Electronics

beenuseren · Joined: 06 Jul 2006 Posts: 3

Hi,

I have a doubt.

This is with respect to transistor.

In CE configuration, how does the increase in base current reduces the width of depletion region in the CB junction? can anyone explain this theoritically?

thanks,
beenu

neon · Joined: 25 Feb 2006 Posts: 570

I am going to give a try Electrons in the base region wander ramdomly while repelling one another called [diffiusion]rapidly spreading throughtout that region. some that wander close to the collector junction are collected because of the strong electric field. If the base region is narrow only a few can reach the base connection and the rest are collected. Collected electrons comprise E to C current whereas those not collected comprise undesired E to B curent. Another source of undersired E to C current results from holes emitted from the base region into the emiter region. If current into the base is sufficient it will reduce the space charge density close to the collector and it is insuffiecient to neutralize the fixed charge density of donors and acceptors.Eventualy forward biasing both junction and current will flow by directionaly.

beenuseren · Joined: 06 Jul 2006 Posts: 3

thanks Neon for the reply.

However, as you said " If current into the base is sufficient it will reduce the space charge density close to the collector ".

My question that sentence itself, how does the sufficient current into the base reduce the space charge density close to the collector? Whats physics behind this?

neon · Joined: 25 Feb 2006 Posts: 570

Physics of how they do it I don't know exactly or how they dope the crystals or the mechanical inplemantation. Try the library physic dept. I am not a physic major so while i got the idea on how they work I never searched for the nitty gritty. But collector capacitance is defined as Cc alpha Vc minus square root of n. n changes value with the type of tanx. IT has all to do with the depletion area in the collector width why I DON'T KNOW. take care.

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