Switch mode power supply

Question

I am currently using a 5V DC, 1 amp wall wart to my circuit which is on a PCB. The wall wart plugs into the PCB using a barrel jack. All in all, my circuit uses around 300mA and can take between 3.3 and 5V.

However, I am really not a fan of the wall wart. I thought about trying to "hide" it in the enclosure but it doesn't fit well. So I have been looking into alternatives.

I came across the LNK304, LNK305, and LNK306, an "efficient off-line switcher IC that can support , -boost and flyback topologies". It looks promising to me. Specifically, on page 4 of the datasheet there is this picture.

My question is, is this a viable replacement for my wall wart? Is there a better option? What else would I need to get this to 5V, 300mA? Would it be Ok to add the circuit to my PCB (with proper spacing for tracks on the board)? Should I put this in a metal case connected to ground or a plastic case? Is there anything else I should know that would help in making this transition?

If you need more information, let me know. Any information on this would be great. Thanks.

Answer 1

This is not suitable for your project, as it is not isolated. This means that your entire circuit will be potentially at high voltage. You don't actually mention what the circuit is, but I'm assuming it's not of the kind where a non-isolated supply would be acceptable.

You need a supply that uses a transformer, which will isolate your circuit from the mains. If you are not experienced with designing power supplies, I would advise purchasing a ready made module this time round, both for safety and the fact switching supplies are little more complex than linear supplies.
There should be plenty of suitable switching modules around, check Farnell, Mouser, eBay, etc.

Answer 2

Since you don't seem to have the experience to tell that your power supply is non-isolated I would say it's safer to stick with the wall wart, and keep the mains voltage out of your enclosure. If you really have to I'd go for a ready-made solution. In another answer Jeanne came up with one of these:

They contain the same as a switching wall wart, but for PCB mount. Compact (32 mm x 27 mm) and can supply 550 mA at 5 V.

Keep a safe distance of minimum 10 mm between your mains and the low voltage part of your circuit. And use a screw connector

to connect your power wires to the PCB, never solder them.