My grandsons and hot summer stopped the project for a wile, autumn will kick it again.
Damir
What is the best You can hope for? Class-A, push-pull means that the standing (quiescent) current must be at least half the maximum current You want to push or drag from the load. Something like 7-8 amps.
Your problem is Vce times quiescent current. To keep this down AND be able to apply 7-8 amps to the load You must have an efficient way of varying Vc so Vce stays more or less constant as Vload varies.
To me that translate into a Class-C amplifier power supply. The class-C amplifier can be implemented as a Class-D amplifier or as a pure Class-C amplifier and then it would look like class-G or class-H.
Good Luck!
I have toyed with another idea based on error-correction. Let us assume that You accept a bridged configuration. Then I believe You could make one arm of the bridge a class-A amplifier and the other arm a class-B amplifier or what ever.
Your problem is Vce times quiescent current. To keep this down AND be able to apply 7-8 amps to the load You must have an efficient way of varying Vc so Vce stays more or less constant as Vload varies.
To me that translate into a Class-C amplifier power supply. The class-C amplifier can be implemented as a Class-D amplifier or as a pure Class-C amplifier and then it would look like class-G or class-H.
Good Luck!
I have toyed with another idea based on error-correction. Let us assume that You accept a bridged configuration. Then I believe You could make one arm of the bridge a class-A amplifier and the other arm a class-B amplifier or what ever.
I am not sure from your text that you have read this thread from beginning .
For variable high voltage power supply I will use modified Class D amp, and Class A OPS use low voltage power supply and could be biased in class A, but also in class B to increase efficiency.
It's uses so called serial configuration of Class A and Class D.
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Perhaps you will be interest in
https://www.google.com/patents/US4115739
Sano, et al #4,115,739 from 1977.
This patent is later cited by Carver Corp and Pass Labs.
https://www.google.com/patents/US4115739
Sano, et al #4,115,739 from 1977.
This patent is later cited by Carver Corp and Pass Labs.
Perhaps you will be interest in
https://www.google.com/patents/US4115739
Sano, et al #4,115,739 from 1977.
This patent is later cited by Carver Corp and Pass Labs.
Thank you to point this patent, I did not know about it, but I knew I am not doing anything new here. Just a hobby.
Do you know any built amplifier of that kind?
you also never heard Pass Labs?
google will enlighten you
Could you enlighten me, which Pass amp uses this technology?
From what I read that would be a Class-G or Class-H amplifier.
I don't understand how You like to bias the low power supply class-A amplifier. It would still have to be able to handle all the current You want to pass to the load.
To me it reads like You are trying to achieve current dumping.
I don't understand how You like to bias the low power supply class-A amplifier. It would still have to be able to handle all the current You want to pass to the load.
To me it reads like You are trying to achieve current dumping.
No, no, read the patent from Nelson Pass link in post #65.
It is not low power but low voltage Class A.
I read the patent #65 but I'm lost when i comes to calculate the total efficiency.
To me it is still very much a question of how much current You want to pass through the output stage when idling.
To keep the efficiency up and the heat generated down the amplifier in the patent uses six power supplies, two of them floating and a secondary power-amplifier to drive the mid-point of the floating power supplies.
To me two Class-D amplifiers driving Vcc+ and Vcc- respectively looks like a more attractive option. I guess You would need two additional power supplies for the input stage and VAS of the Class-A amplifier.
High power Class-D stereo amplifiers are not that expensive off the shelf so the thing could be built without going bankrupt in the process.
To me it is still very much a question of how much current You want to pass through the output stage when idling.
To keep the efficiency up and the heat generated down the amplifier in the patent uses six power supplies, two of them floating and a secondary power-amplifier to drive the mid-point of the floating power supplies.
To me two Class-D amplifiers driving Vcc+ and Vcc- respectively looks like a more attractive option. I guess You would need two additional power supplies for the input stage and VAS of the Class-A amplifier.
High power Class-D stereo amplifiers are not that expensive off the shelf so the thing could be built without going bankrupt in the process.
Technics produced an amplifier which used it. I always thought the design
very clever, and years later patented a circuit which did a similar thing but
in a different way, thus the citation.
That was patent #5343166, and Pass Labs did not build it as a product.
The diagram on the first page:
Attachments
Thank you Nelson, you are very kind.
I will try to make working prototype, I modified Class D amp(bought on ebay) moving FB after output inductor, and for Class A I will use my CFA amp.
Damir
Why do You want to move the FB pick-up point? You don't need very low distortion in this context. Stability is as important as ever and moving the FB to after the inductor might jeopardize stability.
Will You use an additional floating power supply for the CFA driven by the Class-D amplifier?
You need the linear and switching amplifiers to have matched gain magnitude and phase for all frequencies and load conditions. Class-D with pre-filter feedback has a load-dependent frequency response and it seems sensible to achieve the matching between the linear and switching amplifiers by making the class-D response better rather than the linear part worse.
I find the approach risky. I would not assume that a commercial class-D amplifier responds nicely to mowing the feedback pick-up point.
To low pass filter the input to the CFA so that it matches the high frequency response of the class-D amplifier would not change to stability of either amplifier. You must of course make sure that the gain of the two amplifiers matches.
Another work around, assuming this is for audio use and not for delivering 20kHz at 200 Watts, would be to simply add some extra margin to Vcc+ and Vcc-. This would sacrifice some efficiency.
Which brings to mind another question. Isn't the low frequency response almost as important as the high? Does the Class-D amplifier be DC-coupled from input to output?