AN1902 Datasheet, PDF (25/32 Pages) STMicroelectronics – DEVICES TO DRIVE 58W TL TUBES

AN1902 - APPLICATION NOTE
4.4.3 IGNITION PHASE
Figure 29 shows the main waveform during the ignition phase. The peak current is limited to ~2A thanks
to the overcurrent protection network made by D1, Dz1 and R6 (see figures 19 and 20). In fact as soon
as the voltage on the sec pin overcomes ~40V the frequency capacitors charge becomes faster (see
CAP1 waveform) anticipating the device switch-off.
Figure 29: Ignition phase
LS CAP1 pin voltage
LS SEC pin voltage
t(s) ^{Choke current}
duc _{Mid point voltage}
olete ^{Pro 4.4.4 STEADY STATE}
s _{Figure 30 shows the steady state phase main waveforms. The working frequency is ~34KHz with a peak}
b _{current of ~700mA.}
) ^{- O} Figure 30: Steady state phase
Obsolete ^{Product(s LS CAP1 pin voltage}
Choke current
LS SEC pin voltage
Mid point voltage
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