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What is the smallest Transformer-less AC to DC design

Mosi
Intellectual 735 points
Other Parts Discussed in Thread: CC2530, UCC28880

Hi there

For an Smart Home application I'm looking for a small Transformer-less AC to DC design. There are plenty of designs but I'd rather the smallest one cause I want to implement it into a wall light switch somehow. And od course some if these designs are not too good for long term uses and they're not that much safe and or stable. So it has to provide a safe and stable voltage considering I'm using it for a Zigbee wireless controller.  

Input voltage is 220V AC and the output voltage is 3.3V/100mA DC (for my board which is a CC2530 Zigbee based controller) although 5V is good enough and I can use another LDO to convert that to 3.3V. I don't need that much output current.

Normally I don't care if it's non-isolated or isolated but I think I have to go with non-isolated because of its much smaller size and the fact that it doesn't use a Transformer.

But I don't know if it's a good idea to use a non-isolated power for wireless controllers like CC2530. Is it?

I saw this but it seems kind of big because of those two inductors and some other components. 

So do you guys have something better in mind? 

  • 0
    TI__Expert 4015 points
    Smallest would probably be a cap dropper circuit such as described here "ww1.microchip.com/.../00954A.pdf" and here "www.designercircuits.com/DesignNote1a.pdf", but the efficiency, standby power and heat generated in the wall switch make it unrealistic in this application I think. Other performance parameters like output ripple might also be quite poor.

    I would recommend the UCC28880 which is targeted at applications like this. It is a non-isolated buck controller, which has the advantage that the magnetic is smaller than a transformer.
    See "www.ti.com/.../tidu856c.pdf" for an example similar to your application.

    Regards
    Billy
  • 0 in reply to Billy Long
    Intellectual 735 points
    Thank you.
    No I don't like cap dropper circuits at all. I want it to be safer than that.
    I've seen UCC28880 before. But still it's kind of big and has a lot components. For now I think I go with a ready to use AC/DC converter module like those Mornsun has. They're small and well protected and a good case which will result in fewer problems.