I studied in sedra and smith 'microelectronic circuits' that in saturation, beta gets changed and becomes less than the original beta (which is constant for a transistor). How is it possible? Because in saturation the drop at collector base junction is approx 0.2V which is larger than that in active mode, and applying KVL in the outer circuit (let's say in common emitter amplifier) gives more value of Ic in active mode. So what is this contradication? I also want to know whether kvl rule is applicable for active region or not?
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\$\begingroup\$ This question has been asked before: electronics.stackexchange.com/questions/51405/… \$\endgroup\$– The PhotonMar 9, 2013 at 6:47
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\$\begingroup\$ You have a mistaken understanding here: "in saturation the drop at collector base junction is approx 0.2V which is larger than that in active mode". In forward active operation the collector-base voltage will be greater than the saturation voltage (0.2 V). \$\endgroup\$– The PhotonMar 9, 2013 at 6:50
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2\$\begingroup\$ Your question is really hard to read without proper interpuntion / capitals. \$\endgroup\$– jippieMar 9, 2013 at 10:12
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2 Answers
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I think you are asking how beta can be less in saturation than in active mode when it appears from a calculation of Ic that Ic is highest in saturation. If that is your question, the answer is that in saturation, if you increase the base current this fails to further increase the collector current. So in betasat = Ic/Ib, Ib increases but Ic does not, hence betasat reduces.
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Because of increase in Resistance. RC increases, and IC failes to increase with increasing IB.
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2\$\begingroup\$ This is really unclear. Try writing in complete sentences. \$\endgroup\$ Apr 9, 2013 at 4:39