1, the filtering effect, in the power circuit, the rectifier circuit of the AC into pulsating direct current, and after a rectifier circuit access large-capacity electrolytic capacitor using the charge and discharge characteristics (storage effect), so that the rectified pulsating DC voltage becomes relatively stable DC voltage. In practice, in order to prevent the parts supply voltage generating circuit changes due to load changes, so that at the output of the power supply and the power input side of the load connected with an electrolytic capacitor generally tens to hundreds of microfarads. Since the large-capacity electrolytic capacitor generally have certain inductance, high frequency and pulse interference signal can not effectively filter out, so at both ends in parallel with a capacity of 0.001--0.lpF capacitor to filter out high frequency and pulse interference.
2, coupling: transmission and amplification process in the low-frequency signal, in order to prevent interaction quiescent operating point before and after the two circuits, often using capacitive coupling in order to prevent the low-frequency component signal loss in rhyme too large, generally representing a total capacity use. large electrolytic capacitors.
Then we have to look at the electrolytic capacitor judging method
Electrolytic capacitor common faults, reduce capacity, capacity disappeared, and a drain short-circuit breakdown, where capacity change is caused by the gradual drying up due to the use of electrolytic capacitors or electrolytic solution during its internal placement, and the breakdown and leakage is generally added voltage is too high or poor quality caused itself. The quality of the power supply capacitor determine the general use multimeter to measure the resistance profile specific method: two pins shorted capacitor discharge, then the positive electrolytic capacitor with a multimeter black pen. Red pen then negative (for multimeter, when measured with a digital multimeter table pen intermodulation), normal table.
The needle should first swing in the direction of small resistance and then gradually return until infinity. The larger the hands of swings or returns more slowly, indicating that the greater the capacity of the capacitor, otherwise explain the smaller capacity capacitor such as hands somewhere in the middle means no change, indicating that this capacitor leakage, such as resistance indicated value is small or zero, it indicates that this capacitor is short-circuit breakdown. battery voltage multimeter use is generally low, so when measuring low-voltage capacitors more accurate, and when a high voltage capacitor, playing despite Measurement normal, but there is a possibility of leakage or breakdown occurs when high voltage is applied.
More needs to understand the use of electrolytic capacitors Note:
1, electrolytic capacitors due to positive and negative polarity, and therefore can not be reversed in the circuit connection use. In the power supply circuit, the output voltage electrolytic capacitor being connected to the power output of the positive, negative ground, when a negative voltage output connected to the output of the negative electrode, positive ground. When the power supply circuit filter capacitor polarity reverse, because the capacitor filtering effect is greatly reduced, causing the power supply output voltage fluctuations on the one hand, on the other hand because of the reverse energized to make this point is equivalent to a heat resistance of the electrolytic capacitor. When the reverse voltage exceeds a certain value, the reverse leakage resistance and capacitance will become very small, so energized work soon, so that the capacitor can overheat and burst damage.
2. Add the voltage across the electrolytic capacitor can not exceed its allowable working voltage, in the actual circuit design should leave a margin depending on the circumstances, in the design of the power supply.
When the filter capacitor, if the AC voltage of 220 to rectifier transformer secondary voltage up to 22V, this time selecting a withstand voltage of 25V electrolytic capacitors generally meet the requirements.
However, if the AC power supply voltage fluctuations are large and likely to rise to more than 250V, the best choice for electrolytic capacitor voltage above 30V.
3, electrolytic capacitors in the circuit should not be close to power the heating element to prevent the electrolyte accelerated by heat leaving dry.
4, for positive and negative polarity of the signal filtering, can take two electrolytic capacitors connected in series with the polar method, as a non-polar capacitor.
5. The capacitor case, the auxiliary lead between the terminals and the positive and negative electrodes and circuit boards must be completely isolated.
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