Small signal transformer

[AnneB]

Hi,

I have an existing circuit producing a sine output variable between 100 kHz and 300 kHz, with 100 ohm output impedance and around 10 volts peak-to-peak (+/- 5v).

I really need to step this up by about 10 to around 100 volts peak-to-peak. But I don't really think I need a voltage amplifier because the output requires essentially no current. It is simply being fed to a pair of air-spaced plates to generate an electric field. Given the area/spacing of the plates, it works out to around 6pF of capacitance. So at 300kHz that is around 80 Kohms impedance.

Ideally, I would just like to use a little high-frequency signal transformer for this. Does anyone know is such a component available? I have searched for many "pulse" transformers etc etc but struggling to find something with around a 1:10 turns ratio!!

Thanks so much!

Anne

 

[Nigel Goodwin]

It's the sort of thing that tends to be custom made, you would probably have to wind your own.

 

[AnneB]

Wow!! Thanks for the quick reply Nigel! I have a variety of ferrite cores in my "bits box" -- do you have any guidance on the best core size, number of turns, etc. I am quite happy to have a go at winding something!

 

[MaxHeadRoom78]

Are the cores Toroidal? This is what you need preferably, they are also the most efficient means of transformation so the turns/volt is not high at all,
Experiment with a couple of windings, Pri & sec and find the the turns ratio (turns/volt)

 

[AnneB]

Thanks Max. I have several small toroidal cores. I will have a go. I am not sure of the correct inductance I would need for the primary so I guess it is a matter of trying it. I was hoping there might be a neat little formula for calculating the turns given the characteristics of the core?

 

[ronsimpson]

Using LTspice, 5Vpk waveform at 100khz. R1 is the 100 ohm impedance of the source. (why is it not 50 ohms?)
L1, L2 is a transformer. C1 is the 6pF load. Teh 330uH is the primary and the 33mH is the secondary stacked on top.
CoilCraft Here is a link to a transformer that is 202uH on the primary. The 5 secondaries need to be wired in series to get a 5:1 boost. It is not 10:1 but is an example of how it could be done.
The coilcraft part has a VT of 35VuS which is about as small as you can go.

 

[AnneB]

Hi Ron - thanks sooo much for your help! Really great - just what I needed to get going.
Anne

 

[Tony Stewart]

You can make this easy with a transistor current controlled-emitter to be resonant but then the Q will be high or driver it with a low impedance emitter follower.

Thus you can make it with high Q or low Q all depending on your source impedance and desired to regulate voltage and current when it arcs. The arc impedance drops with rising current.
Big old car distributor coils have a gain of 100 from 50 Ohms with 20 kHz BW. Modern ones much higher BW.

Impedance ratios will tell me the Q if you want it resonant. If not that's OK too. The Yellow shows 50 Ohms x100 = 5k then if you made it resonant you get another sqrt(impedance ratio) voltage gain at the LC intersection.