New HF Driver Idea

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Chris Bradley
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Re: New HF Driver Idea

Post by Chris Bradley » Sun Oct 26, 2014 6:17 am

Liam David wrote:I have seen that there are a couple of microseconds of shoot-through every time the circuit switches, and with 120v, this might be an issue. I'll see how I can build in a delay between the switches.
Why not buy an H-bridge driver that has a built-in delay, like anyone else would?

(Sorry if I am not getting what the thread is about.)

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Liam David
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Re: New HF Driver Idea

Post by Liam David » Mon Oct 27, 2014 1:58 am

The inside of the core is shiny and metallic, so it's definitely not ferrite. It might be steel. Unfortunately, I can't slide the windings off the core because the core is slightly up-turned where it separates.

Chris,
I'm just trying to build a cheap power supply using mostly parts that I already have laying around or still stuck on circuit boards. Purchasing parts for a ZVS driver capable of driving higher than 24V would cost me over $30, any while that isn't that much money, my limited budget tells me otherwise. What I'm trying to figure out is whether building this circuit and driving my transformer off of it would blow anything up.

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Re: New HF Driver Idea

Post by John Futter » Mon Oct 27, 2014 3:24 am

Liam

chris has given sage advice

you will end up with a bucket of dead silicon and probably the transformer if you continue on this train of thought. Switching psu design is for experts and even experts do not like high voltage such as you want

the best and cheapest option is to drive the transformer with a big audio amplifier with a sine wave generated from your 555 and filtered to get it sinusoidal

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Liam David
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Re: New HF Driver Idea

Post by Liam David » Mon Oct 27, 2014 6:22 pm

Well, in that case I'll drop the circuit and go with something "simpler" and less likely to blow up.

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Andrew Robinson
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Re: New HF Driver Idea

Post by Andrew Robinson » Wed Oct 29, 2014 6:03 am

Hey Liam,

Did you get in touch with "One Tesla" like I recommended? They bought an identical core and have lots of HF experience. You might try asking them for some input on how they are driving their core.

PS, don't forget to submerse the core in oil. For some people, it's easy to forget this critical step when doing testing on the bench with drivers. DONT FORGET haha
I can wire anything directly into anything! I'm the professor!

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Liam David
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Re: New HF Driver Idea

Post by Liam David » Tue Dec 23, 2014 1:52 pm

Well, I posted on the OneTesla forums about the transformer about a month ago and the only reply I got was one recommending posting on 4hv.org. Did the founders/owners of OneTesla buy it?

I found a website that gives away free samples of CCFL transformers. http://www.coilcraft.com/ccfl.cfm. Since these transformers operate at up to 100kHz, would any of these work for driving a HF x-ray transformer (after sec. voltage is decreased by a lot)?
Just trying to find the cheapest and easiest way to drive the transformer.

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Re: New HF Driver Idea

Post by Jeroen Vriesman » Tue Dec 23, 2014 2:35 pm

You could use a ready-made h-bridge driver to avoid shoot-through:

http://cds.linear.com/docs/en/datasheet/11602fb.pdf (max 60V...)

http://www.st.com/web/en/home/catalog/s ... 1501/SC911 (overview)

for example this one:

http://www.st.com/st-web-ui/static/acti ... 290377.pdf (600V, I-out is about 0.3A)

when driving bipolar transistors, see that I-out * hFe > the current you need.

When using mosfets, look at the gate capacity and see that Cgs * Vthreshold < I-out * ( required switching time) by at least factor 5 or so....very rough indication, the exact calculations are more complex, but LTspice simulations can be helpfull, keep in mind that the required switching time should be much less than the dead time (320 ns for the L6398)

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Re: New HF Driver Idea

Post by Jerry Biehler » Tue Dec 23, 2014 10:34 pm


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Liam David
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Re: New HF Driver Idea

Post by Liam David » Wed Dec 24, 2014 1:47 am

If the CCFL transformers won't work, then I will use this full bridge gate driver: http://www.mouser.com/Search/ProductDet ... 453DSTRPBF. So, would the CCFL transformers I linked to work?

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Re: New HF Driver Idea

Post by NicKolas Garrett » Fri Jan 09, 2015 1:15 am

hey guys, I'm super new here! and i didn't expect to be posting so soon :-) but I'm thinking of a solution.
Inside of a crt television you will find just what i think you need. It's called a flyback transformer. The hallmark of the flyback transformer, is it's insane V/turn ratio and turn to turn ratio. You can easily achieve 5-10 volts per turn, and with an estimated 1:100 pri:sec ratio.... Well, lets just say thee lil guys are nice. They're epoxy encapsulated, they are internally rectified and they will happily output an excess of 45kv! On top of that they weigh less then a pound and can output 10's to 100's of miliamps. But the best thing of all! Is they are as common as the transistors/mosfets/igbts you need to drive them!!! you will find at least one suitable mosfet or IGBT very close to the transformer on the PCB inside the television.

Now the best results come from driving them with a (primary resonant or ZVS)fullbridge, And the frequency doesn't really mean much(at least 10khz). The important factor is the duty cycle you drive them at. The most simple and common circuit used for them is the mazzilli ciruit *see attached*. Which operates very close to 50% duty cycle.
This circuit is so simple you can build and have a functional forward converter in less then 1 hour.
Once well optimized these flyback circuit drivers can probably output around 500 watts, so be careful they can be lethal.

If your interested, here is some more information on some of the various ways to drive a flyback. (or any ferrite cored transformer)
http://uzzors2k.4hv.org/index.php?page= ... merdrivers

i hope this can help.
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Mazzilli ZVS Flyback Driver.png
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