How can I design a 5V/5W DC power supply derived from 3 phase 230V AC input supply? My application need to work, even if, only one phase is available.
SMPS operated by AC normally first do rectification of the input voltage, i.e. they work also with DC or pulsating supply voltage.
So you can simply connect all three phases by diodes and use that as input to such a SMPS.
But make sure you use such a SMPS. It will definitely NOT work with a simple 50/60Hz transformer supply.
My application need to work, even if, only one phase is available
Use a 3 phase rectifier like this: -
You'll still need a smoothing capacitor because if one wire is lost, the ripple voltage will worsen. Of course there will be a significantly higher peak voltage using this method.
If you have 3 phase and neutral wires, single half wave rectifiers will suffice for a 5 watt converter: -
And, providing you have a good neutral wire, you can "lose" two phase wires and it should still operate. This produces the same peak DC voltage as a conventional single phase SMPS. However, if you "lose" the neutral wire then this will stop working.
You should use a three phase rectifier with capacitors rated for approximately 500V.
STMicroelectronics Provides a three phase SMPS
You can find the data sheet http://www.st.com/content/ccc/resource/technical/document/application_note/16/e6/c6/e4/08/c8/40/ff/CD00074286.pdf/files/CD00074286.pdf/jcr:content/translations/en.CD00074286.pdf
I think, I can use 3 Hi-link modules ( http://www.hlktech.net/product_detail.php?ProId=60 ), to derive 5W un uninterruptible supply.
The problem here is, I need to use 3 Hi-link modules( Cost is around $9 ) and it require more footprint.