[Professional terminology and hardware] 1, equivalent series resistance ESR Overview and the benefits of a certain amount of ESR capacitors in the voltage regulator circuit

I. ESR overview of equivalent series resistors

ESR is the abbreviation for the equivalent series resistance, the "equivalent series resistor". The ideal capacitor itself will not have any energy loss, but in fact, because the material that makes the capacitance has a resistor, the capacitance of the insulating medium is lossy. This loss is external and behaves like a resistor in series with a capacitor, so it is called an "equivalent series resistor". Some capacitors also have an ESR value (equivalent series resistance), the lower the ESR, the smaller the loss, the greater the output current, the higher the quality of the capacitor.

Analysis of the causes of ESR

There is an ESR in any capacitor, and there is always an electrical resistor between the capacitance electrodes, such as the metal pin resistance, the electrode plate resistance, and the connection resistance between them. Aluminum electrolytic capacitors also include resistors that exist in wet electrolyte solutions, and resistors in aluminum oxides (hydrated alumina) that contain high levels of "water". Represents the formation factor of electrolytic capacitance ESR.

Iii. reasons for choosing low ESR Capacitors

Now electronic technology is moving towards the design of low voltage and high current circuit, the supply of voltage to the components of the trend is getting lower, but the demand for power has not decreased. According to the P=UI formula, to obtain the same power, the voltage is reduced, it is necessary to increase the current. For example, Intel, AMD's latest CPU, the voltage is less than 2V, and the previous 3, 4V compared to the voltage is much lower. But on the other hand, because of the proliferation of transistors and frequencies, the power consumption of these chips is increasing, and the demand for electric current is higher. For example, both power is 70W CPU, the former voltage is 3.3V, the latter voltage is 1.8V. The former, then, is i=p/u=70w/3.3v=21.2a, while the latter's current is i=p/u=70w/1.8v=38.9a, nearly twice times the former current. In the case of a higher current through the capacitance, if the capacitance of the ESR value can not be maintained in a small range, then the higher ripple voltage (the ideal output DC voltage should be a horizontal line, and the ripple voltage is the crest and trough of the horizon), so that the engineer in the design, To use the smallest ESR capacitor.

The relationship between the ESR value and the ripple voltage can be expressed in equation V=r (ESR) XI. The V in this formula represents the ripple voltage, and R indicates that the esr,i of the capacitor represents the current. Higher ESR capacitors, as internal heat becomes more severe, the electrolyte dries up faster, forms a vicious cycle, and leads to circuit failure. It can be seen that when the current increases, the ripple voltage increases exponentially even when the ESR remains constant, so capacitors with lower ESR values are imperative.

Four or one benefits of quantitative ESR

However, there are some good aspects in the existence of the equivalent series resistors. For example, in the voltage regulator circuit, there is a certain ESR capacitance, when the load transients, will immediately generate fluctuations and trigger feedback circuit action, the rapid response to sacrifice a certain transient performance at the expense of the subsequent rapid adjustment, especially the power tube response speed is relatively slow, but also in the volume of the capacitor, Severely limited capacity. This situation is more common in some three-terminal regulators or similar circuits where the MoS tube is used as an adjustment tube, but a low ESR capacitor can reduce overall performance.

V. Variation factors of ESR

First, the resistance of the pin and capacitor electrode plates to the metal can be ignored because they are very small.

The two common factors that cause high ESR are: 1) bad electrical connections, 2) The drying of the electrolytic solution.

for 1) New and old electrolytic capacitors are likely to occur;

for 2) Most of these occur on old electrolytic capacitors.

The poor electrical connection problem is mainly due to the fact that the pin leads connected to the inside of the capacitor are not aluminum metal materials, and aluminum has always been a non-weldable material.

For aluminum electrode plate material and copper pin material, its electrical connection mainly uses so-called "welding" and mechanical crimping method. But both of these methods produce higher ESR. ESR also increases with the evaporation of electrolyte water.

This article helps to:ESR Understanding (section I), ESR benefits and the benefits of ESR capacitors in a regulated Circuit (section fourth, general use of 0402, 0603 is basically ceramic capacitors, voltage regulator circuit with electrolytic capacitors, However, with the progress of the technology some new voltage regulators chip capacitor ESR is not much required)very important point!

[Professional terminology and hardware] 1, equivalent series resistance ESR Overview and the benefits of a certain amount of ESR capacitors in the voltage regulator circuit