Transformerless Power Suppply

[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)!

[NavMicroSystems]

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]

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]

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]

... 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]

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

[NavMicroSystems]

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]

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

[dhouston]

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)!

Melanie,

This may be accurate when talking about UK or European wiring but your advice is both inaccurate and dangerous when it comes to North American wiring. The fuse between neutral and ground shown in FIGURE 3 and FIGURE 4 of TB008 is a safety feature as the authors of the app note state.

Here's a URL which briefly explains the 3-wire system used here for many, many years.

• http://hyperphysics.phy-astr.gsu.edu...ic/bregnd.html

Circuits which might be plugged in either way around will not have the ground wire and thus will not have the fuse and will also require double-insulated, non-conductive enclosures. In fact, the only way to plug a North American two-wire appliance in either way around is to file down the wider neutral prong of the polarised plug.

You might also read...

• http://en.wikipedia.org/wiki/Double_insulated

[Melanie]

You are kidding me!

Neutral and Ground are basically one and the same. In many buildings all over the world (including in the US) the NEUTRAL incommer is tied to the Building GROUND (just as it is at the generating plant).

Go remove that fuse from the NEUTRAL line in figure 3 of TB008. Then stick your finger in the HOT terminal with one hand (or the 1uF Capacitor), and go grip a Water pipe in the other and tell me if you feel anything! They don't label that terminal LIVE for fun.

Oh, btw... I've a whole heap of US plugs and sockets that have the Neutral and Live EXACTLY the same size. So the Neutral terminal being the larger must be a recent innovation for the US.

The Transformerless Power Supply is not designed for portable equipment that can be connected either way around, but more suitable for fixed plant where the installer wires LIVE to LIVE.

[dhouston]

I suggest you actually take the time to read the URLs I cited.

We've had polarized plugs and wall sockets from even before the time the 3-wire system was implemented. I live in a 60+ year old building that predates the 3-wire system and all of the wall outlets are polarized. My memory is a bit fuzzy but I believe the 3-wire system was required from about 1960.

If you have non-polarized plugs and sockets they are likely be for IEC Class II use which you might have grasped had you bothered to read the URLs I cited.

Transformerless power supplies have been used by X-10 in their plug-in modules (some 3-wire, some 2-wire, all polarized) and switches since 1976 or so.

[Melanie]

We'll have to disagree on this one. However I've not killed anybody yet (on the basis it's bad for business) and my designs are used internationally - many with UL certification, so either I'm lucky or I must be doing something right. *smiles*

[Luciano]

Hi,

Ground Fault Circuit Interrupters (GFCI)

A GFCI will trip under a shorted Neutral-Ground condition even
if no load is connected to the circuit -- that is, no load
other than the short between neutral and ground.

Here in Italy the GFCI will trip because of this fuse between
neutral and ground. (See figure 3 and 4 Microchip TB008).



Best regards,

Luciano

[dhouston]

The circuit shown is probably not intended to be plugged into a CFGI nor into any power grid other than in North America.

Here, ground and neutral are not necessarily at the same potential. Recent changes in the National Electric Code call for the ground lead to connect to the center-tap of the utility transformer and for neutral to connect to earth ground at the entrance panel.

I haven't said that fuse should be used in the UK or Europe nor have I, in any way, been critical of Melanie's design skills.