My answer is WHY??!!! Transformers are usually not that expensive and they are very easy to troubleshoot.
Hi
Any Transformer that is going to fit into an enclosure (see Avatar) that is :L=100mm, W=60mm,H=30mm will have to be SMPS in order for there to be any space left for the battery, electronics and so on. As a TV tech that deals with SMPS repairs every day of my working life......I wanted to stay away from any SMPS type circuitry.
I needed extreme electrical reliability with the circuitry having to handle periodic Mains surges of anything up to 300VAC + that kills SMPS's stone dead. (Think small generators on farms that have been known to "run away" and blow up everything until they can be switched off, or our notoriously bad electricity supply in rural areas and townships/squatter camps here that causes anything SMPS to eventually fail or blow up). I needed something that could handle this kind of electrical abuse without any drama.
So in 2009 I started investigating the X2 capacitor to see how it would handle the job as a Mains current limiter. I needed 120mA constant current at a regulated 10VDC which would take care of both charging the battery and powering the LED's.
One VERY important lesson I learned whilst using a cap in this way is NEVER LOOSE THE LOAD. If for some or other reason this happens you are going to have a lot of drama on your plate. The supply voltage from the cap will go sky high and destroy your project and possibly shock you too if you are poking your fingers around inside when it happens. (This happened in the development phase where I was using breadboard...and a wire going to the head (load) came loose. The Electrolytic smoothing cap exploded and the Regulator went to heaven etc). I never got physically shocked but I was still shocked at how quickly all blew up in front of me.
So, learning from this, I decided to put everything on a PCB. The only way I could accommodate everything safely was the board had to be double sided.
So, I designed the first double sided board always keeping in mind creepage distances etc. To cut a long story short, everything worked as expected with the first prototype boards. No nasty surprises.
But as any of you know that has designed or built anything from scratch.....fine tuning is very important.
So the board went through two revisions. Little things here and little things there. One of the parts built into the last revision is a 5W Zener that clamps the output from the Bridge and in so doing aids the series Regulator in staying a bit cooler when overload times come.
So, on the 9th and 10th of June last year 2013, with this little guy in it's ABS casing and 3mm Polycarbonate lens and a small hole drilled to accommodate the heat sensor onto the Regulator and sealed from prying fingers....it was put to the test.
I initially wanted to see if it could handle 400VAC for 30 seconds. I would of been happy with that. So the test began at 400VAC...
30 Seconds came and 30 Seconds went. No problem. I said to my friend "lets try 1 Minute and see what happens". No problem.
Lets try 2 Minutes. No problem.
Ended up a in a 5 Minute run at 400VAC. All good.
So being the kind of person I am and wanting to prove that all my hard work in this was worth the while I said " we are going to do another run @ 400VAC for 5 Minutes". Same result. No problems.
And then the final run @ 400VAC 5 Minutes later while this baby is still recovering. Same result. All OK. This is my personal unit that is exactly the same as the other testing units out there....and still to this day has shown no signs of the abuse I put it through last year in June.
So lets look at stuff here:
1. I agree that Transformerless power supplies can be dangerous to people that do not understand them.
2. I agree that they are bad news for people that are merely hobbyists playing around with a potential shock hazard.
3. I agree that they are bad news for people that won't listen. And then leave in a huff.
BUT:
They are excellent for certain applications ( like mine). Will I ever release a kit that people can put together on their own = NO
Will I ever show the details of my design on a Forum or the NET = NO.
Will I encourage Newbies to try this on their own = NO.
Will I release a a fully built, tested and sealed unit....already done. I have orders. And I am not hasty for money. People that have this little Guy for testing swear by it. They find uses I never dreamed of.
All I am saying is that Transformerless power supplies are out there. Many of them.
And they are crazy over the top reliable if built the correct way.
And thanks to ETO and Mods and all to get this off my chest forever
See this link here:
https://www.electro-tech-online.com...he-public-domain-at-last.136196/#post-1146578
Regards
tvtech