[ARC5] Power Supply Filter Question

[Dennis Monticelli]

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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