Thyristor Structure, Specifications, and Applications

By Miles Pearson

Abstract

different type of thyristors. This will lead into the explanation of all the different modes and regions affiliated with these curves. We will examine the characteristics by taking a look at the I-V curves and construction of mainly the SCR (Silicon Controlled Rectifier). The exploration of certain parameters that limit this device will also be important. Finally, were going to take a look at some specific applications of thyristors and why they are used.

04/17/15 This presentation will cover the structure, specifications and applications of several

Overview

     Expose the main types of thyristors Different modes of operation Important parameters of the SCR Show construction and characteristics of SCR and TRIAC Applications of thyristors

Background On Thyristors

   They name Thyristor comes from two similar device names ‘Thyratron’ and ‘Transistor’ Thyristors are useful due to their ability to handle large current in power applications and fast switching The most common thyristor is the SCR which stands for “Silicon Controlled Rectifier”

Ultra-High Power Thyristor

 Quantitatively understand the upper bound these devices can achieve http://www.datasheetarchive.com/dl/Datasheet-020/DSA00357098.pdf

Main types of thyristors

 SCR (Silicon Controlled rectifier)  TRIAC  GTO (Gate Turn Off)  IGTO (Integrated Gate Turn Off)  MCT (MOS-controlled Rectifier) TRIAC MCT

Equivalent circuits

http://www.allaboutcircuits.com/vol_3/chpt_7/ 6.html

How the SCR operates

 Three modes of operation:  Reverse Blocking mode  Forward Blocking mode  Forward Active conducting mode http://upload.wikimedia.org/wikipedia/commons/thumb/f /f1/Thyristor_I-V_diagram.svg/1280px-Thyristor_I V_diagram.svg.png

How the TRIAC Operates

 Modes of operation:  Forward conducting mode  Reverse conducting mode  Forward Blocking mode  Reverse Blocking mode http://www.onsemi.com/pub_link/Collat eral/HBD855-D.PDF

Construction of the SCR

N N http://www.littelfuse.com/~/media/electronics/application_notes/switching_thyristors/lit telfuse_thyristor_fundamental_characteristics_of_thyristors_application_note.pdf.pdf

Some Important Parameters

    di/dt dv/dt – Critical Rise of On-State Current/voltage  Maximum rise of current/voltage that the device can handle  Things to consider: High frequencies and large amounts of current/voltage I gm V gm – Forward Peak Gate Current/Voltage  Largest amount of current/voltage that can be applied to gate while in conduction mode I H – Holding Current  Minimum current flow (from anode to cathode) to keep device on I L – Latching Current  Current flow applied to anode in order to turn the device on

More parameters…

    t gt – Gate Turn-On Time  Time it takes for a gate pulse to send the SCR into conducting mode or when when the voltage drops giving it negative resistance t q – Turn-Off Time  Time it takes for SCR to start blocking current after external voltage has switched to negative cycle V DRM I leakage – Peak Repetitive Off-State Forward Voltage/current  Maximum repetitive voltage/current applied to Anode that wont breakdown the SCR or damage it V RRM I RRM – Peak Repetitive Off-State Reverse Voltage/Current  Maximum repetitive voltage/current applied to Cathode that wont breakdown the SCR or damage it

Even More Parameters

   I GT V GT – Gate Trigger Current/Voltage  Minimum value of current/voltage that will trigger the device from off to on  Important for considering false triggering I 2 t – Circuit Fusing Consideration  Max non-repetitive over-current capability without damage (typically rated for 60hz) T j – Junction Temperature  Temperature range which this device may operate without damage under load conditions

http://forum.allaboutcircuits.com/attachments/scr-voltage-current-characteristics-jpg.69922/

Characteristics of the SCR N- Regions

   SCR’s have a high resistive N-base region which forms a junction J2 as shown  This region is typically doped with Phosphorus atoms where N D has a range of values from 10 13 to 10 14 cm -3  This regions thickness generally ranges from 1um to 100um depending on the voltage ratings Thicker N-base region increases forward conducting voltage drop The Cathode region is only 2um-5 um thick and has N D cm -3 range of 10 16 to 10 18

Only D1 changing Changing D1 and Newly added N-well

Current Density Map

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More heat dissipation in the thicker N-base region

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Addition of the N-well seems to spread the charge carriers more unformly

Characteristics of the SCR P-Regions

   High voltage SCRs are generally made by diffusing Al or Ga making it a P-region Typical N A values range from 10 15 to 10 17 cm -3 These P-regions are generally on the order of 10-50 um thick

Comparing Doping Concentrations

   Highest Doping Concentration:  Cathode region or n+ Next Highest level of Concentration:  Anode and Gate or p Lowest Doping level:   Mid N-Base region or n However, note that this is the thickest http://www.radio-electronics.com/info/data/semicond/thyristor/structure fabrication.php

Typical Materials Used In SCR

        Si - Silicon SiC – Silicon Carbonite GaN – Gallium Nitride C – Carbon P – Phosphorus Al – Aluminum Au – Gold Pl - Platinum • • Used to create charge carrier recombination sites This slows the switching time but increases forward conducting voltage drop

Trade-Offs In Design

  Forward Blocking Voltage vs. Switching time Forward Blocking Voltage vs. Forward Voltage Drop during Conduction Mode

Applications of Thyristors

     Rectifiers Phase Fired Controllers Light Dimmers Motor Drive Speed Controllers Strobe Lights http://www.renesas.eu/products/discrete/thyristor_triac/ind ex.jsp

Three phase power AC to DC

http://www.allaboutcircuits.com/vol_3/chpt_7/5.html

Stun Gun

  Used in Power Project Pulse rate of about 30-50hz when triggered

Conclusion

     The main types of thyristors specified are the SCR, TRIAC, GTO, and MCT Operation modes for SCR include: Forward Active Conduction, Reverse Blocking, and Forward Blocking Characteristics of the SCR are dependent on large current and voltage Manufacturers strive for a good trade off between forward conducting voltage drop and switching time Applications are mainly centered around control of high current flow

Sources

Academic Sources: Greenburg, R., "Consumer applications of power semiconductors," Proceedings of the IEEE , vol.55, no.8, pp.1426,1434, Aug. 1967 doi: 10.1109/PROC.1967.5846

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1447776 Shurong Dong; Jian Wu; Meng Miao; Jie Zeng; Yan Han; Liou, J.J., "High-Holding-Voltage Silicon-Controlled Rectifier for ESD Applications," Electron Device Letters, IEEE , vol.33, no.10, pp.1345,1347, Oct. 2012 doi: 10.1109/LED.2012.2208934

http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=6286984 Web Content: http://www.onsemi.com/pub_link/Collateral/HBD855-D.PDF

http://electrical4u.com/thyristor-silicon-controlled-rectifier http://www.radio-electronics.com/info/data/semicond/thyristor/structure-fabrication.php

http://www.littelfuse.com/~/media/electronics/application_notes/switching_thyristors/littelfuse_thyristor_fundamental_characteristics_of_thy ristors_application_note.pdf.pdf

http://www.allaboutcircuits.com/vol_3/chpt_7/6.html

http://www.learnabout-electronics.org/diodes_07.php

Concept Check

     Describe the three modes of operation for SCR and where they relate to the I-V curve Are you able to distinguish between the main types of thyristors specified?

What are the significant trade offs in design?

What is the difference between latching and holding current?

If you change the N-Base region thickness of an SCR how will the resulting forward conducting voltage drop change?