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From: "Harry Dellamano"
References: <firstname.lastname@example.org> <3E06A99F.776F9A81@ieee.org> <3E07486E.424879B1@ieee.org> <951O9.102279$4W1.email@example.com> <3E0A3631.4A5C4AC5@ieee.org> <firstname.lastname@example.org> <email@example.com> <%Y8P9.4404$Ab.firstname.lastname@example.org> <email@example.com>
Subject: Re: 87% ... Design requirements are here
X-Newsreader: Microsoft Outlook Express 6.00.2720.3000
Date: Sat, 28 Dec 2002 15:54:04 GMT
NNTP-Posting-Date: Sat, 28 Dec 2002 10:54:04 EST
"Tony Williams" wrote in message
> In article <%Y8P9.4404$Ab.firstname.lastname@example.org>,
> Harry Dellamano wrote:
> > I really can't report on too much because I have your design to do and
> > Analog will probably kick my butt anyway.
> Jeez Harry.... If I can stick my neck out then I'm sure
> that yours will be more than safe. Think of it as
> contributing to the discussion.... rightly or wrongly,
> with being corrected in public part of the exchanges.
> We are (mostly) amongst friends in sed, so who the
> hell cares......
> Tony Williams.
Hi Tony, sorry for sounding like an ass. You and Chris have said so much
that it is difficult to give you a answer to all the dissicussion. I am a
simple man with simple answers.
ZVS is done in many ways but most of the time it's just resonate edges on
the rise and fall time of the main switch. One of the most important
features is to get the main diode to switch at zero current and save trr
losses. Having a non fix frequency allows this to happen. You can talk on an
on but if you saw a working circuit you would realize how simple this is.
Anytime you can charge capacity thru an inductance to twice the input
voltage, it has the ability to resonate to zero and allow the main switch to
turn on at zero voltage. This capacity and inductance is both real and
parasitic. Sometimes you can get both edges to resonate, sometime only one.
An added benefit is that this will happen at or near zero current. The
switching losses are replaced with circulating current losses but with lower
Ron FETs we are winning the battle.
I believe that Zero Current Switching gained wide popularity first (Vicor)
but it was soon realized that the largest parasitics that we must deal with
is FET capacity and if you don't switch at zero voltage the charge dumping
will inflict heavy losses. You notice that Vicor's second generation also
uses ZVS. I only mention Vicor because they are an industry leader, not a
leader in technical expertise. When I initially looked at the problem, ZCS
seem weak compared to ZVS. I have never tried a ZCS topology.
I'm sure Analog and many others could explain this better than I.
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