Re: where can I find a universal linear laptop power supply?

From	Michael Black <et472@ncf.ca>
Newsgroups	comp.sys.laptops
Subject	Re: where can I find a universal linear laptop power supply?
Date	2012-01-28 21:13 -0500
Organization	National Capital Freenet, Ottawa, Ontario, Canada
Message-ID	<Pine.LNX.4.64.1201282106060.4631@darkstar.example.net> (permalink)
References	<jfs0hr$evo$1@dont-email.me> <jfsdpf$v6q$1@dont-email.me> <jftrov$ljc$1@dont-email.me> <jfupc1$m3t$1@dont-email.me>

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On Fri, 27 Jan 2012, cameo wrote:

> On 1/27/2012 1:44 AM, mike wrote:
>> A linear power supply needs several things.
>> A big/heavy transformer that runs at 50/60 Hz. line frequency.
>> A big heat sink and or fan to dissipate the heat.
>> You have to adjust the voltage so that at low line and maximum
>> load, the trough voltage is higher than the output voltage by the
>> headroom required by the regulator transistor. That means at high line
>> you dissipate significant power in the pass transistor.
>> 
>> The switcher uses high frequency, so the transformer and output filter
>> can be MUCH smaller/lighter. The loss in the switching transistor is
>> way less than in a linear circuit, so you don't need the big heatsink/fan.
>> 
>> And since you can easily build a supply that runs from 90VAC to 260VAC,
>> you need only one part number for worldwide application.
>
> Thanks for that thorough explanation. Just one more thing: were switching 
> transformers used for PC-s from the very beginning or they came some time 
> later?
>
>
All the early home computers used linear power supplies, with really hefty 
transformers.

The Apple I didn't come with a power supply, you had to supply your own. 
The Apple II was groundbreaking, since it did use a switching supply. 
It's slightly possible that one of the minor small computers at the time 
used a switching supply, but the Apple II was the first I ever heard that 
used them.  The commercial computers at the time perhaps used switching 
supplies, I don't know.

The "IBM PC" was a copy of the Apple II in many ways, so that may be why 
the IBM had a switching supply.  When it came along in 1981, I'd say it 
was still likely that all or most small computers used linear supplies, 
except for the Apple II.

Then there's a decline, things moving away from a variety of computers, so 
the Apple II and the IBM PC, and the clones were slowly taking over, so 
switching supplies became a lot more common.  But not completely, the 
Atari ST (an example I know first hand) used a linear supply, a chunky big 
external supply.

The interesting thing is that switching supplies didn't show up much in 
radio work, even when high current was needed for transmitting.  Too 
noisy.  When they came, they included interesting things like the ability 
to tune the switching frequency a bit, so if it did interfere with 
receive, one could move it to another frequency where it lessened the 
issue. And they'd also be built differently, higher level of shielding, 
feedhthrough capacitors, even tuned filters in the output lines, to null 
out the switching frequency.  Looked a lot like the sorts of things done 
to ensure the DC voltage out of car alternators was clean enough for 
proper reception.

   Michael

Thread

where can I find a universal *linear* laptop power supply? "Harry Brown" <harrybrown@harrybrown.net> - 2012-01-26 11:55 -0500
  Re: where can I find a universal *linear* laptop power supply? mike <spamme9@gmail.com> - 2012-01-26 10:05 -0800
    Re: where can I find a universal *linear* laptop power supply? "Harry Brown" <harrybrown@harrybrown.net> - 2012-01-27 00:54 -0500
      Re: where can I find a universal *linear* laptop power supply? AaronJ <12465no-mail@no-mail.com> - 2012-01-27 00:55 -0700
      Re: where can I find a universal *linear* laptop power supply? mike <spamme9@gmail.com> - 2012-01-27 02:00 -0800
      Re: where can I find a universal *linear* laptop power supply? Salvador Freemanson <no@spam.com> - 2012-01-29 14:13 +0100
  Re: where can I find a universal *linear* laptop power supply? cameo <cameo@unreal.invalid> - 2012-01-26 12:42 -0800
    Re: where can I find a universal *linear* laptop power supply? mike <spamme9@gmail.com> - 2012-01-27 01:44 -0800
      Re: where can I find a universal *linear* laptop power supply? cameo <cameo@unreal.invalid> - 2012-01-27 10:12 -0800
        Re: where can I find a universal *linear* laptop power supply? mike <spamme9@gmail.com> - 2012-01-27 23:00 -0800
          Re: where can I find a universal *linear* laptop power supply? "BillW50" <BillW50@aol.kom> - 2012-01-28 08:01 -0600
          Re: where can I find a universal *linear* laptop power supply? Sjouke Burry <s@b> - 2012-01-28 17:19 +0000
            Re: where can I find a universal *linear* laptop power supply? Bob_Villa <pheeh.zero@gmail.com> - 2012-01-28 10:26 -0800
          Re: where can I find a universal *linear* laptop power supply? cameo <cameo@unreal.invalid> - 2012-01-28 19:28 -0800
        Re: where can I find a universal *linear* laptop power supply? Michael Black <et472@ncf.ca> - 2012-01-28 21:13 -0500
          Re: where can I find a universal *linear* laptop power supply? AaronJ <12333465no-mail@no-mail.com> - 2012-01-28 20:40 -0700
            Re: where can I find a universal *linear* laptop power supply? Bob_Villa <pheeh.zero@gmail.com> - 2012-01-28 20:34 -0800
              Re: where can I find a universal *linear* laptop power supply? mike <spamme9@gmail.com> - 2012-01-29 00:36 -0800
              Re: where can I find a universal *linear* laptop power supply? AaronJ <12333465no-mail@no-mail.com> - 2012-01-29 10:25 -0700
            Re: where can I find a universal *linear* laptop power supply? Michael Black <et472@ncf.ca> - 2012-01-29 10:25 -0500
              Re: where can I find a universal *linear* laptop power supply? AaronJ <12333465no-mail@no-mail.com> - 2012-01-29 10:03 -0700
        Re: where can I find a universal *linear* laptop power supply? davy <davy.573q95@no.email.invalid> - 2012-01-28 04:34 -0600

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