IRPLCFL3: 26W CFL Ballast, 120 VAC

A system has now been developed, based around the IR2156, where the ballast is able to operate with minimal flicker over a considerable portion of the adjustment range of a dimmer and the light output may be controlled over this range from maximum output down to around 10%.

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 of the Triac and adjusts the lamp current by increasing the switching frequency hence the controlling light output depending on the level set by the dimmer.

It should be noted that if the dimmer is set too low the Triac will never fire when a capacitive load is connected and also when the ballast is running and the dimmer is turned too low there will be insufficient bus voltage for the ballast to be able to operate. Because of these factors it is impossible for the ballast to operate over the complete range of adjustment of the dimmer. There will also be some hysteresis so when the ballast is being dimmed down and reaches the point where the lamp goes out the dimmer has to be turned back up some way before the lamp will strike again.

The CFL3 demo board has two long leads for connection to the 120VAC mains supply. The board must not be connected to a supply greater than 120V. There are four output connections to be connected to a compact lamp. These are located at the opposite side of the board. The two upper connections go to one lamp cathode and the two lower connections go to the other lamp cathode.