NAIT 2000

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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

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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..

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Industrial Electronics

• Typical Applications
• Rectification
• Motor Control
• Amplification
• Regulation
• Process Control

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Transistor

• Capable of performing
• Amplifying
• Switching
• Most common types
• Bipolar junction (BJT)
• Field effect (FET)

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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

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Transistor
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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

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Biasing a Transistor
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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

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Transistor Current Flow
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Transistor Applications

• Developed to replace mechanical switches
• No moving parts
• High resistance when transistor not turned on
• Low resistance when transistor turned on

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Transistor Applications
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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

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Transistors as amplifiers

• Darlington amplifier
• Two transistors used together
• Gain is multiplicative

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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

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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

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IGBT Application
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Special Types of Transistors

• THYRISTOR
• SCR
• DIAC
• TRIAC
• UJT

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THYRISTOR

• Thyra (Greek) - door, inferring either open or
  closed
• Thyristor - generic name for a type of
  semiconductor switch
• Two stable states - ON and OFF
• No intermediate state
• Like a mechanical toggle switch
• Made up of alternating layers of semiconductor
  material

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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

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Silicon Controlled Rectifier (SCR)

• Major element of motor control equipment
• Ratings as high as 2500 Volts and 2500 Amps
• Reverse blocking triode thyristor

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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

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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

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Silicon Controlled Rectifier
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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

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Silicon Controlled Rectifier
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Silicon Controlled Rectifier
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SCR Application

• Gate Turn Off switch (GTO)
• Electronic (pointless) automotive ignition

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TRIAC

• Bidirectional triode thyristor
• Equivalent of two SCRs connected
• Allows gate control of current flow in either
  direction

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TRIAC Operation
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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

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DIAC - Application Brightness of a lamp
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DIAC - Application

• Brightness of a lamp
• 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

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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

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Unijunction Transistor (UJT)
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UJT as a trigger for an SCR
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Industrial Blending Process

• Computer sends bit (5 VDC) to UJT
• UJT sends trigger signal to SCR
• SCR activates and provides power to device

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Application with UJT and SCR
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Application with UJT and SCR
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Inverter AC Motor Control
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Solid State Switching

• Advantages
• No moving parts
• Controllable in the time domain
• Disadvantages
• Low resistance - but substantial heat

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Solid State Switching

• Advice for the future
• If you own stock in a company whos main product
  line is EMRs
• SELL!