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INTRODUCTION TO TRANSISTORS and common applications in mechatronics

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What is a Transistor?

A Transistor is an electronic device
composed of layers of a semiconductor
material which regulates current or
voltage flow and acts as a switch or gate
for electronic circuit.

FET Basics

• Advantages
– low power
– high gate impedance
– low S/D resistance
• Uses
– amplifier
– analog switch
• Design
– gate==base
– source==emitter
– drain ==collector

Power Transistors

• Generally
– Fabrication differences for dissipating more
heat
– Lower gain than signal transistors
• BJT
– essentially the same as a signal level BJT
– Power BJT cannot be driven directly by HC11
• MOSFET
– base (flyback) diode
– Large current requirements:
use parallel MOSFETs

H-bridge example –
Summary

• BJT design:
– Choose TIP31 (NPN) and TIP32 (PNP)
– Must size R to provide sufficient base current to saturate the
transistor
– Controller must supply high current to BJT
• MOSFET design:
– Choose FDN359AN(n-channel) and FDN360P(p-channel)
– Less parasitic power loss than BJT
– Just plug it in!
• HC11 issues:
– HC11 can’t supply negative voltage, so:
• Use only NPN or n-channel
• Control 1 & 3 together, 2 & 4 together