This is a general set of guidelines and recommendations for reducing capacitor power dissipation with increasing ambient temperature.
Recall that depending on the dielectric used the value of a capacitor also changes over temperature.
Refer to this chart for Capacitor Value Change by Temperature per dielectric
General Recommendations:
Capacitors should be derated between 30 and 60% depending on the
material's maximum ambient temperature.
Ceramic capacitors should have a voltage derating factor of 0.60 [110C
max]. [Ceramic capacitor manufacturers]
Glass Dielectric, a voltage derating factor of 0.50 [110C max].
Plastic Film Dielectric, a voltage derating factor of 0.60 [85C
max].
Tantalum Foil a voltage derating factor of 0.50 [70C max]. [Tantalum capacitor manufacturers]
Tantalum Solid a voltage derating factor of 0.30 to 0.50 [70C max / 110C
max].
Derate via Device [Voltage rating] / derate factor = maximum applied
voltage ~ Voltage applies to sum of AC ripple and DC voltages.
Tantalum capacitors should be de-rated as much as possible, more so when
used in low-impedance circuits [by-pass]. When Tantalum capacitors are
used in charging/discharging or switching current circuits, the derate
factor should be 30% [or more], and a series resistor should be used to limit
the current.
The reliability [Failure Rate] of Tantalum capacitors is given by the
following equation: F = FU x FT x FR x
FB
FU = Applied Voltage / Rated Voltage.
FT = Operating Temperature
FR = Series Resistance. FB = Basic
Failure rate
The capacitor manufacture would need to be consulted to obtain the
correction factors. How ever, the correction factors increase with
increasing Temperature, Applied Voltage, and failure rate, but decrease
as the series resistance is increased. The correction factor
[FU] is equal to one for an applied voltage equal to
the rated voltage, but reduces to 0.06 if the capacitor is derated by
50%, and drops to 0.001 if the capacitor voltage is de-rated by 30% of
applied voltage [the applied voltage is 30% of the rated voltage]. The
correction factor [FT] is equal to one for an operating
temperature of 85oC, and drops to 0.2 for a temperature of
55oC. An example of the Basic Failure rate
[FB] might be 1%/1000 hours. The correction factor
[FR] is equal to one for a resistance of 0.1 ohms, and
drops to 0.2 for a series resistance of 1 ohm.
Rule-of-Thumb
Capacitor Stress Ratio = Operating Voltage / Rated Voltage = 75% of operational limits
The Stress Ratio is the same as a Derating Factor
Packaging Considerations:
Package size has a direct relation to power dissipation. The larger the components package the more power the device can dissipate.
Axial Leaded Devices
Metal Can Devices
Surface Mount Devices [SMD]
Common Surface Mount sizes; 0201, 0402, 0603, 0805, 1206, 1210, and 1812.
There are other Standard chip sizes: SMD Capacitor Case Sizes
A manufacturers list of Capacitors
Due to the low capacitive reactance, at high frequencies and with high capacitances, the continuous duty current will usually be reached at a voltage below the maximum rated voltage. Similarly, due to the high capacitive reactance at low frequencies and with low capacitances, the maximum voltage will often be reached before the rated current. Necessary care should be taken to ensure that neither current nor voltage exceed the derated value established by the derating requirements specified for each capacitor type.
When AC operation is required, the peak ac voltage plus any DC bias shall not exceed the derated values established by the derating requirements.
Back to the main Component Derating page for guidelines and temperature curves.
Engineering Key words: Component Derating, Derate, Capacitor, Sizing, Rated Temp, Temperature, Guide, Guideline, Example, Class.
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