# Can't find a low AC input voltage transformer

I have a AC function generator that outputs a maximum of 20 volts. I need to c...Connecticut this generator to a Step Down Transformer, keeping the sine wave on the output, for a small educational project I'm working on.

The problem is that I can't find a transformer with low input voltage anywhere. I've being looking for days already and the only transformers I found are above 117V on the primary.I and

Do you guys have any idea where I can find this type of transformer?

The primary input voltage of a transformer is the maximum voltage that it should be used at, not its working voltage. What is important is the ratio of input voltage to output voltage

It is safe to use a transformer rated at a higher voltage than that which you will be using

What frequency and what stepdown ratio?

So, I can buy 120 volt input AC Transformer and apply let's say 12 volts on it that the output will be proportional to that change, correct?

The frequency will be something from 60Hz to 1kHz. Ideally, it is center tapped, with a 2:1 ratio. For example, if I apply 18 volts on the primary I would like to be able to get 4.5V-0V-4.5V on the secondary.

Any power transformer that is designed for 50/60Hz will not work at 1kHz.

Off hand I can't recommend anything, You may find an audio transformer like that though

A power transformer will probably have a limited frequency response. Typically they are used in the 50-60 Hz range anything above that is a bonus and not part of the design.

There are 400 Hz systems - mainly aircraft, old Mainframes and other places weight is an issue. At 400 Hz less iron is needed so they are smaller and lighter (and will over heat if used at 50-60 Hz.)

This may suit your application but current is limited

It seems that will do! Just for my learning: which query did you use to find it? Did you google it or did you go directly to Digi-Key website?

I do it all the time I use a resistor divider. If I need more current I add an appropriate amplifier. Give us a sketch of what you are trying to connect and the requirements for signal level.

Went to digikey and first selected Audio transformers with a frequency response that covered your range then sorted by price.
Transformers that can handle larger currents start to get expensive.

To expand on what @jim-p said above. If you know a technology pack rat that saves old stuff, see if they have any old modems that you can scavenge parts from. That type of transformer was used in various forms in modems. They were common and dirt cheap decades ago.

In general, yes

If a transformer is specified to output say 10V with a 120V input then, with a 12V input it will output 1V

However, as others have noted in this topic there are other considerations such as the frequency of the input to take account of

Usually function generators are low-current so a voltage divider or pot (as gilshultz suggested) should work.

...And usually function generators have variable output voltage.

Just to make sure you understand the input voltage of that transformer is limlted to 4.47V RMS or 12.6V peak to peak.

I think I got stuck on the audio thing. I thought it was only for audio. Newbie mistake.

Thank you very much for the specifications and tips!

I'll buy more than one. I'm sure I'm going to burn a couple of them while learning.

Thank you!

Thank you. I'll test that!

That's a good tip. thank you!