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SMOOTHING CIRCUITS:THE RESERVOIR CAPACITOR

SMOOTHING CIRCUITS: THE RESERVOIR CAPACITOR II. V1 REPRESENTS THE P.D. DEVELOPED ACROSS THE C1 AND I IS THE RECTIFIER (FULL-WAVE) CURRENT.INITIALLY THE RECTIFIER INPUT P.D. CAUSES CURRENT TO FLOW THROUGH R AND AT THE SAME TIME C1 BECOMES CHARGED ALMOST TO THE PEAK VALUE OF THE INPUT AS SHOWN BY OA

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SMOOTHING CIRCUITS:THE RESERVOIR CAPACITOR

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    1. SMOOTHING CIRCUITS:THE RESERVOIR CAPACITOR TO PRODUCE STEADY D.C. FROM THE VARYING BUT UNIDIRECTIONAL OUTPUT FROM A HALF-WAVE OR FULL –WAVE RECTIFIER, SMOOTHING IS NECESSARY. THE SIMPLEST SMOOTHING CIRCUIT CONSISTS OF A LARGE CAPACITOR, 16µF OR MORE, CALLED A RESERVOIR CAPACITOR, PLACED IN PARALLEL WITH THE LOAD R. C1 IS THE RESERVOIR CAPACITOR AND ITS ACTION CAN BE FOLLOWED FROM THE DIAGRAM SHOWN IN WHICH V1 REPRESENTS THE P.D. DEVELOPED ACROSS C1 .

    2. SMOOTHING CIRCUITS: THE RESERVOIR CAPACITOR II V1 REPRESENTS THE P.D. DEVELOPED ACROSS THE C1 AND I IS THE RECTIFIER (FULL-WAVE) CURRENT. INITIALLY THE RECTIFIER INPUT P.D. CAUSES CURRENT TO FLOW THROUGH R AND AT THE SAME TIME C1 BECOMES CHARGED ALMOST TO THE PEAK VALUE OF THE INPUT AS SHOWN BY OA IN THE DIAGRAM. AT A, THE INPUT P.D. FALLS BELOW V1 AND C1 BEGINS TO DISCHARGE. IT CANNOT DO THAT THROUGH THE RECTIFIER SINCE THE POLARITY IS WRONG, BUT IT DOES THROUGH THE LOAD AND THUS MAINTAINS CURRENT FLOW BY ITS CHARGE STORING OR RESERVOIR ACTION.

    3. SMOOTHING CIRCUITS: THE RESERVOIR CAPACITOR III ALONG AB, V1 FALLS. AT B WHEN THE INPUT P.D. EQUALS THE VALUE TO WHICH V1 HAS FALLEN, RECTIFIER CURRENT I AGAIN FLOWS TO QUICKLY RECHARGE C1 TO THE PEAK P.D. AS SHOWN BY BC. THE CYCLE OF OPERATIONS IS THEN REPEATED. THE D.C. OUTPUT DEVELOPED ACROSS R IS V1 AND ALTHOUGH IT FLUCTUATES AT TWICE THE FREQUENCY OF THE SUPPLY, THE AMPLITUDE OF FLUCTUATION IS MUCH LESS THAN WHEN C1 WAS ABSENT.

    4. SMOOTHING CIRCUITS: RESERVOIR CAPACITOR ACTION THE SMOOTHING ACTION OF C1 ARISES FROM ITS LARGE CAPACITANCE MAKING THE TIME CONSTANT C1R LARGE SO THAT THE P.D. ACROSS IT CANNOT FOLLOW THE VARIATIONS OF INPUT P.D. A VERY LARGE VALUE OF C1 WOULD GIVE BETTER SMOOTHING BUT INITIALLY THE UNCHARGED RESERVOIR CAPACITOR WOULD ACT ALMOST AS A SHORT-CIRCUIT AND THE RESULTING SURGE OF CURRENT MIGHT DAMAGE THE RECTIFIER.

    5. THE CAPACITOR-INPUT FILTER CIRCUIT A RESERVOIR CAPACITOR HAS A USEFUL SMOOTHING EFFECT BUT IT IS USUALLY SUPPLEMENTED BY A FILTER CIRCUIT CONSISTING OF A CHOKE L (i.e. AN IRON-CORED INDUCTOR) HAVING AN INDUCTANCE OF ABOUT 15H AND A LARGE CAPACITOR C2 ARRANGED AS SHOWN IN THE TOP DIAGRAM. THE RESERVOIR CAPACITOR C1 AND THE FILTER CAPACITOR C2 MAY BE ELECTROLYTICS ENCLOSED IN THE SAME CAN.

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