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CCS issue

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In Reply to: I'm not ruling out the Supertex DNxxxx FETs posted by VoltSecond on May 23, 2004 at 22:42:58:

Hi,
I am not an expert on circuit design. But I am very happy with my experience of CCS chip "IXCP10M45S" .
If I have to build CCS myself, I would use 431 and fixed bias reference with FETs ...
Just my two cents about CCS.

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Caution: 431's can be fussy parts. - VoltSecond 23:11:19 05/24/04 (5)
431's can be fussy parts. When I've used them, I've had to roll them off at low frequencies to prevent oscillations.
Where'd you pick up the IXYS part?

Play safe and play longer! Don't be an "OUCH!" casualty.
Unplug it, discharge it and measure it (twice) before you touch it.
. . .Oh!. . .Remember: Modifying things voids their warrantee.
- CCS issue - direct 19:02:24 05/31/04 (0)
  I got them from digikey.
  431 works fine with me. just remember that you need caps at the top leg of the voltage divider to avoid oscillations, they can take current but not be able to deal with voltage drop over 37 volts.
  I usally put them in the source loop to provide current sensing with good results.
- Ain't that the truth! - Paul Joppa 22:26:37 05/27/04 (3)
  Been spending a lot of time the last week or two sorting out some 431 circuits. Like all the chip regulators (in fact, anything with an opamp inside), thay have stability issues. Worst are those with high impedance collectors at the output, where an external RC sets the dominant pole. It's almost impossible to find out what the gain and poles/zeroes are by reading the data sheets, too - very frustrating! I just today ran across an application note that said (re: a low-dropout series regulator) that the reason the data sheet recommends a tantalum 4.7uF capacitor on the output is that the AVX brand tantalum 4.7uF cap happens to have a 1.5 ohm equivalent series resistance at a few hundred kHz, and that resistance is critical to stability. Apparently they assume ("proof by blatant assumption", we used to call it) that all tantalums have the same resistance, since no mention is made of the resistance in the data sheet. Sheesh!
  For anyone else struggling with this, the ON semiconductor 431 data sheet is the only one I've found which has information on design for stability.
  - Re: Like so Mike? Parafeed compact 2A3 - direct 19:19:17 05/31/04 (0)
    It is obvious to me that when using shunt regs you need have resistance in serial with the chip, otherwise .....
    Anyway, I think 431 is a fairly useful chip with any application need <100 ma total current. CCS just happen to be one of the usages. I have build quite a few shunt regs using 431 and found that once it works, it stays there working forever. The quality control of 431 is not that great, a lot of deviations such that it should be used by experienced builders only.
  - CCS issue - direct 19:19:17 05/31/04 (0)
    It is obvious to me that when using shunt regs you need have resistance in serial with the chip, otherwise .....
    Anyway, I think 431 is a fairly useful chip with any application need <100 ma total current. CCS just happen to be one of the usages. I have build quite a few shunt regs using 431 and found that once it works, it stays there working forever. The quality control of 431 is not that great, a lot of deviations such that it should be used by experienced builders only.
  - I've considered a dual loop design. - VoltSecond 23:21:19 05/29/04 (0)
    Use the TL431 to set the DC bias point and use something else for the high frequencies. If you can afford 5-10V drop in a CCS, local feedback alone works really good for high frequencies.
    
    Play safe and play longer! Don't be an "OUCH!" casualty.
    Unplug it, discharge it and measure it (twice) before you touch it.
    . . .Oh!. . .Remember: Modifying things voids their warrantee.

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