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Describewith suitableblock diagrams,action of pn-junctiondioide under forwardand reversebias conditions . Also draw I-V characteristics . |
Answer» Solution :FORWARD Bias :When a battery is connectedacross the junctionsuch that p side is connectedto the positiveterminaland n sideto thenegativeterminalof the source,the p-n junctionis said to be forwardbiased . The appliedvoltageopposesthe junctionp.d. and forvalues of the applied voltage GREATER than the junctionand constitutesa currentin an externalcircuit.This currentriseslinearlywith the appliedvoltagebeyondthe knee voltage . Thus a forward biasedp-n junctionoffers a low resistance.  Reverse bias : When batteryis connected acrossthe junctionsuch that p side is connectedto the negative terminaland n side to the positive terminal , the p-n junction is said to be reverse biased In this case , the appliedvoltage adds to the EFFECT of junction p.d.and hencemajority carrierscannot cross the junction.The currentthroughthe circuit is practically zero.Thus ,reveres bias offersa very highresistancebut small CURRENT of the order of a few mA flowsthrough the circuit due to the minoritycarriersin the p and nregions. As the appliedvoltageis graduallyincreaseda very large currentresultsat a particularvoltage . This voltage is CALLED thebreak down or cut-in voltage. 
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