Groups > misc.news.internet.discuss > #93873

Re: Computer Boot UP

From	Paul <nospam@needed.invalid>
Newsgroups	misc.news.internet.discuss, alt.windows7.general, alt.comp.microsoft.windows
Subject	Re: Computer Boot UP
Date	2021-06-27 01:24 -0400
Organization	A noiseless patient Spider
Message-ID	<sb922q$t7d$1@dont-email.me> (permalink)
References	<58fedgdd8css00f4m6hgkd54n9u5kjq3i2@4ax.com> <sb81ek$2t1$1@dont-email.me> <ms2fdgt27olchbmra05umv2gru5nc3gnha@4ax.com> <sb8gsk$ahf$1@dont-email.me> <rejfdgd745kt2rlafrmsv22hg8uashmrb6@4ax.com>

Cross-posted to 3 groups.

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JAB wrote:
> On Sat, 26 Jun 2021 20:31:15 -0400, Paul <nospam@needed.invalid>
> wrote:
> 
>> So that's a very brief introduction to startup.
> 
> Tidbit - " [ Note: All these voltages will vary slightly for each
> combination of power supply, motherboard, disk drive(s) and various
> peripherals (since the number of electronic components drawing current
> alters a power supply's load), but its output voltages should never
> fluctuate upon reaching normal operating levels. 
> 
> If any of its outputs has an unacceptable amount of noise (or AC
> ripple[1]), then one or more of the motherboard's components, such as
> its Memory, may fail the Power-On Self Test, keeping the PC's
> operating system from ever booting up. ....]"
> 
> <https://thestarman.pcministry.com/PCboot.htm>
> 

This is hardly the best example, but it will
give you some idea how modern stuff works.

http://wiki.laptop.org/go/XO_1.75_Power_Distribution

Now, look down where it says "+1.5V_DDR3". There
is an LDO (linear) making 0.75V for VTT (terminator
voltage rail) and another LDO making +1.2V. They
appear to be powered from a switcher (MP28259).
Which in turn runs from "+VIN". On a desktop,
perhaps they would use the +12V rail for that.

https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP28259-A/document_id/3816/

    * Wide 4.2V to 20V Operating Input Range [good for +5V or +12V PSU]
    * 2A Output Current
    * Low RDS(ON) Internal Power MOSFETs
    * Proprietary Switching Loss Reduction Technique
    * Power-Good Indicator in QFN Package
    * Soft Shutdown
    * Programmable Switching Frequency
    * OCP, SCP, OVP, UVP Protection and Thermal Shutdown
    * Optional OCP Protection: Latch-Off Mode and Hiccup Mode
    * Output Adjustable from 0.815V to 13V
    * Available in a QFN12 (2mmx3mm) Package

And that powers the DDR3 in that computing product.

The circuit can accept a large amount of ripple,
and the output will be clean. The package is 2x3 millimeters
in size. A mere silicon fart. The outboard components next
to the chip, will be bigger than it (needs an inductor L1 2uH).

Even a modern PSU has double forward conversion, so the
crossloading behavior has been mostly eliminated.

     Mains ------ +12V -+------- +12V (many amps)
                        |
                 PSU converter board
                        |
                        +------- +5V   (20 amps max)
                        +------- +3.3V (20 amps max)

The main +12V could have ripple.

If the +12V ripple was bad enough, it might corrupt a hard drive,
but then at some point PWR_GOOD would deassert on
the PSU if the swing was too much.

All the generations are different, in terms of potential
fault modes. The newer stuff is quite good now. I was
debugging something here one day, and my multimeter
was reading a number with several zeros on the end
(as a measure of how precisely it was regulated), and
I remember muttering under my breath "somebody is
showing off!". That's how good the regulation was.
At one time, they "just made the circuits work".
Now they can afford to show off.

    Paul

Thread

Computer Boot UP JAB <here@is.invalid> - 2021-06-26 10:04 -0500
  Re: Computer Boot UP JAB <here@is.invalid> - 2021-06-26 10:57 -0500
  Re: Computer Boot UP Michael Trew <mt999999@ymail.com> - 2021-06-26 16:07 -0400
    Re: Computer Boot UP JAB <here@is.invalid> - 2021-06-26 15:36 -0500
      Re: Computer Boot UP Paul <nospam@needed.invalid> - 2021-06-26 20:31 -0400
        Re: Computer Boot UP JAB <here@is.invalid> - 2021-06-26 19:43 -0500
          Re: Computer Boot UP Paul <nospam@needed.invalid> - 2021-06-26 21:14 -0400
          Re: Computer Boot UP "J. P. Gilliver (John)" <G6JPG@255soft.uk> - 2021-06-27 02:32 +0100
        Re: Computer Boot UP JAB <here@is.invalid> - 2021-06-26 20:06 -0500
          Re: Computer Boot UP Paul <nospam@needed.invalid> - 2021-06-27 01:24 -0400
            Re: Computer Boot UP JAB <here@is.invalid> - 2021-06-27 05:12 -0500
        Re: Computer Boot UP JAB <here@is.invalid> - 2022-02-01 11:17 -0600
          Re: Computer Boot UP VanguardLH <V@nguard.LH> - 2022-02-01 12:26 -0600
            Re: Computer Boot UP JAB <here@is.invalid> - 2022-02-01 12:48 -0600
              Re: Computer Boot UP Michael Trew <michael.trew@att.net> - 2022-02-04 10:14 -0500
                Re: Computer Boot UP JAB <here@is.invalid> - 2022-02-04 10:54 -0600
                Re: Computer Boot UP Michael Trew <michael.trew@att.net> - 2022-02-05 16:40 -0500
                Re: Computer Boot UP JAB <here@is.invalid> - 2022-02-05 16:48 -0600
                Re: Computer Boot UP Michael Trew <michael.trew@att.net> - 2022-02-09 00:12 -0500
                Re: Computer Boot UP rtr <rtr@haraya.invalid> - 2022-02-06 15:16 +0800
                Re: Computer Boot UP Michael Trew <michael.trew@att.net> - 2022-02-09 00:13 -0500

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