE settings right, I used PULSE(0 5 0 1n 1n 15u 31u) for ~31kHz 50% duty cycle.

Then I had a thought, what about a centre taped transformer driven from a pic to generate a ~120VAC output on the secondary and then rectify that back to DC, filter it and use some sort of charge resistor and fet to control the rate of charge of the cap and prevent charging once it reaches a desired level? What you think? pretty convoluted but would probably provide the fastest method of charging a cap with any voltage up to ~120VDC or higher if I wound the transformer for more...
 
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Or think about this one. It's a voltage multiplier. You could drive it with a 555 oscillator. Each stage adds about 12volts to the previous stage so you could put the switch at the voltage you want. Takes about 10 seconds to charge up. It doesn't come close to meeting the load dump spec but it would let you see the voltage at the input to your circuit under a typical transient.
 
Ok, I think I've got a useful solution now... I won't bother posting the entire system as I haven't finished it yet but here is my "testing" portion. I've used 240V rectified to DC and filtered via a High Voltage FET M1 (Controlled by a microcontroller) to vary the charge voltage of a series of capacitors. a 10W 820Ohm resistor slows the rate..
Basically the microcontroller incrementally charges a number of different rated caps, that are isolated from each other to prevent them all charging at once, to create many scenarios of varying voltage and capacitance. At each stage the voltage is measured and the program will maintain constant charge in the caps via their fets. At the end of it there will be an output that goes to the unit to be "tested" and the pressing of a release button will prompt the triggering of the SCR at the end that dumps the energy to the output. I'll use a pot to select the voltage and a 20x4 LCD to display relavent information and probably try and program some base test profiles in to make it easier to choose a scenario to be tested for..

M2 is there as a safety discharge function should the unit be charged or similar and that charge not be wanted anymore :|

All in all a little bit of major overkill for a simple task, eventually I'll finish it into a PCB and write the program for it. I think this one will be potentially the most dangerous electronic device I've built... Hopefully it will provide the testing profile I need.

Let me know your thoughts.

View attachment 65717
 
To be honest since you don't know the pulse that's putting the hurts on your supply I would just model it in spice to get the numbers you want. I think you could use something like this:

When I look at it it seems to want a bigger capacitor. See what you think.
 
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