Posted on Oct 2, 2012

After the first cycle. the relay will normally be energized. When normally closed pushbutton 51 is activated, the SCR turns off, the relay is de-energized, and power is applied to the relaxation oscillator and the load. Mter a time delay varying from less than a second to approximately 2.5 minutes, as determined by the setting of the 10-M!l potentiometer, the unijuction will fire and tum on the SCR.

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The relay will energize until power is removed from the oscillator and the load, and will stay energized until button 51 is pushed again. The UJT trigger output from base 1 directly drives the gate of the SCR. However, where isolation between the UJT trigger or any other type of trigger and the thyristor power circuit is required, then a simple pulse transformer, interfacing the two elements, will suffice.

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