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Creating a Power supply 10 kV to 40 kV a few mA - Questions

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Fredasp

Mon Mar 11 2013, 01:06PM

Registered Member #10754 Joined: Thu Mar 07 2013, 08:04PM
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Posts: 8

Hi,

What I need:
I need a power supply with a range of 10kv to 40kv with few ma (what is safe? max 10ma ?)
This supply will work for 30 min continuously more or less.
I'll use it at work with Electrospinning experiments (like this

What I've done until now
I started with this (well know) schematic:

Then I face a big heat problems with the IRF530. Only few seconds and the mosfet almost melted
Here the video: [

]

I moved to IRFP450. I still have problems with melting mosfet. [ I'll upload new video soon]
I read a lot of threads before post this, and i found this one:

I could implement some improvements, like the parallel capacitor with primary coil and the diode in parallel with mosfet irfp450. Now I got large arcs (at 30khz) , but I only run for 20 seconds before it get really hot.

One thing... I dont need the arcs. I'm opening arcs in order to "measure" the Kv (I know it's not precise)

My questions

Is this single mosfet schematic a good way to go with this project?

What is the proper timing to turn-on /off the mosfet irfp450, the off time is 200us right ?

I belive there is more current than I need here...

What should I do to prevent this heat problem? How to control the voltage range? with the power supply line (12v now)

thank you!

Fredasp

Tue Mar 12 2013, 03:09AM

Registered Member #10754 Joined: Thu Mar 07 2013, 08:04PM
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Posts: 8

Here is the new video

(and now I have this problem with arcs between the pins )

Ash Small

Tue Mar 12 2013, 10:22AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Fredasp wrote ...

(and now I have this problem with arcs between the pins )

Put the flyback under oil. Cheap cooking oil that's been boiled to remove any moisture should do the job.

Fredasp

Wed Mar 13 2013, 06:17PM

Registered Member #10754 Joined: Thu Mar 07 2013, 08:04PM
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Posts: 8

Hi, the requirements was changed: from 8kV to 15 Kv selectable. I think it will help to reduce the heat in the switching mosfet.

I sitll wondering the best way to reduce the output voltage: by PWM, Frequence or at the primary voltage supply....

Anyone ?

HV Enthusiast

Wed Mar 13 2013, 07:43PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Don't make it more complicated that it needs to be.

Just get a neon sign transformer (NST) and a variac. A 12kV, 30mA NST which can be found for free almost anywhere will provide you with everything you need and be practically bombproof.

Fredasp

Thu Mar 14 2013, 03:01AM

Registered Member #10754 Joined: Thu Mar 07 2013, 08:04PM
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Posts: 8

Hi EasternVoltageResearch, sounds good, but the project will be more well implemented later with microcontroler and stuff.

Im reading more and IÂ´ll try the TL494 and a npn-pnp configuration to saturate properly the Mosfet and see if it will help.

Do you know the minimum reliable timing (on/off) of the IRFP450 to use in this HV application?

Fredasp

Mon Mar 18 2013, 12:58PM

Registered Member #10754 Joined: Thu Mar 07 2013, 08:04PM
Location:
Posts: 8

Does my problem are so obvious to solve or too difficult?

Ash Small

Mon Mar 18 2013, 01:53PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Fredasp wrote ...

Does my problem are so obvious to solve or too difficult?

Firstly, what kind of heatsink/cooling are you using for the MOSFET?

Fredasp

Wed Mar 27 2013, 04:34AM

Registered Member #10754 Joined: Thu Mar 07 2013, 08:04PM
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Posts: 8

Hi Ash Small, I had a really had time by trying to fix it, but finally I did.

IÂ´ll post soon the schematic... nothing new, but maybe it iÂ´ll help someone in the future.

Here is a video

The mosfet it not get crazy hot... with the same heatsink/cooling, itÂ´s cold even in haddest moment.

But there's one thing is puzzling me:
Do you saw the video? It was the first try with this flyback - and as giving me like 8cm of spark and loud and huge hiss (and that a fta blue thing - corona discharge right? )

So, after that video, I put all the circuit and flyback in a custom plastic house (mad of PVC) using the very same wires and powering with the same power supply and to my surprise, it wasnt the same as before - now all what I have is 'normal' arc over 2,5 cm - 3cm max....

Something happend inside of the flyback?
any clue? does it happened before in some experiments with flyback previously with you (someone here)?

(still... itÂ´s more a curiosity bc now what i have is perfect for what i need... but in near future i want be able to have those sparcks again ;) )

Fredasp

Thu Mar 28 2013, 01:45AM

Registered Member #10754 Joined: Thu Mar 07 2013, 08:04PM
Location:
Posts: 8

here is the measuring... I stopped in 20 kv .. it's what I need... but it could go a lot further .
Besides the fact that some harmonics returned through the main line and ruined the Agilent power supply (used the logic part) :/

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