Characteristics: Triac - nptel

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Average power dissipation P av ): Specified as a function of the average forward current (I av ) for different conduction angles as shown in the figure 4.9. The current wave form is assumed to be half cycle sine wave (or square wave) for power frequency. P av 30° 60° 90° φ = 180° i F Fig. 4.9: Average power dissipation vs average forward current in a thyristor. In the above diagram 1 φ I av = i o F dθ 2π ∫ 4.10 1 φ P av = v o F i F dθ 2π ∫ 4.11 4.5.3 Gate Specifications ( ) ( ) Gate current to trigger (I GT ): Minimum value of the gate current below which reliable turn on of the thyristor can not be guaranteed. Usually specified at a given forward break over voltage. Gate voltage to trigger (V GT ): Minimum value of the gate cathode forward voltage below which reliable turn on of the thyristor can not be guaranteed. It is specified at the same break over voltage as I GT . Non triggering gate voltage (V GNT ): Maximum value of the gate-cathode voltage below which the thyristor can be guaranteed to remain OFF. All spurious noise voltage in the gate drive circuit must be below this level. Peak reverse gate voltage (V GRM ): Maximum reverse voltage that can appear between the gate and the cathode terminals without damaging the junction. I av φ ωt Version 2 EE IIT, Kharagpur 16
Average Gate Power dissipation (P GAR ): Average power dissipated in the gate-cathode junction should not exceed this value for gate current pulses wider than 100 μs. Peak forward gate current (I GRM ): The forward gate current should not exceed this limit even on instantaneous basis. Exercise 4.3 1) Fill in the blank(s) with the appropriate word(s) i. Peak non-repetitive over voltage may appear across a thyristor due to ________________ or ________________ surges in a supply network. ii. V RSM rating of a thyristor is greater than the ________________ rating but less than the ________________ rating. iii. Maximum average current a thristor can carry depends on the ________________ of the thyristor and the ________________ of the current wave form. iv. The I SM rating of a thyristor applies to current waveforms of duration ________________ than half cycle of the power frequency where as the ∫i 2 dt rating applies to current durations ________________ than half cycle of the power frequency. v. The gate non-trigger voltage specification of a thyristor is useful for avoiding unwanted turn on of the thyristor due to ________________ voltage signals at the gate. Answer: (i) switching, lightning; (ii) V RRM , V BRR ; (iii) case temperature, conduction angle; (iv) greater, less; (v) noise 2. A thyristor has a maximum average current rating 1200 Amps for a conduction angle of 180°. Find the corresponding rating for Φ = 60°. Assume the current waveforms to be half cycle sine wave. Answer: The form factor of half cycle sine waves for a conduction angle φ is given by 1 φ 2 1 I Sin θ dθ RMS 2π ∫o 2 φ ( φ φ) π - Sin 2 F.F = = = Iav 1 1- Cos φ Sinθ dθ 2π ∫o For φ = 180°, F.F = π 2 ∴RMS current rating of the thyristor = For φ = 60°, F.F = 2 π ⎛π - 3 ⎞ ⎜ = 2.778 3 4 ⎟ ⎝ ⎠ Since RMS current rating should not exceeded π 1200 × = 1885 Amps. 2 Version 2 EE IIT, Kharagpur 17
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: I av Amps 120 100 φ = 180° φ = 1
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 and 38: Since V g = 10 - i g R is tangent t
Page 39: 5. As soon as THA is turned on the

Characteristics: Triac - nptel

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