UBA2021_4

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 04 — 25 July 2008

5 of 16

NXP Semiconductors

UBA2021

630 V driver IC for CFL and TL lamps

7.5 Ignition state

protection at the end of the preheat time. Normally this results in a further frequency

frequency in the ignition state is less than that in the preheat mode. During the downward

frequency sweep the circuit sweeps through the resonant frequency of the load. A high

voltage then appears across the lamp. This voltage normally ignites the lamp.

7.6 Failure to ignite

Excessive current levels may occur if the lamp fails to ignite. The IC does not limit these

currents in any way.

7.7 Transition to the burn state

Assuming that the lamp has ignited during the downward frequency sweep, the frequency

normally decreases to the bottom frequency. The IC can transit to the burn state in two

ways:

1. In the event that the bottom frequency is not reached, transition is made after

2. As soon as the bottom frequency is reached.

7.8 Feed-forward frequency

During burn state a feed-forward mechanism ensures that the lamp power will not

increase above the maximum allowed value due to an increased mains voltage. In the

feed-forward range the UBA2021 driver IC can be configured in such a way that the

application is optimized for close to constant lamp power. Above a defined voltage level

the oscillation frequency also depends on the supply voltage of the half-bridge (see

Figure 6). The current for the current controlled oscillator is derived from the current

mA) the feed-forward frequency is clamped. In order to prevent feed-forward of ripple on

Fig 5.

Operation in the preheat mode

mgs992

time

burn state

ignition

state

preheat state