Pulse Withstanding Resistors
Determining the right pulse handling capabilities for a particular application is not always easy. Dealing with inrush current is different than dealing with transient suppression, for example. For pulses of up to five seconds, the industry standard specification is that the resistor withstand five-times its rated power. So a 5W resistor must be able to handle 25W for 5 seconds (125 Joules). For shorter pulses, the mass of the resistance wire determines the Joule rating, which is then dependent upon resistor value and package type. Pulse shape and repetition rate also have to be taken into account. Since every application is different, we urge our customers to contact us to help specify the best resistor possible.
Standard Conditions for Specifications
In Riedon data sheets the nominal power dissipation is mentioned for all resistors. The data is valid for a free standing assembly, for example, a surface mount device assembled on a PCB. The ambient temperature for the power ratings is always 70°C. This means that the power handling capability of the resistor must be derated if the ambient temperature is greater than 70°C. Adding a heatsink or fan can also increase the resistors ability to dissipate heat.