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"Roger Gt" wrote: Check for wire wound resistors, they are most likely to be capable of a high pulse of current. But check for the manufacturers specification on what they have been tested to tolerate. There used to be several sources of these, but I haven't used any for years. Of course a insulated bobbin with copper or iron wire could be used, if size isn't critical. Wind it as a single or double layer to get the heat out. 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? http://www.globar.com/ec/resistor.php.html shows some bulk ceramic resistors. One of their data sheets shows their 1.5 W resistor having a peak energy rating of 75 Joules. The key here is having a lot of physical mass directly in the current path (something that metal film resistors don't do well). PS: What happens when your relay fails? |