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(i) Resistance triggering:
The following circuit shows the resistance triggering.
Figure: 1. 14. Resistance triggering circuit of SCR
In this method, the variable resistance R is used to control the gate current.
Depending upon the value of R, when the magnitude of the gate current reaches the sufficient
value(latching current of the device) the SCR starts to conduct.
The diode D is called as blocking diode. It prevents the gate cathode junction from getting damaged
in the negative half cycle.
By considering that the gate circuit is purely resistive, the gate current is in phase with the applied
voltage.
By using this method we can achieve maximum firing angle up to 90°.
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