David,
This is the point at which a tutorial in power supply filter design would
serve you well. There are many factors that have to be considered in
designing the input and output filters for use with a switching power
supply, and they go beyond the switching frequency, the load current, or
the input current. For one thing, filters are effective in both the
absorbing mode and the reflecting mode, depending upon design. "Absorbing"
is where a large portion of the incident energy from a switcher is absorbed
as heat by the filter choke material, and "reflective" is where a large
portion of the incident energy is reflected back to the noise source.
Both types are effective and many power supply designs use both types of
filters. The problem with reflective types is that unless chosen with the
characteristics of the switcher itself in mind, there is a good likelihood
of blowing components. In effect, a reflective filter causes high SWR back
to the source. Of course, absorption filters affect efficiency, so you
need to consider the losses such filters will cause and figure out how much
net output current/power you will have after filtering. So, bottom line,
if you decide to get "the screamer". I'd buy several, as I see they are
inexpensive and you may end up blowing a few until you tweak the filtering
just right. As for by-pass caps, .001 uf might be a decent start, but it
is likely you will need multiple values to make effective filters.
All of that having been said, I'll offer an alternative for home use (yes,
I know you said home and mobile - well, here's half an idea). How about
considering an inexpensive LINEAR power supply, all built, ready to go, and
it supplies something like 4.5V thru 12V filtered, regulated DC at 2 amps?
If that idea appeals, check out power supplies at MCM Electronics. I've
got one of those on my work bench for those oddball voltage situations and
it's really handy. Usual price is somewhere around $15 and it is all
linear - not a switching device to be found (except for the power on-off
switch, of course!). A front panel selector sets the output voltage.
Good luck with the project.
73,
Dale Svetanoff, WA9ENA
Sr EMC Engineer
E-N-A Systems, LLC
Specializing in shielding applications, system grounding, and lightning
protection
> [Original Message]
> From: qrv@kd4e.com <qrv@kd4e.com>
> To: RFI List <rfi@contesting.com>
> Date: 1/5/2013 10:53:32
> Subject: Re: [RFI] 1.23V-30V DC DC Buck Converter Step Down Module
>
> It would be used around the radio area to fill the gap, home and
> mobile/portable, where I needed a voltage I don't have handy.
>
> Increasing the size and weight somewhat is not a significant matter,
> not adding more RF-trash to the radio environment is.
>
> I'd value any specific recommendations for the common mode chokes,
> etc. I am guessing .001 ceramics for the bypass caps?
>
> Thanks!
>
> David
>
>
> > The answer to your question is partly controlled by your intended
> > application. What do you wish to do with it, if you bought one?
> >
> > A few things are obvious: it is a "bare card", so you would need a
> > conductive housing and INPUT/OUTPUT filtering for starters. Note
> > that the switching frequency is given as 150 kHz and output ripple as
> > 30 mV, max. Keep in mind that they are saying 30 mV of ripple @
> > either 150 or 300 kHz (depends upon whether or not they use full wave
> > rectification). They also don't say if the 30 mV is Pk-to-Pk or RMS.
> > The ripple is also most likely to be as measured differentially
> > (between the pair of output leads), not between an earth ground and
> > either lead (common mode).
> >
> > You could make this work by using a suitable size minibox chassis
> > (with vent holes) and common mode chokes (placed within the chassis)
> > and by-pass caps on the input and output leads. All of that will
> > increase size, weight, and cost, so again - what's the intended app?
> > Maybe you can live with a "screamer".
> >
> > 73, Dale Svetanoff, WA9ENA Sr EMC Engineer E-N-A Systems, LLC
> > Specializing in shielding applications, system grounding, and
> > lightning protection
> >
> >
> >> [Original Message] From: qrv@kd4e.com <qrv@kd4e.com> To: RFI List
> >> <rfi@contesting.com> Date: 1/5/2013 3:52:15 Subject: Re: [RFI]
> >> 1.23V-30V DC DC Buck Converter Step Down Module
> >>
> >> Corrected post & link ...
> >>
> >> What are the chances that this 4V-35V IN to 1.23v - 30v OUT 3A
> >> DC-DC buck converter is a RFI nightmare?
> >>
> >> http://www.ebay.com/itm/110950894139
>
>
>
> --
>
> Thanks! & 73, KD4E.com
> David Colburn nevils-station.com
> I don't google I SEARCH! duckduckgo.com
> Network: groups.yahoo.com/group/qrv
> Restored to design-spec at Heaven's gate 1Cor15:22
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