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Old 17th December 2003, 11:00 PM   #331
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Default meant to part you from your money

now I recognize that AD825AR's cost about $3, and AD797's about $9 when you buy a tube of them -- this is taking profit margin to an extreme:
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Old 1st February 2004, 06:37 PM   #332
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Default instrumentation or differential amp for error amp?

the regulators we discuss in these posts use an error amp open loop. why would one not choose to use more modest gain in a differential configuration?
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Old 2nd February 2004, 08:57 PM   #333
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Question open loop?

The circuit is an emitter follower inside the closed loop of an op amp configured for unity AC gain. The open loop impedance of the follower is divided by the open loop gain of the op amp. The AD 825 is nice because it has a constant open loop gain over most of the audio frequency range instead rolling off at 6dB per octave in this range. A constant output impedance instead of an impedance that rises with frequency is consirdered desirable by many designer as is the transient response in the range where the impedance of a reglator goes from inductive to capacitive ( where the impedance of the output is dominant.The circuit is an emitter follower inside the closed loop of an op amp configured for unity AC gain. DC gain is the output voltage divided by the reference voltage. The open loop impedance of the follower is divided by the open loop gain of the op amp. The AD 825 is nice because it has a constant open loop gain over most of the audio frequency range instead rolling off at 6 dB per octave in this range. A constant output impedance instead of an impedance that rises with frequency is considered desirable by many designer as is the transient response in the range where the impedance of a regulator goes from inductive to capacitive, where the impedance of the output is dominant. You could use cascaded close loop circuits (op amp or discrete or a combination of both) as the error amp as long as stability requirements are met with the loop closed.
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Old 2nd February 2004, 11:51 PM   #334
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Default HORSES FOR COURSES...AGAIN.

Hi,

Quote:
A constant output impedance instead of an impedance that rises with frequency is consirdered desirable by many designer as is the transient response in the range where the impedance of a reglator goes from inductive to capacitive
Yes, yes and yes...

However, there are situations where this can be relaxed...
An RIAA stage is one example...
In short, it all depends where the reg starts to change behaviour and what you want it to do.

Having one that's wide band and has low Zout across the target frequency band hasn't hurt anything yet as far as I know...

Certainly, you can purposely design for less broad passband to keep the nasties out...

Fred may also agree with me here that the nasties should be designed out at the source and not as an afterthought downstream...

Unfortunately, we're all too often at the receiving end.

Cheers,
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Old 14th February 2004, 05:53 PM   #335
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Quote:
Originally posted by janneman

PS On the " Jung regulator - Didden PCB layout" note that the gnd plane was purposefully omitted over some of the more (capacitively) sensitive circuitry. At the time, it seemed to me the best way to avoid making possible oscillatory tendencies worse. Would I make a different layout now, with the hindsight of 8 years of experience and other opamps availble? Yes, in some details. Not in the general grounding and remote sense arrangement. And I would probably leave out the gnd plane, since almost all circuit nodes are low impedance enough to be insensitive to capacitive and RFI interference.

Jan Didden
Jan, are you saying that the layout as you designed it would work just as well without the ground plane, and therefore the board could be single sided? I'm in need of several of these regulators, it would be easy enough for me to copy the layout of the original and burn my own boards from the drawing in the original article. Eliminating the ground plane would make it much easier to do, especially since the ground plane was never published on its own, but with component placement on top of the drawing.

Are there any connections to be made through the groundplane? I can check to see, but maybe you have the info handy.

Thanks,
RonS
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Old 14th February 2004, 11:05 PM   #336
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A quick note on the Jung Super Regulator. The distortion neutralizing capacitor on the AD797 has the feature of reducing the output impedance over frequency. 0.000001 Ohm out to 100kHz was achieved, but this was left out of the articles as too esoteric. Moderators are welcome to spank me if they think I get out of line promoting my own products.
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Old 15th February 2004, 08:28 AM   #337
jcarr is offline jcarr  United States
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As far as I know, Scott is the designer of the AD797, among other Analog Devices devices.

jonathan carr
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Old 15th February 2004, 09:36 AM   #338
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yes, jonathan, you are right - USP 5,166,637 "Distortion cancellation amplifier system"
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Old 15th February 2004, 12:16 PM   #339
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United States Patent 5,166,637
Wurcer November 24, 1992

--------------------------------------------------------------------------------
Distortion cancellation amplifier system


Abstract
A distortion cancellation amplifier system operational amplifier system includes a current mirror circuit having an input, an output and a common terminal; a device for providing a pair of differential current signals to the input and output terminals of the current mirror circuit; a control device, responsive to said output terminal of the current mirror circuit, for controlling the voltage at the common terminal to drive the voltage at the input terminal of said current mirror circuit to track the voltage on the output terminal of the current mirror circuit; an output amplifier stage having a predetermined gain and having an input and an output terminal with its input terminal connected to the output terminal of the current mirror circuit; a gain control device having a predetermined impedance connected with the input terminal of the output amplifier; and a distortion suppression device connected between the output terminal of the output amplifier and the input terminal of the current mirror circuit and having an impedance equal to the predetermined impedance of the gain control device divided by the predetermined gain of the output amplifier for cancelling signal distortion introduced by the output amplifier stage.
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Old 15th February 2004, 12:29 PM   #340
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scott seems to be quite recognized among those who know what they are talking about.

http://www.analog.com/library/analog...editnotes.html

so his major work includes ad524, 712, and 797 which he eluded to in his last post. sounds like AD owes a lot to Scott.

I doubt any of us, even in our own field, has as much success as scott does.
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