2. 1 Electronic Circuits TRANSISTOR PRINCIPLES & APPLICATIONS

3. 2Electronics Principles & Applications Sixth Edition Chapter 5 Transistors Electronic Circuits

4. 3 Transistors as a Solid State Switch OBJECTIVES Describe how a transistor can be used as a switch. Determine if a transistor is turning a circuit on or off using voltage measurements. Construct a solid-state switching circuit. Measure circuit voltages in a transistor switching circuit. Describe how a transistor can be used as a switch. Determine if a transistor is turning a circuit on or off using voltage measurements. Construct a solid-state switching circuit. Measure circuit voltages in a transistor switching circuit. Electronic Circuits

5. 4 How do transistor switches work? Can be viewed as solid state relays: they are either ON or they are OFF. BJT switches are characterized by: high base current (or no base current) low resistance from collector to emitter (or very high resistance) low collector dissipation P C = V CE x I C P C = 0 x I C = 0 W (or P C = V CE x 0 = 0 W)

6. 5 LOAD DRIVER The driver output is zero volts, I B = 0 and I LOAD = 0 The driver output is positive, I B > 0 and the load is onThe driver output is zero volts, I B = 0 and the load is off R CE    R CE  0  R CE    NPN SWITCH Electronic Circuits

7. 6 LOAD DRIVER The driver output is off (high Z): the resistor pulls the base voltage up so that V BE = 0 PNP SWITCH The driver output goes low: the voltage drop across the resistor makes V BE negative The driver output is off (high Z): the resistor pulls the base voltage up so that V BE = 0 LOAD Electronic Circuits

8. 7 PNP SWITCH WITH NPN DRIVER LOAD Electronic Circuits

9. 8 A B C D ABCD STEPPER MOTOR Enhancement mode power MOSFETs used as switches

10. 9 Transistors as a Solid State Switch Describe how a transistor can be used as a switch. Determine if a transistor is turning a circuit on or off using voltage measurements. Construct a solid-state switching circuit. Measure circuit voltages in a transistor switching circuit. Describe how a transistor can be used as a switch. Determine if a transistor is turning a circuit on or off using voltage measurements. Construct a solid-state switching circuit. Measure circuit voltages in a transistor switching circuit. Electronic Circuits