The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: Winfield Hill
Subject: Re: Design for long interval timer
Date: 7 Dec 2002 07:44:42 -0800
Organization: Rowland Institute
References: <email@example.com> <firstname.lastname@example.org> <3DEE0CAB.email@example.com> <3DEE30C2.firstname.lastname@example.org> <3DF20C8C.email@example.com>
X-Newsreader: Direct Read News 4.20
> Spehro Pefhany wrote:
>> Fred Bloggs wrote:
>>> I am also wondering about your choice of film caps in these
>>> high-impedance timing applications where there may not be
>>> enough current to clear a dielectric fault.
>> Dielectric faults are the province of caps subject to damaging
>> transients. Film caps at low voltage just about never fail,
>> they are about as reliable as it gets!
> This is not quite true. Films are reliable because of process and
> materials improvements which include gridded metalization patterns
> designed to fuse the connection to the fault at low currents.
> There are several reasons for dielectric faults which include
> latent film defects, film faults induced by dielectric stress due
> to electric field gradients, and heat. By using the film in an
> ultra high impedance circuit you may be negating the apparent
> reliability of the part because the circuit cannot clear the fault-
> or allow the cap to self-heal in your lingo. Low voltage helps but
> it does not eliminate consideration of temperature effects on
> dielectric deterioration, or inherent defect activation, in
> storage, use, or aging of the part.
Fred, I'll go with Spef's view, rather than yours. In my personal
experience with about 250k of the mil-spec CK05-style ceramic caps
I prefer using - perhaps 1 million-cap-years, I've experienced
only four failed parts, of which two were DOA. By contrast, for a
somewhat smaller number of film caps used at 5 to 10% of the rated
voltage in leakage-sensitive applications, I have experienced zero
failures. But talk is cheap; so I'm going to ask you to kindly
provide us with references for your view.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup