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why does scr not conduct when positive voltage is applied to it?
archit
on 2011-09-13 09:30:00The SCR is switched on, or \"fired\", by applying a positive voltage to the gate (the small lead on the top of the SCR at the top right). When the current passing through the SCR reaches zero, as it does every half AC cycle, the SCR naturally \"switches off\" and will not conduct again until another positive voltage is applied to the gate. By firing the SCR earlier in the cycle a higher average DC voltage is output. This type of voltage control is called Phase Angle Control.
Ajoy
on 2011-09-14 09:30:00scrf has three juncton when we apply positive voltage to scr junction j1&j3 are forward biased but junction j3 is not where gate is connected so a very small current(leakage current) flows through it if we trigger the gate or give a pulse or positive voltage to gate or increase the positive voltage appilied b/w anode and cathode scr will turn on and an avalanche breakdown occur in junction j2