Interesting. More complex than I expected.
A PFC IC, like the TDA4862 or similar, was expected.
The 2842 isn't the bandpass filter you linked. It's almost certainly a current-mode PWM controller
. This is a common chip in various power supplies. A bit surprising to see it as the heart of this ballast, instead of a more specialized IC.
The IR2111 is a half-bridge driver, which would be needed to interface a 2842 to the output MOSFETs.
And finally, eight op-amps in the 2x LM224's. The remaining unidentified chips may just play minor roles.
Thanks for the info. I was curious.