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IR21593 fluorescent ballast IC

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eem2am

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балласт ir21593

Hello,

I have just designed and built a high frequency ballast with IR21593

http://www.datasheetcatalog.org/datasheet/irf/ir21592.pdf

..the problem is, when i used equation (8) on page 23 of the datasheet to find the frequency corresponding to maximum power, the frequency came out as 20.9KHz.

...this could not be right, since my resonant inductor and capacitor are 2.5mH and 10nF respectively, which resonates at some 30KHz.

My DC bus is 400V.

...the frequency for max power could not possibly be below 30KHz......The lamp is started at high frequecy then the frequency moves down..........max power occurs at resonance.......it could not possibly be necessary to go below the resonance frequency.

I also notice that the values obtained from the equations on page 23 do not correspond to the values obtained by the IRF BDA software which is obtainable on the website of IRF.

I think my problem is that i am out of practice with working out how to relate power and frequency in this LC resonant circuit -so i am struggling to do it myself........do you believe Lalplace transforms are the best way forward to find lamp voltage and current at various frequencies ?

There is an app note and circuti diagram for ballast here with IR21592...

http://www.irf.com/technical-info/refdesigns/irpldim2e.pdf

Added after 1 minutes:

Apologies, it should be equation (8), page 23....dont know how the face got in there, must have my finger trouble

Added after 1 minutes:

sorry again....it's equation eight......that face comes up whenever i press key eight
 

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