Most computer mother boards have switch mode regulators on the board to make all the various
voltages needed for the processor(s), memory, north & south bridges, and various other hardware.
Gamer & enthusiasts boards often tout how many regulators/phases they have.
As for radiation, most of the noise is from the leads & tracks on the board of chips themselves,
especially when they are unshielded. A 5, 3.3, or even 1.8 volt signal toggling on-off at a high
rate can radiate quite a bit, with 32 or 64 bits wide all toggling at such high clock rates it will
radiate a lot of hash.... Computers tend to generate & radiate a lot of hash that's one reason the
better made ones have metal cases and metal shielding in key areas. The minor amount of noise/ripple
out of the supply is miniscule compared to the hash from the computer it-self. If a supply is truly
that noisy the noise/spikes on the power would be mistaken for data and foul up the processing.
-Jim- N1JMM, KB1YPL_B
Visit my Pi running ircddb, dvrptr, Apache & many other things:
On 4/7/13 6:15 AM, JJ wrote:
> On 13-04-07 05:49 AM, John B. Cundiff Jr. wrote:
>> Every time any digital device switches from off to on it produces a small spike and every spike
>> as harmonics or RFI ... you can never completely clean up the supply of a computer ...you must
>> design the computer
>> to live with the spikes and RFI.
>> On 04/07/13, Ray Wells<vk2tv@...> wrote:
>> It's more than just spikes.
>> The National Semiconductor recommendation to "tame" the output of the LM2596 smps is to add a
>> series inductor (10mH from memory) and a shunt capacitor. Whilst this may very well result in a
>> power supply that will "please" the Pi, it will do absolutely nothing to suppress RFI, which
>> requires techniques quite different from those that produce a clean DC supply. The problem is not
>> insurmountable but would require some devotion to produce a supply that is both DC and RF clean.
>> It can be done.
>> FWIW, the problem, from a Pi perspective, isn't necessarily spikes. Some smps's produce a distinct
>> sawtooth output under load and whilst there may not be any spikes, there may well be dips below
>> the minimum working voltage of the Pi at the bottom of the sawtooth waveform.
>> Don't believe for one moment that you can assess a supply as being "good" with a voltmeter,
>> digital or otherwise. It is indeed a case where a picture is worth a thousand words and that is
>> where the CRO plays its part. If you don't have a hardware CRO, use a soundcard based device.
>> There is plenty of free oscilloscope software available online.
>> Ray vk2tv
>> On 07/04/13 18:03, John B. Cundiff Jr. wrote:
>>> Wood not a simple choke ...maybe a torridal choke
>>> suppress the spikes every one is worried about .
>>> Put a big value filter capacitor afterwards .
>>> Be a lot more portable .. simpler and ..eleganter etc.
>>> On 04/06/13, Kerry McKenzie<kermck@...> wrote:
>>> a rarely dumb question?
>>> how hard is it to just get an old pc power supply AT or ATX ,.... who
>>> cares either way,... you will get between 15 and 50 amps at 5 volts and
>>> throw a couple of caps across it.
>>> If you crow it,... it will be smooth
>>> if you go to any computer repair shop they will possible give you as
>>> many old ones as you want as most of them still work.
>>> i have 4 or 5 in my workshop down stairs and use them for all sorts of
>>> things and it so easy.
>>> my 2 cents worth.....Kerry
>>> PS Linux is still a bitch and I,m going nowhere with my projects ;-((
>>> Kind Regards
>>> Kerry McKenzie
>>> PO Box 4492
>>> Kirwan QLD 4817
> yes, I agree...I use a vp-1020 satellite card in my computer and the P.S. noise is affecting the
> sensitivity of the card....my ham antennas are more than 100 feet from the house due to the rf
> racket produced by many switching power supplies in the house...even the darn router and cable modem
> supplies were awful, so running as much as I can directly from my solar system 12v rail...but there
> are just so many things nowadays that use these switching supplies it's hard to eliminate them
> all...oh, and then there's a neighbors samsung plasma tv .. 300 feet away from here and it wipes out
> my packet system when it's on...