Dissipation factor
In
quality factor
, which represents the "quality" or durability of oscillation.
Explanation
lumped element model includes a lossless ideal capacitor in series with a resistor termed the equivalent series resistance (ESR) as shown below.[1] The ESR represents losses in the capacitor. In a good capacitor the ESR is very small, and in a poor capacitor the ESR is large. However, ESR is sometimes a minimum value to be required. Note that the ESR is not simply the resistance that would be measured across a capacitor by an ohmmeter. The ESR is a derived quantity with physical origins in both the dielectric's conduction electrons and dipole relaxation phenomena. In dielectric only one of either the conduction electrons or the dipole relaxation typically dominates loss.[2]
For the case of the conduction electrons being the dominant loss, then
where
- is the dielectric's bulk conductivity,
- is the lossless permittivity of the dielectric, and
- is the angular frequency of the AC current i,
- is the lossless capacitance.
If the capacitor is used in an
reactive
power oscillating in the capacitor, or
When representing the electrical circuit parameters as vectors in a
loss tangent
tan δ where
Alternatively, can be derived from frequency at which loss tangent was determined and capacitance
Since the in a good capacitor is usually small, , and is often expressed as a percentage. [citation needed]
approximates to the power factor when is far less than , which is usually the case.
will vary depending on the dielectric material and the frequency of the electrical signals. In low
dielectric constant (low-κ
), temperature compensating ceramics, of 0.1–0.2% is typical. In high dielectric constant ceramics, can be 1–2%. However, lower is usually an indication of quality capacitors when comparing similar dielectric material.
See also
References
- ^ "Basic Considerations: DF, Q, and ESR". Archived from the original on 2009-08-22. Retrieved 2008-11-29.
- ISBN 0-471-58551-3