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Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Here's a design for a 50kV diode 'pcb' I whipped up in illustrator. Seeing as 50kV 1A diodes would be ungodly expensive, I suppose 50 1N4007's would be the next best thing.
Added those diamond gaps to prevent surface tracking, but I'd like to get a second opinion before I waste acrylic...
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
Leakage along the string is not a great problem, but corona leakage due to high potentials at the ends of the string is. A PCB trace at 50 kV would emit corona in all directions. I think that it's safe to use this design in air for +/- 25 kV, but 50 kV-0 would be problematic. You can mount the string in a plastic tube filled with oil, if a small leakage is not a problem. Take a look at microwave oven diodes. They are not too expensive, and support 12-15 kV, 500 mA, with extremely low leakage.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Grenadier wrote ...
Here's a design for a 50kV diode 'pcb' I whipped up in illustrator. Seeing as 50kV 1A diodes would be ungodly expensive, I suppose 50 1N4007's would be the next best thing.
Added those diamond gaps to prevent surface tracking, but I'd like to get a second opinion before I waste acrylic...
Well, to me this looks like an ungodly expensive PCB to make, unless you have a free access to a laser cutter or something.
You don't have to worry about surface tracking much, considering you don't ever want to see more than few hundred V over a single diode. A few mm of copper clearance between two diodes would likely be just ok, although you'll get corona anyway if you push the voltage very high.
I personally wouldn't even bother with a PCB though. Just solder a string of diodes, wind it around a smaller plastic tube and put the whole into a larger tube. Then pour some candle wax or resin over it.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
Did you make the acrylic pattern or just cut it from some part with this shape? My HV diodes are also assembled in zigzag, but I used plain boards (5 kV diodes):
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
I'm surprised that no one has mentioned it yet, but 50 off 1kV diodes in series don't make a 50kV diode.
The first time you reverse bias them, some will turn off faster than others, see an excess share of the reverse voltage, and get killed - usually short-circuit which is good as then the series string keeps on working. This will leave you with a string of the more robust, better matched diodes, that you might hope will continue to work for a long time. But at less than 50kV.
The general rule of thumb for putting non-avalanche rated diodes in series is to run them at 50% of nominal PIV to allow for this.
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50kV diode board
