Dentro de los parámetros fundamentales que debemos considerar al momento de ensayar o seleccionar un capacitor electrolítico es el valor de su Resistencia Serie Equivalente (ESR). En el mundo de las reparaciones, una enorme cantidad de fallas presentes en los equipos electrónicos son generadas por los capacitores electrolíticos y la pérdida de su apropiada ESR. Nos podemos encontrar con capacitores que poseen un valor muy bueno (o aproximado al nominal) de su capacidad y sin embargo son los causantes de miles de problemas e inconvenientes por haber perdido su ESR.
Uno de los principales motivos de fallas en los equipos actuales es la degradación de los capacitores electrolíticos que intervienen en las distintas etapas que componen el dispositivo. Retirar todos los electrolíticos sospechosos de un equipo, para realizarles los ensayos correspondientes, nos llevará a escenarios muy complejos. Los capacitores que pierden su ESR pueden conservar el valor de capacidad (en uF) y con un capacímetro convencional caeríamos en el engaño de creer que todo está bien cuando en realidad, muchos capacitores estarán en mal estado. Por otro lado, la incomodidad y la pérdida de tiempo desalientan a cualquiera en este emprendimiento. Además, la posibilidad de un error al reinstalar los capacitores en buen estado siempre existe y un capacitor electrolítico polarizado de manera inversa provoca explosiones nada agradables que pueden desembocar en peores problemas, respecto a los iniciales.
Más Sobre ESR.
The basics of capacitors are explained in this technical column.
Today's column describes frequency characteristics of the amount of impedance |Z| and equivalent series resistance (ESR) in capacitors.
Understanding frequency characteristics of capacitors enables you to determine, for example, the noise suppression capabilities or the voltage fluctuation control capabilities of a power supply line. Frequency characteristics are therefore important parameters that are essential for circuit design. This column describes two types of frequency characteristics: impedance |Z| and ESR.
1.Frequency characteristics of capacitors
The impedance Z of an ideal capacitor (Fig. 1) is shown by formula (1), where ω is the angular frequency and C is the electrostatic capacitance of the capacitor.
Figure 1. Ideal capacitor
Figure 2. Frequency characteristics of an ideal capacitor
In actual capacitors (Fig. 3), however, there is some resistance (ESR) from loss due to dielectric substances, electrodes or other components in addition to the capacity component C and some parasitic inductance (ESL) due to electrodes, leads and other components. As a result, the frequency characteristics of |Z| form a V-shaped curve (or U-shaped curve depending on the type of capacitor) as shown in Figure 4, and ESR also shows frequency characteristics for values equivalent to loss.
Figure 3. An actual capacitor
Figure 4. An example of |Z|/ESR frequency characteristics of an actual capacitor
The reason why |Z| and ESR form curves like those shown in Figure 4 can be explained as follows.
Low-frequency region: |Z| in regions with a low frequency decreases inversely with frequency, similar to the ideal capacitor. ESR shows a value equivalent to dielectric loss from delay of polarization in the dielectric substance.
Near the resonance point: As the frequency rises, ESR resulting from parasitic inductance, electrode resistivity and other factors causes |Z| behavior to stray from that of an ideal capacitor (red broken line) and reach a minimum value. The frequency at which |Z| is the minimum value is called the self-resonant frequency, and at this time, |Z|=ESR. Once the self-resonant frequency is exceeded, the element characteristic changes from capacitor to inductor, and |Z| starts to increase. The region below the self-resonant frequency is called the capacitive region and the region above is called the inductive region.
ESR is affected by loss caused by the electrode in addition to dielectric loss.
High-frequency region: In frequency zones even higher than the resonance point, |Z| characteristics are determined by parasitic inductance (L). |Z| in the high-frequency region approaches formula (2) and increases proportionately with frequency.
As for ESR, electrode skin effects, proximity effects and other effects begin to appear.
From Wikipedia, the free encyclopedia
In physics, the dissipation factor (DF) is a measure of loss-rate of energy of a mode of oscillation (mechanical, electrical, or electromechanical) in a dissipative system. It is the reciprocal of quality factor, which represents the "quality" or durability of oscillation.Electrical potential energy is dissipated in all dielectric materials, usually in the form of heat. In a capacitor made of a dielectric placed between conductors, the typical lumped element model includes a lossless ideal capacitor in series with a resistor termed the equivalent series resistance (ESR) as shown below. 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 a dielectric only one of either the conduction electrons or the dipole relaxation typically dominates loss. For the case of the conduction electrons being the dominant loss, then
- is the dielectric's bulk conductivity,
- is the angular frequency of the AC current i,
- is the lossless permittivity of the dielectric, and
- is the lossless capacitance.
When representing the electrical circuit parameters as vectors in a complex plane, known as phasors, a capacitor's dissipation factor is equal to the tangent of the angle between the capacitor's impedance vector and the negative reactive axis, as shown in the diagram to the right. This gives rise to the parameter known as the loss tangent δ where
Since the DF in a good capacitor is usually small, δ ~ DF, and DF is often expressed as a percentage.
DF approximates to the power factor when is far less than , which is usually the case.
DF will vary depending on the dielectric material and the frequency of the electrical signals. In low dielectric constant (low-k), temperature compensating ceramics, DF of 0.1% to 0.2% is typical. In high dielectric constant ceramics, DF can be 1% to 2%. However, lower DF