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Japex92

Thu Jan 06 2011, 02:32AM

Registered Member #3334 Joined: Tue Oct 19 2010, 02:24AM
Location: Colombia
Posts: 17

Hi,

This is Jairo PÃ©rez, I am trying to design a portable X-ray unit for dental applications, I have seem many devices that reach 70 KVp but I am not sure how they get it. It looks like they use a powerfull source based on high frecuency conversion, i am wondering if you know how is that. I have used flybacks to obtain high voltages; however, this options is a bit too old.

Any ideas?

Dr. ISOTOP

Thu Jan 06 2011, 02:57AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

I believe such units use an inverter + transformer + multiplier to achieve the necessary 70 KVp.
Steve Ward has a nice HF HV supply here:

Is this for a commercial application or for your own amusement?

Japex92

Fri Jan 07 2011, 04:24AM

Registered Member #3334 Joined: Tue Oct 19 2010, 02:24AM
Location: Colombia
Posts: 17

commercial use, what is the inverter for?

Dr. ISOTOP

Fri Jan 07 2011, 07:08AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Well, you are going for portable, aren't you? If you want battery power, you'll need an inverter.

Xray

Sat Jan 08 2011, 01:53AM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Japex92 wrote ...

Hi,

This is Jairo PÃ©rez, I am trying to design a portable X-ray unit for dental applications, I have seem many devices that reach 70 KVp but I am not sure how they get it. It looks like they use a powerfull source based on high frecuency conversion, i am wondering if you know how is that. I have used flybacks to obtain high voltages; however, this options is a bit too old.

Any ideas?

I don't know what country you are in, but here in the U.S., the laws and standards are very strict when it comes to manufacturing medical and dental equipment, especially equipment that generates ionizing radiation. You will need FDA approval, FCC approval, and probably a host of other government agency approvals before you will be able to market a portable X-ray. I am not trying to discourage you, but I just want you to be aware of what you will be up against. Oh, by the way, you also better carry a ton of liability insurance too!!

Here is a link to a successful (and VERY expensive) portable dental X-ray unit:

You may very well be able to design a portable unit that generates X-rays, but it MUST be shielded to prevent off-axis radiation. Also keep in mind that portable units operate at low mAS (milliamp-seconds) due to the limited size of the X-ray generator and the limited electrical power from a battery pack.

Japex92

Sat Jan 08 2011, 04:29AM

Registered Member #3334 Joined: Tue Oct 19 2010, 02:24AM
Location: Colombia
Posts: 17

Thank you for your recommendations!,

I am aware of what I will be through, do not worry, I am just starting to understand the principles of designing a portable xray unit. I have read that a high frecuency transformer iand CW multipliers are used, the question is how?. For our standard xray units we have the 510K approval by FDA.

Dr. ISOTOP

Sat Jan 08 2011, 04:47AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

The DC from batteries is fed into an inverter, giving AC out. This is stepped up by a transformer, and is further stepped up by a multiplier.

Xray

Sat Jan 08 2011, 05:01AM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

I have worked on a number of different high frequency (Also know as "DC" or "Constant Potential") X-ray tube heads, and they all basically operate the same, but the electronic controls are all different. As for generating the high voltage, that's all done inside the head, and there are two types of voltage multipliers that I've seen used. One type is a standard C.W. Multiplier (actually there are two CW multipliers being driven by a single transformer. One produces positive voltage for the anode, and the other produces negative voltage for the cathode). The other type of multiplier uses multiple secondary windings, each feeding a half-wave voltage doubler, and the outputs of all the doublers are in series which gives a total of 70KV. The control circuit that feeds the head is very complex because it is made up of voltage and current regulator circuits that provide a stable X-ray output. There are also safety circuits that shut down the system if anything goes outside of specified limits. Some switch-mode power supplies run at 30 to 60KHz, and some run at well over 100KHz depending on the make and model. All my experience is with line (mains) operated X-ray systems, but a portable system will probably be very similar only smaller, and operating at lower power (mA).

Japex92

Sat Jan 08 2011, 05:31AM

Registered Member #3334 Joined: Tue Oct 19 2010, 02:24AM
Location: Colombia
Posts: 17

Mr. Anders suggested the clues here are a 350 W battery pack, a ZVS, a microcontroller,a ferrite core transformer running from 100KHz to 300KHz and CW multipliers, see this:http://i55.tinypic.com/111mdjs.jpg. Such transformer must provide 6187,18 V output and 56mA current stepped up by 8-stage multiplier. The goal is to manufacture something like this:http://www.kabdental.com/dental-equipment/x- ray-intraoral/nomad.htm.

There are some manufactures in India that can provide ferrite core transformers I better contact them and see if they can manufacture a customized one, what do you reckon?

James

Thu Jan 13 2011, 04:17AM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

The small dental head I opened up had a small ferrite transformer in the head with a 1:55 turns ratio feeding a 4 stage (8x) cockroft-walton multiplier. Each diode was two DD1600 diodes in series, and each capacitor was two 1nF 15kV disc caps.

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