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  • The role of electrolytic capacitor in the circuit design

    We shall know more about the role of electrolytic capacitor.

    1, Coupling effect: in transmission and amplification process of the low-frequency signal ,to prevent quiescent point of the front and back two level circuit from interaction effect,we often use the capacitive coupling.To prevent too large loss of the low frequency component of the signal in the signal ,we usually use electrolytic capacitors with larger capacity.

    2, The filtering effect: in the power circuit, a rectifying circuit makes alternating current into the pulsating direct current.After a rectifier circuit ,access electrolytic capacitor of larger capacity.Using the properties of charge and discharge makes pulsating direct current voltage become relatively stable direct current voltage.In order to prevent supply voltage of various parts of pcb manufacturing from change because of the change of electronic load, so the output of the power and the input of the power of the load generally have electrolytic capacitors of tens to hundreds of microfarads. Because large-capacity electrolytic capacitors generally have a certain inductance, which can not effectively filter out high frequency and pulse interference signal,so it has a capacitor with a capacity of 0.001–0.1 pF in parallel at both ends to filter out high frequency and pulse interference.

    The judging method of electrolytic capacitors

    Common faults of Electrolytic capacitor : 3)Breakdown , 5) Leakage. Capacity change is caused by the gradual drying of the its inner electrolyte solution during the its use or place.While breakdown and leakage are caused by too high voltage that is added ro by itself poor quality.

    Analyzing quality of the power capacitors of PCB prototype,we generally use the resistance of a multimeter to measure. Specific methods are: make two pins of capacitors short circuit ,to discharge,and then connect the positive of electrolytic capacitor with black pen of a multimeter ,connect the negative with red pen,which is for the pointer multimeter.If for digital multimeter,when measuring,the pens should have intermodulation. Normally hands should firstly swing in the direction of small resistance,then gradually return until infinity.If amplitude of swing of the hands is larger,or the return rate is slower,it indicates that the capacity of capacitor is greater.Otherwise, it indicates the capacity of capacitor is smaller.If the hand means no change somewhere in the middle,it indicates that this capacitor is leakage.If the resistance indicator value is very small or zero,it indicates that this capacitor is short-circuit breakdown.

    Voltage of Battery that multimeter uses is generally low,so it is more accurate when measuring low-voltage capacitors, and when measuring high-voltage capacitor,although the measurement is normal,but when coupled with high pressure,it may appear leakage or breakway.

    The use of electrolytic capacitors

    1) Voltage applied to both ends of the electrolytic capacitor can not exceed its allowable operating voltage. In the actual circuit design , a margin should leave depending on the circumstances.In the design of filter capacitor of stabilized voltage supply,if the voltage of AC power is 220v,secondary rectifier voltage of transformer can be up to 22v.When pcb prototype,using electrolytic capacitors of 25v can generally meet the requirements.However, if fluctuations of the AC power supply voltage are large and likely to rise to more than 250V, it is better to use the electrolytic capacitor of 30V or more.

    2)Electrolytic capacitor has polarity, so the circuit can not be reversed . In the power supply circuit, when the output voltage is positive,then the positive of electrolytic capacitors connect the output of power,and the negative connect the ground.when the output voltage is negative,then the positive connect the output ,and the negative connect the ground.When filter capacitor polarity of the power supply circuit reverse,because the filtering effect of the capacitor greatly reduce,which on the one hand cause fluctuation of power output voltage. On the other hand ,the reverse current makes electrolytic capacitors which is equivalent to resistance heat. When the reverse voltage exceeds a certain value, the reverse leakage resistance of capacitance will become very small,after power,it works soon,which can make the capacitor overheat, and then burst and damage.

    3) Electrolytic capacitors in the circuit should not be close to the heating element with high power, to prevent electrolyte solution from accelerated drying because of the heat.

    4) For the positive and negative polarity signal filtering ,we can use the method that two electrolytic capacitors connect in series with the same polarity,which can be treated as non-polar capacitor.

    5) Capacitor case, the auxiliary leads terminal, the positive and negative ,and the pcb board must be completely isolated.

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