Cut-off and Saturation of BJT

Students seem sometimes not quite understanding what is the condition of BJT cut-off and BJT saturation. These are the two basic modes of operation of transistors and is used widely as ON and OFF or HIGH and LOW in digital circuits. Here is the basic diagram of a transistor circuit:

Saturation and Cut-off condition of BJT
Saturation and Cut-off condition of BJT

Depending on the driving input VBB. The base current determine how the BJT is being cut-off ( very little base current or none or VBB=0V) or BJT is saturated (too much base current, over-driving the BJT).

BJT ON, or SATURATED is when VCE=0V, IC=ISAT (or IMAX), ISAT means saturation current. In this example ISAT=10V/200 ohms.

BJT OFF, or IC=0, VCE(OFF)=VCC. In this case VCE=10V.

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