Ain't that the truth! - Paul Joppa - MagneQuest/Peerless Forum

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Ain't that the truth!

Posted by Paul Joppa (P) on May 27, 2004 at 22:26:37

In Reply to: Caution: 431's can be fussy parts. posted by VoltSecond on May 24, 2004 at 23:11:19:

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.

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Follow Ups Full Thread

Topic - A Compact CCS Ver 1. - VoltSecond 14:02:14 05/22/04 (17)

Hi Paul, - Bas Horneman 14:46:13 05/23/04 (15)

I'm not ruling out the Supertex DNxxxx FETs - VoltSecond 22:42:58 05/23/04 (14)

Can you comment on the IRF710? - Russ57 09:23:25 05/26/04 (6)

Re: Can you comment on the IRF710? - VoltSecond 21:11:54 05/26/04 (5)

Cathode load - Russ57 12:17:41 05/27/04 (4)

Re: Cathode load - VoltSecond 21:53:32 05/27/04 (3)

noise... - Sector-7G 17:35:42 05/31/04 (0)

Re: Cathode load - VoltSecond 22:28:55 05/27/04 (1)

Thanks(nt) - Russ57 04:31:25 05/28/04 (0)

CCS issue - direct 22:39:14 05/24/04 (6)

Caution: 431's can be fussy parts. - VoltSecond 23:11:19 05/24/04 (5)

CCS issue - direct 19:02:24 05/31/04 (0)

Ain't that the truth! - Paul Joppa 22:26:37 05/27/04 (3)

Re: Like so Mike? Parafeed compact 2A3 - direct 19:19:17 05/31/04 (0)

CCS issue - direct 19:19:17 05/31/04 (0)

I've considered a dual loop design. - VoltSecond 23:21:19 05/29/04 (0)

Follow Ups

Ain't that the truth! - Paul Joppa 22:26:37 05/27/04 (3)

Re: Like so Mike? Parafeed compact 2A3 - direct 19:19:17 05/31/04 (0)

CCS issue - direct 19:19:17 05/31/04 (0)

I've considered a dual loop design. - VoltSecond 23:21:19 05/29/04 (0)

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