RESISTORS • CAPACITORS • COILS • DELAY LINES APPLICATION GUIDE R-42 Pulse Capability Derating Factors Unless indicated otherwise on RCD’s data sheet, the resistor peak pulse voltage, wattage, and/or energy ratings are based on single capacitive discharge pulse with RC time constant of 1uS at 25ºC and RH <65% at altitude <10,000 ft. Derate for multiple pulses, longer pulse durations, and environmental conditions as detailed below. The pulse rating shall be the lower of the peak power, voltage, or energy rating after applying the derating factors. Peak Pulse Voltage Rating Peak pulse ratings are in accordance with RCD data sheets when tested per the pulse test circuit is in accordance with DSCC (Defense Supply Center) Drawing 03007 par. 4.11 “Resistance to Pulse Test Circuit” with capacitance value selected to limit the RC time constant to 1uS. Circuit for 1KΩ resistor is illustrated below. For longer pulses, derate in accordance with “Peak Pulse Rating as a Function of Pulse Width” chart below. Resistance Value 1KΩ 10KΩ 100KΩ 100MΩ Capacitance 1000pF 100pF 10pF 1pF Table 1. Capacitance Value to be Utilized in Pulse Test Circuit Peak Pulse Voltage Rating as a Function of Pulse Width: Percentage of Peak Pulse Voltage Rating 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% ≤1uS 10uS 100uS Pulse Width R-42 Rev.A P.1 of 3 1mS 10mS Pulse Energy Rating As A Function of Pulse Width, Series PR & PRM Derating the Single-Pulse Surge Rating for Multiple or Repetitive Pulse Streams: a) Firstly, the pulse must not exceed the single peak power pulse rating given in the applicable Surge Capability chart for given time duration, and also must not exceed the rated peak pulse voltage levels. The peak pulse voltage capability is generally well above the Max. Continuous Voltage Rating and if not listed on data sheet is often available on the Surge Application Guide for the product in question (if not, consult RCD’s engineering department). Note: elevated ambient temperatures can impact surge capability and should be derated accordingly (refer to data sheet). b) Resistors subjected to multiple pulses or repetitive pulse streams must meet the criteria for a single pulse, and the average power must not exceed the published wattage rating. T Average Power = Pt/T P= Peak Power (Watts) t= Pulse duration (Seconds) T= Cycle Time P t Example: Peak Power (P)= 1000W, pulse duration (t) = 10uS, cycle time = 60Hz (.01667S)... 1000W x .00001S / .01667S = .6 Watts average power. c) The single pulse rating is based on Cycle time/Pulse duration (T/t) ratio of 10,000 or greater. For smaller T/t ratios, derate pulse capability according to following chart. Complete RCD's "Surge Questionnaire Form" if standard or Opt.P (Pulse Tolerant) construction won't suffice so that we can recommend the optimum resistor for your application. Always verify selection by evaluating prototypes under worst-case conditions. 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 10,000 1,000 100 Cycle time/Pulse duration (T/t) ratio R-42 Rev. A Page 2 of 3 10 1 Derating Pulse Capability for Elevated Temperatures: Elevated ambient temperatures impact pulse as well as continuous performance capability and therefore require derating of peak and continuous power, voltage, and energy ratings. Continuous power and voltage ratings are to be derated according to “derating” section on data sheet. Peak pulse voltage, power and energy are to be derated according to chart below. Percentage of Energy, Peak Pulse Voltage, or Peak Pulse Power Rating 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 25 50 75 100 125 150 175 200 225 240 Ambient Temperature (ºC) Derating Pulse Capability for High Altitudes and Humidity: Power capability is affected by altitude. Operation at high altitudes can also result in corona and arcing, especially in high humidity environments. Peak pulse voltage, power and energy ratings are to be derated 10% per 10,000 feet. RCD has not established a derating factor for high humidity, however offers hermetically sealed designs for products utilized in harsh environments such as tropical or naval. RCD COMPONENTS INC, 520 EAST INDUSTRIAL PARK DR., MANCHESTER, NH 03109 USA TEL:(603)669-0054 FAX:(603) 669-5455 WWW.RCDCOMPONENTS.COM R-42 Rev.A P.3 of 3