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i have made a flyback transformer for some HV experiments and am hoping to get around 35kv from it, which i want to use to charge a capacitor, so i will need to rectify the output... i think perhaps some kind of asimetrical spark gap might be able to do the trick but was hoping and wondering if I would be able to string together a load of diodes in series to do the job?

I have some 1n4007 diodes with a max reverse voltage of 1k... if I put 40 in series will it work, or will they all just melt? something I read suggested that I would need resistors somehow involved with the diodes to make it function? how would that work?

if the answer is no, does anyone have any suggestions about ways to do this?

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  • \$\begingroup\$ Just get some microwave diodes and put those in series, much less physical distance. Also how much current do you need? cockroft walton might make more sense and has less requirements for the components. \$\endgroup\$
    – PlasmaHH
    May 18, 2015 at 15:41
  • \$\begingroup\$ current isn't really important, ican always wait a bit longer for the cap to charge... I had thought about putting together a kelvin's thunderstorm thing or wimshurst machine but went with the flyback as I had some wire to hand... it's really just a joule thief with a big output coil... \$\endgroup\$ May 18, 2015 at 17:20

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1N4007 are not really suitable for such a high frequency circuit due to their slow recovery time (microseconds). At mains frequency you could use series string. You could try a series string of UF4007 diodes (75ns recovery time).

You can buy packaged 80kV 200mA 100ns rectifier stacks for about $30 if you look around.

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  1. to get higher voltage I used voltage multiplier circuits to generate 60kv 1 mA supply where diodes are inbuilt in each stage. I used 20KV selenium diode used for black & white TV HV supply.
  2. one can use silicon HV diodes used in colr monitor of computer.series connections of 1N4007 to suit such HV may require equilising circuit and may become combursome. vtingole
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  • \$\begingroup\$ I was hoping I could get away with the 1n4007 string just because I have them here now... for now the tidiness of the setup isn't an issue so long as it works... what do you mean by an equalising circuit? one of the other answers mentions resistors in series... does that mean I need to put a resistor between each diode in the chain? wouldn't that drop the voltage massively along the whole length? I think the thing I read before said there should be a resistor across each diode, implying that the resistors are parallel to the diodes. sorry, but I'm confused. thanks to all for the replies btw \$\endgroup\$ May 18, 2015 at 17:16
  • \$\begingroup\$ Yes you are right one has to equalise the reverse voltage resistance of each diode. If you want to know more pl. read what is STRING EFFICIENCY in HV supply. vtingole \$\endgroup\$ May 19, 2015 at 14:33
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I have seen many years ago EHT circuits inside the old CRT televisions which employed voltage multiplier (doubler/tripler) circuits using diodes and capacitors.

Something like this: just ensure you use appropriately rated diodes and capacitors.

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You can place multiple diodes in series in order to handle higher rated voltages. Might not be a bad idea to place a resistor in series so that if a diode does break down and go short circuit, it will limit the current and not cause too much damage. But again, calculate the voltages carefully and ensure you don't exceed the working voltage for any individual component.

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