ESR, Dissipation Factor, and Quality Factor
The summarized losses in ceramic capacitors are ohmic AC losses. DC losses will be specified as "leakage current" or “insulating resistance” and are negligible for an AC specification. These AC losses are nonlinear, and may depend on frequency, temperature, age, and for some special types, on humidity. The losses result from two physical conditions,
- the line losses with the internal supply line resistances, the contact resistance of the electrode contact, the line resistance of the electrodes
- the dielectric losses out of the dielectric polarzation
The largest share of these losses in larger capacitors is usually the frequency dependent ohmic dielectric losses. Regarding the IEC 60384-1 standard, the ohmic losses of capacitors should be measured at the same frequency used to measure the capacitance. These are:
- 100 kHz, 1 MHz (preferred) or 10 MHz for ceramic capacitors with CR ≤ 1 nF:
- 1 kHz or 10 kHz for ceramic capacitors with 1 nF < CR ≤ 10 μF
- 50/60 Hz or 100/120 Hz for ceramic capacitors with CR > 10 μF
The measuring results of the summarized resistive losses of a capacitor may be specified either as equivalent series resistance (ESR), as dissipation factor(DF, tan δ), or as quality factor (Q), depending on the application requirements for the capacitor types.
Class 2 ceramic capacitors are mostly specified with the dissipation factor tan δ. The dissipation factor is determined as the tangent of the reactance - and the ESR, and can be shown as the angle δ between imaginary and the impedance axis in the above vector diagram, see paragraph “Impedance”.
If the inductance is small, the dissipation factor can be approximated calculated as:
Class 1 ceramic capacitors with very low losses are specified with a dissipation factor and additional often with a quality factor (Q). The quality factor is defined as the reciprocal value of the dissipation factor.
The Q factor represents the effect of electrical resistance, and characterizes a resonator's bandwidth relative to its center or resonant frequency . A high Q value is for resonant circuits a mark of the quality of the resonance.
In accordance with the applicable standards IEC 60384-8/-21/-9/-22 ceramic capacitors may not exceed the following dissipation factors
| Temperature coefficient of the ceramic |
Maximum dissipation factor |
|---|---|
| 100 ≥ α > −750 | tan δ ≤ 15 • 10−4 |
| −750 ≥ α > −1500 | tan δ ≤ 20 • 10−4 |
| −1500 ≥ α > −3300 | tan δ ≤ 30 • 10−4 |
| −3300 ≥ α > −5600 | tan δ ≤ 40 • 10−4 |
| ≤ −5600 | tan δ ≤ 50 • 10−4 |
| For capacitance values < 50 pF the dissipation factor may be larger |
|
| Rated voltage of the capacitor |
maximum dissipation factor |
|---|---|
| ≥ 10 V | tan δ ≤ 350 • 10−4 |
| For capacitance values < 50 pF the dissipation factor may be larger |
|
The ohmic losses of ceramic capacitors are frequency, temperature, and voltage dependent. Additionally, class 2 capacitors are time dependent because of aging. The different ceramic materials have different changes in the losses over the temperature range and the operating frequency. The changes in class 1 capacitors are in the single-digit range while class 2 capacitors have much higher changes.
Read more about this topic: Ceramic Capacitor, Electrical Characteristics
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