tech notes SPEER ELECTRONICS, INC. ETS-054-D Limitations of Potential Pulsing on Metal Film Resistors KSE types ML, MF, RN, MS50SS and SN2C Surface mount rectangular flat level for flat chip resistors in chip resistors are susceptible to pulse applications. For Pulse Power limitations failure under some high voltage of KOA's ML, MF, RN, and conditions. In circuitry where there is a possibility of transient SN2C resistor types, please potentials, considerable high refer to the graph, fig. 1. Power voltage may be applied to a below that specified on the resistor for a short period of graph will, generally, not cause time. This bulletin is intended to any significant degradation of the resistor, but note that the aid the Design Engineer in determining a "safe" potential resistance value may vary (A) slightly due to repeated pulsing over a long period of time. The circuit designer should also be cognizant of the fact that the pulse voltage is limited even under the conditions on which the graph, fig. 1, is based. The maximum peak pulse voltage for a KOA thick film chip resistor isthe lessor of(A) or (B) below. (B) V peak = Po x R SN2C ML07, MF55 RN55, MS50SS ML20, MF60, RN60 Where, "Po" is the pulse limit power taken from the graph, "R" is the resistor value in ohms. The peak power is defined as the maximum power dissipated at any point in time regardless of the waveform shape. 600V 750V 750V 750V 1000V 1000V Po t T off PAGE 1 1/2000 Bolivar Drive P.O. Box 547 Bradford, PA 16701 USA WWW.KOASPEER.COM 814-362-5536 Fax 814-362-8883 tech notes SPEER ELECTRONICS, INC. ETS-054-D The pulse waveform, if other than a square wave, must first be converted to an approximated square wave as shown on the right. Wp Wp Approximate Wo Wp: Peak Power Wo: Rated Power t: Time to attenuate down to the rated power Wo O O t t/2 Wp Wp Approximate Wp Approximate Wo Wo Wo O O O t/2 t -Wp Wp: Peak Power Wo: Rated Power t: Time to attenuate down to the rated power PAGE 2 1/2000 Bolivar Drive P.O. Box 547 Bradford, PA 16701 USA WWW.KOASPEER.COM 814-362-5536 Fax 814-362-8883 tech notes SPEER ELECTRONICS, INC. The following design rules determine if derating of the Pulse Limit Power (Po) obtained from the graph isrequired for repetitive pulse applications Notes: 1. Graph pulse power (Po) is for ambient operating temperatures of 70oC or less. For ambient operating temperatures greater than 70oC, pulse power (Po) or (Pm) must be further derated by 1.18% per oC above 70oC in accordance with the power derating schedule of the resistor. ETS-054-D 1. If Toff < 4u Sec, or Toff < 5m Sec and (Toff/t) < 1, then the peak power is treated as continuous power and, therefore, Pm = the resistor's rated wattage. 2. If Toff is > 4u Sec, but is < 100u Sec, and (Toff/t) < 700, then Pm = Po x .01 x (Toff/t)0.7. 3. If Toff is > 100u Sec and (Toff/t) < 200, then Pm = Po x .01 x (Toff/t)0.85. 4. If Toff > 4u Sec but is < 100u Sec, and (Toff/t) > 700, or Toff is > 100u Sec and (Toff/t) > 200, then Pm = Po as obtained from the pulse power graph. Where: Pm = Po = Toff = t= Derated Pulse Power (W) Pulse Power from graph below (W) Off time between pulses (sec) Pulse width (sec), approximated as a square wave 2. If derated pulse power (Pm) is calculated to be less than the resistor's rated continuous power, the resistor's rated wattage should be used. PAGE 3 8 '97 Bolivar Drive P.O. Box 547 Bradford, PA 16701 USA WWW.KOASPEER.COM 814-362-5536 Fax 814-362-8883 tech notes PULSE LIMIT POWER SPEER ELECTRONICS, INC. ETS-054-D Pulse Limit Power (One Pulse) KOA Type ML20, MF60 and RN60 100W Pulse Power (PO) 10W 1W 0.1W 0.1µSec 1µSec 10µSec 100µSec 1MSec Pulse Width (t) page 5 1/00 Bolivar Drive P.O. Box 547 Bradford, PA 16701 USA WWW.KOASPEER.COM 814-362-5536 Fax 814-362-8883 tech notes PULSE LIMIT POWER SPEER ELECTRONICS, INC. ETS-054-D Pulse Limit Power (One Pulse) KOA Type ML20, MF60 and RN60 100W Pulse Power (PO) 10W 1W 0.1W 1mSec 10mSec 100mSec 1Sec 10Sec Pulse Width (t) page 5 1/00 Bolivar Drive P.O. Box 547 Bradford, PA 16701 USA WWW.KOASPEER.COM 814-362-5536 Fax 814-362-8883 tech notes PULSE LIMIT POWER SPEER ELECTRONICS, INC. ETS-054-D Pulse Limit Power (One Pulse) KOA Type ML07, MF55, RN55, MS50SS 100W Pulse Power (PO) 10W 1W 0.1W 0.1µSec 1µSec 10µSec 100µSec 1mSec Pulse Width (t) page 6 1/00 Bolivar Drive P.O. Box 547 Bradford, PA 16701 USA WWW.KOASPEER.COM 814-362-5536 Fax 814-362-8883 tech notes PULSE LIMIT POWER SPEER ELECTRONICS, INC. ETS-054-D Pulse Limit Power (One Pulse) KOA Type ML07, MF55, RN55, MS50SS 100W Pulse Power (PO) 10W 1W 0.1W 1mSec 10mSec 100mSec 1Sec 10Sec Pulse Width (t) page 7 1/00 Bolivar Drive P.O. Box 547 Bradford, PA 16701 USA WWW.KOASPEER.COM 814-362-5536 Fax 814-362-8883 tech notes PULSE LIMIT POWER SPEER ELECTRONICS, INC. ETS-054-D Pulse Limit Power (One Pulse) KOA Type SN2C 10 Ohm and above 100W Pulse Power (PO) 10W 1W 0.1W 0.1µSec 1µSec 10µSec 100µSec 1mSec Pulse Width (t) page 8 1/00 Bolivar Drive P.O. Box 547 Bradford, PA 16701 USA WWW.KOASPEER.COM 814-362-5536 Fax 814-362-8883 tech notes PULSE LIMIT POWER SPEER ELECTRONICS, INC. ETS-054-D Pulse Limit Power (One Pulse) KOA Type SN2C 10 Ohm and above 100W Pulse Power (PO) 10W 1W 0.1W 1mSec 10mSec 100mSec 1Sec 10Sec Pulse Width (t) page 9 1/00 Bolivar Drive P.O. Box 547 Bradford, PA 16701 USA WWW.KOASPEER.COM 814-362-5536 Fax 814-362-8883