# What will happen if I connect a 9v ac input with a step down transformer (80V ac to 24V ac)?

I'm doing a university project and we're not allowed to use mains. Hence, I planned to use a 9V input and step it up to 24V.

However, I couldn't find any transformers online which have a 9V ac input; all I found are designed for mains (220V/110V).

I'm using a switch mode circuit to convert the 9V dc to 9V ac, then step it up to 24V ac and use a rectifier circuit to convert it back to dc.

So my question is what will happen if I bought a 80Vac "input" to 24V ac "output" transformer and used a 9V ac as the input?

I know the voltage will lower in the secondary because the voltage is much lower in the primary. If that is so, how can I calculate the difference?

Also, I'm using a voltage regulator (0 to 40V input) -> (24V output) after the rectifier circuit. Any solutions? Thanks in advance.

• If you don't have enough background knowledge to answer this yourself, it's a good thing you're not allowed to use mains! Do some basic reading on what transformers do, and tell us what you think will happen.
– user16324
Feb 19, 2016 at 12:10
• Hey Brian ! you're correct I don't have good understanding about transformers. What I know using 9V on a 80Vin and 24Vout is the out put will decrease a lot because the secondary winding is related to the primary winding. However, I'm not sure about the safety operations as I asked Mr Olin below, "80V in and 220V out, 220/80 = 2.75, hence for 9v its 24.75 will that work ? If so could it damage the transformer?" this is my only concern. Thanks ! Feb 19, 2016 at 12:21