About output characterstics of a npn transistor in CE configuration

[keep@science]

Q1.when transistor[NPN transistor in CE configuration] is in saturated state ,then,in output characteristic curve on increasing voltage across collector -emitter,the current in the output circuit increases linearly but my confusion is that we know that in saturation state transistor's base -collector junction is forward biased ; on increasing collector emitter voltage there is no effect on base-emitter voltage but it increases voltage across base collector such that it opposes the forward bias condition so, according to my view it should decrease the current in the output circuit.

Q2.when transistor is in cut off state , the input voltage is zero and in output characteristic
curve it is shown that current in the output circuit should also be zero whatever the value of collector base voltage;but according to my view due to low potential at input circuit and high at output circuit the current should flow from input circuit to output through collector base junction in reverse bias condition and there should be a current in output circuit.

Q3.why in active state of transistor output current for a fixed value of collector emitter voltage,increases on increasing current in input circuit?

 

[Valerie Park]

A1. In the saturated state of a NPN transistor, the base-collector junction is forward biased, so increasing the voltage across the collector-emitter will increase the current in the output circuit. This is because the base-collector junction has a negative temperature coefficient, meaning that as the voltage across the collector-emitter increases, the current flowing through the base-collector junction also increases and this causes the current in the output circuit to increase. A2. In the cut-off state, the input voltage is zero and the base-collector junction is reverse biased. As such, the current in the output circuit should be zero regardless of the value of the collector-base voltage. This is because there is no current flowing through the base-collector junction and therefore no current can flow from the input to the output circuit. A3. In the active state, the transistor is operating in the linear region and the output current for a fixed value of collector-emitter voltage increases with increasing input current. This is because increasing the input current causes an increase in the current flowing through the base-collector junction and therefore an increase in the current flowing through the output circuit.