where can I find a universal *linear* laptop power supply?

[Harry Brown]

Looking for a reasonable cost, universal linear (NOT switching) laptop power
supply. Where might I find one?

Thank you,
Harry

[mike]

I don't recall ever seeing a linear laptop supply.
You'll need to determine the voltage and current you need.
Perhaps an open-frame OEM power supply and a box to put it in.
And it ain't gonna be portable. And you won't like the quantity 1
price. But it will keep your feet warm on those cold winter nights.

You haven't stated why you would want to do such a thing,
so we can't offer alternatives.

[cameo]

On 1/26/2012 8:55 AM, Harry Brown wrote:

> Looking for a reasonable cost, universal linear (NOT switching) laptop
> power supply. Where might I find one?

That reminds me: what is really the difference between the two and
what is being "switched" and why?

[Harry Brown]

"mike" <spa...@gmail.com> wrote in message
news:jfs4ng$8mu$1...@dont-email.me...

I am a shortwave radio listener and I use an external radio module that
plugs into the laptop via USB port. However, these switching supplies are
making horrendous noise and harmonics all across most shortwave radio bands.
I can reduce the noise a little bit by moving the supply to a different spot
or winding the incoming/ outgoing power cords through chokes, but this still
isn't enough. The only alternative I could see was switching to a linear
supply if one is still made for laptops.

Harry

[AaronJ]

On Fri, 27 Jan 2012 00:54:22 -0500, "Harry Brown"
<harry...@harrybrown.net> wrote:

>I am a shortwave radio listener and I use an external radio module that
>plugs into the laptop via USB port. However, these switching supplies are
>making horrendous noise and harmonics all across most shortwave radio bands.

Where is the noise entering the radio? If it is coming in from the
antenna try relocating the antenna. If you're a serious SW listener
the antenna should be located outside high and away from other
objects. It might also help to feed it with shielded cable so that it
won't pick up noise while exiting through the house. If the antenna is
the problem, eliminating the laptop switching supply noise may not
help that much since virtually every other electronic device these
days (TVs, your neighbors computers, cable boxes, ect) use switching
supplies and most will make a certain amount of SW noise to be picked
up by your antenna. Hams with extensive antenna systems even hear it
since it's virtually impossible to completely eliminate.

>I can reduce the noise a little bit by moving the supply to a different spot
>or winding the incoming/ outgoing power cords through chokes, but this still
>isn't enough.

If the noise is entering the radio module by other means then it is
probably the receiver with inadequate filtering on another lead.. This
is easy to check, just unplug the antenna and see if the noise is
still there. If so then the noise is coming through another lead, and
not the antenna. If the noise is coming in through the USB port from
the laptop then changing to a linear supply feeding the laptop may
very well help. But before that try a choke on the USB cable. Also one
on the receiver module power supply (if it has one and is not powered
by the laptop).

>The only alternative I could see was switching to a linear
>supply if one is still made for laptops.

You're probably not going to find a linear supply made for your
laptop. As another poster said find the voltage/current requirements
and try to find a linear supply replacement. That may be difficult and
if you get it wrong you may damage your laptop.

[mike]

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.

[mike]

I assume you've done the obvious???
Run the laptop on battery and the noise goes away?
There's a switcher or two inside the laptop.

Also assume that you've got no other sources. Virtually every
electronic device in your house has a switching supply.
Virtually every
electronic device in your neighbor's house has a switching supply.

Also try it with the power supply plugged in but not connected to the mains.
Then try connecting just the ground or neutral wire to the mains.
You're trying to determine how the noise is being coupled in.
It may not be radiated.
If you get noise with only the ground connected, a liner supply
ain't gonna help you.

Plug the power supply into the mains, disconnected from the laptop
and note the noise. You may have to load the supply with something,
like a resistor or light bulb.

Depending on the voltage of the power supply, you may be able to run it
from a 12V linear supply you can get from radio shack.
I've had 18V computers that ran just fine on 12V. Just wouldn't charge
the battery. YMMV
By tweaking a resistor you can usually get a little more
volts out of a linear supply if you don't load it heavily.

You still haven't disclosed the voltage/current you need.

[cameo]

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?

[mike]

I've never seen a linear supply in a Post-IBMPC computer.
Don't know about the early apples.
Commodore 64 was linear.
Timex Sinclair was linear.

[BillW50]

In news:jg06h1$hip$1...@dont-email.me,

Here is a good write up about the two:

Switching vs. linear power supplies
http://urgentcomm.com/mag/radio_switching_vs_linear/

Here is an article that states linear was still being used for 286 PCs.

Switching power supplies...
http://www.targetpc.com/technology/reviews/12.html

Also those Asus EeePC 700 series wall warts looks very suspiciously as a
linear power supply. I should crack one open one of these days to find
out for sure. Although the label says 100vac to 240vac. And that is a
pretty clear sign that it too is probably using a switching supply.

Here is a discussion about running a linear supply on a Mac Mini and how
much better the sound is. And it sounds like linear power supplies can
be found for computers today. But they cost between the $400 to $600
range.

Mac Mini - Linear Power Supply | Computer Audiophile
http://www.computeraudiophile.com/content/Mac-Mini-Linear-Power-Supply

Jameco Electronics sells both linear and switching power supplies.

How to Choose a Wall Adapter Power Supply
http://www.jameco.com/Jameco/content/walladapter.html

--
Bill
Gateway M465e ('06 era) - OE-QuoteFix v1.19.2
Centrino Core Duo T2400 1.83GHz - 2GB - Windows XP SP3

[Sjouke Burry]

mike <spa...@gmail.com> wrote in news:jg06h1$hip$1...@dont-email.me:

I am still using a 12V linear supply resqued from
a pdp 11-03.(about 1980??)
Still works too....

[Bob_Villa]

On Jan 28, 11:19 am, Sjouke Burry <s@b> wrote:

>
> I am still using a 12V linear supply resqued from
> a pdp 11-03.(about 1980??)
> Still works too....

I suppose if you're "still using" it...it "still works"! (unless you
were "using" it for a paperweight) B^)

[Michael Black]

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

[cameo]

On 1/27/2012 11:00 PM, mike wrote:
> I've never seen a linear supply in a Post-IBMPC computer.
> Don't know about the early apples.
> Commodore 64 was linear.
> Timex Sinclair was linear.

OK, now that I know the difference, I still wonder what is *linear*
about linear transformers. How did they get that name?

[AaronJ]

On Sat, 28 Jan 2012 21:13:05 -0500, Michael Black <et...@ncf.ca>
wrote:

>The interesting thing is that switching supplies didn't show up much in
>radio work,

The first radio switching supplies I remember from my youth used a
mechanical switcher:

http://radioremembered.org/vpwrsup.htm

[Bob_Villa]

These "vibrators" were used when radios were introduced to
automobiles. Switching the DC on and off allowed the voltage to be
stepped-up by transformer to power the filaments of the vacuum tubes.

[mike]

HuH??? Did you write what you actually meant to say?

[davy]

It should be easy to build a linear regulated power supply that will
handle a couple of amps.... how about using a High current 13.8 Volt
power supply and modifying it for the voltage required... this is
usually a resistor change, or using an external variable voltage
regulator should lower than 13.8V is required - *this is for the
experienced constructor mind!*

You will find some brands of laptop supplies are worse than others....
one way perhaps is to do a little experimenting.... get some High Mu
ferrite cores wrap as many turns as you can get on them, one at the
output and another at the mains input end.... then perhaps placing the
unit in a diecast box and grounding the box to the stations earth,
obviously they need tp be pretty large diameter because of the cable
thickness, then there is the ferrite clamp types that simply clamp
around the cable.

The problem stems from the harmonics generated from the 22Khz switching
frequency. The way these work is they rectify the mains, say 240V ac
after rectification and being smoothed you will end up with 240ac x
1.414 volts which equals about 340V dc, this is fed to a chopper
transistor or FET via the step down isolating transformer and then
switched rapidly off and on at 22,000 times a second or 22Khz.

The racket they can produce can be heard well over 30Mhz, well into the
50Mhz 6Mtr ham band... the input filtering on many leaves a lot to be
desired, thus the mains lead makes an effective antenna to radiate the
hash.

The advantages being smaller components particularly transformer and
lower value smoothing capacitors, they are more efficient but noisier...
same with mod-con TV sets.

davy

[Salvador Freemanson]

Run it from a car battery, or two car batteries in series with a dropper
resistance, depending on the required supply voltage.

In fact, now I come to think of it, most laptops have a battery built-in
these days. Why not use that? Some models have extra large external
cells as an option.

Or, how about a solar pannel?

[Michael Black]

Yes, and I almost said something about those. The closest I got to a
vibrator power supply was the 2M RCA Carfone I got 40 years ago, and which
I used at home by taking out the vibrators and feeding 12v or so AC into
the rig where the vibrators were.

Of course, I was thinking in terms of external supplies, those didn't turn
to switching until relatively recently.

Michael

[AaronJ]

On Sun, 29 Jan 2012 10:25:36 -0500, Michael Black <et...@ncf.ca>

wrote:

>On Sat, 28 Jan 2012, AaronJ wrote:
>
>> On Sat, 28 Jan 2012 21:13:05 -0500, Michael Black <et...@ncf.ca>
>> wrote:
>>
>>> The interesting thing is that switching supplies didn't show up much in
>>> radio work,
>>
>> The first radio switching supplies I remember from my youth used a
>> mechanical switcher:
>>
>> http://radioremembered.org/vpwrsup.htm
>>
>Yes, and I almost said something about those. The closest I got to a
>vibrator power supply was the 2M RCA Carfone I got 40 years ago, and which
>I used at home by taking out the vibrators and feeding 12v or so AC into
>the rig where the vibrators were.

The beauty of that old stuff was that you could actually get your
fingers into it and modify away. How easy would it be to modify a
switcher today?

>Of course, I was thinking in terms of external supplies, those didn't turn
>to switching until relatively recently.

Yes you are correct. Most would not think of those old vibrator
supplies when 'switchers' are mentioned.

BTW when searching for "vibrators" to find that link I posted, you
would be amazed the pages I found. Now most of those vibrators
definitely looked linear... ;-)

[AaronJ]

On Sat, 28 Jan 2012 20:34:44 -0800 (PST), Bob_Villa
<pheeh...@gmail.com> wrote:

>On Jan 28, 9:40 pm, AaronJ <12333465no-m...@no-mail.com> wrote:
>> On Sat, 28 Jan 2012 21:13:05 -0500, Michael Black <et...@ncf.ca>
>> wrote:

>> The first radio switching supplies I remember from my youth used a
>> mechanical switcher:
>>
>> http://radioremembered.org/vpwrsup.htm
>
>These "vibrators" were used when radios were introduced to
>automobiles.

Also in military equipment. For example coast watchers used them.

>Switching the DC on and off allowed the voltage to be
>stepped-up by transformer

True. Another technology of the day, the Dynamotor (motor-generator),
could supply the high voltages that tubes needed without using a
transformer. Boy were those things noisy though. Compared to the
vibrators quiet humming they sounded like a vacuum cleaner.

>to power the filaments of the vacuum tubes.

Nope. Generally the filaments were directly powered from the battery.