Nemco Electronics Performance Info - Manual (Page 6)

General Performance Information
z AC Operation Ripple ratings for all devices can be calculated with the power dissipation rating and ESR rating of the com-
ponent. Calculated ripple ratings are based on a free air environment. In an AC application heat is generated within the capac-
itor by both the AC component of the signal (which will depend upon the signal form, amplitude and frequency), and by the
DC leakage. For practical purposes the DCL is insignificant. Permissible AC ripple voltage and current are related to ESR
and power dissipation capability. Actual power dissipated can be calculated from the following formula:
P = I 2 R = E 2 R (substituting I = E )
Z 2 Z
I = rms ripple current (amperes)
R = equivalent series resistance at specified frequency (ohms)
E = rms ripple voltage (volts)
P = power dissipated (watts)
Z = impedance at frequency under consideration (ohms)
Using this formula it is possible to calculate the maximum a.c. ripple current and voltage permissible for a particular
application.
Maximum allowable rms ripple voltage or ripple current may be determined taking into account three limiting factors.
1. The d.c. working voltage of the capacitor must not be exceeded by the sum of the positive peak of the applied a.c. voltage
and the d.c. bias voltage.
2. The sum of the applied d.c. voltage and the negative peak of the a.c. voltage must not allow a voltage reversal in excess
of that defined in “Reverse Voltage”.
3. The power dissipated in the ESR of the capacitor must not exceed the power dissipation rating for the case size.
NOTE: Temperature derating factors to power dissipation ratings for case size must be considered in calculations.
RIPPLE CURRENT RIPPLE VOLTAGE
I
RMS
= P
MAX
T
DF
E
RMS
= (X
L
- X
C
) 2 + (ESR) 2 • I
RMS
ESR
E
RMS
= rms ripple voltage
I
RMS
= rms current (amps) X
L
= 2
πƒh ƒ = Frequency (of interest)
P
MAX
= Power Dissipation rating (watts) h = Inductance (Negligible at Low
ƒ)
T
DF
= Temperature derating factor X
C
= ½ πƒc ƒ = Frequency (of interest)
c = Capacitance (Farad)
ESR = ESR (at ƒ of interest)
I
RMS
= rms ripple current
√
√
85°C = 0.90
125°C = 0.40