L6567D 查看數據表（PDF） - STMicroelectronics
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L6567D Datasheet PDF : 15 Pages
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Figure 2. Preheating and ignition state.
FREQUENCY
FMAX
FMIN
preheating
state
ignition
state
burning state
TIME
L6567
Ignition mode
At the end of the preheat phase the frequency decreses to the minimum frequency (FMIN), causing an increased
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 CL (the capacitor across the lamp).
The ignition phase finishes when the frequency reaches FMIN or (at maximum) when the ignition time has
elapsed. The ignition time is related to TPRE: TIGN = (15/16) · TPRE. The CP capacitor is charged 15 times with
the same current used to charge it during TPRE.
The frequency shifting slope is determined by CI.
During the ignition time the VRS monitoring function changes in the capacitive mode protection.
Steady state operation: feed forward frequency
The lamp starts operating at FMIN, determined by RREF and CF directly after the ignition phase. To prevent too
high lamp power at high mains voltages, a feed forward correction is implemented. At the end of the preheat
phase the RHV pin is connected to an internal resistor to sense the High Voltage Bus. If the current in this resistor
increases and overcomes a value set by RREF , the current that charges the oscillator capacitor CF increases
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 VHV voltage, the ripple is filtered with capacitor CP on pin 8 and an integrated resistor RAVERAGE.
Figure 3. Burn state
FREQUENCY
FMIN
feed forward mode
Irhv
7/15
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