Posted on Apr 27, 2012

Industrial applications sometimes require that power be only briefly applied to a load following the closure of a switch, such as a microswitch or foot switch. The load could be a heating element for use in sealing plastic bags, a de motor that is indexed or stepped with each application of power, or a de solenoid which is to be energized for a brief time-for example, a staple gun.

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The phase angle at which the SCR triggers on is determined by the charging rate of C2 through R7 and potentiometer RS. When the breakover voltage of the gate triggering device, a silicon unilateral switch, is reached, the SCR turns on. The average de voltage to the load is determined by the setting of RS.

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