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Author Topic: Only 60V on the HV supply?  (Read 6696 times)
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« on: March 31, 2011, 12:59:13 PM »

Hey All,
       I'm rebuilding my project described in this post:
http://www.robotpirate.com/forums/index.php?topic=296.0
And here:
http://blog.wingedvictorydesign.com/2010/10/13/my-nixie-clock-build/

So I'm using the Arduinix circuit and a modified version of the software, but with my own layout to fit within my enclosure.  So I'm rebuilding my board after a hardware failure with the inclusion of a heatsink for the mosfet, but I'm only getting 60V on the HV supply.  When I adjust the voltage trim I can get as much as 70V, but that's about it.  Any idea what component I should look at?  I'm really wanting to get this finished up.

Thanks!
Max
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« Reply #1 on: April 02, 2011, 07:14:57 PM »

Hey All,
       I'm rebuilding my project described in this post:
http://www.robotpirate.com/forums/index.php?topic=296.0
And here:
http://blog.wingedvictorydesign.com/2010/10/13/my-nixie-clock-build/

So I'm using the Arduinix circuit and a modified version of the software, but with my own layout to fit within my enclosure.  So I'm rebuilding my board after a hardware failure with the inclusion of a heatsink for the mosfet, but I'm only getting 60V on the HV supply.  When I adjust the voltage trim I can get as much as 70V, but that's about it.  Any idea what component I should look at?  I'm really wanting to get this finished up.


I'd  have a look at the timing capacitors that control the 555 chip.  Those are very sensitive to the amount of power you get from the ArduiNIX.  Hope that helps!

Thanks!
Max
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« Reply #2 on: April 03, 2011, 12:34:48 PM »

Thanks for the tip, I'll definitely take a look at that.  I did find that when I connected a pot to pin 5 of the 555 and adjusted the control voltage, I was able to get the voltage up to 120V, so it's definitely somewhere in the 555 control circuitry.
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« Reply #3 on: April 23, 2011, 11:06:05 PM »

Okay, I'm completely stumped.  I've replaced everything in the 555 control circuitry including the 555 and the high voltage generator parts, part by part, and I'm getting a consistent max voltage of 80V.

At this point, I'm thinking that it might be because my board geometry is quite different than the stock configuration, because that top voltage is so consistent. 

So if I wanted to increase the max voltage range, how would I do that?  I tried reducing capacitor C3 to 1pF, but that had no effect that I could see.  I also tried different values for R17+R18, and was able to get lower minimum voltage but I wasn't able to raise the maximum voltage.  Thoughts?  Thanks so much, I'm so close to having this thing done.
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« Reply #4 on: May 03, 2011, 12:57:03 PM »

Okay, it was a board geometry problem.  I had some large areas of copper trace for the MOSFET as a heatsinking measure, and apparently that added capacitance was throwing everything off.  I redid the board with just a large ground plane and all of the high voltage components moved adjacent to each other, and thus far it's performing beautifully.

Another thing I discovered: if you ground the metal mounting plate of the MOSFET (where the screw goes through), it won't work?  Which seems like a really strange design by the manufacturer of the IRF730, I would expect that plate to be connected to the ground lead if anything.  So if your system is not producing high voltage, check that, I guess.
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« Reply #5 on: May 06, 2011, 09:27:56 AM »

Okay, it was a board geometry problem.  I had some large areas of copper trace for the MOSFET as a heatsinking measure, and apparently that added capacitance was throwing everything off.  I redid the board with just a large ground plane and all of the high voltage components moved adjacent to each other, and thus far it's performing beautifully.

Another thing I discovered: if you ground the metal mounting plate of the MOSFET (where the screw goes through), it won't work?  Which seems like a really strange design by the manufacturer of the IRF730, I would expect that plate to be connected to the ground lead if anything.  So if your system is not producing high voltage, check that, I guess.

Really glad you got it working! good info on the Fet, I didn't know that.  I normally don't do anything with that grounding tab.
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