I read in !emc-pstc that LEUNG YAT WAH DEREK <[email protected]> wrote (in <[email protected]>) about 'Heat sink thermal impedance.' on Thu, 1 May 2003: > >> Who can tell me what is the difference between "thermal impedance" and >> "thermal resistance" when talk about heat sink, thanks. >> Well, theoretically they are different. By analogy with an electrical circuit, thermal resistance corresponds to resistance, but any mass also has the property of storing heat, and in a direct (as opposed to gyratory) analogy, in which temperature corresponds to voltage and heat flow to current, the storage property is analogous to capacitance. (Temperature rise lags the heat flow causing it.) So, if you are considering transient or fluctuating heat generation, you may need to take into account both thermal resistance and heat storage capacity.
Heat storage is the principle on which silicon diode surge-limiters work. They are zener diodes bonded to big blocks of copper, which hold the die temperature within acceptable limits for up to a few hundred microseconds, after which the transient has ended anyway. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
