Uc3842/45 is a standard driver known in most PC power supplies and
monitors. It has all requirements you need except is not working with
power supply less then 8...9V. The other requirements can be easily
achieved. So, I propose to keep your actual design and to built a cheap
( two transistors and a few other components ) oscillator who may run from
under 9V and to supply the UC3842 with minimum 11V all the time.
Vasile

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