The most popular electronic circuits contains resistors, capacitors and inductors. Theoretically a capacitor can be considered as a pure capacitor with capctitive properties, but in practical a capacitor will also have some resistance and inductance features coupled with it. It is like a parasite so we call it parasitic resistance and prastic inductance. The unwanted resistance and inductance exist in the capacitors which decrease its pure capacitor properties.
For simply capacitor design, the value of parasitic reistance and inductance will be very small, it could be neglected in circuit design in this case. However, for high power and high frequency capacitor design, the complicated internal connection is applied, where the parasitic inductance and resistance come along with it which refer to equivalent resistance(ESR) and equivalent series inductance (ESL) . Therefore in high power or high frequency application, the ESR and ESL can very critical factors which may cause lower power efficiency and output results.
- ESR in capacitors
The resistance comes from the dielectric material, leakage in an insulator or in the separator. Base on this, the ESR will have different values in difference types of capacitors based on its capacitance value and construction.
- How to measure ESR in capacitors?
The resistance is not a pure DC resistance due to the capacitor property. Capacitor block DC and pass the AC. Therefore, a specific ESR meters are necessary. These typical ESR meters use alternating current, such as square wave in a specific frequency across the capacitor. Based on the change in frequency of the signal the ESR value of the capacitor can be caculated.
Another way to caculater ESR of the capacitor is to measure the ripple voltage and ripple current of the capacitor and then the retio of both will give the value of ESR in the capacitor.
- How ESR affects the capacitor performance?
ESR value will affect the capacitor output. Since ESR is a resitive that cause some energy to be lost in the form of heat. High ESR capacitor will come with unusual heat problem in high current application, result in capacitor lifespan decrease, as well as malfuncation for the whole equipment. For example, in power supplies where high current is concerned, the low ESR capacitor are required for filtration purposes.
For instance, in high frequency application, typically ranging from hundreds of MHz to several GHz, ESR plays a vital role in power delivery factors.
- ESL in capacitor
ESL causes a magnetic field to buildup in devices. This buildup of magnetic field interferes with how the current rises to the peak and falls back.
Same as ESR, there are a stray resistance as well as stray inductance.Normally, ESL is highly dependable on the current loop; increase in current loop also increases the ESL in capacitors. The distance between the lead termination and circuit connecting point (including pads or tracks) also influences the ESL in capacitors because increased termination distance also increases the current loop resulting in high Equivalent series inductance.
- How to measure ESL of a capacitor?
The capacitor designer usually provide with ESL value. It can be observed from inpedance versus frequency graph. The impedance of capacitor changes when the frequency across the capacitors is changed.
By derteming a inflection point from the graph, the formula can be used: Frequency = 1 / (2π√(ESL x C))
- How ESL affects the capacitor?
The capacitors output degrades by increased ESL. ESL causes a magnetic field to buildup in devices. This buildup of magnetic field interferes with how the current rises to the peak and falls back. Especially in high-frequency applications. ESL increases circuit impedance, which may result in increased loss during signal transmission and affect circuit overall performance. Also contribute to waveform disorder which may cause signal distortion and affect accurate transmission.
Due to the large ESL value, the response speed of the capacitor is limited, especially at high frequency signals, the response time is prolonged, affecting the dynamic performance of the circuit.
- The Importance of ESR and ESL value for capacitors
As we know from above, the ESR and ESL are crutial and unpleasant to a capacitor. Because it usually cause a performance reduction in electronic circuit, especialy in high power, high frequency and high current applications. High ESR value contribute to power loss of capacitor, as well as brings noises and high voltage drop.
So for some specific industry, like induction heating application, a non-inductive winding and construction is required. The induction heating capacitors usually apply for the polypropylene film as the dielectric and aluminum foil as the electrode , non-inductive winding construction, epoxy resin coated or insulation oil immersed.
Lower ESR and ESL capacitors are preferred as output filters. High quality low ESR and low ESL capacitors are benficial for smooth output and stable power delivery to the Load.
The need to maintain high performance, miniaturization and low cost is the main motive towards new types of capacitors. By using advanced technologies, capacitor manufacturers are driving to develop advanced technologies to meet the higher performance requirements of nowdays’ power electronics. High-performance film capacitors with very low ESLs are increasingly replacing conventional capacitors.
We are progressively advancing capacitor manufacturing technology to meet the performance demanded by today’s high power,high frequency, high current electronics.
