It seems when all the hardware engineers about the quality of the electrolytic capacitor, finally there will always be a capacitor, to choose the ESR parameters of the low point of the company but, according to the requirements of the purchaser to purchase capacity, can only choose a good brand, because the buyer knew that ESR was a good brand of capacitance parameters is low. Why not ESR capacitor marked, temperature characteristics not marked. Let's first analyze the parameters of the capacitance.
First, ESR.
As an output rectifier filter capacitor of switching power supply, capacitance is often the primary choice. The capacitance of aluminum electrolytic capacitors can meet the requirements, while the ESR is relatively high. ESR can be reduced by multiple parallel methods. The larger capacitance can also be selected to reduce the ESR
ESR is the most important performance parameter in high frequency electrolytic capacitors. Many capacitor suppliers emphasize the performance characteristic of "LOW ESR", that is, the ESR value is very small. So, how can we correctly understand the LOW ESR practical significance? Now due to the development of electronic technology, the supply voltage to the hardware is showing more and more low trend, such as FPGA, DSP, RAM series power supply voltage are very low, some circuit voltage is less than 2V, compared to the previous 3, hundreds of 4V to low voltage much. But, on the other hand these chips because the transistor and the frequency of explosion, power demand is increasing, so according to the P=UI formula, the current requirement of these devices is more and more high.
For example, on the computer motherboard, for example, two power consumption is also 70W's CPU, the former is 3.3V, and the latter is 1.8V. So, the current of the former is about I=P/U=70W/3.3V about 21.2A. The current of the latter is I=P/U=70W/1.8V=38.9A, nearly twice as much as the former. In the current through the capacitor more and more high, if the capacitor ESR value can keep on a smaller scale, it will produce the ripple voltage higher than in the past (the output DC voltage of the ideal should be a horizontal line, and the ripple voltage is horizontal line wave peak and valley).
In addition, even if the ripple voltage of the same effect on the low voltage circuit is larger than in the case of a high voltage. For example, 3.3V MCU, 0.2V ripple voltage small proportion is not enough to form a deadly effect, but the 1.8V power supply for the FPGA, DSP, is also the ripple voltage of 0.2V, the error of judgment the proportion is enough to cause a digital circuit.
Then the relationship between ESR value and the ripple voltage is? We can be represented by the following formula:
V=R (ESR) x I
This formula in V that the ripple voltage R, said capacitor ESR, I current. As you can see, when the current increases, even if the ESR remains unchanged, the ripple voltage will be doubled, the capacitance lower ESR value is imperative. This is why the current board and other hardware devices used on the capacitor, more and more emphasis on low ESR reasons.
Two. Again why manufacturers are reluctant to mark out ESR?
Considering the production process of electrolytic capacitors, the resistance of the electrolyte is the main part of the equivalent series resistance (ESR) of the aluminum electrolytic capacitor. Most of the producers of aluminum electrolytic capacitors do not give ESR data. The main reason is that the ESR of aluminum electrolytic capacitors is too large compared with other dielectric capacitors. For example, 1 u F/16V ordinary aluminum electrolytic capacitor, its ESR is about 20 omega; 100 mu F aluminum electrolytic capacitor, its ESR is also between 1.5~2 Omega.
It is thought that such data will certainly affect the application's confidence in the application of aluminum electrolytic capacitors. Therefore, in a certain way, the application of aluminum electrolytic capacitor is a helpless choice. It will affect the application of aluminum electrolytic capacitor.
Most aluminum electrolytic capacitors manufacturers do not give ESR data for the commonly used aluminum electrolytic capacitors. For the low ESR aluminum electrolytic capacitors used in switching power supply or the larger pin capacitors, the data is given.
Three. By the way, there are several reasons why the capacitance parameters are not marked.
In fact, as a hardware engineer, there is always such a feeling that the parameters of the capacitance are divided into "explicit parameters" and "recessive parameters". The so-called "dominant parameter" is the basic parameters printed on the surface of the capacitor, which can be found directly after we see a capacitor. For example, capacitance capacity (such as "470 F", etc.), capacity deviation range, temperature range, voltage value (such as "16V").
The so-called "recessive parameter" is the parameter that we need to query according to the model of the capacitance. For example, we often say that the ESR value has become an important parameter to distinguish capacitance performance. We can not see this parameter on capacitor. We have to go to relevant website to inquire by capacitance type. There are many similar parameters of the same fate as ESR, including the following:
1., rated ripple current. The rated ripple current will generate loss on its ESR and cause the aluminum electrolytic capacitor to generate heat. The limit of ripple current is the rated ripple current value. It is defined as the maximum ripple current of the rated life time of the aluminum electrolytic capacitor at the maximum working temperature. Most aluminum electrolytic capacitors manufacturers do not give the rated ripple current data for the commonly used aluminum electrolytic capacitors. The data for the low ESR aluminum electrolytic capacitors or the larger pin capacitors for switching power supply are given.
2. ripple current can tolerate value; explain the existing above.
3., the tangent (TAN) of the loss angle is equivalent to the ratio of reactive power to active power, which is related to the quality of the capacitor and the amount of heat. The smaller the value, the better the capacitor performance.
4. leakage current value; no matter how large the insulator is, there will always be a slight current leakage of capacitance, and this value represents the specific leakage. And this parameter manufacturer is not willing to specify in detail.
5. ESL equivalent inductor; equivalent inductor ESL will often become a part of ESR, and ESL can also cause some circuit failures, such as tandem resonance, etc. But relative capacity, the ratio of ESL is too small, the probability of problems is very small, coupled with the progress of capacitor manufacturing technology, now has gradually ignored ESL, and ESR as the main reference factor besides capacity.
In fact, care of these capacitive parameters, is concerned with the service life of capacitance, not much specific, other materials or online have a large number of introductions.
As a result, most manufacturers of aluminum electrolytic capacitors do not give ESR data. The main reason is that the ESR of aluminum electrolytic capacitors is too large compared with other capacitors. Among the many manufacturers of aluminum electrolytic capacitors in the world, the equivalent series resistance (ESR) of the aluminum electrolytic capacitors that they are produced is very small. There is no such data (such as many domestic manufacturers of aluminum electrolytic capacitors), while others are in need of technical secret, of course also feel their production of aluminum electrolytic capacitor of the ESR value is too large, too shy, out indelicate.