OITPC - Output inclusive TPC (not TMC)

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Damir, what about this compensation method ? I'm just before the PCB design is finished. Last chance to change something :) ( I know R30,35 should be replaced by CCS, but improvement is only few ppm)

K61-lg.png

K61-sch.png
 
Damir, what about this compensation method ? I'm just before the PCB design is finished. Last chance to change something :) ( I know R30,35 should be replaced by CCS, but improvement is only few ppm)

View attachment 699119

View attachment 699120

This is similar to TMC, I can't comment just from schematic, and for LG plot better use Tian probe instead, more accurate.
 
CFA TMIC ? or how to call it ?

this compensation has better transient response (no sqr wave overshoot), fewer components and the result is very good indeed

tian probe - it is the same

square wave test - input PULSE(-1 1 0 10n 10n 50u 100u), output 56Vpp@4R

K61-lg-tianp.png

K61-sqr10k.png
 
Last edited:
CFA TMIC ? or how to call it ?

this compensation has better transient response (no sqr wave overshoot), fewer components and the result is very good indeed

tian probe - it is the same

square wave test - input PULSE(-1 1 0 10n 10n 50u 100u), output 56Vpp@4R

View attachment 699151

View attachment 699152

Leslie, this looks as very good amp with interesting compensation, why don't you open a new thread and attach LTspice file. You would need to add output mosfet protection and could get more suggestion from others.
Probably need to change some BC transistors for higher voltage ones. There better models for output mosfets too.
Damir
 
I'll think about it :)

All transistors use Cordell models, except Q2,3. Up to +-50V PSU it's safe as it's drawn. D3,4 - flying catch diodes, protect gates from overdrive and also function as natural current limiter. (Cordell book - figure 11.14, page 237/238)

Here are IRFP240/9240 models with better subthreshold area:


* VDMOS ksubthres models
*
* IRFP240Ckst VDMOS copyright Cordell Audio December 20, 2014
.model irfp240Ckst VDMOS(nchan Vto=3.0 Kp=4.8 Lambda=0.0032 Rs=0.01 Rd=0.1 Rds=1e7 Cgdmax=2600p Cgdmin=10p a=0.35
+Cgs=1250p Cjo=3000p m=0.75 VJ=2.5 IS=4.0E-06 N=2.4 ksubthres=190m)
*
*
*
* IRFP9240Ckst VDMOS copyright Cordell Audio December 20, 2014
.model irfp9240Ckst VDMOS(pchan Vto=-2.76 Kp=9 Lambda=0.004 Rs=0.064 Rd=0.1 Rds=1e7 Cgdmax=1200p Cgdmin=15p a=0.26
+Cgs=1130p Cjo=2070p m=0.68 VJ=2.5 IS=4.0E-06 N=2.4 ksubthres=107m)
*
 
Hi

Damir: In post 2 or so you show the phase plot of the amp and it is rippley. Isn't that a problem?

Borys: The 100uF in the ground leg of the feedback loop is too low a value. Yes, Self still shows 220uF in his schematics originally drawn in the 1990s and never updated to his new thinking, but no reason to do it to yourself. Higher vaalues will improve the phase response at low-frequencies and reduce THD even at 1kHz. I use 10mF minimum, but more typically 33mF. (m=milli)
 
Hi Damir

Actually, all the plots in post-1 and the ones in post-6, but especially the fourth in post-1.

That ripple in the phase response does not look right to me. other plots I've seen for amps with less sophisticated compensation have smoother phase response. So I wonder is this a fact of the compensation, or more about topology?
 
I would like to explain my novel compensation

Hi Damir

I wanted to study this more closely since you first posted, and finally made the effort.
I suspect that you have some positive feedback via C8 and C6||C9.
This is not a criticism, I think it may even be beneficial, as below.
Could you put a Tian probe in series with C8 and show the result?

To explain more clearly here is CFA simu[l]ation with enhanced VAS. To remove peak...

I think this peak is not necessarily a problem, theoretically it can be beneficial.
I would be a little careful, of course, hence my interest in the C8 feedback.

Best wishes
David
 
Actually, all the plots in post-1 and the ones in post-6, but especially the fourth in post-1.

So I wonder is this a fact of the compensation...?

If I may answer for Damir because he is perhaps too modest to explain how nice his implementation is.
The phase response complexity is not just a fact but intentional and beneficial.
This is explained by Bode, the book is now public domain and available on-line.

Best wishes
David
 
Hi Damir

I wanted to study this more closely since you first posted, and finally made the effort.
I suspect that you have some positive feedback via C8 and C6||C9.
This is not a criticism, I think it may even be beneficial, as below.
Could you put a Tian probe in series with C8 and show the result?



I think this peak is not necessarily a problem, theoretically it can be beneficial.
I would be a little careful, of course, hence my interest in the C8 feedback.

Best wishes
David

Hi David,
I will do that simulation today and come back with the result.
Best regards
Damir
 
Hi Damir

Actually, all the plots in post-1 and the ones in post-6, but especially the fourth in post-1.

That ripple in the phase response does not look right to me. other plots I've seen for amps with less sophisticated compensation have smoother phase response. So I wonder is this a fact of the compensation, or more about topology?

Hi nauta,
This ripple is a fact of two pole compensation, nothing to do with topology.
Here I use a bit more than simple two pole compensation to enhance it, like splitting output leg and bypassing VAS emitter resistor with suitable capacitor, all that to get better PM and GM wile maintain flat loop gain up to 20 kHz. More detail explanation by Bode.
BR Damir

Thanks David for your help here.
 
Last edited:
Member
Joined 2011
Paid Member
For HF C7/R22 and C14/R30 (from schematic in post 1 and 6) can be seen as paralleled - shorted via C27/C28. I'm sure you can save some parts here if the pcb is carefully designed.

C8: I have tried this variant (cherry?) and the only GM/PM benefit was during simulation. In real life the amps where more prone to oscillation. See discussion with user kgrlee, Dave Zan and others in thread around post +/- 500.

BR, Toni
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.