ESR/ESL/capacitance

ESR is equivalent series resistance. The emergence of ESR caused the behavior of capacitors to deviate from the original definition. ESR is equivalent "series" resistance, which means that connecting two capacitors in series will increase this value, while connecting them in parallel will reduce it. Another concept similar to ESR is ESL, which is equivalent series inductance. ESL (Equivalent Series Inductance) is the equivalent inductance parameter. It and ESR (equivalent resistance) are two parameters of capacitors. A capacitor will produce various impedances and inductive reactances due to its construction. The more important ones are ESR equivalent series resistance and ESL equivalent series inductance - this is the basis of capacitive reactance. Capacitors provide capacitance, why do they need resistance? Therefore, ESR and ESL are also required to be low... low; but low ESR/low ESL are usually high-end series. Early rolled capacitors often have high ESL, and the larger the capacitance of the capacitor, the greater the ESL. ESL often becomes part of ESR, and ESL can also cause some circuit failures, such as series resonance. However, compared with the capacity, the proportion of ESL is too small, and the probability of problems is very small. In addition, with the advancement of capacitor manufacturing technology, ESL has gradually been ignored, and ESR has been used as the main reference factor besides capacity.

ESL is equivalent inductance, and ESR is equivalent resistance. Whether it is resistors, capacitors, inductors, diodes, transistors, MOS tubes, or ICs, we must consider their equivalent capacitance and inductance values ​​at high frequencies.

By the way, capacitors also have a quality factor Q similar to inductors. This factor is inversely proportional to ESR and is related to frequency, so it is rarely used.

Circuit failures caused by ESR are usually difficult to detect, and the impact of ESR is easily overlooked during the design process. A simple approach is that when simulating, if the specific parameters of the capacitor cannot be selected, you can try to artificially connect a small resistor in series with the capacitor to simulate the impact of ESR. Generally, the ESR of tantalum capacitors is usually below 100 milliohms, while that of aluminum electrolytic capacitors is higher than this value. The ESR of some types of capacitors can even be as high as several ohms.

The relationship between ESR value and ripple voltage can be expressed by the formula V=R(ESR)×I. In this formula, V represents the ripple voltage, R represents the ESR of the capacitor, and I represents the current. It can be seen that when the current increases, the ripple voltage will increase exponentially even if the ESR remains unchanged.

The larger the capacitance, the smaller the ESR, just like the larger the cross-sectional area of ​​a conductor, the smaller the resistance. Therefore, multiple small capacitors are often connected in parallel in a circuit to reduce the ESR value.