what type of diode is better for make high voltage diode?

[thedark]

I plan use 1n4007 diode for make high voltage diode, it better thru hole type or smd?

[klugesmith]

Didn't know they came in SMD.  In one kind, the round wires from traditional axial package are formed into a kind of J-lead, and molded plastic shape is prismatic.  The other kind appears to be a MELF.


So here are questions, not answers, for you.  Would you solder SMD parts to each other, or to some circuit-board-like substrate?   What's your plan for cooling the diodes?  How will you meet air gap and surface creepage spacing rules for the working voltage? 
Are you making a high frequency rectifier, and are 1N4007 diodes fast enough?

[edit] For applications where long string of 1N4007's is appropriate, stacking those MELF parts in an insulating tube without solder could be very handy. Must consider contact pressure, cooling, and corrosion.

[Max]

stacking those MELF parts in an insulating tube without solder could be very handy.

That's such a simple and brilliant idea! Have to remember that one. Probably works for resistors, too.


Kind regards,
Max

[thedark]

So here are questions, not answers, for you.  Would you solder SMD parts to each other, or to some circuit-board-like substrate?   What's your plan for cooling the diodes?  How will you meet air gap and surface creepage spacing rules for the working voltage? 

I plan solder that with thin and put them in oil

Are you making a high frequency rectifier, and are 1N4007 diodes fast enough?

Is necessary use fast diode for CW multiplier?

[klugesmith]

Is necessary use fast diode for CW multiplier?

It depends on the frequency. As far as I know, Cockroft and Walton got their high voltage without high frequency. i might ask if anybody here know the dynamics of HV vacuum rectifiers. But the answer is on the Internet for self discovery.

[thedark]

It depends on the frequency. As far as I know, Cockroft and Walton got their high voltage without high frequency. i might ask if anybody here know the dynamics of HV vacuum rectifiers. But the answer is on the Internet for self discovery.

I plan use a ZVS that frequency affect the diodes?

[MRMILSTAR]

I'm not a CW voltage multiplier expert. I've only built one, although it is a nice 14-stage one. You can see info about it in this section. I also use a ZVS driver. The ZVS driver in combination with a flyback transformer merely forms a high voltage oscillator to drive the multiplier stack. The diodes need to be fast enough to respond to the driving frequency. High voltage diodes with reverse recovery times of 100 ns are commonly available and work well with typical driving frequencies. That's what I use.

[John123]

What about matching and balancing? Some diodes might end up taking more of the reverse voltage due to slight leakage current variations, they make avalanche diodes to help with this issues.

[MRMILSTAR]

I believe that matching and balancing is only an issue for diodes in parallel. In a series configuration it doesn't really matter as long as the individual diodes are the same type. Diodes in a series connection is the standard method of implementing a high voltage diode. As an example look at the HV rectifier circuits for X-Ray transformers. They consist of many diodes in series.

[John123]

I believe that matching and balancing is only an issue for diodes in parallel. In a series configuration it doesn't really matter as long as the individual diodes are the same type. Diodes in a series connection is the standard method of implementing a high voltage diode. As an example look at the HV rectifier circuits for X-Ray transformers. They consist of many diodes in series.

Can't find the thread now but there was lengthy discussion about diodes in series for HV in a 4hv thread from long ago, here's a related post. Right click and open image in new tab to see the text.

[davekni]

Can't find the thread now but there was lengthy discussion about diodes in series for HV in a 4hv thread from long ago, here's a related post. Right click and open image in new tab to see the text.

That clip from 4hv explains the issue quite succinctly.  I can say from experience and many fried diode strings that Trr matching and/or extra series diodes is critical.  Likely much less so at line frequency.  My use is for a CW multiplier feeding my rapid-fire Marx generator.  4-stage multiplier fed with +-11kV 30kHz input to generate +22kV and -22kV DC.  Even with avalanche-rated diodes, many extra are needed.  Had no success at all with normal (not avalanche rated) fast diodes even with 2x diode count.  Leakage current is so small that diodes can handle that fine in avalanche breakdown.  It is all Trr driven.