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From: Keith R. Williams
Subject: Re: Smallest component to step down 240VAC to 18VDC?
Date: Tue, 15 Oct 2002 00:06:07 -0400
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In article , email@example.com
> They make some regulators for stepping down up to 265VAC to
> DC switching regulators, but I don't think they are isolated.
I looked at that. Neat chip! It's basically a phase-controlled
regulator with some post processing switching stuff.
Great! ...but where do you tie the ground end of the bridge? If
you tie it to neutral, you'd better hope with your life it really
is neutral. If you tie it to the safety ground you have current
in the ground (and violate every rule in the book). Tie it to
hot: *ZAP* you're dead (see: neutral tie with a misfired
service). The problem is there is no isolation, so no safe way
to reference the DC to ground. You must therefore assume the DV
will be riding on top of 120V, which might work for appliances
(note the dire warning on the first page of the spec).
No, I'll pass, as should every sane person. Neat chip though.
Thanks for pointing it out.
> "Keith R. Williams" wrote in message
> > In article <firstname.lastname@example.org>, a?n?g?e?
> > email@example.com says...
> > > On Wed, 9 Oct 2002 13:51:47 -0400, Keith R. Williams
> > > wrote:
> > >
> > >
> > > >Even if it were 230V that it would take 30 regulators ( (230-16)/7 ) if
> > > >each was 7V. But since it's 320V, that's *43* regulators.
> > >
> > > >Well, the power dissipation would be (230V-16V)*4.5A or over 1300W (and
> > > >you think Athlons are hot ;-)! You could dry your hair while you
> > > >design your web pages!
> > >
> > > I'm not going to do it, since obviously it's not a good idea. (No
> > > thanks, I do not plan on having my 3 minutes of fame by getting a
> > > Darwin)
> > More like three seconds of flame! ;-)
> > > But I would like to understand why, since I'm still confused on this
> > > thousand watt figure being raised by everybody. I think I sorta get it
> > > now.
> > >
> > > ie current through all parts should be the same, thus even after I
> > > split the 230V over x regulators, the 230V will still see the 4.5A and
> > > I still get thousand over watt dissipation?
> > Again, it's 320V (your 230 is RMS, times 1.4 gets peak), and yes.
> > 4.5A times 320V, is...
> > Well, your laptop will take 16V times 4.5A of the juice. SO that
> > means (320-16)*4.5=1300W. Hot.hot.hot.
> > > Speaking of the no ground... I realize I don't really know which pin
> > > of the AC plug does power come in. Does the AC oscillates between the
> > > live and neutral, or does it do the +/-230V wrt to the ground pin?
> > I believe you have a Brit system in .sg. They have a single
> > phase 230V and neutral (rather than our split phase 120-N or 120-
> > N-120). Your hot oscillates between +320V and -320V (with
> > respect to neutral). Your neutral should be very close to ground.
> > BTW, 320V is not my typical dyslexic tupo. I mean 320V (1.4*
> > 230V)!
> > I don't know if your system is "polarized" (hot differentiated
> > from neutral at the outlet) as ours is. Our neutral socket is
> > larger than the hot. Devices that need to know hot (typically
> > upper-right) from neutral (upper left) have a larger spade for
> > the neutral or are keyed off the ground pin (low-center).
> > ...though at work they insist on mounting the outlets upside-down
> > (their theory is that any falling metal should hit the ground
> > pin).
> > ----
> > Keith
> > ----
> > Keith
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