L6567 STMicroelectronics, L6567 Datasheet - Page 7

• Manufacturer Part Number: L6567
• Description: HIGH VOLTAGE DRIVER FOR CFL
• Manufacturer: STMicroelectronics

Figure 2. Preheating and ignition state.
Ignition mode
At the end of the preheat phase the frequency decreses to the minimum frequency (F
coil current and a high voltage appearing across the lamp. That is because the circuit works near resonance.
This high voltage normally ignites the lamp. There is no protection to avoid high ignition currents through the
MOS transistors when the lamp doesn’t ignite. This only occurs in an end of lamp life situation in which the circuit
may break. Now the lowest frequency is the resonance frequency of L and C
The ignition phase finishes when the frequency reaches F
elapsed. The ignition time is related to T
the same current used to charge it during T
The frequency shifting slope is determined by C
During the ignition time the V
Steady state operation: feed forward frequency
The lamp starts operating at F
high lamp power at high mains voltages, a feed forward correction is implemented. At the end of the preheat
phase the R
increases and overcomes a value set by R
too. The effect is an increase in frequency limiting the power in the lamp. In order to prevent feed forward of the
ripple of the V
Figure 3. Burn state
HV
HV
pin is connected to an internal resistor to sense the High Voltage Bus. If the current in this resistor
voltage, the ripple is filtered with capacitor C
FREQUENCY
F
F
RS
MAX
MIN
MIN
FREQUENCY
monitoring function changes in the capacitive mode protection.
F
, determined by R
MIN
preheating
state
PRE
REF
PRE
: T
IGN
.
, the current that charges the oscillator capacitor C
I
.
= (15/16) · T
ignition
state
REF
and C
feed forward mode
MIN
P
F
PRE
on pin 8 and an integrated resistor R
directly after the ignition phase. To prevent too
or (at maximum) when the ignition time has
burning state
. The C
P
capacitor is charged 15 times with
L
TIME
(the capacitor across the lamp).
Irhv
MIN
), causing an increased
F
AVERAGE
increases
L6567
7/15
.