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We are designing a power supply for a MCU design, which must run directly from mains 230VAC.

We have previous used a "traditional" 230VAC to 6VAC transformer, and used a simple bridge capacitor solution to generate DC supply.

The solution we are working with is the bp5048-15 from ROHM, which would do the job.

www.rohm.com/products/databook/pm/pdf/bp5048-15.pdf

But since this is a non-isolated solution, we get the mains supply to be common with the PCB ground. Which possible could be dangerous, if PCB ground is exposed.

We want to sell this product in Europe in the future, and therefore we need a CE approval.

The CE directive on high-voltage (>48V) is pretty complicated.

What are the safety demands when designing this kind of circuit?

Can it be done non-isolated, or is this a hard way to go?

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To expand on what Martin said, you can also buy pre-certified "power bricks" that are like the wall wart except are intended to be internal to your unit. Most of these nowadays handle universal line power in. You provide a universal line cord socket on your unit. That connects only to the power brick with a fuse in series. The other side of the power brick provides isolated and regulated DC.

The power brick market is very competitive. These bricks don't cost much more than a big iron transformer to handle the same power. Mean Well, Astec, Artesyn, and CUI are just a few companies in this space that come to mind. Do a little digging and you can find more.

 

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Unless you are going to sell lots and lots of these devices, source an off-the-shelf wall-wart type power supply.

The design, validation and approval of mains-connected equipment is not cheap. The wall-wart suppliers have done this work for you and can amortise it over a very large quantity of parts, so the cost to you is very small. This is the reason that lowish-volume and value electronics comes with a wall-wart these days. Only high volumes and/or very high sale price (think high-end pro-audio) can support the extra work required.

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I have only a small amount of European CE certification experience and that was long ago. But, as soon as your supply is non isolated the equipment MUST be entirely "double insulated" and is in about the same class as the inside of a toaster that uses electronics. As you can buy electronic toasters in Europe it's obviously doable. Looking at how they achieve it may be instructive, but ...

Agh! Just looked up ROHM IC on Digikey. Horrendously priced - $US4.50/1000 !!!.

My query would be, why make it non isolated?
The method of operation of the ROHM device is not obvious from the "datasheet". It is either a clever but nasty near-zero-crossing-gating type circuit or a buck converter. Either way, you can almost certainly make an electronic converter that is not much larger, not much dearer and fully isolated. The TOPSwitch type devices and their several emulators come to mind.

What Wattage do you want?

For about $US0.70/1000 Digikey you get eg the TOP252-PG which is good for 9 to 15W at 230 VAC or more (model Wattage unclear from datasheet).

The basic circuit can be as seen below. The final circuit can be nastily worse - up to you.

enter image description here

A small iron transformer starts to be almost attractive :-).

I have seen isolated electronic 'high frequency" supplies which were utter simplicity. One made to operate a 12V, 4A Peltier cooler used what looked to be a one transistor oscillator and a few low voltage side transistors. Given enough cleverness a supply that was simpler than the Topswitch type design should be possible BUT the preponderance of "proper" smps in wall wart and similar use suggests that the current typical approach is econpmic enough.

Why non isolated ? What power level?
What price constraints?

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    \$\begingroup\$ Yeah, I see your point. I think the best / easiest solution for now will be to go with the "power bricks" as Martin said, and maybe later if the production volume gets high enough, we can build our own supply on the PCB. \$\endgroup\$
    – JakobJ
    Commented Mar 7, 2012 at 7:15
  • \$\begingroup\$ Oh, sorry, As Olin said.. ;-) \$\endgroup\$
    – JakobJ
    Commented Mar 7, 2012 at 11:58

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