BJT Transistor as an Electronic Switch: Experiment with LED and DC Motor, Study notes of Earth science

Download BJT Transistor as an Electronic Switch: Experiment with LED and DC Motor and more Study notes Earth science in PDF only on Docsity!

ELECTRONIC DEVICES AND CIRCUITS (LAB)

Experiment No. 13: BJT Transistor as a Switch

Experiment No. 13

BJT Transistor as a Switch

To observe the action of a BJT transistor as an electronic switch.

✓

To measure the voltage across the BJT transistor when it is in ON or OFF state.

Equipment Required:

DMM

• • DC Power Supply =5V (fixed)
  • Function Generator (having a facility of variable duty cycle)
  • Resistor: 1-kΩ [Qty =2]
  • Power Resistor: 22-Ω/5W [Qty =1]
  • Si Diode (1N4001) [Qty =1]
  • Transistor: 2N4401 [Qty =1]
  • LED [Qty =1]
  • DC Motor [Qty =1] Theory:

Transistor is a semiconductor device which can be used for switching purposes in

electronic networks. A BJT transistor can be driven back and forth between saturation and cutoff

region to act as a switch as demonstrated in Figure 1.

Figure 1

Part 1: BJT Transistor as a switch to glow LED

a. The schematic of Figure 11 shows how a BJT transistor is used to switch the LED. The

circuit operation of schematic diagram can be categorized in two different modes.

b. When the input voltage (Vin) is equal to 0V, BJT is in cutoff region. In the cutoff region

(both junctions are reversed biased), the voltage across the collector-emitter junction is

very high. Since input voltage (Vin) is zero, both base and collector currents are zero,

it to protect the circuit. By switching the transistor in cutoff and saturation regions, we

can turn ON and OFF the motor repeatedly. It is also possible to regulate the speed of

the motor from standstill to full speed by switching the transistor at variable duty cycle.

We can generate this variable duty cycle from a microcontroller IC or from a control

circuitry.

Procedure:

a. Construct the circuit of Figure 3 on the breadboard.

Figure 3

b. Set the input voltage (Vin) equal to 0V. Observe the rotation of DC motor. Is it rotating or

not?

Motor is not rotating due to input voltage is zero.

c. Set the input voltage (Vin) equal to 5V. Observe the rotation of DC motor. Is it rotating or

not?

Motor is now rotating.

d. Using function generator, apply an input square wave signal (Vin) having two amplitudes 5V

(peak) and -5V (peak). Set the frequency of square wave to 100-Hz with duty cycle equal to

50%. Observe the rotation of DC motor. Is it rotating or not?

Motor is rotating.

Part 2: BJT Transistor as a switch to drive DC Motor

OBSERVATIONS

For observing ON & OFF state of Motor, the frequency should be very small 100mHhz so that

the time period increased. And the On and OFF state of motor can be easily observed.

CONCLUSION

In this lab we understand the Use of BJT transistor as a switch .We performed LED and motor

experiments with it and observed its ON and OFF state