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Constant Current Source (CCS) For Audio Applications
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Old 28th July 2016, 03:31 PM   #21
Mark Johnson is offline Mark Johnson  United States
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Constant Current Source (CCS) For Audio Applications
Let your mind roam free. Let your triply nested .STEP PARAM statements be wide-ranging. Copy Elvee's technique of putting three independent sources into the simulation, sinewaves whose frequencies are relatively prime, at three different positions in the circuit where unwanted ickynoise might be present. Then see which frequency(s) appear on the output.

To name one example of a random idea that spontaneously pops into a freely roaming mind: does anything good happen if you replace R5 with an Nchannel JFET like 2SK879 [datasheet attached]? Does anything bad happen?

Edit- now that I see jerluwoo's excellent post -- do you get any additional goodness if you replace his "R3" with an Nchannel JFET?
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File Type: pdf 2SK879_datasheet_en_20140301.pdf (291.9 KB, 75 views)

Last edited by Mark Johnson; 28th July 2016 at 03:35 PM.
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Old 28th July 2016, 03:34 PM   #22
jerluwoo is offline jerluwoo  United States
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Quote:
Originally Posted by AndrewT View Post
I copied and moved the two models.text files to my LTspicefiles folder.
I opened the .asc
"run" but it can't find the models.
Where do I put the .txt files so that the .asc can find them?
I have to place them in the lib/sub directory for it to find them in my install.
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Old 28th July 2016, 03:41 PM   #23
jerluwoo is offline jerluwoo  United States
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Here is the model I have for tl431.

*Programmable Precision Reference pkg:TO-92 2,3,1. pkg: DIP8 6,1,8
.SUBCKT XTL431 2 3 1
*Reference input stage
Q1 3 1 10 QINPUT
RIN 10 2 500K

*Internal reference voltage
VR 20 2 DC 1.7791
RVR 20 2 1G

*Pole/Zero modeling
GM 0 30 10 20 1
RGM 30 0 1MEG

*Pole/Zeros: Pole 1= RGM & CP2, 10KHz
* Pole 2= RP2 & CP2, 60KHz
* Pole 3= CP1 & RZ1, 500KHz
CP1 30 40 15.9P
RZ1 40 0 20K
RP2 30 50 10MEG
CP2 50 0 0.265P

*Gain stage voltage clamp
DC 0 30 DCLAMP

*Output stage
GO 3 2 50 0 2.5U
DR 2 3 DNOM

.MODEL DNOM D(IS=100E-15 RS=7)
.MODEL DCLAMP D(IS=0.1)
.MODEL QINPUT NPN (BF=1 VAF=11.15)
.ENDS XTL431
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Old 28th July 2016, 03:51 PM   #24
jkuetemann is offline jkuetemann  Canada
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Quote:
Originally Posted by Mark Johnson View Post
Let your mind roam free. Let your triply nested .STEP PARAM statements be wide-ranging. Copy Elvee's technique of putting three independent sources into the simulation, sinewaves whose frequencies are relatively prime, at three different positions in the circuit where unwanted ickynoise might be present. Then see which frequency(s) appear on the output.

To name one example of a random idea that spontaneously pops into a freely roaming mind: does anything good happen if you replace R5 with an Nchannel JFET like 2SK879 [datasheet attached]? Does anything bad happen?

Edit- now that I see jerluwoo's excellent post -- do you get any additional goodness if you replace his "R3" with an Nchannel JFET?
Assuming you mean using the JFET to provide a constant current in place of the resistors, then yes there is benefit. However, the result is not better than the 2 JFET and needs more parts.

I will try finding some of Elvee's examples and see if I can't learn something from the way his simulations are set up.
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Old 28th July 2016, 09:14 PM   #25
Mark Johnson is offline Mark Johnson  United States
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Constant Current Source (CCS) For Audio Applications
I started to do some measurements but quit early; went out to the pool for some sun and a T&T about half way thru. This is as far as I got. JFETs are notorious for their wide spread of parameters and maybe this might be a small piece of confirming evidence.
Attached Images
File Type: jpg Two_JFETs.jpg (250.4 KB, 624 views)
File Type: png IVCURVE.png (45.2 KB, 611 views)
File Type: png j112_model.png (9.3 KB, 606 views)
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Old 28th July 2016, 10:47 PM   #26
john_tracy is offline john_tracy  United States
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Fairchild makes a low tempco version of the TL-431 called the KA-431. I use it in a CCS where the KA-431 sets the gate voltage of a power MOSFET. This is used as the cathode current sink in the output stage of a KT-120 PPP differential amp. At 300mA the bias current stays within +- 0.25mA cold to hot.
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Old 29th July 2016, 03:20 AM   #27
bimo is offline bimo  Indonesia
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Quote:
Originally Posted by jerluwoo View Post
Although you won't see any improvement in sims with perfect dc rails, in a real world circuit with noise this can have a major improvement in psrr.
I use this CCS in my VSSA
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Old 29th July 2016, 03:46 AM   #28
jerluwoo is offline jerluwoo  United States
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Looks like those J112's need a minimum 5 volts drain to source plus the voltage across the source resistor to be effective. Not very practical in many applications. Like everything in this hobby, it's always choosing the what,where, and how that makes things interesting.
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Old 29th July 2016, 07:56 AM   #29
Calvin is offline Calvin  Germany
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Hi,

it´s always good if You can work with high values of the source resistor.
It reduces tolerances and increases impedance.
So I´m not at all convinced about ´audio´ JFETs like the SK170 as really good optimum choice for a ccs - at least in single fashion.
Heavily degenerated high Idss types are imho better here (if Youcan afford the loss in headroom due to their higher Vds/Vdg.
Things improve alot with a cascode and the 2N4393 and 2N4391 (or the MMBF/SMMT Variants) are excellent partners for SK170 or BF862.
Their low en of 3nV/sqr(Hz) isn´t bad either.
Btw. the output impedance of a current mirror source rises vastly by cascoding the output leg bipolar with a JFET or a depletion mode FET - similar to the cascoded JFET ccs.

jauu
Calvin
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Old 29th July 2016, 08:09 AM   #30
padamiecki is offline padamiecki  Poland
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Hi!
maybe I was not clear in post 12 with added link,
there are many ccs configurations which might have low niose, worth checking, the comparsions attached, I hope this will not rubbish the thread...
Attached Images
File Type: gif CCS-Test-2.gif (38.4 KB, 572 views)
File Type: gif ccs1.gif (47.7 KB, 580 views)
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