OK I need to step down mains voltage to 12V, and the 12V side needs 25A approx. Any thoughts on ways to approach this?
I presume the first thing is to convert the AC to DC, then switch regulate it down to 12V? If so, what is recommended for efficiency - bridge rectifier/diode → switching regulator.
If there is an efficient way to go from 240VAC to 12V in one step, what would that be?
The main problem I see here is getting the 25A. I am almost certain it would involve parallelling multiple supplies to increase the amps.
Yes I was thinking of basically PSU supplies but I was concerned about the efficiency of transformers and that’s why I was wondering if there was any kind if ICs out there similar to DC-DC Switch mode regulators but AC-DC instead, and at this rating, but I don’t think there are?
How efficient are transformers in general, and computer PSUs?
angelsix:
I was wondering if there was any kind if ICs out there similar to DC-DC Switch mode regulators but AC-DC instead, and at this rating, but I don’t think there are?
There are integrated switcher chips for dropping mains voltages to low-voltage DC, but you are correct that at these power ratings they would need external transistors. Anyway, there would still need to be a bunch of external components, and the PCB layout would be tricky. Realy not worth it IMO, since pre-made supplies are readily available.
angelsix:
How efficient are transformers in general, and computer PSUs?
Large transformers can be more than 95% efficient, but you also need to consider the losses in the switching devices & rectifiers etc. Decent computer power supplies are more than 85% efficient.
That’s a 300W output power supply! You’re not likely to be able to design something more efficient than an off the shelf one unless you want to spend the time becoming an expert in power conversion. This is a case where buying a solution is going to be a much better idea than designing one.
The only thing I’d be concerned with is if a computer PS is acceptable. Cheap ones are often borderline and if you’re going to draw 25A continuously from the 12V output, it may not be able to hold up for long. Maybe look for an open-frame supply from a reputable vendor?
OK thanks for all the feedback guys, I guess the answer is that a computer PSU is the way too go as the most efficient route. I have brought a 580W HE (high efficiency) supply and that will do me just fine. I just thought I would check first in case there were other more efficient ways.
A switch mode power supply (like the one you have) is going to be the most efficient overall design. There are various tweaks you can do to the basic design to improve this, but its a lot better than a mains frequency transformer, rectifier, and linear regulator.