Transistor as a switch
Transistor as a switch is an interactive experiment in Electronic Components, a free simulation from StudyFi Lab that runs right in your browser.
A small base current I_B controls a large collector current I_C. With no base current the transistor is off (cut-off). In the active region I_C = β·I_B, where β is the current gain (here 100). When β·I_B would be more than the load allows, the transistor saturates: U_CE falls almost to zero and it acts like a closed switch — the LED is fully on.
Try this: Close the base switch, set R_B = 100 kΩ and slowly raise U_B: watch I_C grow together with β·I_B and then stop in saturation.
Frequently asked questions
What does the “Transistor as a switch” experiment show?
A small base current I_B controls a large collector current I_C. With no base current the transistor is off (cut-off). In the active region I_C = β·I_B, where β is the current gain (here 100). When β·I_B would be more than the load allows, the transistor saturates: U_CE falls almost to zero and it acts like a closed switch — the LED is fully on.
How do I try “Transistor as a switch”?
Close the base switch, set R_B = 100 kΩ and slowly raise U_B: watch I_C grow together with β·I_B and then stop in saturation.
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