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ST7LITE0xxx MICROCONTROLLED BALLAST

2 BALLAST STATES

The ballast goes through different states, from the system power-on to steady state running,

End of Life or system power down. An explanatory timing diagram (not in scale) of all the

states is shown in Figure 8. Some of the states are common to the classical ballast applica-

tions; some are improved thanks to the microcontroller solution.

Figure 8. Frequency Timing Diagram

2.1 INIT STATE

During the init phase, the microcontroller sets the PWM frequency at 100kHz and keeps it

steady for 200ms. This feature has been implemented to charge up the blocking capacitor

(C5). In Figure 9 and Figure 10 there are the situations with and without this feature. When the

application goes directly into the preheat phase (as is usual in systems without the microcon-

troller), the voltage on the lamp can exceed maximum values due to a premature ignition. Of

course, if you want to skip this phase, it is still possible just by changing a single line of code.

Init

Preheat

Ignition

Lamp stabilization

Run

time

Figure 9. Lamp Voltage with Init State

Figure 10. Lamp Voltage without Init State