Owner's manual

EXPERIMENT #17: STANDARD TRANSISTOR BIASING CIRCUIT

Connect the circuit and press the switch while turning the variable resistor from right to left (from 0Ω to 50kΩ). The 100kΩ

and variable 50kΩ are a voltage divider that sets the voltage at the transistor base. If this voltage is less than 0.7V then

the transistor will be off and no current will flow through the LED. As the base voltage increases above 0.7V a small base

current starts to flow, which is amplified to produce a larger collector current that lights the LED. As the base voltage

continues to increase the transistor becomes saturated and the LED brightness will not increase further.

This circuit will normally be used with the voltage divider set so that the transistor is turned on but is not saturated. Although

this circuit does not have many applications by itself, when a small alternating current (AC) signal is applied to the base

then a larger copy of the signal will appear at the collector - a small-signal amplifier!

+9V

1kΩ

100kΩ

3.3kΩ

50kΩ

VARIABLE

RESISTOR