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Subject: Re: SMT non-polar electroLYTIC capacitors?

Date: 03/20/00 at 5:55 AM
Posted by: John Dunn - Consultant
E-mail: ambertec@ieee.org
Message Posted:

In Reply to: Re: SMT non-polar electroLYTIC capacitors? posted by Dominique A. Bovey on 03/20/00 at 2:41 AM:

Hi, Dominique:

I'm sorry I misread X5R as X7R. That was a slip. However, I still have strong reservations about electrolytics in regards to leakage current, and now I also see, dielectric absorption.

May I make a suggestion about circuitry:

In Electronic Design for January 9, 1992, page 130, I published an Idea For Design entitled "AC Amplifier Passes Low Frequencies" in which I showed an amplifier with a low frequency cut-off of 0.4 Hz using only 0.1 F for an input capacitor. The trick was to bootstrap the amplifier's input impedance way, way up. When I was developing this circuit, I played a little bit by going to 1.0 F. It's interesting to watch the settling effects that occur with an amplifier whose cut-off frequency is 0.04 Hz!

Anyway, at 0.1 F, you can go to dielectrics far better suited to low leakage and low dielectric absorption, such as polypropylene, without having to have something overly large.

If you can't find a copy in a nearby engineering library, let me know and I'll send you a copy of the item.

Good luck.

John Dunn - President
Ambertec, Inc.
ambertec@ieee.org


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