[iyonix-support] Re: Iyonix hanging (was Re: EtherK not starting up reliably)
- From: Dave Higton <davehigton@xxxxxxxxxxxxx>
- To: iyonix-support@xxxxxxxxxxxxx
- Date: Thu, 24 Aug 2006 19:49:26 +0100
In message <2679675b4e.steve@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Steve Fryatt <lists@xxxxxxxxxxxxxxxxxx> wrote:
> On 24 Aug, Peter Bell wrote in message
> <f213655b4e.peter@xxxxxxxxxxxxxxxxxxxxxxxxx>:
>
> > A panic buy at Maplin produced a 250W ATX unit at =A318.98 (WF87U) -
> > 'white-box', and not even described as low-noise, but it does have a
> > variable speed fan, and seems quiet enough. The Iyo has been running
> > for two hours without any obvious problems. However, the 5V rail is
> > measuring 5.15V!
>
> Even allowing for the calibration (or otherwise) of people's DVMs, the
> kind of voltage tolerances being thrown about on this list are utterly
> meaningless in the context of ATX power supplies.
>
> Unless the standard spec has changed significantly since I stopped
> designing the things three years ago, the 5V rail is usually given as
> 4.75V to 5.25V. The nominal often sits a little high of centre (say about
> 5.1V), due to the realities of transformer design, but even this isn't
> guaranteed.
>
> Exactly where any given PSU will operate under the 'standard' Iyonix load
> is impossible to say, but it could fall anywhere within 0.25V either way
> of 5V and still be within spec. The exact voltage at any time will depend
> on the loadings of most of the PSUs other outputs when the measurement is
> taken (and hence on hard disc activity, whether the CD is in use for
> reading or burning, etc), not to mention component tolerances in the PSU.
Don't forget that the requirement is that the voltage AT THE PINS
OF THE CHIPS is within tolerance. The average voltage being
launched from the PSU is higher than the voltage arriving at the
chips because of various resistive losses. Then you need to allow
for noise, which is "randomly" varying in magnitude and sign. To
keep the voltage at the chip pins within tolerance, the average
(i.e. DC) voltage from the PSU needs to be (a) within a closer
tolerance (because of noise), and (b) slightly high on average
(because of unavoidable resistive losses).
Dave
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