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#17
November 27th 03, 06:06 PM
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"John Robertson" wrote in message ... Not an expert on instantaneous surges in resistors (you could ask my daughter - she is in third year physics ;-) but I would suggest that you consider using Flame-Proof resistors in this application. these are resistors that open internally and do not burn up your board when they fail...sometimes known as a fuse resistor.... John :-#)# On 24 Nov 2003 22:50:40 -0800, (Jason Hsu) wrote: It's part of a design for a T/R sense circuit for a noise cancellation device. I won't bore you with too many details. One thing I noticed in a design I'm looking at is that 1W resistors could be subject to as much as 50W of power apiece during the time it takes for a relay to respond. This response time is 7msec. The overall duty cycle will be low (well under 1%). Can the 1W-51 ohm resistors handle this 50 RF volts 0-peak (about 50W PEP) for .007 sec? 50W over .007 seconds is .35 Joules. .35W for 1 second is also .35 Joules, which a 1W resistor should have no trouble handling. Can the resistors be damaged during that .007 seconds? No, it will not be damaged. Also, how much time does it take to damage a toroid? If it can handle X units of flux density continuously, how much flux density can it handle for .007 seconds with a low overall duty cycle (like well under 1%)? This is an entirely different situation. The maximum flux density is fixed by the core material, and cannot be exceeded, no matter how much current you feed through the coil. Jason Hsu, AG4DG usenet AAAAATTTTT jasonhsu.com |
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