Controlling Transformer Output

Question

I want to control the output of a transformer. So the input is 220V, 50 Hz. I am stepping it down to 24V. Now I want a switch that can vary the output between 0-24v. How do I make such a switch? If I put a resistance for dropping the voltage, I am afraid it might get heated or it might result in some noise. What do I do? Any suggestions?

Update:

Just for clarification: I want Ac ranging from 0-24, so the user can control the output like 0-5v ac, 0-15v ac , 0-24v ac.. and so on. Sorry for not giving this detail in my question.

Answer 1

It is not clear from your question whether you want a controllable 0-24V AC or a 0-24V DC. You will need to answer to that in order to get much further input.

If you want DC then you will want to rectify the output of the transformer and build a variable DC voltage regulator. A linear regulator is possible bit it can get really hot when operating at full load current at the lowest voltages. A better solution would be a switchmode regulator.

If you want AC then your solution may very well be a device called a Variac. These are basically a variable transformer. Google to find further details.

Answer 2

You can't really control the output of the transformer. It will be what it will be.

What you want is to first rectify the AC from the transformer to make DC, then to use a "buck converter" to make a lower and regulated DC voltage from the higher and unregulated DC coming straight from the rectifier.

This is a very common issue, so surely there is much written about it out there. Your question as it stands is too broad to answer here. We can help with specific problems as you try to build your power supply.