Almost embarrassing to ask such a dull question but I must.

I need a PSU to give me 12 VDC @ 300ma from a mains input. I can easily build this using a tranny, bridge rect, cap bla..bla but its about time I stopped being lazy and learn something new. I would like to build this using SMD components.

Can anyone point me in the direction of a schematic of a modern switching circuit that would give me such power?

Cheers

 

I appreciate your need to learn but these things can be bought for very little money it's like reinventing the wheel.

This one from CPC for example is only £4.84!

 

Very true. If I only needed one it would be a lot easier to do it this way.

This PSU will be part of a circuit I am building. If it all works out well, I will be getting PCB's made and producing around 200 of them.

 

I will be getting PCB's made and producing around 200 of them.

Do you plan on selling the end product? If so there are many regulations and certification costs involved.
For only 200 home-built units you may find the cost of the components would exceed the cost of off-the-shelf units.

 

Building a switched mode power supply is not as simple as one using a mains frequency transformer. I do not think you will be able to buy a ready made transformer so you will have to design and build your own or get one manufactured to your specifications. As you are asking the question I don't think you will have the knowledge to design a high frequency transformer. You also have to design the filtering circuits to limit the high frequency switching noise from being injected back into the mains supply and radiated.

Les.

 

I agree with LesJones.
Stay away from trying to build a mains switcher. Unless, of course, you like trouble.
Getting certified for it is important. You need to ensure the supply is safe.
There are a number of board mounted switch mode supplies you can just buy, or use a plug pack.
Switch mode supplied are getting easier to make, but still, in my opinion, require a degree in black magic to make them work well
You could go with a mains transformer, bridge and cap, then feed a switch mode regulator.
I'd advise you to keep with low voltage for a start.

 

Hello,

Making a SMPS power supply will take some effort.
Here is an example with the NCP1200 from ON:
https://www.arrow.com/en/reference-...power-supply/114945f0e13a177590542911c206b7d4

Bertus

 

Do you plan on selling the end product?

Not selling these. Some equipment at work is so old its becoming harder to find the parts to repair them. Easier to redesign and build.

As you are asking the question I don't think you will have the knowledge to design a high frequency transformer

You are spot on, I do not know enough.

The other day I stumbled on this part
https://www.cui.com/product/resource/psk-6b.pdf

I figured if you can now purchase such a package, maybe they also do something along the switch mode type. From all your responses, for now I will stick to plan 'A' and keep things old school.

 

I figured if you can now purchase such a package, maybe they also do something along the switch mode type.

The supply in the link is a switch-mode type.

 

The supply in the link is a switch-mode type.

Yes I did spot that but looking at the component count, I don't see it as much of an advantage for what I need.

 

Not selling these. Some equipment at work is so old its becoming harder to find the parts to repair them. Easier to redesign and build.

It will still need certification. Without that, any injuries (shock) or fires caused by said equipment would invalidate any insurance the company carries.

If you buy 12V power supplies, they'll have the necessary certifications.