KA7543 Datasheet, PDF (6/16 Pages) Fairchild Semiconductor – Advanced Feedback Dimming Ballast Control IC

KA7543
Operating Description
lamp feedback
lamp change
soft moving on dimming
Vcs
2Lamp
2V
1V
0.5V
2V
1V
0
Vfb
Vdm
1Lamp
t[sec]
Figure 1. Operation Characteristics
The KA7543 is an advanced, lamp current feedback ballast dimming control IC which drives half bridge converter. This
control IC provides all the necessary features to implement wide range dimming control, soft-start and constant power
consumption for the intelligent electronic ballast system. The number of external components can be minimized by adopting
the KA7543. Protection circuitry, no lamp protection, abnormal protection, one lamp detection, UVLO and restart on lamp
adding have been included in the KA7543. Fig. 1 shows the operational characteristic of the KA7543 according to time and
lamp count variation. When the Vcc voltage reaches the start-up threshold voltage(9.5V), the soft start capacitor begins to be
charged. When the Cs pin voltage, Vcs is over 2V, the soft start operation ends. During the soft start operation, the reference
voltage which controls the lamp current is proportional to Vcs. Dimming operation starts when Vcs becomes 4V and the
change rate of dimming is determined by the capacitor connected to the Cdm pin. The more smooth dimming can be
accomplished by the larger capacitor connected to the Cdm pin.
UVLO(Under Voltage Lock Out)
Vcc
To output
Reset Cs
UVLO
9.5V
- ^1.8V
3
+
7V Vz
Supply
sw
2V Vref
(bandgap)
2V
Internal
bias
7V
bias
Figure 2. UVLO
Until the Vcc voltage reaches the start-up threshold voltage(9.5V), UVLO circuit lowers the IC operating current below
270µA. When the Vcc voltage reaches the start-up threshold voltage, it generates IC reference voltage(Vref) and supplies bias
current for the whole circuitry. The hysteresis of UVLO circuit is 1.8V.
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