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Little 1:10 audio transformer as HV transformer

Little 1:10 audio transformer as HV transformer

Thse are small transformers with a ferrite core, specified as 6H secundair, and turns ratio 1:10. (conrad nr 516260). The idea was to make 400 V from 5 V with a PIC. That requires at least 40V peak primary. I tried some BC547B, but changed to a IRLZ434N MOSFET, as this one has the reverse diode for free, I tried many frequencies and pulse widths to see what gave the best efficiency, and ended up with the lowest I could make with the current PIC circuit prescaler and PWM unit (at this clock), 250 uS period time (4 kHz). I get 600 V DC after rectification, 11 mA consumption at 5V. The 600 V is into a 10 MOhm load. Diode is a 2 kV 500 us Semicron SMA FR 1Y Cap is the Wima 2kV 47 nF. I calculated efficiency at about 43 %. There is a lot of ringing with this transformer, its own resonance seems to be about 100kHz, but tuning into that, and using say fifth harmonic or 4th only decreases efficiency (core loss at 100 kHz?) On top of that that resonance seems to change depending on current flow. For example going to a 25 kHz drive frequency drops efficiency to below 5 %... So these clearly are LF transformers, as specified...

+5 FR1Y | ---------|>|--------------------- + 600V }|( | | 1 )|( 10 === [ ] )|( | 47 n | 10M | |____________________| | |-- |--------- PIC PWM --| |-- /// 230/255 |--| | IRLZ34N ///

Interesting is that the limiting factor in this circuit is the MOSFET, it has a build in avalanche protection zener, and will clip at about + 60 V, resulting in the 600 V secondair as maximum.

I wanted to test the little 'no name no spec almost' audio transformers before winding my own with 1:20 ratio.... These transformers have nice separated primary and secondairy, I think we are only limited here by the enamel isolation of wires, usually also about 600V.

The drive pulse is on for 230/255 x 250 uS = 225 uS for max output >= 600 V. The whole thing will be stabilised hysteretic by having the PIC comparator looking at the 600V (divided of course) and switching off the PWM early.

Often you see these HV generator circuits with a whole bunch of diodes and caps, sort of of a HV multiplier, and then even from a higher voltage, say 9V, and even then not stabilised. This proves there is no need for that even without winding your own transformers.

Reply to
Jan Panteltje
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iency,

escaler

to be about 100kHz,

efficiency (core loss at 100 kHz?)

Think about using one of Baxandall's class-D oscillators

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It's a sine wave oscillator, which gives you an appreciably higher peak voltage for a given DC drive, and it's obviously much more tolerant of the stray capacitance within the transformer, which - rumour has it - is why Baxandall invented it in the first place.

I'd be thinking in terms of an H-bridge to drive the primary, with a Conrad 1:1 transformer as the (split) inductor. The gates of the MOSFETs in the bridge could be driven from the drains of the transistors on the other side of the bridge if they could tale the voltage.

-- Bill Sloman, Nijmegen

Reply to
Bill Sloman

about 100kHz,

efficiency (core loss at 100 kHz?)

transformers.

One problem with flybacks is that you lose energy charging the parasitic capacitances, namely the fet drain and the transformer windings. If you remove the diode and probe the xfmr output with a low-c probe, you can see the maximum flyback voltage, which is limited by all the inductive stored energy getting transferred into the parasitic capacitances. If you want efficiency, keep the output voltage well below that point.

Often a C-W multiplier helps here.

As Bill notes, resonant converters don't suffer from charging and discharging the parasitic capacitances; they just go with it.

John

Reply to
John Larkin

On a sunny day (Sat, 17 Sep 2011 09:16:12 -0700) it happened John Larkin wrote in :

prescaler

about 100kHz,

efficiency (core loss at 100 kHz?)

caps,

transformers.

Yes, that is why u use the own resonance, make the drive pulse width so it resonates in the flyback, that is how teevee output stages work. I think I mentioned the harmonics issue.

Well of course I did all that, and as I mention before at different frequencies. Getting it to resonate needs a close to 100kHz frequency where the MOSFET can no longer be driven directly from the PIC (Cgs). A transistor works better there, but the efficiency drops, maybe because of core losses at 100kHz. I can make it resonate at a much lower frequency by adding a cap primary, now it sees about 220pF MOSFETcap. Maybe tomorrow, Was winding some transformers, got some nice small Ecore sets with formers. Got a whole of lot fascinating stuff in today, and more high tech coming. Fun.

I think about 50% efficiency is not bad here, it is a bit of elusive number, as for example what is the efficiency at 'no load'? Then it drops incredibly :-) LOL As it stabilises hysteretic, and the load is pretty much irregular impulses, think PMT, the thing will only fire to keep the cap up to charge every now and then. The resonance and multiplier you propose is big compared to this, for the other PMT:

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Takes to much space for my liking, works very well tough, good for several kV. That one runs at 15 kHz, HV coil tuned to third harmonic, I use a TIP 140 to drive it (darlington with build in reverse diode). This one uses a small PMT and has a les space available.

Reply to
Jan Panteltje

On a sunny day (Sat, 17 Sep 2011 08:47:40 -0700 (PDT)) it happened Bill Sloman wrote in :

Global warming is a lie.

Reply to
Jan Panteltje

efficiency,

prescaler

be about 100kHz,

efficiency (core loss at 100 kHz?)

caps,

transformers.

core losses at 100kHz.

it sees about 220pF MOSFETcap.

then.

PMT:

Here's a little flybackey thing I did for a friend, to demo a PLZT electro-optical gadget he invented. It makes about 900 volts from 5v in.

ftp://jjlarkin.lmi.net/Z206.pdf

ftp://jjlarkin.lmi.net/Z206_pcb.JPG

The multiplier string made the flyback part a lot easier.

John

Reply to
John Larkin

Or at best it's a guess:

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It's interesting to search, say, google news for this, and see who covered it and who didn't.

To be fair, Al Gore's 24-hour alarmathon didn't get a lot of press either. It's been called "Death by PowerPoint."

John

Reply to
John Larkin

loman

fic=3D

pr=3D

ms =3D

es =3D

So much for your grasp of reality.

-- Bill Sloman, Nijmegen

Reply to
Bill Sloman

Sloman

ffic=3D

t pr=3D

ems =3D

ses =3D

Check out "Merchants of Doubt"

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for other examples of elderly physicists with strong opinions about subjects they don't know much about.

-- Bill Sloman, Nijmegen

Reply to
Bill Sloman 

--
... "it is a tale
Told by an idiot, full of sound and fury,
Signifying nothing."


Macbeth

SCENE V. Dunsinane. Within the castle.
Reply to
John Fields

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

I guess that?s about 1 or 2ua output? 2nf is pretty small.

Cheers

Reply to
Martin Riddle

...Jim Thompson

--
                  [On the Road, in New York]

| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Sloman

That evokes images of a child snickering behind the teacher's back.

Reply to
John S

Sloman

His points were very sensible:

"In the APS, it is ok to discuss whether the mass of the proton changes over time and how a multi-universe behaves, but the evidence of global warming is incontrovertible?"

"The claim (how can you measure the average temperature of the whole earth for a whole year?) is that the temperature has changed from ~288.0 to ~288.8 degree Kelvin in about 150 years, which (if true) means to me is that the temperature has been amazingly stable, and both human health and happiness have definitely improved in this 'warming' period."

Speaking of elderly people ranting about things they don't know much about, well, face it, getting worked up about AGW is *so* last millenium. Even Obama has other priorities lately.

John

Reply to
John Larkin

Sloman

Where would this electronic design group be without the thoughtful and original contributions from our most geezer\\\\\\ senior members?

John

Reply to
John Larkin

Yeah, the PLZT load is basically a few 10s of pF, no DC at all. This was for my friend Alex, who discovered and patented some interesting effects in PLZT ceramics, like attenuation/modulation/deflection of light beams.

John

Reply to
John Larkin

Sloman

effic=

pr=

=
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Oh, crap! I gave you an opening, huh? You're as tenacious as a booger.

Reply to
John S

Sloman

effic=

pr=

seems =

decreases =

Another tasteful and insightful contribution.

John

Reply to
John Larkin

Sloman

effic=

pr=

seems =

decreases =

Yes. Exactly like this one...

On 9/17/2011 4:02 PM, John Larkin wrote: "Where would this electronic design group be without the thoughtful and original contributions from our most geezer\\\\\\ senior members?

John"

Reply to
John S

Sloman

effic=

circuit pr=

seems =

decreases =

Well, it's not as if they often have anything useful to say on-topic.

What's your opinion about using audio transformers to make high voltages?

John

Reply to
John Larkin

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