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From: firstname.lastname@example.org (Dale Chisholm)
Subject: Re: three-terminal regulator question
Date: 9 Jan 2003 12:24:38 -0800
NNTP-Posting-Date: 9 Jan 2003 20:24:38 GMT
Winfield Hill wrote in message news:...
> John Larkin wrote...
> > Ernst Baumgartner wrote:
> >> Is it possible to connect a few (say four) three-terminal regulator ic's
> >> (such as 78xx) in series in order to obtain a higher output voltage?
> > - - - SNIP - - -
> A better HV-regulator circuit using common parts is more like
> this, based on an old posting of mine (which I haven't tried),
> . 200V FET _____ LM317 1.2 to 125V
> . IN o----+----, ,-+-----+--| |--+---+----+-----o OUT
> . | | | | s | | | | | | 0 to 200mA
> . | _|_V_|_ | |_adj_| 240 | |
> . 2.2M ----, | | | | | 0.47uF
> . 1/2 W | '-||--+-----+ | ===
> . | | 68pF | | | 250V
> . '--------+---|<|-----------|---' |
> . / 10V zener | 2.7 ohms
> . 25k |
> . pot gnd
> . |
> . gnd
> - Win
"There's nothing new under the sun save that which is forgotten."
I believe something awfully close to that very circuit was the subject
of several articles in "Audio Amateur" magazine (later "Audio
Electronics" & now "Audio Xpress") in the early or mid 1980's. They
were regulating the plate supplies in vacuum tube power amps; probably
Dynaco or Harmon-Kardon units. I think they had some pretty extensive
(for a "hobby" publication) design notes and circuit analyses. Even
down to measured values of dynamic output impedance versus frequency.
They may have used a BJT horizontal deflection transistor, or 2n3439,
rather than the MOSFET. I think they also concluded that the zener
voltage wanted to be close to the LM317's max in/out differential
(35V?) but I don't recall why.
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