an-1038| Application Note
Application Note AN-1038
Low Voltage DC Supply Dimmable Ballast for 1 x 36W T8 Lamp
By Peter Green, Senior Lighting Systems Engineer
Table of Contents
Page Introduction ..........................................................................................1 Functional Description..........................................................................1 Selection of the Output L and C Values ...............................................2 Preheating and Cathode Heating .........................................................2 Control IC Auxiliary Component Selection ...........................................3 Layout Issues .......................................................................................6 Step-Up Transformer Design ...............................................................7 Output Inductor Design ........................................................................8 Bill of Materials.....................................................................................9
It is possible to design an effective dimmable ballast based around the IR21592, that is powered from a low voltage DC supply instead of the AC line. A non-dimmable version based around the IR2156 is also possible using the same basic configuration as described here. This application note shows a ballast for a single 36W T8 lamp driven from a 30V DC supply. Lower supply voltages are possible, however the IR21592 control IC requires up to 13V supplied to the VCC pin before it will operate, also as the current is high large conductors are needed to keep losses at an acceptable level (for a 36W ballast operating from a 30V supply the input current is around 1.25A).
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