CBSE Class 12-science Answered

Transistor as a Switch

In a grounded-emitter transistor circuit, such as the light-switch circuit, the base and collector current rise exponentially as the base voltage raises, and the collector voltage drops because of the collector load resistor. The equations are as given below:

V_RC = I_CE × R_C, the voltage across the load (the lamp with resistance R_C)

V_RC + V_CE = V_CC, the supply voltage shown as 6V

If V_CE could fall to 0 (perfect closed switch) then Ice could go no higher than V_CC / R_C, even with higher base voltage and current and the transistor is then said to be saturated. Thus, the values of input voltage can be chosen such that the output is either completely off, or completely on.

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