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20 VAC Lamp Dimmer Schematic

20 VAC Lamp Dimmer Schematic20 VAC Lamp Dimmer Schematic

The abounding beachcomber appearance ascendancy circuit beneath was activate in a RCA Power circuits book from 1969. The amount is placed in alternation with the AC band and the four diodes accommodate a abounding beachcomber rectified voltage to the anode of a SCR. Two baby arresting transistors are affiliated in a about-face agreement so that back the voltage on the 2.2uF capacitor alcove about 8 volts, the transistors will about-face on and acquittal the capacitor through the SCR aboideau causing it to activate conducting.

The time adjournment from the alpha of anniversary bisected aeon to the point area the SCR switches on is controlled by the 50K resistor which adjusts the time appropriate for the 2uF capacitor to allegation to 8 volts. As the attrition is reduced, the time is bargain and the SCR will conduct beforehand during anniversary bisected aeon which applies a greater boilerplate voltage beyond the load. With the attrition set to minimum the SCR will activate back the voltage rises to about 40 volts or 15 degrees into the cycle.

To atone for basic tollerances, the 15K resistor can be adapted hardly so that the achievement voltage is abreast aught back the 50K pot is set to maximum. Increasing the 15K resistor will abate the ambience of the 50K pot for minimum achievement and acceptance versa. Be accurate not to blow the ambit while it is affiliated to the AC line.