[ARC5] Power Supply Filter Question

Sat Dec 21 20:18:28 EST 2013

Bruce,

I can agree with that statement.  The circuits are reproducible and
components affordable, but the gotcha's should a tube-trained person try to
roll his own design are just too numerous.  The high power FETs do have
better SOA, but robustness issues remain.

Dennis AE6C

On Sat, Dec 21, 2013 at 11:02 AM, Bruce Long <coolbrucelong at yahoo.com>wrote:

> You are correct Dennis to a large extent, however i think it is fair to
> recast your comments as:  "Active, robust HV power supply regulation is
> well within the capabilities of the amateur community but its adoption has
> been extremely limited because there is essentially no documentation or
> traditional use within the amateur literature".  Notice this conversation
> on receiver HV power supply design started up with a reference to the
> information on this subject in the ARRL handbook, information that has been
> mature for about 80 years.  You can buy 200 Watt power fets for no more and
> sometimes even significantly less then the cost of a new 20 Watt resistor.
> In my day job I have had to make test loads in the range of a few hundred
> to a few thousand Watts and unless i use water heating elements mounted in
> a 55 gallon drum of water it is easier and much-much cheaper to use a
> gaggle of power fets each with a simple op-amp control loop to mimic the
> effect of a fixed value power resistor.
>
> I have a voltage regulated, over current and transient protected power
> design for a ARC-5 receiver sitting in my freeware schematic capture
> software for almost two years now. I even have parts sitting on my shelf.
> The idea was to breadboad the design, document the performance and publish
> an article in the amateur literature.  Problem is I am a co-founder of a
> technology start up business that is approaching viability and i have two
> young kids who want to do things with daddy.
>
> To be clear i have absolutely no problem with people building traditional
> style power supplies for traditional equipment but filter chokes are
> somewhat hard to get, somewhat expensive, and certainly big and heavy. It
> is not unreasonable to consider another design approach making use of
> modern, mass produced and therefore inexpensive power electronics devices.
>
> Yes i agree the choke and HV transformer availability situation has
> improved somewhat recently and i am grateful for that but i think the point
> still remains.
>
>
>
>
>   On Friday, December 20, 2013 10:48 PM, Dennis Monticelli <
> dennis.monticelli at gmail.com> wrote:
>  I use power transistors to filter and regulate the HV for my ARC-5
> transmitter, but it is not as easy as using L's and C's because the HV
> transistors need fast-acting protection circuitry.  The Safe Operating
> Curves for power transistors leave a lot to be desired.  The breakdown
> voltage may be there but you will find that they cannot simultaneously
> conduct even a small fraction of their rated current when fed from near
> their max voltage.  I do not recommend it for someone that doesn't have
> experience with semiconductor power electronics.
>
> Dennis AE6C
>
>
> On Fri, Dec 20, 2013 at 7:05 PM, Bruce Long <coolbrucelong at yahoo.com>wrote:
>
> It might offend the traditionalists but in my opinion power semiconductors
> are so cheap that active - as opposed to passive LC filtering- needs to be
> seriously considered.  Bruce   KJ3Z
>
>
>
>
>
> On Friday, December 20, 2013 9:35 PM, K5MYJ <macklinbob at gmail.com> wrote:
>
> If there are two capacitors and an inductor in the supply you could try
> leaving out the input capacitor. The output of an inductor input filter is
> lower than that of a capacitor input filter.
>
> Bob Macklin
> K5MYJ
> Seattle, Wa.
> "Real Radios Glow In The Dark"
> ----- Original Message -----
> From: "Robert Eleazer" <releazer at earthlink.net>
> To: <arc5 at mailman.qth.net>
> Sent: Friday, December 20, 2013 6:04 PM
> Subject: [ARC5] Power Supply Filter Question
>
>
> > Back when I first started learning about boatanchors I read the usual
> ARRL
> > material that described the classic way to build a power supply: a
> > capacitor, an choke inductor, and a capacitor.  I soon found out how rare
> > and expensive the required inductors were.
> >
> > I was amused last year when I rebuilt the AC power supply on a BC-348-N.
> > It was classic - literally right out of the Surplus Conversion Manual -
> > using two fairly low valued high voltage caps and a pretty big inductor.
> > I used some new, bigger, caps when I rebuilt it but left the inductor in
> > place.  Of course, it was also running the B+ way too high and I added
> > some power resistors in both the AC input line and the B+ line.  Got the
> > B+ from over 250VDC down to about 200 VDC.
> >
> > Now, we have available high voltage caps that have much larger values
> that
> > those 20 mfd cans we used to use and are a lot smaller as well.  But I
> > wonder if adding some inductance to the power supply circuit would do
> some
> > good?  Would winding some wire around a piece of steel or even around a
> > nail provide better filtering than just some big caps?
> >
> > Thanks,
> >
> > Wayne
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