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NAIT 2000
The Use of Transistor
Technology in
Manufacturing
Thomas E. Scott, Ph.D.
Ohio University
For your own personal copy of this presentation
www.ent.ohiou.edu/~tscott
Solid State Switching
January 3, 2000
EXTRA!!! EXTRA!!
EMR is DEAD
As the 21st century commences, we bid fond
adieu to one of the mainstays of industrial
electronics, the electro-magnetic relay.
Surviving are numerous antiquated
installations where EMRs continue to…..
Industrial Electronics
• Typical Applications
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Rectification
Motor Control
Amplification
Regulation
Process Control
Transistor
• Capable of performing
• Amplifying
• Switching
• Most common types
• Bipolar junction (BJT)
• Field effect (FET)
Transistor
• A three terminal device that controls
current through the device depending on
the amount of voltage applied to the base
• PNP or NPN
• emitter, base, collector
• bipolar device - both holes and electrons
are used as internal carriers for
maintaining current flow
Transistor
Biasing a Transistor
• Base/emitter junction must be forward
biased
• emitter more negative than the base
• base/collector junction must be reverse
biased
• base is more negative that the collector
Biasing a Transistor
Transistor Current Flow
• Forward bias of base/emitter causes
emitter to inject electrons into the
depletion region between the emiitter and
the base
• Biasing process is the “turn on” action
Transistor Current Flow
Transistor Applications
• Developed to replace mechanical switches
• No moving parts
• High resistance when transistor not turned on
• Low resistance when transistor turned on
Transistor Applications
Transistor Applications
• May be used as amplifiers
• Transistors gradually shut off
• By carefully controlling the base/emitter
junction bias, possible to control varying
degrees the through put of the
emitter/collector current
• Acts as an amplifier
Transistors as amplifiers
• Darlington amplifier
• Two transistors used
together
• Gain is multiplicative
Field Effect Transistor
• Like Bipolar Junction transistor except
• BJT is current controlled
• FET is voltage controlled
• Two types
• JFETs – Junction FETs
• MOSFETs – Metal Oxide Semiconductor FETs
• Power MOSFETS have high power
capability
Insulated Gate Bipolar
• Has attractive features of both MOSFET
and BJT
• Very fast on/off times (1 micro second)
• Extensively used in
• Inverters
• High frequency welding systems
IGBT Application
Special Types of Transistors
• THYRISTOR
• SCR
• DIAC
• TRIAC
• UJT
THYRISTOR
• Thyra (Greek) - door, inferring either open or
closed
• Thyristor - generic name for a type of
semiconductor switch
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Two stable states - ON and OFF
No intermediate state
Like a mechanical toggle switch
Made up of alternating layers of semiconductor
material
THYRISTOR Applications
• Used in lamp-dimming circuits, motor speed
control, ignition systems, charging circuits
• Control the transfer of power to various AC
loads
• SCRs, TRIACs, DIACs, and UJTs
Silicon Controlled Rectifier (SCR)
• Major element of
motor control
equipment
• Ratings as high as
2500 Volts and 2500
Amps
• Reverse blocking
triode thyristor
SCR - Continued
• Three terminals
• anode - P-layer
• cathode - N-layer (opposite end)
• gate - P-layer near the cathode
• Three junctions - four layers
Connect power such that the anode is
positive with respect to the cathode - no
current will flow
NOTE: Blocked by the reverse bias of
junction 2
SCR - Continued
• Positive potential applied to the gate
• Current will flow - TURNED-ON
• Once turned on, gate potential can be
removed and the SCR still conducts
CALLED LATCHING
• Holding current maintains latch
Silicon Controlled Rectifier
SCR - Continued
• Phase controller produces a trigger pulse
to permit on a portion of the positive half
cycle to get through
• Average power delivered is thereby
controlled
Silicon Controlled Rectifier
Silicon Controlled Rectifier
SCR Application
• Gate Turn Off switch (GTO)
• Electronic (pointless) automotive ignition
TRIAC
• Bidirectional triode
thyristor
• Equivalent of two
SCRs connected
• Allows gate control of
current flow in either
direction
TRIAC Operation
DIAC
• Bi-directional device without a gate
• Conducts in both directions but waits for a
breakover voltage
• Therefore, always the same and not
controllable
• Acts like two zener diodes in series, but
conducts in both directions
• Excellent for controlling TRIAC
DIAC - Application
Brightness of a lamp
DIAC - Application
• Brightness of a lamp
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beginning half cycle, TRIAC off
capacitor charges based on RC time constant
eventually DIAC is activated
TRIAC is activated and conducts
Process repeated for each half cycle of the AC sine
wave
• Adjust the brightness by changing the variable
resistance which effects charging time
Unijunction Transistor (UJT)
• Simple two layer transistor
• Operates using the principle of avalanche
breakdown producing a saw tooth output
• Used to trigger an SCR or TRIAC
• Also used within pulse circuitry
• Output from photocells, thermistors, and
other transducers can be used to trigger
Unijunction Transistor (UJT)
UJT as a trigger for an SCR
Industrial Blending Process
• Computer sends bit (5 VDC) to UJT
• UJT sends trigger signal to SCR
• SCR activates and provides power to
device
Application with UJT and SCR
Application with UJT and SCR
Inverter AC Motor Control
Solid State Switching
• Advantages
• No moving parts
• Controllable in the time domain
• Disadvantages
• Low resistance - but substantial heat
Solid State Switching
Advice for the future
If you own stock in a company who’s
main product line is EMRs
SELL!