Forums

0.2MHz - 2MHz step up transformer

Started by Paul Jackson January 22, 2012
On Mon, 23 Jan 2012 09:47:38 -0600, amdx <amdx@knology.net> wrote:

>On 1/22/2012 11:58 AM, John Larkin wrote: >> On Sun, 22 Jan 2012 08:01:45 -0600, amdx<amdx@knologynotthis.net> >> wrote: >> >>> On 1/22/2012 6:05 AM, Paul Jackson wrote: >>>> I am looking for an impedance matching transformer that will convert >>>> the 50 Ohm output of my function generator and to a 1K Ohm resistive >>>> load. >>>> >>>> That provides a 20x step-up as well, so with losses 10V yields maybe >>>> 100V. >>>> >>>> Frequency range is anywhere between 200KHz to 2MHz. Required current, >>>> up to 20mA. >>>> >>>> I would definitely prefer a ready-made transformer. Does anyone know >>>> under what application heading one might be found? >>>> >>>> Paul Jackson >>> >>> If you want 20 ma at 100 volts, I don't think you generator will supply >>> the power you need. >>> If the generator supplies 10V into 50 ohms that is 20 ma. >> >> 200 mA, short-circuit current. >> >> John > > > >Hi John, > Oh, redid the math. You're right :-) > Mikek
I have this background thing that runs in the back of my head and checks the math on everything. It's really annoying to read the newspaper. Journalism schools don't seem to teach advanced concepts, like the difference between an amount and a rate, or the difference between a million and a billion. This morning's catch: somebody had men and women rate pain on a scale of 0 to 10, and concluded that women feel 20% more pain. John
Jan Panteltje wrote:
> On a sunny day (Sun, 22 Jan 2012 16:58:20 -0800) it happened Joerg > <invalid@invalid.invalid> wrote in <9o3pleF6n6U1@mid.individual.net>: > >> Believe it or not but I never owned an EPROM programmer. > > Oh, I believe it, you chiseled the bits in no?
Nah, I used punch cards :-) -- Regards, Joerg http://www.analogconsultants.com/
John Larkin wrote:
> On Mon, 23 Jan 2012 09:47:38 -0600, amdx <amdx@knology.net> wrote: > >> On 1/22/2012 11:58 AM, John Larkin wrote: >>> On Sun, 22 Jan 2012 08:01:45 -0600, amdx<amdx@knologynotthis.net> >>> wrote: >>> >>>> On 1/22/2012 6:05 AM, Paul Jackson wrote: >>>>> I am looking for an impedance matching transformer that will convert >>>>> the 50 Ohm output of my function generator and to a 1K Ohm resistive >>>>> load. >>>>> >>>>> That provides a 20x step-up as well, so with losses 10V yields maybe >>>>> 100V. >>>>> >>>>> Frequency range is anywhere between 200KHz to 2MHz. Required current, >>>>> up to 20mA. >>>>> >>>>> I would definitely prefer a ready-made transformer. Does anyone know >>>>> under what application heading one might be found? >>>>> >>>>> Paul Jackson >>>> If you want 20 ma at 100 volts, I don't think you generator will supply >>>> the power you need. >>>> If the generator supplies 10V into 50 ohms that is 20 ma. >>> 200 mA, short-circuit current. >>> >>> John >> >> >> Hi John, >> Oh, redid the math. You're right :-) >> Mikek > > > I have this background thing that runs in the back of my head and > checks the math on everything. ...
Careful. That can quickly ruin an engineer's marriage. There are things that are better left non-calculated :-) -- Regards, Joerg http://www.analogconsultants.com/
Jan Panteltje wrote:
> On a sunny day (Mon, 23 Jan 2012 01:57:39 -0500) it happened Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote in > <4F1D04E3.A0684B56@electrooptical.net>: > >> HardySpicer wrote: >>>> I am looking for an impedance matching transformer that will convert >>>> the 50 Ohm output of my function generator and to a 1K Ohm resistive >>>> load. >>>> >>>> That provides a 20x step-up as well, so with losses 10V yields maybe >>>> 100V. >>>> >>>> Frequency range is anywhere between 200KHz to 2MHz. Required current, >>>> up to 20mA. >>>> >>>> I would definitely prefer a ready-made transformer. Does anyone know >>>> under what application heading one might be found? >>>> >>>> Paul Jackson >>> an emitter follower perhaps? transformers are so last Tuesday... >> Your computer runs off AA alkalines, I gather. ;) >> >> Cheers >> >> Phil Hobbs > > The OP mentions'transformer'. > But this sounds like a simple video output CRT driver: > > +120V > +5 | > | R 1000 C2 > R |----------||----------- 100Vp Z=1k > C1 | c > ----||----------- b > | e NPN BF??? (video output driver) > | | > R 10k R 100 > | | for a gain of about 10 > /// /// > > You could use a dozen 9V batteries :-)
And if you bias it in the middle you better had liquid cooling for that transistor :-) It was possible with the old BF types that you could screw onto a heat sink but AFAICT they don't make those no more. -- Regards, Joerg http://www.analogconsultants.com/
Bill Sloman wrote:
> On Jan 23, 4:40 am, "Tim Williams" <tmoran...@charter.net> wrote: >> "BillSloman" <bill.slo...@ieee.org> wrote in message >> >> news:b109bfa8-5226-482a-a26d-f63d01d15ae3@f1g2000yqi.googlegroups.com... >> >>>> At 2 GHz, yes. But 2 MHz isn't especially fast. >>> It's a 10:1 bandwidth range. Ferrites that are good for 2MHz don't >>> have particularly high permeabilities, and lots of turns to make up >>> for the low permeability of the core tend to leave you with >>> inconveniently low self-resonance frequencies. >> If you were designing a power transformer, this might be the case. >> Typically NiZn ferrites are used, with Bmax ~ 0.3T and mu_r ~ 800, like >> Fair-Rite #43. These might be usable close to Bsat for small >> transformers, but the core loss requires Bmax < 0.1T for most power >> applications. Which is fine, since it doesn't take much core at 2MHz to >> achieve that. >> >> But signal applications under 1W are hardly the concern of core loss. > > 10V into 50R is 2W. >
Piece of cake. #43 ferrite works just fine for that, it's not even expensive. End of last year I designed something similar but for north of 50 watts. Core loss != power to be transferred :-) It takes a lot more to heat up a core. Although I must confess that I have accidentally detonated a two-incher at about 1200W of transferred power but that was as a kid. Should have used a stack of two but that wasn't in the budget back then ...
>> Typically, a pulse transformer is wound on the highest permeability core >> possible (e.g., Ferroxcube 3E5, Magnetics 'W'), which accordingly has very >> high losses at high frequency (complex permeability is essentially >> imaginary), but still has greater total permeability up to several MHz >> than the HF material. This means you can use simpler coil geometry, >> giving a higher SRF despite the higher inductance. As a bonus, the SRF is >> dampened by the core losses at those frequencies. > > Typically pulse transformers are transmission line transformers wound > with a twisted pair transmission line, as I pointed out in my original > response - not a lot of the high frequency flux makes it into the > core. >
Actually, at 2MHz it does.
>>> Do you want to design a suitable more-or-less conventional >>> transformer? I tried it once, and a transmission line transformer made >>> with twisted pair is what worked. >> Honestly, I can make a transformer with that kind of bandwidth by sitting >> on a ball of wire! Typically I see >10MHz from the gate drive >> transformers I carelessly put together, and ~50MHz with interleaving. > > How good are they at 200kHz? >
That depends on the number of turns. You can get to 200kHz with the right material. Then I'd probably opt for something like #77 material but many times the core shape I want only comes in #43. Such as the BN block-style cores. Got to live with what's on the menu. Just don't ever let things saturate with ferrite. With pot cores you can get almost any material but I do not like pot cores too much.
>> If more than that is required, twisted pair gets involved. > > You seem to live in a different universe from mine. >
Then Tim and I must live in the same universe :-) -- Regards, Joerg http://www.analogconsultants.com/
On a sunny day (Mon, 23 Jan 2012 10:51:53 -0800) it happened Joerg
<invalid@invalid.invalid> wrote in <9o5oibFbhgU2@mid.individual.net>:

>> The OP mentions'transformer'. >> But this sounds like a simple video output CRT driver: >> >> +120V >> +5 | >> | R 1000 C2 >> R |----------||----------- 100Vp Z=1k >> C1 | c >> ----||----------- b >> | e NPN BF??? (video output driver) >> | | >> R 10k R 100 >> | | for a gain of about 10 >> /// /// >> >> You could use a dozen 9V batteries :-) > > > >And if you bias it in the middle you better had liquid cooling for that >transistor :-) > >It was possible with the old BF types that you could screw onto a heat >sink but AFAICT they don't make those no more.
Yes, heat sink needed. I once bought a transistor replacement for the PL802 I think it was (IIRC) TV video out tube. It had a FET and a power transistor on a heat sink, and a large wirewound resistor so it would not interrupt the 300 mA heater chain. http://www.radiomuseum.org/tubes/tube_pl802t.html Anyways, finally managed to get dvb-terrestrial, plus DVB-satellite HD (DVB-S2) working on this laptop, it is recording now, testing if I can screw it up by doing lots of other things at the same time. This will replace my media PC, still have to test HD. A hundred patches and compiles and recompiles were needed. And it runs smooth in Linux, unlike in redmond7 virus,
On Mon, 23 Jan 2012 07:57:49 -0800, Joerg <invalid@invalid.invalid>
wrote:


>If you could let us know some more details about what the objective is >maybe there'd be other options. For example, if it's just pulsing a >piezo or PZT5H with an adjustable amplitude that does not require a >clean amplfier. >
I am intending to drive electrodes with a variable 200Khz to 2MHz sinewave, at around 100Vpp, in an experiment to inhibit soil bacteria. Hence the specified 1K Ohm inductance at the output. If it matters, 50V output would possibly be adequate to get me started Of course this can easily be done at audio with an off-the-shelf amp and PA mathcing transformer. I had hoped to extrapolate this to IF. If I just used a HV amp, a load matching netweork might still be needed anyway. Any further suggestions, or transformer fabrication details, would be most appreciated. Thank you for the replies so far. Paul
Jan Panteltje wrote:
> On a sunny day (Mon, 23 Jan 2012 10:51:53 -0800) it happened Joerg > <invalid@invalid.invalid> wrote in <9o5oibFbhgU2@mid.individual.net>: > >>> The OP mentions'transformer'. >>> But this sounds like a simple video output CRT driver: >>> >>> +120V >>> +5 | >>> | R 1000 C2 >>> R |----------||----------- 100Vp Z=1k >>> C1 | c >>> ----||----------- b >>> | e NPN BF??? (video output driver) >>> | | >>> R 10k R 100 >>> | | for a gain of about 10 >>> /// /// >>> >>> You could use a dozen 9V batteries :-) >> >> >> And if you bias it in the middle you better had liquid cooling for that >> transistor :-) >> >> It was possible with the old BF types that you could screw onto a heat >> sink but AFAICT they don't make those no more. > > Yes, heat sink needed. > I once bought a transistor replacement for the PL802 I think it was > (IIRC) TV video out tube. > It had a FET and a power transistor on a heat sink, and a large > wirewound resistor so it would not interrupt the 300 mA heater chain. > http://www.radiomuseum.org/tubes/tube_pl802t.html >
Ah, that reminds me of the old days. Somewhere I still have that article "Torrenbuizen" from the Dutch ham radio magazine of the VERON. No, it was not in the Vonkenboer :-) Years ago there was an issue in the test set of a client. We were eating lunch and I said "Oh, that's easy, we'll just use a video transistor". Shouldn't have said that. Back in the engineer's cubicle we quickly found out that those had gone the way of the dinosaurs, extinct.
> Anyways, finally managed to get dvb-terrestrial, plus DVB-satellite HD (DVB-S2) > working on this laptop, it is recording now, testing if I can > screw it up by doing lots of other things at the same time. > This will replace my media PC, still have to test HD. > A hundred patches and compiles and recompiles were needed. > And it runs smooth in Linux, unlike in redmond7 virus, >
You guys must watch a lot of TV. My wife would not want a PC in the living room and I don't either. We watch the evening news and maybe one old movie. That's it. -- Regards, Joerg http://www.analogconsultants.com/
Paul Jackson wrote:
> On Mon, 23 Jan 2012 07:57:49 -0800, Joerg <invalid@invalid.invalid> > wrote: > > >> If you could let us know some more details about what the objective is >> maybe there'd be other options. For example, if it's just pulsing a >> piezo or PZT5H with an adjustable amplitude that does not require a >> clean amplfier. >> > > I am intending to drive electrodes with a variable 200Khz to 2MHz > sinewave, at around 100Vpp, in an experiment to inhibit soil bacteria. > > Hence the specified 1K Ohm inductance at the output. >
Ok, so no big capacitive load. That helps.
> If it matters, 50V output would possibly be adequate to get me started >
Nah, why not go all out and do 100V? :-) BTW, if neither electrode has to be grounded you can drive push-pull. One goes to +50V while the other goes to -50V and vice versa.
> Of course this can easily be done at audio with an off-the-shelf amp > and PA mathcing transformer. I had hoped to extrapolate this to IF. > > If I just used a HV amp, a load matching netweork might still be > needed anyway. > > Any further suggestions, or transformer fabrication details, would be > most appreciated. >
Just add a few Versa-Pac transformers to your next order, maybe VPH4-860: http://www.cooperindustries.com/content/dam/public/bussmann/Electronics/Resources/Data%20Sheets/BUS_Elx_PM_4301_VERSA_PAC.pdf 100-200uH per winding would be good. They aren't truly bifilar, just a little, but then again 2MHz ain't that high. Maybe it works. Drive one winding, stack the five others. Hang a 2nd one parallel on the primary and stack its five remaining secondaries in series with the five of transformer #1. Buy a few lower inductance variants as well, in case the 680 won't get you to 2MHz. If they don't perform well enough then an order at Amidon-Corp is required. Some big fat #43 ferrite toroid or double-hole core, some wire, and wind your own. Rule of thumb: The Z (2*Pi*f*L) should be about four times whatever the transformer load impedance is. At the lowest frequency you want to use. For example, if you made a 1x plus 9x transformer where the 9x gets stacked on top of the 1x primary then with a 1k load the source gets loaded with about 10ohms. So about 35uH per winding would be ok. Way to wind them is you take a bundle of ten wires, twist that slightly, then would that "long sausage" around the core as many times as it takes to get to The Amidon BN-43-7051 core is pretty good if you can get the wires through the holes. Should be possible because 200mA is not a lot and that goes only for the primary. All the secondaries can be much skinnier wire. Two turns is kinda skimpy but could be enough here and I don't think you can squeeze three through there. https://www.amidoncorp.com/items/62 Now drive this hard with 10V. The really good buffers from my youthful days are extinct but you could try these: http://www.ti.com/lit/ds/symlink/buf634.pdf Use the TO220 version and a heat sink because they'll get hot. -- Regards, Joerg http://www.analogconsultants.com/
In article <4f1dc6fd.4139937@news.tpg.com.au>,
Paul Jackson <pauljackson@thermalux.com> wrote:

>Any further suggestions, or transformer fabrication details, would be >most appreciated.
One suggestion - limit the frequencies you emit, to those which are FCC-categorized as being in one of the ISM bands. Although it may seem counter-intuitive, soil driven in this way can make a fairly good antenna. Certainly, RF currents flowing through the soil structure do play a very important role as part of the "ground plane" of many ground-mounted vertical antennas, both for receiving and for transmitting. If you simply frequency-sweep through the 200 kHz - 2 MHz range willy-nilly at the power levels you are mentioning, you will almost certainly radiate enough RF signal to create Cthulhu's own amount of RF interference through several different bands, including AM broadcast and the amateur 160-meter band. You may generate enough harmonics to interfere with the 75- and 80-meter bands as well. You're likely to have people (hams, AM-radio listeners, and the FCC itself), showing up on your doorstep and asking you more or less politely to Cut It Out Right Now. -- Dave Platt <dplatt@radagast.org> AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads!