Forums

0.2MHz - 2MHz step up transformer

Started by Paul Jackson January 22, 2012
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
On Jan 22, 1:05=A0pm, pauljack...@thermalux.com (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?
The only kind of transformer that has a hope of offering that kind of bandwidth is a transmission line transformer. Impedance goes as the square of the step-ratio, so you are asking for step-up ratio of 4.47, which is difficult to realise in a transmission- line transformer - impossible in a low-order transformer http://home.earthlink.net/~christrask/TraskTLTTutorial.pdf If you can live with a more accessible impedance transformation ratio, a transmission line transformer could be perfectly practicable, and possibly even practical. Some off-the-shelf small pulse transformers are bifilar wound, which makes them transmission line transformers, but the characteristic impedance of a twisted pair is around 110R, which won't suit your set-up. It should be easy enough to wind something with miniature coax on a biggish ring core or two. -- Bill Sloman, Nijmegen
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. With a 1 to 10 voltage step up you generator would need to supply 200 ma. Just my thoughts, Mikek
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
Being a function generator as the source, I think you better start thinking of HV amplifiers instead. A DC coupled one to be exact. 2 Mhz isn't much of a problem for non reactive type amps. Jamie
amdx 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. >>
As Mike hinted, the math doesn't compute here. 50ohms into 1k is not a 10x voltage step-up.
>> 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
The transformer has to be of multi-filar winding technique in order to provide the required bandwidth. Not sure if two of these would work: http://www.cooperindustries.com/content/dam/public/bussmann/Electronics/Resources/Data%20Sheets/BUS_Elx_PM_4301_VERSA_PAC.pdf One winding, both transformers parallel, for the input. Five plus five in series on the output side. Should result in 10:1. Three of them could give 15:1. I've never tried to use them for that but have used them in switch-mode converters and they behaved very nicely. You could also check Mini-Ciruits. Rule of thumb: The cumulative inductance on each side should represent a Z of four times the presented impedance. It's ok if the "stated impeance" in the datasheet is lower, then the transformer just has to be listed for much lower frequencies than 200kHz.
> > 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. > With a 1 to 10 voltage step up you generator would need to supply > 200 ma.
If Paul's generator is too weak to drive loads under 10ohms then he'd need to find or build a staunch buffer. -- Regards, Joerg http://www.analogconsultants.com/
>> >> 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. >> With a 1 to 10 voltage step up you generator would need to supply >> 200 ma. > > > If Paul's generator is too weak to drive loads under 10ohms then he'd > need to find or build a staunch buffer. >
I'll add to that, some signal generators have an amplifier with a very low output impedance and a series 50 ohm resistor. If you have this type and want to load it at 10 ohms, make sure the 50 ohm resistor is rated for the wattage needed, especially if you expect continuous use. I have seen blacked 50 ohm output resistors. I won't name any HP names. Mikek
amdx wrote:
> >>> >>> 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. >>> With a 1 to 10 voltage step up you generator would need to supply >>> 200 ma. >> >> >> If Paul's generator is too weak to drive loads under 10ohms then he'd >> need to find or build a staunch buffer. >> > I'll add to that, some signal generators have an amplifier with a very > low output impedance and a series 50 ohm resistor. If you have this type > and want to load it at 10 ohms, make sure the 50 ohm resistor is rated > for the wattage needed, especially if you expect continuous use. I have > seen blacked 50 ohm output resistors. I won't name any HP names. > Mikek >
Essentially you can do this using a PNP/NPN follower pair driven by an opamp, and then a resistor from bases to emitters for the crossover region. Just make sure the transistors are sufficiently SOA rated. One of those situation where the old American saying holds, if the transistors ain't big enough get bigger ones :-) Much cheaper than trying to obtain some extinct buffer. -- Regards, Joerg http://www.analogconsultants.com/
On Sun, 22 Jan 2012 04:55:02 -0800 (PST), Bill Sloman
<bill.sloman@ieee.org> wrote:

>On Jan 22, 1:05&#2013266080;pm, pauljack...@thermalux.com (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? > > >The only kind of transformer that has a hope of offering that kind of >bandwidth is a transmission line transformer.
At 2 GHz, yes. But 2 MHz isn't especially fast. John
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
> With a 1 to 10 voltage step up you generator would need to supply >200 ma. > Just my thoughts, > Mikek
On Sun, 22 Jan 2012 12:05:59 GMT, pauljackson@thermalux.com (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.
--- Voltage (turns) ratio goes as the square root of the impedance ratio, so instead of a step-up of 20, you'll only get a step-up of 4.47. That means that if you want 100 volts out you'll need to input about 24 VAC. ---
>Frequency range is anywhere between 200KHz to 2MHz. Required current, >up to 20mA.
--- If you want to push 20mA through a 1000 ohm load, then the transformer's output voltage needs to be 20V, not 100. then, since the step-up is 4.47, the input to the transformer would need to be 4.47V and the current from the generator would need to be 89.5mA
> >I would definitely prefer a ready-made transformer. Does anyone know >under what application heading one might be found?
--- Wide-band transformers? BTW, Arnold Engineering had a nice little DOS transformer winding program called: "MAT 4.1" and they still make reference to it here: http://www.arnoldmagnetics.com/Search.aspx?searchtext=MAT%204.1&folderid=0&searchfor=all&orderby=id&orderdirection=ascending Their web site is at: http://www.arnoldmagnetics.com/ -- JF