AN2640 datasheet(13/36 Pages) STMICROELECTRONICS

13 / 36 page

AN2640

ST7LIT19BF1 - 8-bit MCU

13/36

Figure 12.

PFC Vin waveform circuit

●

Pin 7: AIN3 - average current. In the ballast during the run state the inductor current is

controlled by monitoring the voltage across Rsense.

Figure 13.

Average current circuit

The voltage across C22 is proportional to the current that flows in the Power MOSFET which

is related to the discharge current in the tube.

When ballast frequency is changed, a current regulation is performed.

●

Pin 8: AIN4 - lamp type detection. This circuit is used to distinguish between lamps

having different cathode resistances. When the NPN transistor Q5 is in the cutoff

region, the PNP transistor Q4 is also, producing a voltage close to zero at pin 8 "Lamp

Type Detection". When the NPN transistor Q5 is in the saturation region, the PNP

transistor Q4 is also, producing at pin 8 "Lamp Type Detection" a voltage that depends

on the resistor of the lamp electrodes. Normally the NPN transistor Q5 is kept in the

cutoff region so that the whole circuit is disabled. This circuit is enabled just to

recognize the lamp family, after recognition, it is disabled.

AN2640 Datasheet(PDF) 13 Page - STMicroelectronics