Transformerless Power Suppply

[psdayama]

It's not cost saving, but size too...

When this thread started, I put forward an example of a Fan Controller. This fits inside a standard size wall recess which can be as shallow as 15mm. They just don't make transformer bobbins that small - and consider you have to wind around 8,000 turns of 0.01 or 0.008mm wire for a 0.5VA transformer primary - and even then it'll run warm because you really need about 12,000 turns at that rating and you quickly discover that there are minimum sizes for sensible transformer manufacture. Wire that thin is scary stuff to work with as it's so fragile.

Cost of course is a factor. A small Capacitor, a Diode and an Opto-isolator makes for a simple 'Fuse Blown' or 'Power Fail' detect circuit. Whilst a Transformer is nice, it just takes up too much PCB space - and you can't do it for 20 cents.

Finally, my choice of X2 Capacitors is deliberate. If you correctly chose your Capacitor, series Resistors are unnescessary. In all the years I've been designing these kinds of circuits, I've never had any failures of X2 Capacitors. Actually, I can't ever recall having a defective X2 Capacitor in any circuit. Chose your components wisely from reputable sources and you'll not have any troubles.

Your very first statement is exactly opposite to end one.
Check size of X2 capacitor and normal metallised film capacitor. You will
find X2 atleast 2times bigger than normal. Obivously no manufacturer can
provide X2 at same price so they are atleast 3times expensive.
Metallised film caps which are supplied by UL approved manufacturers will
NEVER short. They may become open with overload. So either way the
argument is pointless! A serries resistor costs less than a cent and it is
wise to limit inrush current.(In all situations). You may have not recieved any complaint with
X2 capacitor as they if not used properly become open circuit SLOWLY. If
anybody notices difference in EMI after 6months or years later, it will be
sheer accident!

I have designed and made a fridge controller (Blind type) with 555 and
similiar transformerless power supply some 3-4 years ago. I have used
normal 680n / 250V capacitor --( our system is 240V 50Hz) and those are
working nicely last 3-4 years and saving 100s of Rs. every month for the
users without any recall.