Electrolytic capacitor knowledge
1, the nominal parameters
Is the value listed on the capacitor shell.
* Capacitance, expressed in UF. Not much to say.
* Working voltage (working voltage) referred to as WV, should be the nominal safety value, that application circuit, shall not exceed this nominal voltage.
* Temperatures are mostly 85 degrees, 105 degrees. High temperature conditions (such as pure Class A amplifier) to the preferred 105 degrees nominal. Under normal circumstances the preferred high temperature coefficient for improving the performance of other parameters also have a positive help.
2, dissipation factor dissipation factor (DF)
Sometimes the DF value is also represented by the loss angle tan. DF value is high or low, and temperature, capacity, voltage, frequency ... ... have a relationship; when the same capacity, the higher the value of the lower DF pressure. The higher the frequency the higher the DF value, the higher the temperature the higher the DF value. DF value is generally not marked on the capacitor or the specification above. Select the capacitor in the DIY, you can give priority to select a higher voltage, such as the working voltage of 45V, the choice of 50V is not very reasonable. Although the use of 50V from the normal working voltage is not inappropriate, but from the DF value to consider the lack of some. The use of 63V or 71V pressure will have a better performance. Of course, the high price on the uneconomical.
Equivalent series resistance
ESR level, with the capacitor capacity, voltage, frequency and temperature ... are related to ESR requirements, the lower the better. When the rated voltage is fixed, the larger the capacity, the lower the ESR. When the capacity is fixed, the choice of high-rated voltage of the species can reduce the ESR. ESR is high at low frequencies, low ESR at high frequencies, and high temperatures can also cause ESR to rise. Equivalent series resistance ESR Many brands can be found from the specification sheet.
4, leakage current
A look to understand that is leakage! Aluminum electrolytic capacitors are the existence of leakage, which is the physical structure of the decision. Needless to say, the leakage current is, of course, the smaller the better. The higher the capacitor capacity, the greater the leakage current; reducing the operating voltage can reduce leakage current. In turn, the selection of higher pressure resistance of the species will also help reduce leakage current. Combined with the above two parameters, the same conditions, select the high pressure species is indeed a simple and feasible way; reduce internal resistance, reduce leakage current, reduce the loss angle, increase the life. Is really a lot of benefits, only the price will be higher. There is a saying, both electrolytic capacitors work at much lower than the rated voltage, because it can not be effective enough to maintain the electrode with the electrolyte between the depolarization effect, will lead to electrolytic capacitor polarization and reduce the ripple current, increasing Large ESR, and thus early aging. However, the premise of this statement is "much lower than the rated operating voltage", a number of long-term practical experience, select the rated nominal voltage of about 2/3 of the normal operating voltage, is more reasonable to *. Amateur cases can be electrolytic capacitor leakage current roughly estimate. The same capacity of the electrolytic capacitor in accordance with the rated voltage to withstand the charge, place a period of time before the voltage across the capacitor to detect the degree of decline. The lower the drop voltage, the smaller the leakage current.
5, ripple current Irac
Ripple current for stone machine filter circuit, is a very important parameter. The ripple current Irac is as high as possible. His level is related to the frequency of work, the higher the frequency Irac the greater the lower the frequency Irac smaller. Traditionally, we think we need to have a high ripple current at low frequencies in order to achieve good high-current discharge characteristics, making the low frequency more robust, flexible, and good control-driven characteristics; Of the ripple current on the sound of the positive help is also great, can make a better high-frequency extension and reduce the roughness.