[SI-LIST] Re: 48V power distribution
- From: "Gourari, Alexandre" <Alexandre.Gourari@xxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 25 Oct 2004 16:22:43 +0100
But I thought that Steve's original suggestion about safety on 48V was
right. Given you are not going to use linear regulator to power logic from
48VDC some sort of buck converter is necessary, so your voltage swing at the
switcher will be >48VAC peak-to-peak (due to voltage drop on recirculating
diodes) exceeding 42Vp-p safety threshold.
Best regards,
Alex Gourari
-----Original Message-----
From: steve weir [mailto:weirsp@xxxxxxxxxx]
Sent: Friday, October 22, 2004 7:00 PM
To: lorber@xxxxxx; tcuratolo@xxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: 48V power distribution
Walter thanks. I went back and reviewed the standard. Stupid me, I have
had 42.4VDC erroneously stuck in my head for a long time.
As to Tom's question, I didn't see it before-
Tom, an one issue that can come up is of battery return. One of the nice
things about isolated power supplies at the card entry is that they
facilitate a battery return isolated from the signal common. That frees
one to tie the signal common to the package frame without a safety issue as
the frame cannot become the battery return, and therefore doesn't carry
risk of electrification. If you push the power converters inward, and you
want to maintain this important safety characteristic, then you will still
be stuck keeping the battery return DC isolated from the frame. It isn't
the end of the world, but you will want to watch it. The other thing that
I think you really want to look at is the physical size of the magnetics
that will be needed, and I mentioned before.
Regards,
Steve
At 04:34 PM 10/22/2004 -0500, Lorber, Walter wrote:
>The SELV limit is 60VDC or 42.4VAC in IEC 60950
>With best regards,
>Walter
>
>
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of tompegbel
>Sent: Friday, October 22, 2004 4:22 PM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: 48V power distribution
>
>
>Thanks Steve, I appreciate your insight. I guess I really wanted to
>focus on the issue of isolation versus non-isolation at the point of
>entry for the PCB power distribution provided it is within SELV
>limits. Provided components are available and cost of implemenation
>is acceptably low, is there any major drawbacks with isolation at the
>point of load versus isolation at the point of entry?
>Regards,
>--Tom
>
>--- In si-list@xxxxxxxxxxxxxxx, steve weir <weirsp@xxxx> wrote:
> > Tom, the biggest issue is that 48V exceeds the 42V low-voltage
>safety limit
> > and so requires substantially greater clearances. A 24V system is
>under
> > that limit and does not face the same problem. 48V also changes
>the
> > dynamics of available semiconductors. 12V systems and to a certain
>extent,
> > 24V systems can leverage the super low on resistance and low
>capacitance
> > FETs and diodes. The last issue is one of magnetics and practical
> > form-factors. Given you work for Vicor, you should be pretty
>familiar with
> > those and how taller primary to output ratios aggravate same.
> >
> > Regards,
> >
> >
> > Steve
> > At 02:04 PM 10/19/2004 +0000, tompegbel wrote:
> >
> > >Is there a good resource/document for addressing the concerns in
> > >bussing 48V power in a multilayer board? The recently popular 12V
>or
> > >lower intermediate bus approach has limitations as voltages get
>lower
> > >and current gets higher. There appears to be new approaches of
>using
> > >a higher bus voltage (24V or 48V) for distribution since this was
> > >explored in the 80's with the advent of distributed power and now
> > >more recently with VoIP type designs. Any assistance appreciated
> > >
> > >
> > >
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