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Re: Powering the Raspberry & TNC.

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  • Stephen
    The reason you use a 5 volt LDO regulator after a SMPS is to greatly reduce power supply ripple. Set your switchmode regulator a little above the LDO regulator
    Message 1 of 53 , Apr 6, 2013
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      The reason you use a 5 volt LDO regulator after a SMPS is to greatly reduce power supply ripple. Set your switchmode regulator a little above the LDO regulator voltage to avoid wasting too much power.

      73s Steve G0XAR

      --- In Raspberry_Pi_4-Ham_RADIO@yahoogroups.com, Roger Elmore <relmore@...> wrote:
      >
      > OK, so a 7805 or 317 is considered wasteful of energy. My electronics knowledge peaked in the late 80s when they were in vogue, when I was doing consumer electronics, pro PA, musical instrument and lighting and arcade video game repairs. Got out of it when I got a "real job" in networking/telecom (and component level repairs got too difficult due to SMDs).
      >
      > Anyway, re: SMPS, thoughts on the NFN40-7607 available from Marlin P. Jones for $6?
      >
      > http://www.mpja.com/download/17721ps.pdf
      >
      > +5.1 for the two PIs, +12.0 for the fan and the -5.0 left unused. Since my application is a rack mount enclosure, using AC mains voltage instead of the Astron 50M's 13.8V DC wouldn't be a big issue.
      >
      > --
      > Roger KJ4AJP
      >
      > >>>>>>>>>>>>>><<<<<<<<<<<<<<
      >
      >
      > Ray Wells wrote:
      >
      > Edit for anyone who thought I'd actually run the Pi off 12V.
      >
      > I favoured the use of a smps over a linear supply for the Pi to reduce energy wastage. To run the Pi from a 12v supply (car battery) and assuming 1A load, 7W would be dissipated as heat
      > in the 5V regulator, twice the energy input of the Pi itself.
      > ...
      >
      > Ray vk2tv
      >
      > On 06/04/13 08:10, Ray Wells wrote:
      >
      > That part is identical with the units I bought from Hong Kong. My CRO shows the output under 1A load to be quite dirty, a lot dirtier than another supply I used that cause problems with the Pi. I do believe, however, that external
      > output LC filtering as suggested by National Semiconductor would make the supply suitable as far as output quality is concerned. My secondary concern is the amount of RF pollution the device might cause, important to me because I use the Pi in a radio application.
      > A ventilated metal enclosure with filtering appropriate for RF might provide an answer. Having spent less than $8 for five of these devices, I wasn't particularly inclined to spend a lot of time and effort to make them environmentally (my environment) friendly.
      >
      >
      >
      > I favoured the use of a smps over a linear supply for the Pi to reduce energy wastage. To run the Pi from a 12v supply (car battery) and assuming 1A load, 7W would be dissipated as heat, twice the energy input of the Pi itself.
      >
      >
      >
      > Ray vk2tv
      >
      >
      >
      > On 05/04/13 23:57, Roger Elmore wrote:
      >
      >
      >
      >
      > This is what I've got heading across the pond:
      >
      >
      >
      > http://www.amazon.com/gp/product/B009HPB1OI/ref=oh_details_o02_s00_i00?ie=UTF8&psc=1
      >
      >
      >
      > Looks like a similar parts count but a rectangular PCB with solder I/O as opposed to the square format and I/O header connections yours has.
      >
      >
      >
      > My idea was set the LM2596 module at 5V no load, then power the PI and TNC-PI and adjust the LM2596 for 5V at TP1 and TP2 on the PI. With a fixed 5V LM2940 following the LM2596, I assume that adjustment ability would be lost.
      >
      >
      >
      >
      > I'm working on parts placement with this drawing:
      >
      >
      >
      > http://www.utm.edu/staff/relmore/PICase.gif
      >
      >
      >
      > so you can see I have lots of room in the interior of the 2U case (the PCBs will be mounted on plastic stand-offs on the 203.2mm x 254mm dual-sided copper-clad board, the location of the TNC and PIs will swap if the 50.8mm flexible Bivar light pipes work out).
      >
      >
      >
      > Since I have so much interior room and a fan that could blow directly on heat sinks, what are the thoughts of simply using an old school TO-220 package LM317?
      >
      > --
      >
      > Roger KJ4AJP
      >
      >
      >
      > >>>>>>>>>>>>>>><<<<<<<<<<<<<<<
      >
      >
      >
      > Stephen wrote:
      >
      >
      >
      > > Hi again,
      >
      > >
      >
      > > I made a mistake. I used one of these which has a variable output
      >
      > > voltage :-
      >
      > >
      >
      > >
      > http://www.ebay.co.uk/itm/5pcs-LM2596-DC-DC-Converter-4-40V-1-5-
      >
      > > 35V-Step-down-Power-Supply-Module-
      >
      > > /180903490175?_trksid=p5197.m1992&_trkparms=aid%3D111000%26algo%3
      >
      > > DREC.CURRENT%26ao%3D1%26asc%3D14%26meid%3D6745660872094298825%26p
      >
      > > id%3D100015%26prg%3D1006%26rk%3D1%26sd%3D180903490175%26
      >
      > >
      >
      > > 73s Steve G0XAR
      >
      > >
      >
      > > --- In
      > Raspberry_Pi_4-Ham_RADIO@yahoogroups.com, "Stephen"
      >
      > >
      > <squirrox@> wrote:
      >
      > > >
      >
      > > > Roger,
      >
      > > >
      >
      > > > I use the same module, but I clean up the output by passing it
      >
      > > through a LM2940 3 leg 5 volt LDO regulator (with the caps each
      >
      > > side as you would use for a standard application). I don't have
      >
      > > any objective measurements but the data sheet quotes an output
      >
      > > noise voltage of 150 uV. The whole lot fits into an altoids tin.
      >
      > > >
      >
      > > > Hope this helps,
      >
      > > >
      >
      > > > Steve G0XAR
      >
      > > >
      >
      > > > --- In
      > Raspberry_Pi_4-Ham_RADIO@yahoogroups.com, Ian Bennett
      >
      > > <ibennett@> wrote:
      >
      > > > >
      >
      > > > > Hi Ray,
      >
      > > > > I think I have the same type and managed about 2A (ish)
      >
      > > output at
      >
      > > > > 5V with very respectable ripple (read: hardly noticeable on
      >
      > > the
      >
      > > > > cro). I was a little disappointed seeing the output at 4.85V
      >
      > > but was withing spec.
      >
      > > > > I have been bitten a few times because I didn't read the
      >
      > > data sheet
      >
      > > > > correctly, so I read the thing many many times whilst waiting
      >
      > > for
      >
      > > > > mine to arrive.
      >
      > > > > The one thing (ok, there was two) that stuck in my mind was
      >
      > > the use
      >
      > > > > of low leakage electros and the low loss "tracks" required
      >
      > > )shown in
      >
      > > > > bold in the recommended circuit).
      >
      > > > > I built mine on vero board and the the low loss connections
      >
      > > were
      >
      > > > > constructed using additional tinned copper wire following the
      >
      > > copper
      >
      > > > > and a heap of solder to fill the gaps. If nothing else, it
      >
      > > won't
      >
      > > > > blow away in the wind ;-)
      >
      > > > > My coil came out of a few trashed UPS'. I was ratting them
      >
      > > for the
      >
      > > > > toroids but luckily I kept a few intact.
      >
      > > > >
      >
      > > > > Ian
      >
      > > > >
      >
      > > > >
      >
      > > > > On 05/04/13 08:51, Ray Wells wrote:
      >
      > > > > >
      >
      > > > > >
      >
      > > > > > I bought 5, smps adjustable output modules using the LM2596
      >
      > > from
      >
      > > > > > Ebay
      >
      > > > > > ($1.52 each including freight from Hong Kong to
      >
      > > Australia!). These
      >
      > > > > > are branded Leivin and the PCB layout and circuit is as per
      >
      > > the
      >
      > > > > > National Semi datasheet. A preliminary test with a 1A load
      >
      > > showed
      >
      > > > > > a very noisy output on the CRO. When time permits I'll try
      >
      > > the NS
      >
      > > > > > recommendation of an LC filter in the output. I think the
      >
      > > device
      >
      > > > > > has potential but not "off the shelf" for running the RPi.
      >
      > > > > >
      >
      > > > > > Ray vk2tv
      >
      > > > > >
      >
      > > > > > On 05/04/13 00:58, Roger Elmore wrote:
      >
      > > > > >>
      >
      > > > > >> Charles wrote:
      >
      > > > > >> > I am looking at another device to replace the converter
      >
      > > because
      >
      > > > > >> > this device is not adjustable and is set for 5 V. I need
      >
      > > to
      >
      > > > > >> > increase that to 5.25 to compensate for the drop across
      >
      > > the
      >
      > > > > >> > polyfuse.
      >
      > > > > >>
      >
      > > > > >> I've begun collecting the parts for a pair of PI+TNC-PI
      >
      > > combos
      >
      > > > > >> (for an APRX digi/IGate and a Linux RMS Gateway) in a rack
      >
      > > mount
      >
      > > > > >> case powered from the same Astron RS-50M as the two radios
      >
      > > and
      >
      > > > > >> going to give the $7
      >
      > > > > >> LM2596 module (bought from Amazon) a try. 3-40V in and
      >
      > > 1.5-35V
      >
      > > > > >> out at 3A. My plan is to use a separate LM2596 fused at 1A
      >
      > > for
      >
      > > > > >> each PI's input, with a 6A rear panel accessible fuse
      >
      > > common to
      >
      > > > > >> the 13.8V input of each LM2596 and a 80mm fan. Here goes
      >
      > > nothing...
      >
      > > > > >>
      >
      > > > > >> On a different note, has anyone experimented with light
      >
      > > pipes to
      >
      > > > > >> bring the PI's LED status to the front panel of a chassis?
      >
      > > I've
      >
      > > > > >> used the Bivar SLP3-450-100-F on a NHRC Micro repeater
      >
      > > controller
      >
      > > > > >> previously but the LEDs on the PI are too close together
      >
      > > for
      >
      > > > > >> those. I was looking at the flexible Bivar LC-2.0 at the
      >
      > > Mouser
      >
      > > > > >> website and was wondering if those might work. Any input
      >
      > > from anyone?
      >
      > > > > >> --
      >
      > > > > >> Roger KJ4AJP
      >
    • Jim Thisdale
      F.Y.I. 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
      Message 53 of 53 , Apr 14, 2013
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        F.Y.I.

        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:
        http://n1jmm.no-ip.org

        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:
        >>
        >> John,
        >>
        >> 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:
        >>>
        >>> Guys
        >>> 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
        >>> Australia
        >>>
        >>
        > 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...
        > grr...
        >
        >
        >
        >
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