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High Voltage Planar Ferrite transformers. ( Intial Experiments )

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Patrick

Wed Oct 01 2014, 10:36PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Electra wrote ...

Patrick good to see it progressing, don't think I was expecting to see so small mosfets. Out of curiosity what devices are they?

Trouble is I'm too set in my ways, to me I still think lots of power needs to be huge heatsinks with rows of big mosfets, and a few gigantic capacitors for reassurance. I can see now if you need it very light and small, conventional won't cut it.

Semi's are:

-555 monostable timer
-Basic Stamp 2
-FAN7382 half bridge driver
-MOSFET = NTD4857NT4G ( 25 V, 78 A, 0.0057 Ohms )
-MOSFET = SUD50N03 ( 30 V, 50 A, 0.0095 Ohms )
-5 and 12 voltage regulators

Wire:
Polyester/Polyamideimide NEMA MW 35 C (32 awg ?)

ill use one or the other MOSFET not both, obviously. If i remember the contiuous current limit of the D0-252 case is 50 Amps. so 11 to 20 V input at 5 to 25 amps, mostly i think.

This board was only intended for 20 to 8 uS pulses every 1 to 3 seconds, unipolar. Its a experimental board to evaluate the transformer cores and windings. to see what work and doesnt with and a primary waveform and a secondary waveform being measured.

( 50khz to 125kHz is the goal )

EDIT: newest pic

Dr. Slack

Fri Oct 03 2014, 04:19PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Patrick

Do I take it from the way the board looks that each MOSFET drives a primary on a single core? If so, this means you will already implementing effectively 1/3rd primary turns correctly if you drive the MOSFETs in parallel.

Now if the primary drives are separate, instead of being a single wire drive, this means that balance between the cores is *not* required for operation, though it may or may not be obvious that it will be most efficient to balance them. Although the MOSFETs might be driven in parallel, by the magic of magnetics, they appear in series at the secondary terminal, as each is contributing X amount of change of flux linkage per second coupling into the secondary. If the primaries are unbalanced, the turns ratio at each core will be different, and simply different currents will be drawn from each primary to balance the cores. But for this to work, they must all be driven at the same time.

Patrick

Fri Oct 03 2014, 08:27PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

yep i was hoping someone would see that. I hope im not crazy for thinking a full 1 turn around each core equates to 0.33 turns total. then with 300 secondary turns around all 3 cores, that means a 1:900 ratio or so. next at 25 V/t, 900t x 25 = 22.5 kV or there abouts.

Im wondering how much quadruple insulated 35 awg wire costs.

the blue line is how im running the primary wire.

the input could be 10-20 or so volts at 200 amps then 20 or 30 kV out, all in a single ferrite SMPS step.

After everyone advised me on the difficulty in fractional turns, i was really wanting to go back and think on flux lines them selves changing. I had this idea of multiple primaries in parallel, a secondary in series for quite a while. At least 6 years, the TI / Unitrode articles that made me think on the simple life of a flux line.

so right now im trying to get the 555 monostable to trigger but it wont.

Ash Small

Fri Oct 03 2014, 09:30PM

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

Patrick wrote ...

I had this idea of multiple primaries in parallel, a secondary in series for quite a while.

This is the same topology I came up with in my electronic ignition thread, based on pulse generator theory, but mine uses flyback topology to generate ~50kV.

Patrick

Fri Oct 03 2014, 09:35PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

did you series the flyback secondaries? i think youll be stuck after two. Ive done bipolar iggies and flybacks but it seems limited to two devices.

As for Dr. Sparks comment on driving at the sametime, ive got really fast MOSFETs being driven by a gate driver, and at 100kHz (10uS) they shouldnt be all that out of sync, though on a better version ill use ground floods and better gate source transmission paths.

Ash Small

Sat Oct 04 2014, 10:17AM

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

Patrick wrote ...

did you series the flyback secondaries? i think youll be stuck after two. Ive done bipolar iggies and flybacks but it seems limited to two devices.

My current plan is to use toroidal iron powder cores with distributed gap (not finalised yet), with very fast MOSFETS, maybe four per core, with one turn solid aluminium primaries (some pulse generators I've linked to use 12 MOSFETS per primary, for very fast primary half cycle), and a secondary that passes through all the toroidal cores in series. I think it's on the last page of this thread (the pulse generator details are on page 4, there is a link from the post with my proposed schematic.):

Suitable MOSFETS are very expensive (the ones used in the pulse generator were Â£40 each last time I checked. I'm expecting them to get more affordable as other manufacturers release new profucts. The pulse generator is standard push-pull transformer topology, but I'm adapting it for flyback operation.

EDIT: Sulaiman posted some details of something more similar to your project in the post underneath.

EDIT: See my comments on representing the series secondary on the schematic in one of the subsequent posts

Patrick

Sat Oct 04 2014, 02:45PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i see the internal HV diodes are present in sereis with each flyback coil, but how do you prevent a 30 kv flyback from breaking down at 90kv or 120 kv to the core?

Patrick

Sun Oct 05 2014, 03:50AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

im not able to figure out why the 555 wont trigger in the monostable mode. i may have to switch to a 8038 function generator IC. i hoard them since there not made anymore, but the risk is worth it, since this transformer may help a whole lot of us out.

i guess i see a few on ebay.

Sulaiman

Sun Oct 05 2014, 07:17AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

The trigger pulse for a 555 in monostable mode
MUST return high at least 10 us before the end of the timer period.

This is commonly achieved by putting a capacitor in series with the trigger signal
and a pull-up resistor from +Vs to the trigger pin.

R.C for the trigger input must be smaller than the timer period.
(google 555, download 555 datasheet from ti.com, see page 7 )

e.g. R=10k, C=100pF .... t = 1 us

Ash Small

Sun Oct 05 2014, 11:52AM

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

Patrick wrote ...

i see the internal HV diodes are present in sereis with each flyback coil, but how do you prevent a 30 kv flyback from breaking down at 90kv or 120 kv to the core?

I'm not using 'flyback transformers', I'm just using 'flyback mode' topology.

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