IntroductionDesign Tool # 5Pulse CalculatorIntroduction: The pulse performance of resistors is important in inrush, protection and discharge applications.The way in which this performance is presented depends upon resistor technology. Wirewound resistors havean energy capacity in Joules which depends on ohmic value, but not on short pulse duration. Thick and thin filmresistors have a peak power depending on pulse duration. However, the energy capacity is not fixed and thereis less dependence on ohmic value.In order to relate the pulses experienced in an application to the pulse performance stated on the datasheet,it is necessary to calculate peak power for film or energy for wirewound. Common exponential pulse shapes mustbe converted to rectangular pulses of equivalent energy as rectangular pulses are generally used to characteriseresistor performance. Finally, if pulses are continuous, the mean power dissipation must be calculated so as toensure that the power rating is not exceeded.The calculators on sheets 2 and 3 perform these tasks and provide links to relevant Welwyn product data.For further technical help visit the Welwyn website:Welwyn Websiteor contact:info@welwyn-tt.comS J OxleyThe data and formulae in this file are believed to be correct but are provided for guidance only and no liability is accepted for consequences of errors.

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Single PulseSingle Pulse CalculatorColour CodeINPUTALTERNATIVEOUTPUTRESISTORResistor Value (ohms)PULSE AMPLITUDEPeak Voltage Vpk (V)OR Peak Current (A)6PULSE LENGTHRectangular Pulse Duration Tp (ms)OR Exponential Decay Pulse Time Constant T (ms)OR (Dis)charged Capacitor Value (uF)10Peak Power of Pulse is0Wfor effective duration of0msPulse Energy is0JFor data and application notes on pulse withstanding resistors:Pulse Withstanding ChipsDouble Sided ChipsSMD WirewoundAxial WirewoundClick hereClick HereClick hereClick here

The ohmic value of the resistor being exposed to pulse stress.Peak pulse voltage - an instantaneous value in the case of an exponential pulse. Leave this blank if entering Peak Current.Peak pulse current - an instantaneous value in the case of an exponential pulse. Only used if Peak Voltage is left blank.The duration of a rectangular pulse. Leave blank if pulse is exponential.Time constant (RC) of exponential pulse. Only used if Pulse Duration is left blank.Capacitance giving rise to exponential pulse. Only used if Pulse Duration and Time Constant are both left blank.Peak pulse power - an instantaneous value in the case of an exponential pulse.Rectangular pulse duration, or 1/2 the RC time constant of an exponential pulse (which has equal energy.)Total energy contained in the pulse, converted to heat in the resistor.A single pulse condition relates to pulses which are sufficiently infrequent as to make mean power negligible. In other words, the resistor cools completely to ambient temperature between successive pulses.A subsidiary of TT electronics plcTimeVoltageVpk -TpSingle PulseTVpk/2.7 -RectangularExponentialClick hereClick hereClick hereClick Here

Continuous PulsesContinuous Pulse CalculatorColour CodeINPUTALTERNATIVEOUTPUTRESISTORResistor Value (ohms)0.033CONTINUOUS BACKGROUND DISSIPATIONBackground Voltage Vbg (V rms)0.21.2121212121OR Background Current (A rms)PULSE AMPLITUDEPeak Voltage Vpk (V)0.5529.2334545455OR Peak Current (A)PULSE LENGTHRectangular Pulse Duration Tp (ms)57Peak Power of Pulse is9.2334545455WOR Exponential Decay Pulse Time Constant (ms)for effective duration of57msOR (Dis)charged Capacitor Value (uF)Pulse Energy is0.5263069091JPULSE FREQUENCYPulse Repetition Frequency (Hz)Mean Power is1.3950076121WOR Pulse Repetition Period Tpr (s)2.50E+002.5Duty Cycle is2.3%0.0For data and application notes on pulse withstanding resistors:Pulse Withstanding ChipsDouble Sided ChipsSMD WirewoundAxial WirewoundClick hereClick HereClick hereClick here

The ohmic value of the resistor being exposed to pulse stress.Continuous voltage present between pulses, if any. Leave this blank if entering Background Current.Continuous current present between pulses, if any. Only used if Background Voltage is left blank.The duration of a rectangular pulse. Leave blank if pulse is exponential.Peak pulse voltage - an instantaneous value in the case of an exponential pulse. Leave this blank if entering Peak Current.Peak pulse current - an instantaneous value in the case of an exponential pulse. Only used if Peak Voltage is left blank.Time constant (RC) of exponential pulse. Only used if Pulse Duration is left blank.Capacitance giving rise to exponential pulse. Only used if Pulse Duration and Time Constant are both left blank.Number of pulses per second. Leave blank if entering Repetition Period.Number of seconds between the starts of successive pulses. Only used if Repetition Frequency is left blank.Peak pulse power - an instantaneous value in the case of an exponential pulse.Rectangular pulse duration, or 1/2 the RC time constant of an exponential pulse (which has equal energy.)Total energy contained in each pulse, converted to heat in the resistor.Average power dissipated due to pulses plus background.Pulse duration as a proportion of the repetition period.A subsidiary of TT electronics plcA continuous pulse condition relates to pulses which are repeated sufficiently frequently to give cumulative heating. In this case the mean power dissipation must be kept below the resistor power rating.TimeVoltageVbg -Vpk -TpContinuous PulsesTprClick hereClick hereClick hereClick Here