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Old 7th July 2012, 06:53 PM   #981
EUVL is offline EUVL  Europe
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We have already tested a JFET-cascoded version which has less distortion of its own, to the degree that we cannot reliably measure anything.
But what is the point if the distortion of the DAC is the limiting factor.

When you use JFETs as the input device, you essentially limit the distortion to mainly 2nd and 3rd.
And after you cancel the 2nd in balanced, mode, you are left with very little distortion at all.

So in terms of performance vs simplicity, the published circuit is still the one to beat, IMHO.
But then of course I am totally biased.

We also tested multiple BJT versions. In the end the SEN is still our own choice.


As Nic said, just build and enjoy the music,
Patrick
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Old 7th July 2012, 06:58 PM   #982
bcarso is offline bcarso  United States
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I like it a lot. And as you say if the DAC is the limitation what is the point. However, future DACs may benefit from still higher performance I-V. I also have no bias in favor of simplicity per se, although I don't wish to clutter up designs gratuitously either.

And although bipolars are wonderful for many things, I have a deep affection for JFETs. If only they made a few with higher breakdown voltages.
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Old 7th July 2012, 08:29 PM   #983
EUVL is offline EUVL  Europe
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2SK223 is HV (unfortunately now obsolete), or you can always use a BJT cascode.

I think the wish should be that they make some low-noise P-JFETs.
There is practically none at this moment.



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Old 7th July 2012, 09:32 PM   #984
bcarso is offline bcarso  United States
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Agree that some nice P parts would be welcome (I wonder how LIS is coming with the LSA74?).

BJTs as cascodes are somewhat problematic owing to the biasing issues. Enhancement-mode DMOS is also a bit annoying for providing the positive bias and also because, in bootstrapped connections to pump drain-gate displacement currents back into the lower device, you still contend with the body diode and its voltage variability ---although some of that is less deleterious if the preceding JFET has a high-enough impedance at its drain. Worse is if there's a very fast positive voltage change on the upper drain, which can couple through and break down the lower JFET. Admittedly, these are usually small or unlikely effects.

The depletion-mode DMOS parts, the very few of them, don't have a sufficiently large gate-source voltage for most cascoding purposes. And they also have body diodes.

Years ago (thanks here to a reference found by Walt Jung) some high voltage JFETs were made for incorporation in "Fetrons", cascode compound parts groomed as direct replacements for vacuum tubes. In an article about them the author remarks on the difficulty of making high-breakdown JFETs.
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Old 8th July 2012, 04:36 AM   #985
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Quote:
Originally Posted by EUVL View Post
You can download the article online free of charge by following the link at post#969.
Courtesy of Jan Didden.


Patrick
Yes, I realized that after I ordered the hard copy. I'd rather pay Jan than download a free article. Thanks.
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Old 8th July 2012, 04:43 AM   #986
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I think this PCM1794a is too difficult to work with, and maybe not worth the effort. The -6.2mA current offset on the output pins of this DAC has a very serious effect on the Zen type of I/V stage in my sim's, and dealing with that to make the offset zero requires a lot more parts from what I gather on this thread. Someone mentioned that there was a simple way to deal with this, but it'll have to wait until I receive the article in the mail.
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Old 8th July 2012, 04:55 AM   #987
EUVL is offline EUVL  Europe
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I admire your respect for intellectual properties.

But you already bought a hard copy, so you already paid Jan.
On top of that it is an arrangement between me and Jan to make the article available online after 6 months.
So you do not have to feel guilty about it.

You can make the PCM1794 to work with an additional current drain, I think.
That means e.g. an extra battery, a TL431, a NPN and a resistor.
I do not think you will have a thermal stability issue.
The TL431 has a tempco of 50ppm/C, and you can also use a low tempco resistor.
I do not consider this 4-component circuit to be complicated ?

Please refer to post #784, or Fig.13, 14 of the Fairchild datasheet :

http://www.fairchildsemi.com/ds/TL/TL431A.pdf


Patrick
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Last edited by EUVL; 8th July 2012 at 05:19 AM.
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Old 8th July 2012, 05:18 AM   #988
bcarso is offline bcarso  United States
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Originally Posted by dirkwright View Post
Yes, I realized that after I ordered the hard copy. I'd rather pay Jan than download a free article. Thanks.
And there a lot of other good things in that issue
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Old 15th July 2012, 04:22 AM   #989
EUVL is offline EUVL  Europe
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There is a question about using the Charger calculator in :

Zen -> Cen -> Sen, evolution of a minimalistic IV Converter

I have attached here a Version 2 which is functionally the same as V1, but with some cosmetic changes.
Download the zip file. Unzip and open the excel sheet as Read Only.
You can change the values of the two cells marked with green background to suit your configuration.
E.g. doubling the mAH capacity would reduce the series resistor by half to double the charge current. etc.

I have double checked to make sure it works as intended, with different no of cells and capacity.
If you can still find any mistake please do not hesitate to let me know.


Patrick
Attached Files
File Type: zip XEN NiMH Charger V2.zip (149.8 KB, 101 views)
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Old 15th July 2012, 06:08 AM   #990
NicMac is offline NicMac  Italy
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Patrick,

The spread sheet does all the correct calculations - if it fed the right information by the user....

The value used in the example is for a nominal 18V pack using two 9V 200 mA batteries in series (i.e. 7 cells/battery = 14 cells, 200 mA).

For a nominal 27V pack using three of the same batteries in series the values to be inserted would be 21 cells and 200 mA.

For a nominal 9V pack using three 9V 200 mA batteries in parallel the values to be inserted would be 7 cells and 600 mA.

I hope I get it right now as I have be over-chargeing a bit lately

Being extremely satisfied with the SEN I will power also the DAC supplies of batteries for coherence and to get the hole thing of the grid. The shunt supplies I am using here are a bit hungry so I need to parallel batteries.

Cheers,

Nic
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