EFS Datasheet, PDF (8/14 Pages) STMicroelectronics – STARLIGHT-KIT

EFS
4/ AUXILIARY POWER SUPPLY:
In order to reduce the number of components, an
auxiliary power supply is integrated in the ASD™.
This active power supply works directly on the
mains and requires only a low voltage capacitor
16V - 22µF. The operating mode of this supply
varies with the starter operating phase:
POWER SUPPLY SCHEMATIC
R2 R1
DRIVER
D1
R6
G1
ASD
TUBE
7.68
VCC
7.57
C SUPPLY
GND
Supply operation during preheat phase:
During preheat phase, the driver manages alone the supply function (neither the driver nor D1 and R6 are
involved). A part of the current flowing through the ASD™ is used, at the beginning and at the end of each
positive mains half cycle, to charge the output capacitor.
Supply operation during standby phase:
When the lamp is lit, the monitors its supply voltage (Vcc). At the beginning of each positive mains half
cycle, when Vcc is lower than 7.57V, the driver closes the ASD™ supply switch. The capacitor is charged
to provide the standby current of the driver. During this phase the tube lamp is short circuited by the
ASD™. When the supply voltage reaches 7.68V, the driver opens the ASD™ supply switch. Since this
current is also flowing in the ballast, the supply turn off provides across the lamp an additional voltage
spike. After running few minutes the lamp becomes warm and this spike voltage naturally decreases.
SUPPLY DURING PREHEAT PHASE
SUPPLY DURING STANDBY PHASE
(Without E.M.I. Capacitor nor R6 nor D1)
Starter current
Starter voltage
at the ignition
5min after
ignition
To reduce dramatically this repetitive voltage spikes across the lamp, the R6 resistor with the diode D1
provide a part of the supply current. Thus, the ripple voltage of the supply voltage is reduced, as well as the
level of the switched off current. On the other hand, this increases the safety margin of the RF noise
(versus the IEC 55015 limits)
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