Quote from: paulj on March 27, 2021, 11:37:59 AM

Hello, for amateur radiography, take the two terminals of the filament (by testing the resistance) and connect one to the ground of your high voltage power supply.

don't forget that even limited in power, radiation is very dangerous.

My 40kv tube produces 13 Sv / h

Hi! Thank you for your answer  I only have one concern about this: if I connect it this way, can I power the filament directly with a DC-DC step down converter (current limited) or will this connection damage the DC-DC converter? I'm asking this because in this way the ground of HV part of the circuit will be directly connected with the DC-DC converter.

Yes I'm aware of the danger involved with radiation, I have many lead panels that I will use as shelding, and a Geiger counter to measure radiation. Thanks for your advice 

I used a stepdown converter from ebay to power the filament, no problem, as long as you care for grounding.

I missed this thread before too, but thanks for sharing your results!  Do you have any traces of the gate signal(s)?  Also, can you talk some about how you picked the various resistor values?  Are they just what you had or did they need to be tuned using the oscilloscope?  I've found these circuits to be very sensitive to the particular components and layout, so without a scope it's mostly trial and error for me.

This is the signal to the input of the Mosfet driver:


There is a peak at the beginning that I suspect it's caused by the UF4007 when they block current suddenly so a voltage peak it's produced there, but the TPS2814P manages it well.

This is the mosfet's gate signal at 200W:


There is ringing, but the mosfets stay cold. This is a stress test I did at high power (200W) but the x-ray machine is below 100W. At less power, the ringing is also smaller, but it's frequency what contributes the most to it. The frequency here is high (>100kHz).

Talking about the resistors, I knew that a big resistor at the IC inputs would reduce ringing there, but these inputs also has a capacitance, so a big resistor would have made the input activation a bit slower, I chose 1k because they worked well. I also placed 100ohm resistors next to the diodes because I could see that the fast ringing seen at the gates when turning off was caused by the 100mH inductor in all ZVS. I could see that, at the exact time mosfets are switching, this inductor causes a voltage peak to both drains that also block both diodes, and this causes a small voltage peak at the IC inputs, I could see that placing a 100ohm ressitor there reduced this noise a lot, I think it's because that resistors make the IC inputs discharge just a bit slower (due to the input capacitance), so the turning off process is delayed some nanoseconds and the other mosfet has time to turn ON, preventing the scenario where mosfets are switching and we can't consider yet that one of them is fully on, so the voltage peak produced by the 100mH inductor is smaller.

This is hard to explain and harder to understand, I had to think a lot what was causing that noise when the mosfet is turning off, until I discovered that the 100mH inductor was causing it.

This thread went under the radar for me, which is a shame, because a active drive addition to the Mazilli ZVS is a great improvement against cross-conduction failures at low input voltage.

Does it have built-in dead-time to avoid cross-conduction and possible improve it with a separate drive power supply with a large capacitance on it, in order to make sure that gate drive is the last to shut down when pulling the main power or tripping a breaker.

Thanks for sharing.

Hi Mads

I'm not an expert on this stuff (I'm a physicist not an electronics engineer). With "dead-time" and "cross-conduction", you mean to avoid enabling both Mosfets at the same time?

Talking now about the driver being the last thing to turn off, this circuit is inside the x-ray machine, that also has 2 relays, one of them is for the filament and the other feeds the Mosfet driver of the ZVS. I programmed the arduino board to first shutdown the main 48V psu via TTL signal, waits 200ms, and then shutdown the relay that feeds the Mosfet driver, this way any energy left in the LC circuit of the ZVS will leave through a fully ON Mosfet.

Hi,

Thank you for helping out, I destroyed a few stepdown converters for fillament heating due to wrong connecion.
I got my tube on E-bay long time ago, like two years back. As you can see it came with a capacitor but I guess I will remove it an install 20kV as you said and resistor as well.
I am usind DC to drive the tube but I guess that HV needs to be incresed ass well so my HV supply will get three more stages of cascades.
Your solution is much neater having everything in one box in oil, tube as well as HV.
As you can see I had tube outside and HV separately connected via HV cables.
Can you please comment on my resistor connected on HV+ it is 2,2MOhm and I put it there to prevent current surge inside the tube?
You have none so I wonder is it needed at all then?
My plan is to get this to work and then build nice looking Box to put everything in. I am thinking controlling it by Futaba RC remot that is left from an old drone I had long time ago.
Cool that are more then one self building this kind of devices.
Thanks again.
//OCV

Yes, remove the capacitor the tube has, I did that.

Don't use that 2,2M resistor, the tube's grid is in charge to manage the current through the tube, as long as you configure it with the 47k resistor. Be sure to have a good grounding, this is critical or you may break the stepdown converter.

Congratulations on getting mentioned first row in hackadays newsletter!

Yes, I'm very happy I wasn't expecting that they published it so quickly.

Hi neukyhm!


Great to see the developpment documented in your video. Really nice job and fascinating results! Some shots seem to have quite a high resolution.

X-rays are fascinating, and one day, I'll make my own experiments for sure. However, I'm very, very concerned about shielding. In the video description, you write:

Quote from: neukyhm

it has proper lead shielding. I also used a Geiger counter to make sure there were no radiation leaks.

I cannot see any shielding there. Is the whole room shielded? In any case, I'd alway be concerned about leaks, as your case can never be completely sealed (you need holes for cables, etc).
And, as I've a working x-ray tank (well, the full bridge and control circuit is missing, but transformer, rectifier, voltage divider, etc is all there) capable of a few kW, I consider shielding as crucial. My problem is, if there are any leaks, I and possibly others would be exposed while searching them.

Therefore any details about shielding would be highly appreciated!


Kind regards,
Max

Hi Max!

At 4:24 in the video, I'm attaching the lead shielding to the box. The thing is that using a lot of lead all around the box and taking care of the holes for the cables and everything is pretty much pointless because of reflexion. The x-rays will reflect on the room walls and you will have radiation going backwards.

What I did is using 1mm of lead that removes around 97-99% of the photons energy. Taking into account that the machine is activated remotely (with a countdown or via teamviewer to send the command to arduino) I think it's safe to operate. You are just waiting in another room or outside the house.

Using teamviewer you can even activate the machine from another country.

Hi neukyhm and welcome to HVF

That is a nice little machine you built, you really went all in on the details in the construction, which leads me to say that its a wonderful build process video. I like the body cam / CAD overlay combination.

Now for the questions

What body cam are you using?

What kind of intensifying screen is it that you are using? I have on/off been looking for phosphorus casettes for future project, but never found any reasonable priced.

What kind of control do you have between the Arduino UNO and the ZVS HV supply? Is it just on/off control of the supply voltage or did you extend the ZVS driver with more active driver circuitry?

Hi Mads, thanks for the welcome

I'm using a Gopro Hero 4, wich is not the best option. These cameras are really bad at low light conditions, you can see in the video that it captures very well only the part of the table where the lamp is.

My screen is an old Fuji Speed Green I got at an auction on eBay for 6€, I was very lucky. If you are looking for screens, I have seen some Kodak Lanex on eBay too, they are a bit expensive though

In the video you can see that I'm mounting a relay module with two relays. One of them cuts the x-ray tube's filament and the other one turns on and off the ZVS, no extra circuitry, just this relay between the power supply and the ZVS.