Piotr - Treating the PTC as a 'fixed impedance' is only a convenience and a way to avoid treating the PTC as a fuse or other current limiter [PTCs fit into a nebulous area, in terms of traditional product safety; there aren't (or weren't when §2.5 was created) many safety standards that deal with thermistor type devices]. If you were to look at IEC 60730-1 (my copy is a 1995 edition of the EN version), the requirements for PTCs don't really fit the application of §2.5, but it provides some basis for demonstrating a consistently reaction of the component.
The feature of a PTC that's relevant to safety is the trip current. Then, just as with a fuse (ignoring the many finer points of each type of components' actual operation), treat it as having a step function between the low impedance and high impedance states. Regards, Peter L. Tarver, PE [email protected] > From: Piotr Galka > Sent: Wednesday, October 11, 2006 9:33 AM > > Peter, > > I'm not sure if I understand you well. > Do you mean, that if my PTC has (for example) 1 ohm in normal > operation I > should assume that only 1 ohm is what is limiting the source power ? > > Regards, > Piotr > > CONFIDENTIALITY This e-mail message and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail message, you are hereby notified that any dissemination, distribution or copying of this e-mail message, and any attachments thereto, is strictly prohibited. If you have received this e-mail message in error, please immediately notify the sender and permanently delete the original and any copies of this email and any prints thereof. ABSENT AN EXPRESS STATEMENT TO THE CONTRARY HEREINABOVE, THIS E-MAIL IS NOT INTENDED AS A SUBSTITUTE FOR A WRITING. Notwithstanding the Uniform Electronic Transactions Act or the applicability of any other law of similar substance and effect, absent an express statement to the contrary hereinabove, this e-mail message its contents, and any attachments hereto are not intended to represent an offer or acceptance to enter into a contract and are not otherwise intended to bind the sender, Sanmina-SCI Corporation (or any of its subsidiaries), or any other person or entity. _____________________________________________________________________________ Scanned by Sanmina-SCI eShield _______ _____________________________________________________________________ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
