• For light-triggered SCRs, a slot (niche) is made in the inner p-layer. • When it is irradiated, free charge carriers are generated just like when gate signal is applied b/w gate and cathode. • Pulse light of appropriate wavelength is guided by optical fibers for irradiation. • If the intensity of this light thrown on the recess exceeds a certain value, forward-biased SCR is turned on. Such a thyristor is known as light-activated SCR (LASCR). • Light-triggered thyristors is mostly used in high- voltage direct current (HVDC) transmission systems. 11
5. dv/dt triggering • With forward voltage across anode & cathode of a thyristor, two outer junctions (A & C) are forward biased but the inner junction (J2) is reverse biased. • The reversed biased junction J2 behaves like a capacitor because of the space-charge present there. • As p-n junction has capacitance, so larger the junction area the larger the capacitance. • If a voltage ramp is applied across the anode-to-cathode, a current will flow in the device to charge the device capacitance according to the relation: • If the charging current becomes large enough, density of moving current carriers in the device induces switch-on. • This method of triggering is not desirable because high charging current (Ic) may damage the thyristor. 12
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- Fall '18
- Rashid Baloch
- Alternating Current, Turn LP, High-voltage direct current, Turn, Turn-On