電解電容在電路中的作用

1，濾波作用，在電源電路中，整流電路將交流變成脈動(dòng)的直流，而在整流電路之后接入一個(gè)較大容量的電解電容，利用其充放電特性，使整流后的脈動(dòng)直流電壓變成相對(duì)比較穩(wěn)定的直流電壓。在實(shí)際中，為了防止電路各部分供電電壓因負(fù)載變化而產(chǎn)生變化，所以在電源的輸出端及負(fù)載的電源輸入端一般接有數(shù)十至數(shù)百微法的電解電容．由于大容量的電解電容一般具有一定的電感，對(duì)高頻及脈沖干擾信號(hào)不能有效地濾除，故在其兩端并聯(lián)了一只容量為0.001--0.lpF的電容，以濾除高頻及脈沖干擾．
2，耦合作用：在低頻信號(hào)的傳遞與放大過(guò)程中，為防止前后兩級(jí)電路的靜態(tài)工作點(diǎn)相互影響，常采用電容藕合．為了防止信號(hào)中韻低頻分量損失過(guò)大，一般總采用容量較大的電解電容。

二、電解電容的判斷方法

    電解電容常見(jiàn)的故障有，容量減少，容量消失、擊穿短路及漏電，其中容量變化是因電解電容在使用或放置過(guò)程中其內(nèi)部的電解液逐漸干涸引起，而擊穿與漏電一般為所加的電壓過(guò)高或本身質(zhì)量不佳引起。判斷電源電容的好壞一般采用萬(wàn)用表的電阻檔進(jìn)行測(cè)量．具體方法為：將電容兩管腳短路進(jìn)行放電，用萬(wàn)用表的黑表筆接電解電容的正極。紅表筆接負(fù)極(對(duì)指針式萬(wàn)用表，用數(shù)字式萬(wàn)用表測(cè)量時(shí)表筆互調(diào))，正常時(shí)表針應(yīng)先向電阻小的方向擺動(dòng)，然后逐漸返回直至無(wú)窮大處。表針的擺動(dòng)幅度越大或返回的速度越慢，說(shuō)明電容的容量越大，反之則說(shuō)明電容的容量越小．如表針指在中間某處不再變化，說(shuō)明此電容漏電，如電阻指示值很小或?yàn)榱悖瑒t表明此電容已擊穿短路．因萬(wàn)用表使用的電池電壓一般很低，所以在測(cè)量低耐壓的電容時(shí)比較準(zhǔn)確，而當(dāng)電容的耐壓較高時(shí)，打時(shí)盡管測(cè)量正常，但加上高壓時(shí)則有可能發(fā)生漏電或擊穿現(xiàn)象．
三、電解電容的使用注意事項(xiàng)

1、電解電容由于有正負(fù)極性，因此在電路中使用時(shí)不能顛倒聯(lián)接。在電源電路中，輸出正電壓時(shí)電解電容的正極接電源輸出端，負(fù)極接地，輸出負(fù)電壓時(shí)則負(fù)極接輸出端，正極接地．當(dāng)電源電路中的濾波電容極性接反時(shí)，因電容的濾波作用大大降低，一方面引起電源輸出電壓波動(dòng)，另一方面又因反向通電使此時(shí)相當(dāng)于一個(gè)電阻的電解電容發(fā)熱．當(dāng)反向電壓超過(guò)某值時(shí)，電容的反向漏電電阻將變得很小，這樣通電工作不久，即可使電容因過(guò)熱而炸裂損壞．
2．加在電解電容兩端的電壓不能超過(guò)其允許工作電壓，在設(shè)計(jì)實(shí)際電路時(shí)應(yīng)根據(jù)具體情況留有一定的余量，在設(shè)計(jì)穩(wěn)壓電源的濾波電容時(shí)，如果交流電源電壓為220~時(shí)變壓器次級(jí)的整流電壓可達(dá)22V，此時(shí)選擇耐壓為25V的電解電容一般可以滿足要求．但是，假如交流電源電壓波動(dòng)很大且有可能上升到250V以上時(shí)，最好選擇耐壓30V以上的電解電容。
3，電解電容在電路中不應(yīng)靠近大功率發(fā)熱元件，以防因受熱而使電解液加速干涸．
4、對(duì)于有正負(fù)極性的信號(hào)的濾波，可采取兩個(gè)電解電容同極性串聯(lián)的方法，當(dāng)作一個(gè)無(wú)極性的電容。Electrolytic capacitors in the circuit in the role of
1, filtering effect, in a power supply circuit, rectifier circuit to the AC into pulsating DC, while in the rectifier circuit after access to a larger capacity electrolytic capacitor, the charge and discharge characteristics, make rectified pulsating DC voltage into a relatively stable DC voltage.In practice, in order to prevent the each part of the circuit power supply voltage due to the load change and produce change, so the output end of the power supply and the load of the power input end is generally connected with tens to hundreds of micro method for the electrolytic capacitor. Due to the large capacity electrolytic capacitor has certain inductance, high frequency and impulse interference signals can effectively filter therefore, in the parallel connected with both ends of a capacity of 0.001--0.lpF capacitor, to filter out high frequency and pulse interference.
2, coupling effect: in the low frequency signal transmission and the amplification process, in order to prevent the before and after the two stage circuit static working point of mutual influence, often using capacitive coupling. In order to prevent signal in the rhyme low-frequency loss is too large, generally the larger capacity of electrolytic capacitors.
In two, the judging method of electrolytic capacitor
Electrolytic capacitor common fault, reduced capacity, capacity disappear, short circuit breakdown and leakage, in which capacity change for electrolytic capacitor in use or placed in the process of its internal electrolyte dry up gradually, and breakdown and leakage for the voltage too high or itself caused by poor quality.Judging power capacitor is generally use a multimeter to measure resistance profile. The concrete method is: will the capacitance of the two pin is shorted to discharge, with a multimeter the black table document connected electrolytic capacitor anode.The red pen is connected with the negative pole (the pointer multimeter, using the digital multimeter measuring pen intermodulation), normal hand shall first apply to small resistance direction swing, then gradually returned to infinite big.Hands swinging larger amplitude or return more slowly, that the capacity of the capacitor is more big, otherwise, the capacity of the capacitor is smaller. As hands in somewhere in the middle of no change, the capacitor leakage, such as resistance indicator values are very small or zero, it indicates that the capacitor has breakdown short circuit for million. Use the table using the battery voltage is generally very low, so the measurement of low voltage capacitor is more accurate, and when the capacitor voltage is high, although measurements of the normal play, but coupled with high pressure is possible leakage or breakdown phenomenon.
Three, note the use of electrolytic capacitor
1, electrolytic capacitors with positive and negative polarity, thus used in the circuit can not be reversed.In a power supply circuit, output positive voltage electrolytic capacitor anode is connected to the power output end, negative ground, output negative voltage output end is negative, positive ground. When the power supply circuit of the filter capacitor polarity reverse connection, due to capacitor filtering effect is greatly reduced, on one hand the power supply output voltage wave, on the other hand, because of the inverse power make it the equivalent of a resistance electrolytic capacitor heating. When the reverse voltage exceeds a certain value, the capacitor leakage resistance will become very small, so the electric work soon, can make the capacitance due to overheat and burst damage.
2 plus in the electrolytic capacitor voltage should not exceed the allowable working voltage, in the design of practical circuit should be based on specific circumstances leave some margin, in the design of regulated power supply filter capacitor, if AC power is 220~ voltage transformer secondary rectifier voltage up to 22V, the selection pressure for 25V electrolytic capacitor can generally be to meet the requirements. However, if AC power supply voltage fluctuation and is likely to rise to more than 250V, the best choice of pressure above 30V electrolytic capacitor.
In 3, the electrolytic capacitors in the circuit should not close to the high power heating elements, to prevent the electrolyte accelerated by heat to dry up.
4, the positive and negative polarity signal filtering, can take two electrolytic capacitors homopolar series method, as a non polar capacitor.