UBA2021 datasheet(6/20 Pages) PHILIPS

6 / 20 page

2001 Jan 30

Philips Semiconductors

Product speciﬁcation

630 V driver IC for CFL and TL lamps

UBA2021

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.

Failure to ignite

Excessive current levels may occur if the lamp fails to

ignite. The IC does not limit these currents in any manner.

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.

Feed-forward frequency

Above a defined voltage level the oscillation frequency

also depends on the supply voltage of the half-bridge

(see Fig.6). The current for the current-controlled oscillator

is in the feed-forward range derived from the current

through RRHV. 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 and 1.6 mA) the feed-forward frequency is clamped. In

order to prevent feed-forward of ripple on Vin, the ripple is

filtered out. The capacitor connected to pin CP is used for

this purpose. This pin is also used in the preheat state and

the ignition state for timing (tph and tign).

Capacitive mode protection

When the preheat mode is completed, the IC will protect

the power circuit against losing the zero voltage switching

condition and getting too close to the capacitive mode of

operation. This is detected by monitoring voltage VRS at

pin RS. If the voltage is below VRS(cap) at the time of

turn-on of T2, then capacitive mode operation is assumed.

Consequently the frequency increases as long as the

capacitive mode is detected. The frequency decreases

down to the feed-forward frequency if no capacitive mode

is detected. Frequency modulation is achieved via pin CI.

handbook, halfpage

MGS992

time

burn state

ignition

state

preheat state

fstart

Fig.5 Operation in the preheat mode.

For calculations refer to Chapter “Design equations”.

handbook, halfpage

MGS993

bottom

frequency

feed-forward

range

(kHz)

IRHV (mA)

Fig.6 Feed-forward frequency.

For calculations refer to Chapter “Design equations”.

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