basic transformer question

[autx790]

I feel dumb asking this question but can anyone help me remember what i'm doing wrong here. I'm trying to pass a small AC (1V) signal through a step-up transformer. I've tried 1:100 and 1:50 turns ratio but as soon as I connect the function generator to the primary, it gets loaded and the input goes to zero. I've tried open secondary, 100ohm, high kOhms, capacitors, etc but I can't get anything. What am I ignorant of here? If I short the secondary I get the primary signal to show up but it's still way too attenuated.

- - - Updated - - -

Nevermind. stupid question it was. the primary is essentially a short

 

[crutschow]

Is this a power transformer?

What signal frequency are you using?

 

[autx790]

Yeah, just a power transformer. Trying with some I wound my self for a flyback and also some I got that were professionally wound. I'm trying to use low frequency (20-500Hz) but even with higher frequencies in the kHz range, I have the same trouble. I see a slight result with higher frequency but still quite attenuated.

 

[jiripolivka]

If you feed a POWER transformer from a function generator, its source resistance may be too high and the small number of turns of your transformer shorts it.
To transform acoustic signals, find a "microphone transformer" used with ribbon microphones years ago. Such transformers worked well with a low-impedance source. Maybe you can get a suitable signal from a radio speaker output like 4 or 8 Ohms. Then you should insert an audio amplifier after your function generator to get some output on the secondary.

 

[schmitt trigger]

Indeed, as the previous poster mentioned, it is best to use an audio transformer, like the following:

http://www.hammondmfg.com/5caud.htm

Use one the signal level devices.

 

[autx790]

Thanks for the feedback. Ill look into those. I've used a bunch of different kinds, power, current sense, self wound. I tried putting a series resistance in the primary but that didn't help. I'm not trying to pass acoustic signals but am working with an energy harvesting application. Looking at flyback transformer. It too has a 1:100 turns ratio with a 85mOhm primary DC resistance. This is one of the ones I've tried as well.