Transformerless Power Suppply

[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.

[Luciano]

Here, ground and neutral are not necessarily at the same potential.

The fuse will like that!

Best regards,

Luciano

[Melanie]

Actually Dave you quoted me as "both inaccurate and dangerous".

I challenge that.

I don't care what part of the world you're in, the Fuse in Figure 3 of TB008 is a complete waste of time, offering NO protection - let's repeat that in case anyone missed it first time around - offering NO protection to the User of that circuit. If that Fuse is in or out, the circuit will be LIVE. Microchip have dropped a bollock on this one - so let's direct the "inaccurate and dangerous" where it's needed - the author of TB008.

[Pic_User]

Hi All,

There seems to be a great deal of confusion among hobbyists and new professionals concerning ground and circuit ground.

I stopped calling the “common” connections in electrical / electronic circuits, “ground”, 30 years ago. Most of us, have worked out the dual meaning of ground. On one hand we actually mean earth ground, next we simply mean a common connection in our circuit.

This dual meaning is okay most of the time, but sometimes it causes misunderstandings and even dangerous situations. Transformerless power supplies are a common battle ground for the semantics of the term, “ground”. This is because, the misunderstandings lead to safety problems. Problems that cannot be ignored.

Melanie, as usual is the voice of reason and spot on. The TB008 application note, is right out of the twilight zone. The author, obviously has some confusion about “ground” and “common”.

I post this diagram to help illustrate what Melanie already pointed out.

[Luciano]

Hi,

What I have in my house.

(Click to enlarge).

Best regards,

Luciano

[Acetronics2]

Hi, Luciano

Seems not only for the Englishmen ...

3 Phases ... Your home really is a Castle !!!

Alain

[JIM A]

The big difference between ground and "common" or "neutral" is the voltage drop that is developed on the neutral wire due to the fact that it has the same current flow as the line conductor (What goes out must return) (Load current x DC resistance of neutral conductor between receptacle and breaker box= Voltage difference between neutral and ground at the receptacle). Normally the voltage drop is neglible except in long circuit runs with higher current loads. The neutral and ground wires are normally connected together (bonded) at the breaker box. I totally agree that the fuse definitely needs to be in the "hot" or "line" or "mains" line to perform a safety function.

[mvs_sarma]

Hi all
All said and done, we have to accept that what we try to design and implement will be used by us only and that there would not a future occassion to extend the equipment using such PSU to other eqpt, which might create ground loops- a possible shock.

many times we will be pre occupied and would like forget the non isolated psu and take it for granted that we will be safe--

AS SUCH I SUUGEST THAT WE SOULD NOT PRACTICE THIS MODE AT ALL-- ok for academic interest.

[comwarrior]

Strangely, i have a design for a transformer-less PSU in the making...
My reason for not using a transformer is because to have a transformer that drops 110V and 240V down to a more usable voltage and supply the current i need would be massive and it costs >£50 each...

I'm not going to post details of the PSU because i intend on filing for international copyright.
The reason for this is because it will handle any single phase voltage, frequency and amount of noise (or noise only) you can throw at it.
It will even operate in a brown out with sustained unstable voltages as low as 24V (maybe lower).
It can also handle stepped AC, Square wave and saw tooth signals provided it is alternating...

Also, Mel is absolutely right, that AN is written for one purpose and one purpose only... TO KILL PEOPLE!

[psdayama]

Hi All,

There seems to be a great deal of confusion among hobbyists and new professionals concerning ground and circuit ground.


I post this diagram to help illustrate what Melanie already pointed out.

Nice to see the modified diagram but U have missed a vital component.
There should be small resistor like 22 Ohm( Ur LAW) to 47 ohm in serries
with 1uf/250V capacitor ( Melani wont approve of this ).Otherwise in few
days that capacitor will be reduced to open circuit (if of metallised film
type) or get short (if Film foil type) and whole ckt will go up in smoke.
The resistors should be atleast 1/2 watt type ( 1watt better). A high value
resistor like 220K is better placed across capacitor to protect user if he
accidently touches capacitor even when ckt is disconnected from mains.

[Pic_User]

Psdayama,

Thanks for the knowledgeable input. Makes the thread valuable to anyone reading it.
http://www.picbasic.co.uk/forum/atta...1&d=1163524317
-Adam-

[sayzer]

...offering NO protection to the User of that circuit. If that Fuse is in or out, the circuit will be LIVE...

In this case, the circuit will protect itself but kill the user !


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