UBA2021 データシートの表示（PDF） - NXP Semiconductors.

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UBA2021

630 V driver IC for CFL and TL lamps

NXP Semiconductors. 

NXP Semiconductors

UBA2021

630 V driver IC for CFL and TL lamps

fstart

fB

preheat state

Fig 5. Operation in the preheat mode

ignition

state

burn state

time

mgs992

7.5 Ignition state

The RS monitoring function changes from VRS(ctrl) regulation to capacitive mode

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

decrease down to the bottom frequency fB (approximately 43 kHz). The rate of change of

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

reaching the ignition time tign.

2. As soon as the bottom frequency is reached.

The bottom frequency is determined by RRREF and CCF.

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

through RRHV in the feed-forward range. The feed-forward frequency is proportional to the

average value of the current through RRHV within the operating range of Ii(RHV), given the

lower limit set by fB. For currents beyond the operating range (i.e. between 1.0 mA and 1.6

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

UBA2021_4

Product data sheet

Rev. 04 — 25 July 2008

© NXP B.V. 2008. All rights reserved.

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