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Old 4th September 2004, 03:48 AM   #21
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Quote:
Originally posted by Konrad
This seems to work!

Basic circuit without classd4sure's input stage.

The input/controll-cuircuit shown by classd4sure would improove performance as open loop gain also in higher.

Abt the open loop gain have someone tried higher open loop gain?
I mean like replacing the resistors R121 and R122 with smal caps in Classd4sure's input stage ?
Yeah I had tried that, wasnt' able to get it to converge, doesn't mean it can't work of course. Also tried a cap parallel with the feedback resistors you mentioned .... and in series...sadly, non converged.
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Old 5th September 2004, 08:15 PM   #22
Konrad is offline Konrad  Norway
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Quote:
Originally posted by classd4sure


Yeah I had tried that, wasnt' able to get it to converge, doesn't mean it can't work of course. Also tried a cap parallel with the feedback resistors you mentioned .... and in series...sadly, non converged.

It will not ! until you insert the common mode rejektion transistors.
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Old 6th September 2004, 10:46 PM   #23
Konrad is offline Konrad  Norway
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MK II


comments apprepiacated
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Old 6th September 2004, 11:47 PM   #24
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Hi,

Kind of hard to follow it but..

The diodes in the comparator will pass no current.... it will actually "compare" with them totally removed, but not as good. I'll go out on a limb by saying this but I think they add a small measure of hysteresis to it which it seems to like. I've changed them to schottky's as well for the "hot carrier" aspect, trr characteristic.. faster and cleaner switching I thought. Maybe someone more qualified can comment on that.

What's the purpose of the ground between RC going to Q13?

That should be a small signal schottky diode for the baker clamp.

15V for the drivers will add a bit more delay as JohnW was saying, with 12V drive you get about 10Volts at the gate which is perfect to fully enhance, I've tried 15V as well with every other version of the circuit and it was always far worse, I guess because of that added delay.

I'm messing around with the driver stages tonight, see how far I get with that, will also try to implement your balance circuit.
I think JohnW had an excellent suggestion with the added follower.

We'll compare notes ?

How is shoot through on it, I've found it difficult to balance things to minimise it, and I'm wondering how it is with your balance circuit added.

Glad to see you're still at it!

Regards,
Chris
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Old 7th September 2004, 05:10 AM   #25
Konrad is offline Konrad  Norway
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Quote:
What's the purpose of the ground between RC going to Q13?
its for the balance if impedances seen by the bases of the common mode transistors. ; the sorce resistanse seen by the bases of Q13 and Q14 should bee equal. The first path is the paralell R18, R19, the 2nd is R20 wich should bee 5k. ( i set it to 4.7k as it is standard that i have somwere in my draver ).

ABT driving voltages and diodes, yes/ well i havnt payd much attention to them yet. Thanks for comments.
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Old 7th September 2004, 09:01 AM   #26
Konrad is offline Konrad  Norway
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Quote:
Originally posted by classd4sure
Hi,

Kind of hard to follow it but..

The diodes in the comparator will pass no current.... it will actually "compare" with them totally removed, but not as good. I'll go out on a limb by saying this but I think they add a small measure of hysteresis to it which it seems to like. I've changed them to schottky's as well for the "hot carrier" aspect, trr characteristic.. faster and cleaner switching I thought. Maybe someone more qualified can comment on that.

What's the purpose of the ground between RC going to Q13?

That should be a small signal schottky diode for the baker clamp.

15V for the drivers will add a bit more delay as JohnW was saying, with 12V drive you get about 10Volts at the gate which is perfect to fully enhance, I've tried 15V as well with every other version of the circuit and it was always far worse, I guess because of that added delay.

I'm messing around with the driver stages tonight, see how far I get with that, will also try to implement your balance circuit.
I think JohnW had an excellent suggestion with the added follower.

We'll compare notes ?

How is shoot through on it, I've found it difficult to balance things to minimise it, and I'm wondering how it is with your balance circuit added.

Glad to see you're still at it!

Regards,
Chris

YPP ! There is definetly som more attention abt the clamping to bee done, as the shot thru in MKII is high(!) the implement of "Bruno clamping" and some value adjustments/rearrangement, it became much better.

Also adjusting the Ton time ( switch losses then neads attention) by adjusting R11, R12, R14 andR16.
i belive we will end up with somthing like Toff<Ton+(R*Cin) choose biger than minimum R will increase losses caused by exstended Ton. At the same time bigger R will reduse shot thru, here is definetly some energy / timing to take care of, after the clamping net is improoved.

But with better or 'Bruno clamping' and 'minor' adjustments in the resistor network arrangement is the place to improove the circuit "ballansed comparator with added feedback" as i see it as a unit behavior. In a different tread under Digi amp there were som suggestion on a simplified way to calculate the fiter/ and outer timing and internal delays.

Abt lower driving voltages for the output dev ; Yes lover voltage is a must! there is in some datasheats a internal zener gate-sorce it's important not to damage or overdrive, current limited by R, V drive and 'internal-zener'.
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Old 7th September 2004, 05:35 PM   #27
Konrad is offline Konrad  Norway
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Uh! these output devices !

Well after a little fidling;
Different clamping- "Bruno clamping"
Timing controll to remoove shot thru; Ton>Toff
Feed forward switch diodes in pre switching stage.

It simulates ok, a little bit slow maybee.
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Old 8th September 2004, 08:55 AM   #28
Konrad is offline Konrad  Norway
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Am i writing all for my self?

Redusing the ripple on the output, using different filtering, and NOT taking care of the phenomenas in the output filter itself.



I belive it is abt ready for a PID control loop to take care of the outer loops. Or maybee someone has a better idea?

At this stage things are getting werry interesting!
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Old 8th September 2004, 09:54 AM   #29
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I miss the "lead" part in the NFB on the latest incarnation of your circuit.
BTW: Even if a simulation looks better when taking feedback from a different filter than the one the load is connected to, I wouldn't do it. NFB doesn't "see" the real output signal in this case but a "varnished" one.

Regards

Charles
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Old 9th September 2004, 10:55 AM   #30
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Hi,

Is common mode feedback truly a necessity? It's my understanding a truly "differential" circuit does a fine job of rejecting common mode voltage, and it certainly seems to.

Granted if you can get a decent cmfb working well, great, but I don't feel it truly requires it. Rejection can be further improved by a simple change to the output filter as well.

Regards,
Chris
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