>The point of concern is the impedance of the capacitor at the >frequency of interest. Yes >Although smaller capacitors may have less lead >inductance, the higher capacitance of the larger ones may result in a lower >impedance at that frequency, giving better performance. > >Any analysis I've seen has always indicated that higher capacitance is >better, even at reasonably high frequencies (e.g., 20 MHz). E.g., a 10 uF >tantalum is superior to a 0.1 uF tantalum or ceramic. Unfortunately, it's not just LEAD inductance. Electrolytic (and other) capacitors can have a significant inductive component internally. Using a small capacitor optimised for high frequency performance as well as the requisite ecap is often a good idea. A 10uF tantalum AND a 0.1 uF tantalum in parallel would probably work better than either alone. That said, - I know you just mentioned tantalum capacitors as an example but I would recommend NEVER using a tantalum in a power supply decoupling application unless I had taken extraordinary steps to ensure that the voltage never EVER exceeded the tantalum's voltage rating. Tantalums become very effective non-fusible shorting links when exposed to voltages only very slightly above their rated voltage - even for VERY short periods of time. Use of solid Aluminium (OK solid Aluminum for the USA ers) will meet most of the problems that Tantalums are specd for without the extra problems. Tantalum caps make very amusing toys - you can get any mix of smoke, flame, smell, noise (from whistle and shriek through to explosion) by injudicious application of voltage. I've seen / heard / smelled all of these from a single failure. Russell McMahon _____________________________ >From another world - www.easttimor.com What can one man* do? Help the hungry at no cost to yourself! at http://www.thehungersite.com/ (* - or woman, child or internet enabled intelligent entity :-)) -----Original Message----- From: Robert A. LaBudde To: PICLIST@MITVMA.MIT.EDU Date: Wednesday, 10 November 1999 11:42 Subject: Re: [OT] Re: Adjustable Power Supply HELP