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Old 9th April 2010, 05:43 PM   #11
HMKD is offline HMKD  China
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Default 专利

Quote:
Originally Posted by kenpeter View Post
far as i know: The easiest way to assure operation in this class is to cross
deliberately underbiased schottkys. Thus forcing them to operate upon the
square law curve. You then use this law to re-curve your power transistors
for a super-smooth b crossing! Plus the reserve current always bled by r1.

It doesn't matter that schottkys operate in class b and turn off. There is
no significant tail current, and they recover fast. The slow transistors are
always conducting the reserve current, and thus in class a at all times.

It doesn't matter the exact quiescent current of an underbiased schottky
b crossing. Its always more than zero, and less than would blow anything.
Will probably drift a bit with temperature. You can bond q3 q4 to heatsink
if you want to assure hot drift always floats deeper into b rather than ab...
It probably isn't necessary.

Remember: We are talking about a deliberate underbias. No more than one
half the schottky stack can ever be fully on at once. We strictly regulate
the voltage sum across the stack, so that could never happen. Runaway
just isn't a likely event, even if you did nothing to thermally compensate.
Whats a schottky diode gonna dissipate in this application? Less than 2w.
To-220 packages are common, so thermals are going nowhere! Hot power
devices only do the work, but are never trusted to make the decisions.

The smoothness of the crossing is assured by the quasi-complimentary
square laws, and not by a specific bias current that has to be controlled.
No attempt is made to define what actual small b crossing current might
be? The extra reserve current bleeder assures the power devices will be
operating well above the small crossing of the schottkys.
早在一年前这线路做成功了,现在已经获得中国专利。你这线路含有专利的一部分。
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Old 9th April 2010, 06:20 PM   #12
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The Sansui Tanaka patent is US4401951. It also has the discussion of a few other "nonswitching" patents.
The common mistake with this approach is to leave Power stage with the new type of distortions due to unpredictable nonlinearity of P. transistors currents at the small levels (and near the signal zero crossing!).
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Old 9th April 2010, 06:38 PM   #13
Bigun is offline Bigun  Canada
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I spent some time researching non-switching outputs and found there are quite a few techniques, as already mentioned. I went as far as simulating a few designs to see that they do in fact work as promised.

But I didn't build any - I was not convinced that the additional complexity would result in an improved listening experience.

Has anybody listened to one of these non-switching designs, even an old Sansui, and compared it with a good 'regular' type Class AB amplifier ? - if so what did you discover ?
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Old 9th April 2010, 06:52 PM   #14
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Quote:
Originally Posted by Bigun View Post
Has anybody listened to one of these non-switching designs, even an old Sansui, and compared it with a good 'regular' type Class AB amplifier ? - if so what did you discover ?
Yes, sort of I say sort of because i built a few amplifiers based on the original Technics design that used an output stage that was fully biased into class A & ran at a low voltage.

The idea was you have a standard class B or AB amp drive the floating ground of the low voltage class A stage & the output of the class A stage was connected to the speaker. Therefore any or should i say most of the distortion produced by the AB amp would be corrected by the class A amp simply because the A amp is also in the feedback loop. In my case the A amp was unity gain so had it's own feedback to correct any problems. Open loop gain of the front end of the amp was about 400 & closed loop was 20. The result was as good as a true class A amplifier, though i used a few tricks like nested differential feedback loops. I doubt it needed that though.
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Old 9th April 2010, 07:20 PM   #15
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I will show one "well forgotten" circuit from the '60s with the interesting properties.
It is SRPP (in Cl. A bias), but is Non-Switching in Cl. AB bias.
T11 will never switch off. The Non-switching condition for T12 is
V(D5)≥0.5V + V(D6)max.
D6 should be Schottky (to minimize power waste) with the appropriate current rating and in TO-220 or TO-3P case.
Obviously, it is the voltage follower/power buffer and T1 provides the Error Correction function for Pushing and Pulling action of T11, T12.
The bias with the shown values: T1, T12 ~0.4 mA, T11 ~10 mA, D6 is (may be) non conducting. D5 is generally not necessary (only for non-switching T12 and Cl. A bias) and can be shorted. C61 provides bootstrapping for R59.
The circuit can be easily modified for bipolar supplies and scaled for the higher voltages/power.
And now you can explore the quietly ignored "new" idea along these lines from Andreas Wahlberg :
Self regulating Class A
espacenet — Bibliographic data
Attached Images
File Type: jpg SRPP Bipolar Cl. B.JPG (40.0 KB, 891 views)
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Last edited by StevenOH; 9th April 2010 at 07:28 PM.
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Old 9th April 2010, 08:26 PM   #16
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Quote:
Originally Posted by HMKD View Post
早在一年前这线路做成功了,现在已经获得中国专利。你这线路含有专利的一部分。
Automaticly translate: A year ago to do this line a success, and now has received patents in China. You are part of this line with the patent.
what means this exactly?
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Old 9th April 2010, 08:34 PM   #17
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Quote:
Originally Posted by tiefbassuebertr View Post
This the famous Nelson Pass patent, indeed. Thanks 1000 times for reminding us. It is panicking to see those japanese companies (Matsushita, JVC, Pioneer, Sansui) rushing around 1978-1979 for Non-Switching Class AB, while Nelson Pass had it done as soon as Feb 1975, with his US patent granted Nov 1976. What are the commercial amplifiers made, and what are the DIY amplifiers made, using Nelson Pass schematic ?
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Old 9th April 2010, 09:28 PM   #18
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Re: schematic #15 just above...

The top transistor works just as advertised.
Can't seem to bias the bottom one out of B.
Whats the problem here?
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File Type: txt ABTest.asc.txt (2.4 KB, 102 views)
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Old 9th April 2010, 10:05 PM   #19
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Kenpeter, to change the bias to Cl. A, select D5 to produce higher voltage
drop ~1...1,2V (IR diode, or voltage multiplier) to produce
V(D5)=0.8V(VbeT12) + 0.2V(Schotk. D6),
and reduce R58, R59, to accomodate the bias currents in all transistors, using corresponding betas (current gain).
In class A both diodes will always conduct. That is SRPP.
D5 will conduct in all modes/time.
In cl. AB D6 does not have to conduct when T12 is supplying the current in it's half cycle.
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Old 9th April 2010, 10:14 PM   #20
Bigun is offline Bigun  Canada
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the schematic posted looks like it was extracted from a patent. The purpose of a patent is to say just enough to get ownership of the IP and avoid saying what is necessary to actually make the darn thing.
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