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#25
November 25th 03, 02:02 PM
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In article ,
Bill Turner wrote: On 24 Nov 2003 22:50:40 -0800, (Jason Hsu) wrote: 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? __________________________________________________ _______ You really need to ask the manufacturer of the resistor. They are well aware of the problem - if you get to the right person. Having said that, here is a generalization: If the resistor's element is a solid block of material, such as in a carbon composition type, it will have very good pulse power ratings. On the other hand, if the element is a film, it may develop tiny hot spots during pulsing and eventually fail. Many years ago I analyzed a problem with resistors which were discoloring in the field. This involved two identical circuits with identical singal inputs. In one circuit, a resistor kept turning brown over time, in the other it did not. We were getting field returns as a result of troubleshooting that focused on the brown resistors. What was the difference? The resistor which did not discolor was resting on two metal traces which ran under it, the one which discolored, was resting on the PCB. That tiny amount of heatsinking provided by the traces was the difference. Obviously, the circuit needed to be redesigned, but it worked great on the breadboard when it went into production. Al -- There's never enough time to do it right the first time....... |
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