AN2459 - Application note

Signals measurement, processing & control

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Figure 15.

Lamp restart - behavior of the control loop

Note:

Brown = DC bus voltage; Blue = lamp filament current.

4.3

Zero Current Detection

Detection of a zero current crossing the PFC inductor is extremely important. As described

in Section 2: Power Factor Correction (PFC), a ZCD defines the moment when the switch

should be turned-on again. A well-known method used in other analog PFC applications has

been implemented for the digital ballast. The secondary winding of PFC inductor (1:10

winding ratio) gives a correct signal for the autoreload timer (Chapter 2.2). Typical signals

are shown in Figure 16.

Lamp removed

Lamp inserted