Toridal Mains Transformer

The capacitor input filter.

Do you think the storage cap discharges to zero every cycle ?

Graham

I read in sci.electronics.design that Pooh Bear wrote (in ) about 'Toridal Mains Transformer', on Thu, 8 Sep 2005:

Well, you CAN push it to 75 W, but you need to get rid of more heat. Below 50 W, the transformer loss is often enough, without adding resistance or inductance in series with the rectifier.

No. And it doesn't look too likely that we'll get anywhere next November either. It's a crazy situation.

I read in sci.electronics.design that Pooh Bear wrote (in ) about 'Toridal Mains Transformer', on Thu, 8 Sep 2005:

We do have standard definitions of 'displacement power factor' (cos phi) and 'distortion power factor', but it's true that IEC/EN 61000-3-2 and-12 don't use the terms.

I read in sci.electronics.design that Pooh Bear wrote (in ) about 'Toridal Mains Transformer', on Thu, 8 Sep 2005:

More every week, but I don't have a list. Most of SE Asia, now. Russia and some of its neighbours.

If the product is not going to the Americas, and operates from *public* mains supplies over 200 V at 50 Hz, it probably need to conform to IEC/EN 61000-3-2. Japan has its own version, which is, I think, still not mandatory. But it will be; I ha a message today indicating that they are working on it.

The original usage of power factor relates to leading or lagging of the load current wrt voltage.

This entirely diiferent. The standards don't call it 'Harmonics' withouy good reason. The problems it creates are also entirely unlike any that's associated with simple power factor issues.

Simply not so.

Totally irrelevant.

You're trolling aren't you ?

Graham

Most of what you say about linear supplies is accurate Phil, except for how they are usually used in the real world - and here I am not talking about piddling wall warts. You will be aware that the closer the loading approaches the design maximum (assuming proper component specification) the closer the pf will be to ideal, and that will be much higheer than 0.5.I doubt very much that linear power supplies are generally operated with no load and that is where the pf is worst.

Actually Phil, Most PFC pre-regulators are included directly on the mains side ahead of the SMPS proper. The only thing between the PFC and the smps proper is the EMI/RFI filter and bridge rectifier and input filter capacitor. I have never seen a transformer used purely for isolation and then follow it with the PFC regulator ahead of the smps proper. The very fact that most PFC regulators are designed for a wide range ac input infers that they are intended to be directly interfaced to the mains supply. Check any of the IC manufacturers and this fact will be verified. Her's one to start with

Graham, you are entitled to your opinion - as am I.

Well, maybe an on-off switch, fuse and input connector. I wasn't exactly trying to specify a parts build list, it was a general statement of what is most commonly found. Perhaps you can nominate a smps which requires more than these items? It is bound to be specific to some esoteric application, I'll bet.

So now you want to enter into a "my dick is bigger than your dick" competition. Don't worry, I know yours is bigger :-)

You are introducing a new topic for discussion here. This particular EMI is a spin-off from introducing an additional switching technique (pfc pre-reg) which is intended to compensate for the negative aspects of the principal switching technique (smps proper). The total EMI is bound to be greater than for either one of these stages by itself and it hardly matters whether the pfc pre-reg is 'noisier' than the smps itself. All that matters is that the situation is worsened by including a pfc pre-reg. Such a negative effect due to the pfc pre-reg will demand yet more techniques for noise control.

The kindest thing I can say is that I think the entire contents of the thread to date simply whizzed over your head !

Btw, your statement that " The only thing between the PFC and the smps proper is the EMI/RFI filter and bridge rectifier and input filter capacitor " is simply staggeringly wrong !

Did you know that PFC stages actually produce *more* EMI than a typical smps designed for the same load ?

Graham

Got a source for that info - or is it your own analysis based on experience?

So, you are not going to dispute this fact,- simply offering a retort eh? If you perceived that my pointing out a 'fact' to you as 'talking down' to you, then I apologise. It was not intended.

That fact that I haven't seen this technique used may not be relevant to the OP's post or yours, but what I am inferring is that such a technique is unusual and rarely seen in smps design. After all, when you elect to use an smps you do so to eliminate the requirement for a heavy mains transformer. Perhaps I have been wrong about this all along...

Did the OP mention this as a requirement?

Of course the transformer will provide isolation, the question is why does he need it. Or more importantly, does he really need isolation at all? Unless he speaks up about what he really needs we are all guessing.

The op simply inferred that he wanted a transformer coupled dc psu with pfc - no other requirements. Without stating the useage the requirement for ground isolation is not known. His original plan may have been hastily reorganised if he has now discovered he doesn't really need a transformer.

Incidentally, the op is particularly quiet on this thread and has not come forth to clarify further what he is trying to do....

You misunderstand.... Let me put it another way. There is nothing between the mains supply and the smps proper except the EMI/RFI filter, the bridge rectifier and input capacitor, AND the PFC regulator. I made no mention or inferrence of there being anything between the PFC reg and the SMPS proper. Anyone knows that the PFC reg directly connects its output to the input of smps switcher itself.

thread to

proper is

simply

If you want to get down to the specifics of actually specifying all the parts required in order to conform to EMC legislation, then I can. However, this thread has been talking in generalities, not the nth degree of design and conforming to legislation. Get real.

Reviewing what I wrote... You are correct. I did mean to say exactly what I said in my last response to you on this point. I should have reviewed what I had typed prior to hitting the send button.

Even you have had to recant when accidentally typing something you didn't mean to say.

You are correct Graham. It's not what I intended to say or understood about the real situation at all, simply a failure to review before sending.

What *I* think is irrelevant.

See IEC61000-3-2 ( single phase < 16A )

You may also be interested to know that harmonics ( the real killer is

Poor 'power factor' ( I use the term to humour Phil Allison ) - sorry really Harmonics - results in a very large current in the neutral conductor of 3 phase distribution systems. That's assuming it's star connected btw ! God knows what happens to delta wired systems.

Anyway - the neutral conductor can fail. Bad news.

Graham

Yes, I noted that you pointed it out as well.

You have somehow included this statement I made in my reply to Phil, and I didn't say this to you.

Yes I did say that. Sometimes in the heat of battle one doesn't always check things properly and it can lead to embarrassment and recanting.

Oh, I agree, it will work and if you do need the isolation, then fine. I note that you say you have 'even considered it myself', so why did you decide not to proceed down this path (I assume you did proceed down some path)? Could it have been that it would seem sort of counter productive to use a small efficient smps behind a heavy mains transformer?

to

is

You clearly are unaware of legislation that requires relevant EMC measures.

Or you have a wacky idea of how to build a PSU.

Graham

I see that your brain cells aren't totally fried then !

Graham

That's not what you originally said. And explains why you got pulled up on it.

Graham

It has to be said that there is something to be said for this. Hmm repetition - oh wtf !

I'm not aware of any UK failures of this type for example. I believe we tend to be generous in sizing conductors.

For sure.

I also gather that harmonics can take their toll on classic Power Factor Correction components btw. A power factor correcting cap will 'pull' more current when there are harmonics around and may overheat.

Graham