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Old 18th March 2012, 04:34 AM   #3671
jcx is offline jcx  United States
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I posted some tail current ccs options in Searching the "best" CCS

a resistive bootstrap ccs is used by Hugh Dean, "Aska"

combining the bootstap tail ccs with a 2 term fet/crd ccs gives very low simmed distortion in the tail current
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Old 18th March 2012, 09:57 AM   #3672
dvv is offline dvv  Serbia
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Quote:
Originally Posted by jcx View Post
I posted some tail current ccs options in Searching the "best" CCS

a resistive bootstrap ccs is used by Hugh Dean, "Aska"

combining the bootstap tail ccs with a 2 term fet/crd ccs gives very low simmed distortion in the tail current
JCX, just one question: how much, in your opinion, does the actual quality of the power supply influence CCS results?

I did read a few pages of the link you posted, and it seems the discussion was started by a man from Germany who uses simple RC filtered power lines. But what if the power lines were all of that, and then additionally filtered by a full voltage regulation circuit?
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Old 18th March 2012, 12:44 PM   #3673
tvrgeek is offline tvrgeek  United States
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More reading, more ideas. Cool. Yes, even I have figured out the model is several viewpoints among many and truth comes on the bench and in the listening. One of the things I found out was the odd glitch double bounce was an artifact of the feedback, not the ccs itself. Of course, how it handles it is the question. I am going to simplify the model today. What I think I should be looking for is how it handles a step in load. My reasoning tells me that implies the impedance as well as the transient behavior. So I have been looking at a plot of the tail current with a square wave load. Consistency over absolute impedance. Reasonable? Then in a complete amplifier model to look at the distortion.
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Old 18th March 2012, 02:01 PM   #3674
tvrgeek is offline tvrgeek  United States
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Yup. Built a couple of ccs versions in isolation and that shows a really big difference. Makes more sense.
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Old 18th March 2012, 03:19 PM   #3675
tvrgeek is offline tvrgeek  United States
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Ok, so the LED is a lot better, and a cascode BJT/FTE much better still. Now, to figure out how to put offsets on the Spice traces to make comparisons more obvious. Plot is current through the load.

Transistor selection was by what was in Spice. Current adjust to be close, not any magic value.
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File Type: png ccs-test.png (14.6 KB, 96 views)
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Old 18th March 2012, 03:20 PM   #3676
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by tvrgeek View Post
Consistency over absolute impedance. Reasonable? Then in a complete amplifier model to look at the distortion.
A non-ideal tail current source will cause common mode related problems, if the impedance is relatively low and frequency dependent we are in trouble.

JCX's "resistive bootstrap" comments came at a good time (as did Dejan reminding me of paralleling small signal parts), as it completed at least for the concept stage something I have been fuzing and munzing with, so at least now I have something to feed to LT-Spice (if I can find models for 2SK214/2SJ77) or just do re-build for real...

FWIW, here my take on what to implement in a nice case, with a pair of 0.3K/W heatsinks and a 1200VA mains transformer...

Anyway, we want the CCS impedance both high, linear and frequency independent.

Ciao T

PS, the attachment has not been build or tested (yet), but is intended to be implemented to some existing hardware, using existing PCB's and as many existing parts as possible, while getting something more to my liking.

There are details not shown (such as the ferrite beads or resistors as base/gate stoppers, protection circuitry, other housekeeping and so on which is in place in the actual unit and will be retained) and the final compensation is not fully worked out yet, it will probably need two small miller compensation caps as well.
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File Type: gif Sir Pottymouth.gif (38.3 KB, 99 views)
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Old 18th March 2012, 03:21 PM   #3677
tvrgeek is offline tvrgeek  United States
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What, no plot? Try again. Oh, does not like WMF. After all, Windows is a virus isn't it?
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File Type: png ccs-plot.PNG (147.0 KB, 98 views)
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Old 18th March 2012, 04:14 PM   #3678
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by tvrgeek View Post
Ok, so the LED is a lot better, and a cascode BJT/FTE much better still.
Try the attached...

Click the image to open in full size.

The LM329 you can probably get a good aproximation with a voltage source, a resistor and an inductor... Rest can use real devices, BC550C simply means small signal NPN high beta...

Ciao T
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File Type: gif CCS.gif (6.3 KB, 106 views)
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Old 18th March 2012, 04:35 PM   #3679
bcarso is offline bcarso  United States
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Jung's been doing a lot of study of various current sources recently --- I haven't checked to see if he's "published" them on his website.

One of the things that came out was the brief note in a paper by Jaeger about adding a JFET to the output of a simple bipolar I source, and returning the gate to the emitter. This of course resembles a "Hawksford" cascode (with actual priority for biploars probably accorded to Aldridge in 1962 as I've babbled about before), and besides the convenience of biasing, returns the Cdg displacement current to the emitter, and vastly reduces the effective output capacitance (and hence any distortion associated with its variation with voltage). As well thermal shifts in the bipolar with signal swing are reduced. The drawbacks include voltage burden.
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Old 18th March 2012, 04:40 PM   #3680
bcarso is offline bcarso  United States
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Quote:
Originally Posted by tvrgeek View Post
Ok, so the LED is a lot better, and a cascode BJT/FTE much better still. Now, to figure out how to put offsets on the Spice traces to make comparisons more obvious. Plot is current through the load.

Transistor selection was by what was in Spice. Current adjust to be close, not any magic value.
tvr, have you tried an ideal current source to see its effect on your overall circuit performance? Your results with LEDs and standard diodes are suspicious, particularly the absence of effects from shunt C (and btw you can make that as big as you like --- take advantage of Simland for the purposes of education!).

There can be, of course, compensatory effects in circuits from the departure from the ideal in one place complementing something nonideal elsewhere.
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