Schmitt Trigger - zero crossing circuit

L

Thread Starter

Laily

I'm not sure whether I've put my topic in the subject... Just want to have an explanation about the topic for my final year project. I'm doing "speed control using a thyristorised dc drive via microcontroller". If anybody can help me, do email me.
 
Thyristors, and SCR's, need a zero-crossing so that the devices can turn off (stop conducting). The current must drop to a certain value before the device will switch off. This usually happens at the end of the sine wave, when the voltage is lower (around 150 degrees). The turn- off should occur on the same cycle as when the gate firing signal is removed.
 
Top