| The current is always limited by the impedance of the choke (the same way as any other series reactor ballast, only the operating frequency is high, therefore the choke small and has nearly no losses).
But the impedance is a function of the operating frequency.
And the frequency is generated by the inverter.
And in the way, how the frequency is steered, the ballast concepts differ.
Some use really fixed frequency (steered by an RC time constant), so the reactance is constant, so the current depend on the actual load voltage (the elliptical characteristic, like normal magnetic ballast). This concept is most frequently used with intelligent programmed start ballasts, where such oscillator is the simplest solution.
Some designs utilize the frequency dependency of the coil impedance and so steer the frequency so, the resulting current is about constant in quite wide range of load and line voltages. This behavior is intrinsic to the ring core transformer feedback self oscillating ballasts (the switching points, so the current, is dictated by the ring core saturating).
And most dimmable ballast use a feedback system adjusting the oscillator so to get the desired lamp current according to the actual dimmer setting. There it is necessary mainly because tat low setting the actual current becomes extremely sensitive on any component variation, so without the feedback it would require unfeasible accuracy of all involved components (include the lamp). The feedback then works the same way at full power setting, just the set current corresponds to the full rated current.
The F36T8 and F58 have about the same arc voltages, so the current will remain the same on any of the ballast concepts...
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