UBA2024 datasheet(4/11 Pages) PHILIPS

4 / 11 page

2004 Feb 03

Philips Semiconductors

Product speciﬁcation

Half-bridge power IC for CFL lamps

UBA2024

When entering the sweep mode, the oscillator starts at

2.5 times the nominal bridge frequency and sweeps down

to the nominal bridge frequency fnom; see Fig.4. During this

continuously decreasing of the frequency, the circuit

approaches the resonance frequency of the load. This

causes a high voltage across the load, which normally

ignites the lamp.

The sweep time tsweep is determined by the charge current

Ich(sw) and the external capacitor CSW. The sweep to

resonance time should be much larger than the settling

time of the supply voltage on pin HV to guarantee that the

full high-voltage is present at the moment of ignition.

The amplitude of the RC oscillator is equal to the minimum

value of VRC(h) and VSW + 0.4 × VRC(h).

During the sweep time a current is flowing through the

lamp electrodes for pre-heating the filaments.

Glow time control

The drawback of cold-started CFL lamps is its inherent

glow time which reduces the switching lifetime of the

electrodes (lamp). To make this glow phase as short as

possible, the maximum power is given to the lamp during

the glow time via a special control; see Fig.4.

Non-overlap time

The non-overlap time is defined as the time that both

MOSFETs are not conducting. The non-overlap time is

internally fixed.

handbook, halfpage

MDB031

VRC

VOUT

drive

time

half

bridge

Fig.3 Oscillator, drivers and output signals.

handbook, halfpage

VHV

VDD

0.8VRC(h)

VSW

fosc

Vlamp

Vign

Vglow

Vnom

2.5fnom

fnom

VDD(start)

MDB032

time

minimum glow time control

tsweep

Fig.4 Start-up frequency behaviour.

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