Phase-control

  
This circuit uses a PUT for phases control of an SCR. The relaxation oscillator formed by Q2 provides conduction control of Ql from 1 to 7.8 ms or 21.6° to 168.5°. This constitutes control of over 97% of the power available to the load.

Only one SCR is needed to provide phase control for both the positive and negative portion of the sine wave by putting the SCR across the bridge-composed of diodes Dl through D4.




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