KA7543

6

Operating Description

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)

Figure 2. UVLO

Until the Vcc voltage reaches the start-up threshold voltage(9.5V), UVLO circuit lowers the IC operating current below

270

µA. 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.

2V

1V

0.5V

2V

1V

0

Vdm

t[sec]

soft moving on dimming

lamp change

lamp feedback

Vcs

Vfb

1Lamp

2Lamp

3

bias

2V

sw

2V Vref

(bandgap)

Internal

bias

7V

9.5V

1.8V

7V Vz

Supply

Reset Cs

UVLO

+

-

Vcc

To output