Developing an AC/DC Converter

[devonsc]

Hi there, I'm trying to build an Buck AC/DC Converter, currently I have not developed anything and still at the study stage of it.

Chiefly, my main implementation of this AC/DC converter is for charging battery purposes. Since I'm using it for charging purposes, is it true to say that:

a.) It is not advisable for me to build one without the usage of a transformer as the user will have a direct contact to the AC supply?

b.) I'm going to need very large heatsink?

I'm concern about the size of the transformer that I am going to need in this circuitry as I was trying to keep it as small as possible. Buck from a level of 240V AC to approximately 12V to 15V DC.

Any advice or guidance is very much needed. Thanks in advance....

 

[andy1]

The size of the tranformer will depends on VA product you are looking for.

If you need a lot of current to charge the batteries then you will probably need a large tranformer and a large heet sink.

What are the specs you are trying to meet?

If it is just a small battery that requires a small current then you might not need a heat sink at all.

Usually a tranformer does not require a heat sink but a voltage reg. will need one, although with clever design a switching voltage req. may not need a heat sink.

 

[nicleo]

The size of 'circuit' is dependent on the topology of power converter that you're going to choose. Which type of battery that you're going to charge?

If the charging current is small, probably you may consider OFF-Line converter. This converter also provides electrical isolation. For a given output power, the transformer used in OFF-Line converter is much smaller than the AC power transformer. Let's talk about the charger for mobile phone. Years ago the charger was very heavy mainly because of the AC power transformer insides the charger. However the charger today is much lighter than the OLD one because the transformer used is much smaller. The topology employed in modern day mobile phone charger is OFF-Line converter.

You may find more information in the following ebook:
Advanced DC/DC Converter


You may find some photos of Nokia mobile phone charges circuitry here:

 

[andy1]

I am a little behind terminology so I might have forgotten what's an off-line converter is.

Actually you may be able to get away with not having a transformer all together. I guess having a transformer provides some isolation (among other things) which is related to safety. But I've seen some design that does not have a transformer at all.

I guess if you can design correctly, you do not have to use a transformer.