Download Slide 1

• Introduction
Final
Control
• Thyristors
–SCR
–TRIAC
–DIAC
• Stepping Motors
• Summary
1
A thyristor is a four-layer semiconductor
device, consisting of alternating P type
and N type materials (PNPN). A thyristor
usually has three electrodes: an anode, a
cathode, and a gate (control electrode).
The most common type of thyristor is the
silicon-controlled rectifier (SCR).
Thyristors are used in motor speed controls,
light dimmers, pressure-control systems,
and liquid-level regulators.
•Thyristor
SCR-Silicon
Controlled
Rectifier
Triac
Diac
etc
SCR Symbol
Hockey Puck SCR
http://www.larkinpower.com/Thyristors.htm
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A commercially practical solid state rectifier has been
operated by engineers at General Electric's Clyde,
New York Rectifier Engineering Laboratory. This
silicon-controlled rectifier operates in the same
manner as a thyratron, and is capable of switching
1000 watts. A power rating of this magnitude is
sufficient for most military and commercial
applications. The device is expected to be first used
in missiles.
The size of the silicon controlled rectifier is
approximately twice that of a signal type transistor
and 1/100 the size of a thyratron. The predicted life
of the device is over 300,000 hours as compared to
the 1000 hour life of a thyratron.
(Electronic Design, Jan. 8, 1958, p. 7)
The first SCRs were compared to thyratrons because
that's what vacuum-tube era engineers understood.
For today's engineer, we'd probably have to reverse Technical Papers
the analogy--a thyratron, a gas-filled grid-controlled
rectifier, was like an SCR.--Steve Scrupski
Thyratron Power Supply at Fermilab
SCR Origins
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Operation of an SCR
http://www.tpub.com/neets/book7/26c.htm
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Igate
(turn-on)
0.8-25 mA
Gate
Controlled
(Main) turn-on time
Imax
.8-7
Amps
<2 usec
http://www.nteinc.com/Web_pgs/SCR.html
SCR Characteristics
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VAK= 1-1.5 volts
I
Very High
V
Very High
Reverse voltage
to break it down
http://www.tpub.com/neets/book7/26d.htm
SCR V-I curve
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Characteristics of 2N1595
Peak Reverse Blocking Voltage = 50 volts
RMS Forward Current (max) = 1.6 amps
Typical Gate Trigger Current= 2 mA
Typical Gate Trigger Voltage= .7 volts
Turn-on time = .8 usec Turn-off time=10 usec
SCR Circuit
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SCR Output
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Vin
Computer
SCR for Overvoltage
Protection
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Characteristics of 2N1595
Phase Control
with an SCR
http://www.fairchildsemi.com/pf/1N/1N4148.html
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SCR Phase Control
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Diac
Triac
Diacs and
Triacs
• The Diac and Triac are bilateral thyristors,
meaning that they conduct current in both
directions
• The Diac is designed to conduct when
breakdown occurs in both directions The
triac is like two parallel SCR’s, with one in
each direction.
• Triac’s have less current carrying ability
than SCR’s
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Τau = RC = .12 msec
A Triac Full-Wave Circuit
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Τau = RC = 3.8 msec
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A Triac Full-Wave Circuit
Power Control with Thyristors and Triacs
Diac-Triac Phase Control
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http://www.geocities.com/tjacodesign/dimmer/dimmer.html
Diac-Triac Light Dimmer
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A stepper motor system is an electro-mechanical rotary actuator that converts
electrical pulses into unique shaft rotations. This rotation is directly related to
the number of pulses. The speed is synchronous to the rate of pulsing.
Stepper motors feature bi-directional control, built-in braking, variable torque,
power control, precision accuracy, high resolution, open-loop control, and
direct interface to digital systems.
Stepper Motors - General Description
A step motor converts electrical energy into discrete motions or steps.
The motor consists of multiple electrical windings wrapped in pairs (phases)
around the outer stationary portion of the motor (stator).
The inner portion (rotor) consists of iron or magnetic disks mounted on a shaft
and suspended on bearings.
The rotor has projecting teeth which align with the magnetic fields of the
windings. When the coils are energized in sequence by direct current, the teeth
follow the sequence and rotate a discrete distance necessary to re-align with
the magnetic field.
The number of coil combinations (phases) and the number of teeth determine the
number of steps (resolution) of the motor. For example, a 200 step per rev (spr)
motor has 50 rotor teeth times 4 coil combinations to equal 200 spr.
There are no brushes between the rotor and stator assembly; a stepper motor is a
multipole (polyphase) brushless DC motor.
These multiple coil pairs can be connected either positive or negative resulting in
four unique full steps. When the coils are sequenced correctly, the motor
rotates for- ward. When the sequence is reversed, the motor rotates in reverse.
http://www.cs.uiowa.edu/~jones/step/#introduction
http://www.doc.ic.ac.uk/~ih/doc/stepper/
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Stepper Motors
In the KP4M4-001 stepper motor, the
permanent magnet lies North - South
along the shaft. It is encased in two
"stacks" each with 25 teeth round
the rim. The teeth on the South stack
are out of phase with the teeth on
the North stack by half the gap
between teeth as can be seen in the
photo of the shaft shown above.
http://www.doc.ic.ac.uk/~ih/doc/stepper/kp4m4/
A Stepper Motor
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Permanent Magnet or can also be switched
Simple
Stepper Operation
http://www.st.com/stonline/books/ascii/docs/1679.htm
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Summary
• Introduction
• Thyristors
– SCR
– TRIAC
– DIAC
• Stepping Motors
• Summary
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