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From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: sci.electronics
Subject: Re: high voltage Power Supplies
Message-ID: <628@neoucom.UUCP>
Date: Sat, 18-Jul-87 23:43:23 EDT
Article-I.D.: neoucom.628
Posted: Sat Jul 18 23:43:23 1987
Date-Received: Thu, 23-Jul-87 03:45:07 EDT
References: <1811@ttrdc.UUCP> <100500016@datacube>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 36
Summary: Switchers aren't as bad as you think


OK, I'll conceede that if you want to perform linear regulation at
tube type voltages, a tube for the pass element is a good idea. If
you accidentaly short the output cathode to ground, you've a few
seconds to rectify (*a pun *) your mistake, rather than the
microseconds you'd get before you send a transistor off to stick in
the ceiling.  A 6L6 is an easy to get tube that makes a good pass
element.  A pentode is would be a good idea to isolate your 0A2,
0D2, or whatever reference you use.  There are some VR circuits in
the old RCA receiving tube catalogs and probably old ARRL ham radio
books.

As far as switchers go, they aren't too bad if you design carefully
so that it can operate in the MHz region, rather than KHz.  Any
noise wouldn't be audible.  With a switcher, you can use something
like a .1 uF fancy "audio grade" capacitor to get all the filtering
you need.  It's getting downright difficult to get decent n hundred
uF capacitors* that are required for 60 (120) Hz operation.  60 Hz
magnetics weigh a lot.  Of course, building RF switchers calls for
very careful design, and care at bypassing leads, etc.  I think I'd
put a linear VR circuit after the switcher for extra insurance.

* at least, not at tube voltages!

We have RF switchers in medical equipment that amplifies uV signals
and don't have any noise trouble.  Using an RF power supply is
required so that ~5 cm. air gap can separate the primary and
secondary of the *air core* power transformer.  This baloney is
necesary for "patient safety".-- although our patients are lab
rats.

Bill Mayhew
Division of Basic Medical Sciences
Northeastern Ohio Universities College of Medicine
Rootstown (what a name), OH  44272-9989  USA  phone: 216-325-2511
(wtm@neoucom.UUCP  ...!cbatt!neoucom!wtm)