A ballast that is dimmed from a (phase cut) dimmer


Posted on Apr 10, 2012

Virtually all domestic and professional dimming systems are based on triacs. These devices will conduct once they have been fired, only while current flows in excess of the holding current of the device. These dimmers work very well with a resistive load such as an ordinary Tungsten filament light bulb as the triac can be fired at any point during the mains half-cycle and will continue to conduct until very close to the end of the half-cycle as current is drawn continuously over this period. In this way the lamp current can be adjusted from maximum to zero.



In this system the front end of the ballast has been designed so that when the triac in the dimmer has fired, it will remain on continuously until almost the end of the mains half-cycle. In addition to this there is circuitry that detects the firing angle




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