optimized transformerless PS

[cheetha]

Assalam-o-alekum
i am in need of transformer-less power supply to drive microcontroller, 7 segment, LCD and relay, The input AC line rms voltage may vary from minimum to 500V. plus voltage fluctuation in extreme cases may be considered
I have seen many designs but unable to determine optimized design.
(Optimize in sense of cost efficient, component rated values, stable o/p voltages etc)




Plz help

 

[thylacine1975]

Heya Cheetha - I had a very similar requirement myself a few weeks ago.
After *much* juggling of protection circuitry, regulators, power dissipation, cost, board area required etc I came to the conclusion I was wasting my time - anything more than a rugged and reliable transformerless 5-10mA was going to cost more and involve more tradeoffs than I could achieve with a tiny SMPS... and I came across a nice solution!

NXP have a reference design: https://www.nxp.com/demoboard/TEA1721ADB1062.html
I've sourced the magnetics through Wurth Electronik (https://www.we-online.com/web/en/wuerth_elektronik/start.php) - the common mode choke is ~$1.80 (in 10-off quantity) and the flyback transformer ~$3.80. The active devices are only a couple of dollars as well, giving me 5 watts in a tiny area, sub $10, and over an input voltage range of 85-500 Vrms. Perfect

I think I've finally sworn off transformerless designs for good... and I'm happy about it! Good luck

 

[mtwieg]

For anything other than very low power (like 500mW or less) and non-critical applications, transformerless power supplies are a very poor choice. At a certain point the cost and size of huge capacitors and zener diodes necessary to deliver high power across a wide input range becomes far greater than that of a well designed offline SMPS.

I think I've finally sworn off transformerless designs for good... and I'm happy about it! Good luck

Congrats on your successful rehab!

 

[cheetha]

thanks alot for the advice but i was willing to have transformerless PS. i have tried to drop down with a voltage divider with 1W resistors but need to know how to optimize it. actually motivated by some commercial circuits from broken devices they dont use transformer. its very difficult to understand their PCB connections.

plz help

 

[cheetha]

any help ???????????

 

[godfreyl]

The commercial circuits probably use SMPS. See post 2.

 

[tpetar]

Only optimized thing what You will get is small fire or electrical shock. If you are adult and you are healthy then you have good chance to survive this.

 

[crutschow]

Switching power supplies operating directly from the mains use transformers, but they are much smaller than a main's transformer since they operate at the high switching frequency instead of the low main's frequency. Virtually all main's power supplies use some form of transformer isolation for safety reasons.

 

[schmitt trigger]

thylacine:
Thanks for providing the link to this NXP device.
It used to be that 85 to 265V was considered universal, but now it covers all the way to 500V......you can use the same device for home or a light industrial application, anywhere in the world...wow!

 

[shivakumar.r]

look at below design
http://www.powerint.com/sites/default/files/PDFFiles/der58.pdf

look at below link
**broken link removed**