APRIL 1999 This note discusses relationship current handling, pow

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APRIL 1999 This note discusses relationship current handling, pow

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CAPACITOR CURRENT POWER
APRIL 1999
This note discusses relationship current handling, power dissipation, applied voltage maximum rated voltage multi-layer ceramic capacitor. Either maximum voltage rating maximum power dissipation part limits maximum current through capacitor. capacitance value operating frequency determine which becomes governing limit. lower values capacitance given frequency, lower frequencies given capacitance, voltage limitation generally reached before power dissipation limitation. voltage limitation depends capacitors reactive impedance (Xc), where power dissipation depends resistive impedance equivalent series resistance (ESR) capacitor. calculated Xc=1/[2 FC], where frequency hertz Capacitance farads. maximum allowable peak current flow through capacitor (without exceeding capacitors rated voltage) calculated I=Er/Xc, where capacitors rated voltage, peak current flow amperes. actual current flow through capacitor calculated I=Ea/Xc, where applied working voltage. following examples illustrate these variables effect voltage/current limitation some specific capacitors given frequency. EXAMPLE Volt capacitor used 1000 MHz: Xc=1/[2(3.14)(1000x10 6)(0.1x10 -12)]=1591 ohms; Ipeak=500/1591=0.315 Apeak 0.22 Arms. exceed this current, will exceed voltage rating capacitor. EXAMPLE Volt capacitor used 1000 MHz: Xc=1/[2(3.14)(1000x10 6)(1.0x10 -12)]=159 ohms; Ipeak=500/159= 3.15 Apeak Arms. exceed this current, will exceed voltage rating capacitor. EXAMPLE Volt capacitor used 1000 MHz: Xc=1/[2(3.14)(1000x10 6)(10x10 -12)]=15.9 ohms; Ipeak=500/15.9=31.5 Apeak 22.2 Arms. This current level actually never reached because this frequency, values over approximately limited power dissipation capacitor. IMPORTANT NOTE: power dissipation limited data assumes infinite heat sink capacitor terminations. heat transferred ignored. 10pF, 500V capacitor 1000 would actually power limited about 7Apeak which about Arms. this current level temperature capacitor would rise about degrees reliable operation, would practical limit current Arms with decent heat sink, even 3Arms there very good heat sink terminations.
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APRIL 1999 This note discusses relationship current handling, pow

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