Characteristics: Triac - nptel

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∫ 2 i dt = ∫ -2 10 2 0 ( 1556 Sin 100 π t) ( 1556) 2 ∫ -2 10 [ ] = 1 - Cos 200 π t dt 2 0 -2 2 4 2 = 1 × 10 ( 1556 ) = 1.21 × 10 A Sec 2 4. At the beginning of the turn on process the thyristor starts conducting through the area adjacent to the gate. This area spreads at a finite speed. However, if rate of increase of anode current is lager than the rate of increase of the current conduction are, the current density increases with time. This may lead to thyristor failure due to excessive local heating. However, if the contact area between the gate and the cathode is large a thyristor will be able to handle a di relatively large a without being damaged. dt The maximum dia dt will occur when the thyristor is triggered at ∝ = 90°. Then di L a = 2 × 220 Sin 90 dt 0 Since di a dt 6 Max = 50 × 10 A Sec 2 × 220 -6 L min = = 6.22 × 10 H = 6.22 μH ⎛dia ⎞ ⎜ ⎝ dt ⎟ ⎠ Max V C t off 200 V v THM dv / dt t i C 20 Amps. t Version 2 EE IIT, Kharagpur 38
5. As soon as THA is turned on the load current transfer from THM to C. the voltage across THM is the negative of the capacitance voltage. Figure shows the waveforms of voltage across the capacitor (v c ), voltage across the main thyristor (V THM ) and the capacitor current i c . From dv i figure = c dt c dv Now i c = 20 Amps & Max = 500 v μs dt ∴ i 20 dv 500×10 Max dt c -8 C Min = = 6 = 4 × 10 F = 0.04 μF The circuit turn off time is the time taken by the capacitor voltage to reach zero from an initial value of 200v. This time must be greater than the turn off time of the device. dvc Now C = i c = 20 dt ∴ 20 × Δt Δv c = c Δv = 200 - 0 = 200 Δt = t 20 × 50 × 10 ∴ 200 = C 20 × 50 × 10 ∴ C = 200 -6 -6 off = 5 μF For safe commutation of THM the higher value of C must the chosen ∴ the required value of C = 5 μF. Version 2 EE IIT, Kharagpur 39
Page 1 and 2: Module 1 Power Semiconductor Device
Page 3 and 4: Instructional objects On completion
Page 5 and 6: A A p n - G K p n + n + (a) G (b) K
Page 7 and 8: Where I I +I is the total reverse l
Page 9 and 10: 4.4 Steady State Characteristics of
Page 11 and 12: V g V g max A E c d R g • S 2 P g
Page 13 and 14: Answer: (i) gate; (ii) break down,
Page 15 and 16: I av Amps 120 100 φ = 180° φ = 1
Page 17 and 18: Average Gate Power dissipation (P G
Page 19 and 20: Delay time (t d ): After switching
Page 21 and 22: The reverse recovery charge Q rr is
Page 23 and 24: 1 2 V 2 V V ( ∝) πω π i i H E
Page 25 and 26: G I G MT1 ( - ) I G N 2 I G I G N 3
Page 27 and 28: A 200 Bidirectional ON state curren
Page 29 and 30: vii. viii. To avoid unwanted turn o
Page 31 and 32: Lesson Summary • Thyristor is a f
Page 33 and 34: 1. Explain the effect of increasing
Page 35 and 36: Answers to Practice Problems Versio
Page 37: Since V g = 10 - i g R is tangent t

Characteristics: Triac - nptel

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