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Electronic Circuits

TRANSISTOR PRINCIPLES & APPLICATIONS

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Electronics

Principles & ApplicationsSixth Edition

Chapter 5Transistors

Electronic Circuits

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Transistors as a Solid State SwitchOBJECTIVES

Transistors as a Solid State SwitchOBJECTIVES

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

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How do transistor switches work?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 dissipationPC = VCE x IC

PC = 0 x IC = 0 W(or PC = VCE x 0 = 0 W)

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LOADLOADLOAD

DRIVER

The driver output is zero volts, IB = 0 and ILOAD = 0The driver output is positive, IB > 0 and the load is onThe driver output is zero volts, IB = 0 and the load is off

RCE @ WRCE @ 0 WRCE @ W

NPN SWITCH

Electronic Circuits

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LOAD

DRIVER

The driver output is off (high Z): the resistorpulls the base voltage up so that VBE = 0

PNP SWITCH

The driver output goes low: the voltage dropacross the resistor makes VBE negative

The driver output is off (high Z): the resistorpulls the base voltage up so that VBE = 0

LOADLOAD

Electronic Circuits

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PNP SWITCH WITH NPN DRIVER

LOADLOADLOAD

Electronic Circuits

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A

B

C

D

A B C D

STEPPER MOTOR

Enhancement modepower MOSFETs

used as switches

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Transistors as a Solid State SwitchTransistors 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