Power Electronics BScIII SemV PaperXV Dr S S

Power Electronics BSc-III Sem-V Paper-XV Dr. S. S. Jawale Head and Associate Professor Department of Electronics Yeshwantrao Chavan Mahavidyalaya, Tuljapur 1

Thyristors Most important type of power semiconductor device. Have the highest power handling capability. they have a rating of 5000 V / 6000 A with switching frequencies ranging from 1 KHz to 20 KHz. 2

Is inherently a slow switching device compared to BJT. Used as a latching switch that can be turned on by the control terminal but cannot be turned off by the gate. 3

SCR Symbol of Silicon Controlled Rectifier 4

Structure 5

Device Operation Simplified model of a thyristor 6

Two Transistor Model of SCR 7

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V-I Characteristics 14

Effects of gate current 15

Turn-on Characteristics 16

Turn-off Characteristics 17

Methods of Thyristor Turn-on Thermal Turn-on. Light. High Voltage. Gate Current. dv/dt. 18

Thyristor Ratings First Subscript D off state Second Subscript W working T ON state R Repetitive F Forward S Surge or non-repetitive Third Subscript M Peak Value R Reverse 19

Voltage Ratings 20

Current Ratings 21

Gate Specification 22

Phase Control Thyristors

Thyristor Types Phase-control Thyristors (SCR’s). Fast-switching Thyristors (SCR’s). Gate-turn-off Thyristors (GTOs). Bidirectional triode Thyristors (TRIACs). Reverse-conducting Thyristors (RCTs). 24

Static induction Thyristors (SITHs). Light-activated silicon-controlled rectifiers (LASCRs). FET controlled Thyristors (FET-CTHs). MOS controlled Thyristors (MCTs). 25

Bidirectional Triode Thyristors (TRIAC) 26

Triac Characteristics 27

Gate Turn-off Thyristors Turned on by applying positive gate signal. Turned off by applying negative gate signal. On state voltage is 3. 4 V for 550 A, 1200 V GTO. Controllable peak on-state current ITGQ is the peak value of on-state current which can be turned-off by 28 gate control.

Advantages over SCRs Elimination of commutating components. Reduction in acoustic & electromagnetic noise due to elimination of chokes. Faster turn-off, therefore can be used for higher switching frequencies. Improved efficiency of converters. 29

Advantages over BJTs Higher voltage blocking capabilities. High on-state gain. High ratio of peak surge current to average current. A pulsed gate signal of short duration only is required. 30

Disadvantages of GTOs On-state voltage drop is more. Due to multi cathode structure higher gate current is required. Gate drive circuit losses are more. Reverse blocking capability is less than its forward blocking capability. 31

Reverse Conducting Thyristors 32

Anti-parallel diode connected across SCR on the same silicon chip. This diode clamps the reverse blocking voltage to 1 or 2 V. RCT also called Asymmetrical Thyristor (ASCR). Limited applications. 33

Static Induction Thyristors Turned-on by applying positive gate voltage. Turned-off by applying negative gate voltage. Minority carrier device. Low on-state resistance & low voltage drop. Fast switching speeds & high dv/dt & high di/dt capabilities. 34

time in order of 1 to 6 sec. The rating can go upto 2500 V / 500 A. Process sensitive. Switching 35

Features Low on-state losses & large current capabilities. Low switching losses. High switching speeds achieved due to fast turn-on & turn-off. Low reverse blocking capability. 36

Gate controlled possible if current is less than peak controllable current. Gate pulse width not critical for smaller device currents. Gate pulse width critical for turn-off for larger currents. 37

Example of Triac Ratings Used in heat / light control, ac motor control circuit V / I rating: 1200 V / 300 A. Max. Frequency: 400 Hz. Switching time: 200 to 400 sec. On state resistance: 3. 6 m. 38

Example of Power Transistor Ratings PT ratings go up to 1200 V / 400 A. PT normally operated as a switch in CE config. Max. Frequency: 400 Hz. Switching time: 200 to 400 sec. On state resistance: 3. 6 m. 39

Thank You…. .