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Old 1st March 2009, 04:53 PM   #31
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Hi Syn08,

Have you considered to use a couple of LEDs or a low-noise ref chip to increase the reference? That would increase your loop gain for possibly even better performance. No criticism, just curiosity.

BTW Your remote sensing is right on target

Jan Didden
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Old 1st March 2009, 04:57 PM   #32
syn08 is offline syn08  Canada
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Quote:
Originally posted by analog_sa
Line regulation is something i largely don't care about. Plus i have preregulators. Do you have similar pictures for noise?
No, but obviously if the output impedance is minimized up to RF, so will the output noise.

One thing I can't explain is the positive impact of the CCS instead of the balast resistor. I can't measure any difference up to 10MHz in line regulation, output impedance and noise.

But then, whatever pleases your ear This solution is (to me) much simpler than the Jung regulator and is ideal for class A gain stages (where the power dissipation of the parallel regulator can be minimized).

Glad you like it
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Old 1st March 2009, 05:06 PM   #33
syn08 is offline syn08  Canada
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Quote:
Originally posted by janneman
Hi Syn08,

Have you considered to use a couple of LEDs or a low-noise ref chip to increase the reference? That would increase your loop gain for possibly even better performance. No criticism, just curiosity.

BTW Your remote sensing is right on target

Jan Didden
I've tried:

- LM329 (6.9V) is worse in tems of noise, plus limited bandwidth (up to 500KHz)
- TL431 has very poor noise and limited bandwidth, plus the well known stability issues. I was unable to keep the output impedance low, over 150KHz

Haven't tried multiple LEDs, but it's worth of. I'm though expecting some noise degradation. What I can tell is that only infrared or red LEDs should be used. Anything else (and in particular blue and violet, tempting because they have Vf=3.5-4V) have way to much noise.
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Old 1st March 2009, 05:10 PM   #34
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Quote:
Originally posted by syn08


I've tried:

- LM329 (6.9V) is worse in tems of noise, plus limited bandwidth (up to 500KHz)
- TL431 has very poor noise and limited bandwidth, plus the well known stability issues. I was unable to keep the output impedance low, over 150KHz


Haven't tried multiple LEDs, but it's worth of. I'm though expecting some noise degradation. What I can tell is that only infrared or red LEDs should be used. Anything else (and in particular blue and violet, tempting because they have Vf=3.5-4V) have way to much noise.

Right. I think there are some modern low-noise references around these days, need to look it up. But gain may be small anyway.

Jan Didden
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Old 1st March 2009, 05:21 PM   #35
syn08 is offline syn08  Canada
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Quote:
Originally posted by janneman



Right. I think there are some modern low-noise references around these days, need to look it up. But gain may be small anyway.

Jan Didden
The only thing that I found better in terms of noise was a MAX6126AASA25 2.5V reference. Frequency response was acceptable (up to 500KHz) but unfortunately this IC has a very ugly line and load transient response. And unfortunately it takes only 12V input, so I haven't looked closer...

And of course, at $17 a pop...
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Old 1st March 2009, 05:56 PM   #36
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Iím sorry, I canít see the regulator in post 21ís schematic working at all. The gain of the error amp is set by the feedback loop ratio of R4 & 5, which as pictured is around 26. The LED reference should be around a volt or so for that LED (looking at the data sheet), so that would yield an output voltage of around 26V. The input is only 15 volts in the schematic. Whatís the output voltage supposed to be?? The addition of C1 & 2 across R5 is a positive feedback path and should lead to worse noise, if not outright instability. Perhaps C3 mitigates that to some degree (lag vs. lead)?? Sounds tricky at best. Commonly, despite the pictures, C1 & 2 would be across D1 (C1 would be made somewhat larger in that case), with a counter diode across R5 to protect U13ís input from the charge stored in C1 & 2 at power down. To reduce noise itís common to place a cap across the feedback resistor, in this case R4, though stability issues need to be considered when thatís done. Iím at a loss as to how this regulator can be expected to work optimally as pictured. Am I missing something?? Sorry, donít mean to come across harsh, just at a loss Ö
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Old 1st March 2009, 05:56 PM   #37
housing is offline housing  Hong Kong
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Quote:
Originally posted by syn08


The only thing that I found better in terms of noise was a MAX6126AASA25 2.5V reference. Frequency response was acceptable (up to 500KHz) but unfortunately this IC has a very ugly line and load transient response. And unfortunately it takes only 12V input, so I haven't looked closer...

And of course, at $17 a pop...

How about LT1027?
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Old 1st March 2009, 06:05 PM   #38
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Quote:
Originally posted by kaos
Am I missing something??

As i mentioned earlier on i recalculated resistor values which work. The rest of your post makes perfectly good sense to me as well.
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Old 1st March 2009, 06:20 PM   #39
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Quote:
Originally posted by kaos
Iím sorry, I canít see the regulator in post 21ís schematic working at all. The gain of the error amp is set by the feedback loop ratio of R4 & 5, which as pictured is around 26. The LED reference should be around a volt or so for that LED (looking at the data sheet), so that would yield an output voltage of around 26V. The input is only 15 volts in the schematic. Whatís the output voltage supposed to be?? The addition of C1 & 2 across R5 is a positive feedback path and should lead to worse noise, if not outright instability. Perhaps C3 mitigates that to some degree (lag vs. lead)?? Sounds tricky at best. Commonly, despite the pictures, C1 & 2 would be across D1 (C1 would be made somewhat larger in that case), with a counter diode across R5 to protect U13ís input from the charge stored in C1 & 2 at power down. To reduce noise itís common to place a cap across the feedback resistor, in this case R4, though stability issues need to be considered when thatís done. Iím at a loss as to how this regulator can be expected to work optimally as pictured. Am I missing something?? Sorry, donít mean to come across harsh, just at a loss Ö

The error amp works open loop. The opamp compares the ref with 1/26 of the output, and any error is amplified by the open loop gain and drives the MOSFET to bring the error back to (close to) zero. Works like a charm.

Edit: My comment about using a higher ref voltage means that you can make the 1/26 ratio bigger so that the loop gain increases and the error decreases.

Jan Didden
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Old 1st March 2009, 07:24 PM   #40
syn08 is offline syn08  Canada
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Quote:
Originally posted by kaos
Am I missing something??
Yes. You miss the understanding on how parallel regulators are working Sorry, donít mean to come across harsh, etc...
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