Page 42 - Rashid, Power Electronics Handbook

3

Thyristors

Jerry Hudgins, Ph.D. 3.1 Introduction........................................................................................ 27
Enrico Santi, Ph.D. 3.2 Basic Structure and Operation................................................................ 28
Antonio Caiafa, Ph.D. 3.3 Static Characteristics............................................................................. 30
Katherine Lengel, Ph.D. 3.3.1 Current-Voltage Curves for Thyristors 3.3.2 Edge and Surface Terminations
Department of Electrical 3.3.3 Packaging
Engineering 3.4 Dynamic Switching Characteristics.......................................................... 33
University of South Carolina 3.4.1 Cathode Shorts 3.4.2 Anode Shorts 3.4.3 Amplifying Gate 3.4.4 Temperature
Columbia, South Carolina Dependencies
29208 USA
3.5 Thyristor Parameters............................................................................. 37
Patrick R. Palmer, Ph.D. 3.6 Types of Thyristors............................................................................... 38
Department of Engineering 3.6.1 SCRs and GTOs 3.6.2 MOS-Controlled Thyristors, MCT 3.6.3 Static Induction
Cambridge University Thyristors 3.6.4 Optically Triggered Thyristors 3.6.5 Bidirectional Control Thyristor
Trumpington Street
Cambridge CB2 1PZ, United 3.7 Gate Drive Requirements....................................................................... 45
Kingdom 3.7.1 Snubber Circuits 3.7.2 Gate Circuits
3.8 P-Spice Model ..................................................................................... 47
3.9 Applications ........................................................................................ 50
3.9.1 Direct current-Alternating current Utility Inverters 3.9.2 Motor Control
3.9.3 VAR Compensators and Static Switching Systems
References ........................................................................................... 53

3.1 Introduction thyristor types are controllable in switching from a forward-
blocking state (positive potential applied to the anode with
Thyristors are usually three-terminal devices with four layers respect to the cathode with correspondingly little anode
of alternating p- and n-type material (i.e. three p-n junctions) current ¯ow) into a forward-conduction state (large forward
in their main power handling section. In contrast to the linear anode current ¯owing with a small anode-cathode potential
relation that exists between load and control currents in a drop). After switching from a forward-blocking state into the
transistor, the thyristor is bistable. The control terminal of the forward-conduction state, most thyristors have the character-
thyristor, called the gate (G) electrode, may be connected to an istic that the gate signal can be removed and the thyristor will
integrated and complex structure as part of the device. The remain in its forward-conduction mode. This property,
other two terminals, anode (A) and cathode (K), handle the termed ‘‘latching,'' is an important distinction between
large applied potentials (often of both polarities) and conduct thyristors and other types of power electronic devices. Some
the major current through the thyristor. The anode and thyristors are also controllable in switching from forward-
cathode terminals are connected in series with the load to conduction back to a forward-blocking state. The particular
which power is to be controlled. design of a thyristor will determine its controllability and often
Thyristors are used to approximate ideal closed (no voltage its application.
drop between anode and cathode) or open (no anode current Thyristors are typically used at the highest energy levels in
¯ow) switches for control of power ¯ow in a circuit. This power conditioning circuits because they are designed to
differs from low-level digital switching circuits that are handle the largest currents and voltages of any device technol-
designed to deliver two distinct small voltage levels while ogy (systems with voltages approximately greater than 1 kV or
conducting small currents (ideally zero). Power electronic currents higher than 100 A). Many medium-power circuits
circuits must have the capability of delivering large currents (systems operating at <1 kV or 100 A) and particularly low-
and be able to withstand large externally applied voltages. All power circuits (systems operating <100 V or several amperes)

27
Copyright # 2001 by Academic Press.
All rights of reproduction in any form reserved.