UBA2021T View Datasheet(PDF) - Philips Electronics
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UBA2021T Datasheet PDF : 20 Pages
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Philips Semiconductors
630 V driver IC for CFL and TL lamps
Product specification
UBA2021
handbook, halfpage
fstart
MGS992
fB
preheat state
ignition
state
burn state
time
For calculations refer to Chapter “Design equations”.
Fig.5 Operation in the preheat mode.
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).
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.
handbook, halfpage
f
(kHz)
bottom
frequency
MGS993
feed-forward
range
IRHV (mA)
For calculations refer to Chapter “Design equations”.
Fig.6 Feed-forward frequency.
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.
2002 Aug 02
6
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