Transformerless Power Suppply

**NavMicroSystems** · - 22nd February 2006, 20:19

Originally Posted by Melanie

I have mentioned before that some of Microchips Application Notes are downright dangerous... and that is one of them.

Connecting Neutral and Earth together will trip most ELCB's a small fact that the author of that AN seems to have overlooked. Not fusing the Live is plain stupidity (as is any power distribution system that allows users to plug appliances in either way around)!

I absolutely agree !

Unfortunately DO most european systems allow users to plug in appliances in either way around.

Hey Mel, you must be lucky living on an island with some better system!

There is one thing in addition I would like to mention:

Guess what happens if your mains is only "kind of" 50Hz sine?

Do you see where I'm going?

I have had several portable devices on my bench for repair.
Some of them had poor designed low-cost transformerless PSUs.

i.e. coffee (or espresso) makers a.o.

Users had thought it would be nice to use that coffee maker in their caravan
and hooked it up to one of those low-cost power inverters.
The output of most of the low-cost inverters is not even kind of sine, it is actually square, so all the transformerless PSU did was saying goodby by generating smoke.

You'll wonder what strange ideas users come up with...

**Melanie** · - 22nd February 2006, 21:12

It's a 3-pin ONLY system in the UK. Yes you can get continental 2-pin shaver adaptors, but I'm told you men like to live dangerously in the bathroom.

Let's just look at TB008 for a moment... and just consider...

Neutral is grounded at the Power Station, and at the substation, and probably at the Building incommer... Here we have a fuse between Neutral and Earth... why? It's completely USELESS!!! If the fuse wasn't there (or it blows for whatever reason), you STILL have a FULL conductive path between LIVE and EARTH. Actually he's (I'm assuming 'he' as a girl I'd expect to know better *smiles*) even using EARTH as a return path of his circuit. Plug that circuit into most properly wired homes and the first thing that happens is the ELCB breaker trips! The author of TB008 should be prosecuted for the most dangerous suggestion you could possibly think of!!!

I'm well aware of the square wave inverters... still... the great unwashed (general public) hasn't got a clue... which is why you can market complete crap and they'll still pay good money for it.

**NavMicroSystems** · - 22nd February 2006, 22:19

I'm not using any transformerless PSU's at all.

Some time ago I could get hold of a large number of well designed switching PSU-units at about $0,50 each (stock/production overhead)

They provide well regulated 7,5V @ 600mA
and are very small in size.
(Actually not more in PCB-Space than a good transformerless design would require since they are fully SMD)

I could not even design and build any transformerless PSU at comparable cost.

Why develop/build something that is already available on the market at lowest cost?

OK,
for someone selling 10thousands of units per year it is a different story,
but if you are selling "only" several hundreds of units I still feel it is a good option to search the web for those stock overheads.

The only rule is:
get a sample before your bulk order and test it carefully.
If the sample is OK (meets or exceeds the requirements):
order a quantity that lasts at least to the planned production/life-cycle of your product.

That way I have saved a lot of time & money.

**NavMicroSystems** · - 22nd February 2006, 22:24

Originally Posted by Melanie

... still... the great unwashed (general public) hasn't got a clue... which is why you can market complete crap and they'll still pay good money for it.

Mel, I doubt you would risk your reputation by marketing crap just to make money.
(please correct me if I'm wrong)

**Melanie** · - 22nd February 2006, 22:48

You just have to walk down any High Street in any Town, anywhere in the world to see what I mean...

**NavMicroSystems** · - 22nd February 2006, 22:53

Originally Posted by Melanie

You just have to walk down any High Street in any Town, anywhere in the world to see what I mean...

I'm almost sure I know what you mean and hope you haven't taken my comment too serious ;-)

**nomada** · - 23rd February 2006, 01:37

Hi,

Be carefull, be very carefull, when using a power supply without transformer is like walking in the wire without the net underneath...

Atached you can see the circuit I use to put some power ... in PICs and other stuff. I found this circuit some years ago when I bought a kit (K6713)from Velleman, its a IR receiver to switch on/off a load connected to mains trough a relay.

One more advise, if by any chance you are planning to use this circuit in a touch sensor or similar do not forget to use two resistors in series for the sensor, the contour voltage for a regular 1/4W is less than 200V, unless you like to get a curly hair...

regards

**Melanie** · - 6th March 2006, 01:53

If you're still looking for components, attached PIC I've taken gives you an idea of what to look for... The 11V VDR is pretty small (VDR2 in this pic) - and also laying alongside with a view of a typical Capacitor you can use. If it's an X2 type you're OK, otherwise you'll have to fit one with a 400vDC rating. It's a real good idea to absolutely and positively mark the PCB that it's LIVE... even if it's just for yourself. Some time in the future you'll forget and it'll bite you.