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Old 13th August 2003, 06:43 PM   #1
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Default Re: Re: Re: I agree with Charlie........

Quote:
Originally posted by Charles Hansen
Steve, for a guy with encyclopedic knowledge of everything from Cooper pairs to altered states of conciousness, you sure seem to have a hard time reading. Let me help you out with this one. For an example of an open-loop follower, please refer to the data sheet for the Burr-Brown BUF634:
The BUF-634 being called an open-loop follower is in a completely different context from what you were referring to an open-loop follower. Here they're referring to a multi-stage circuit without a global feedback loop from the output of the last stage to the input of the first stage.

This is what you called an open-loop buffer:

Click the image to open in full size.

Which is incorrect as virtually 100% of its output is fed back to its input by way of the emitter resistor. That's negative feedback. That's closed-loop. Not open-loop.

Quote:
But all of this is really silly. In case you haven't realized it, you've "hijacked" this thread. The original poster had a specific question regarding the construction of a specific circuit. None of this is helpful or illuminating to him (or anyone else, for that matter).
And your berating and belittling jcx was helpful or illuminating to the original poster how exactly? Who's the real hijacker here?

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For you to drag in one of your old arguments from a thread on a completely different forum (Audio Asylum) is out of line and uncalled for. This argumentative behavior that generates heat and no light is exactly why you have been banned from some forums. It is exactly why new rules have been created on other forums. It is exactly why so many people on this forum wish the moderators would ban you.
I only mentioned a claim you had made in public to illustrate the sheer arrogance and hypocrisy of your berating and belitting someone, requesting that they not post at all unless they "really *know*" what they are talking about.

se
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Old 13th August 2003, 07:58 PM   #2
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Default Re: Re: Re: Re: I agree with Charlie........

Quote:
Originally posted by Steve Eddy


.

This is what you called an open-loop buffer:

Click the image to open in full size.

Which is incorrect as virtually 100% of its output is fed back to its input by way of the emitter resistor. That's negative feedback. That's closed-loop. Not open-loop.



se
Mr SE,

A emitter-follower like that in your image is in fact refered to as a open-loop-follwer. If you design a power supply regulator using a zener-diode connected to the base of a BJT, one refers to that regulator as an "open-loop-regulator"



Best regards\Morello

BTW, nice to see you here. You might remember me from AA
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Old 13th August 2003, 10:28 PM   #3
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Default Re: Re: Re: Re: Re: I agree with Charlie........

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Originally posted by Morello


Mr SE,

A emitter-follower like that in your image is in fact refered to as a open-loop-follwer. If you design a power supply regulator using a zener-diode connected to the base of a BJT, one refers to that regulator as an "open-loop-regulator"

Morello,

the fact that somebody referred to this circuit as an "open loop follower" does not change the fact of almost 100% negative feedback in this circuit.

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Old 13th August 2003, 10:49 PM   #4
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Default Re: Re: Re: Re: Re: I agree with Charlie........

Quote:
Originally posted by Morello
A emitter-follower like that in your image is in fact refered to as a open-loop-follwer. If you design a power supply regulator using a zener-diode connected to the base of a BJT, one refers to that regulator as an "open-loop-regulator"
Yes. Though it's not a term I've seen typically used to describe such a circuit. And a Google search for "open loop follower" brings up a whopping 17 hits.

The way I see it, negative feedback is an inherent trait of even the simplest follower. They're effectively a 100% voltage feeback circuit, which is why they have an ideal voltage gain of 1.

Also the way I see it, you can't have negative feedback without a closed loop. So to call an emitter follower an "open loop" circuit is ultimately a misnomer. An emitter follower functions as it does precisely because it's a closed-loop circuit employing 100% voltage feedback.

Quote:
BTW, nice to see you here. You might remember me from AA
Thanks. And ditto. Though I remember you as Mr. Morello there. So I see you've decided to ditch the suit and tie, threw on some jeans and a shirt and became a more casual Morello here.

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Old 13th August 2003, 10:56 PM   #5
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Default Re: Re: Re: Re: Re: Re: I agree with Charlie........

Quote:
Originally posted by x-pro
the fact that somebody referred to this circuit as an "open loop follower" does not change the fact of almost 100% negative feedback in this circuit.
Yes. And it was ultimately the issue of negative feedback which brought about the "open loop follower."

The discussion concerned two emitter follower topologies, the Darlington and the Sziklai (or "complimentary darlington" or "complimentary feedback pair").

It was said that the Sziklai was inferior to the Darlington because it employed vastly more negative feedback than the Darlington. The reason the Darlington had so much less negative feedback being due to the Darlington comprising two "open loop" followers.

However the way I see it, both the Darlington and the Sziklai have fundamentally the same amount of negative feedback. They both function as followers, they both have virtually the same gain multiplication and therefore employ virtually the same amount of negative feedback.

se
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Old 13th August 2003, 11:14 PM   #6
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Hi,

Quote:
However the way I see it, both the Darlington and the Sziklai have fundamentally the same amount of negative feedback. They both function as followers, they both have virtually the same gain multiplication and therefore employ virtually the same amount of negative feedback.
That part I'd agree on..anything else is just a matter of how you'd tag the kid, really.

If you allow me, in tube electronics I've heard many bold claims stating this or that all triode circuit does not use any feedback.

Well just as the follower above uses 100% inherent feedback so do CFs in tube circuits...and surprise surprise, all triodes have feedback built in...chuckling...

Quite often both circuits will be marketed as no FB designs, probably because they meant no additional global NFB loop from output to input is used?

Just don't let appearances fool you, everything else is just BS no one ever cared to define.

And guess what, those "clever" marketing guys just exploit that grey area...can you blame them?

Add to that the fact that most people don't have a clue as to how the AC current flows in circuits and voila, you once again have yourself a new niche to drop your product into...

NFB isn't necessarily a bad thing, just don't use it as an excuse for incompetence.

Cheers,
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Old 13th August 2003, 11:35 PM   #7
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Quote:
Originally posted by fdegrove
If you allow me, in tube electronics I've heard many bold claims stating this or that all triode circuit does not use any feedback.

Well just as the follower above uses 100% inherent feedback so do CFs in tube circuits...and surprise surprise, all triodes have feedback built in...chuckling...
Yup. In a BJT I believe the same is true due to its equivalent emitter resistance, re. So even in a common-emitter configuration without a literal emitter resistor, you've always got some small amount of negative feedback.

Quote:
Quite often both circuits will be marketed as no FB designs, probably because they meant no additional global NFB loop from output to input is used?
Yes, that's how the term's typically used. Some manufacturers actually make the distinction.

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NFB isn't necessarily a bad thing, just don't use it as an excuse for incompetence.
Yup. Whatever gives you the greatest satisfaction in the end is a "good thing" as far as I'm concerned. Well, except when it's Martha Stewart saying "It's a good thing."

se
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Old 14th August 2003, 12:39 AM   #8
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Default Re: Re: Re: Re: Re: Re: I agree with Charlie........

Quote:
Originally posted by Steve Eddy


Also the way I see it, you can't have negative feedback without a closed loop. So to call an emitter follower an "open loop" circuit is ultimately a misnomer. An emitter follower functions as it does precisely because it's a closed-loop circuit employing 100% voltage feedback.


se

Correct....another 'follower' of interest perhaps is the common-base stage.....which possesses 100% current (series) derived, current (shunt) applied, negative feedback....ergo...a current buffer.
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Old 14th August 2003, 03:45 AM   #9
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Default Re: Re: Re: Re: Re: Re: Re: I agree with Charlie........

Quote:
Originally posted by mikek
Correct....another 'follower' of interest perhaps is the common-base stage.....which possesses 100% current (series) derived, current (shunt) applied, negative feedback....ergo...a current buffer.
Aye. So apparently the only open loop configuration would be the common-emitter.

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Old 14th August 2003, 04:24 AM   #10
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Not even that, since it's degenerated by (at minimum) Rbe.
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