UBA2024AP NXP [NXP Semiconductors], UBA2024AP Datasheet - Page 4

• Manufacturer Part Number: UBA2024AP
• Description: Half-bridge power IC for CFL lamps
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
UBA2024_4
Product data sheet
7.5 Oscillation
The oscillation is based upon the 555-timer function. A self oscillating circuit is made with
the external resistor R
To realize an accurate 50
frequency to half the oscillator frequency.
The output voltage of the bridge will change at the falling edge of the signal on pin RC.
The design equation for the half-bridge frequency is:
An overview of the oscillator signal, internal LS and HS drive signals and the output is
given in
When entering the sweep mode (V
nominal bridge frequency and sweeps down to the nominal frequency (bridge), set by
R
swing between V
will continue to increase until V
of the sweep time. The voltage on pin SW however will continue to rise until it reaches
supply voltage level.
During this continuous decrease in frequency, the circuit approaches the resonance
frequency of the load, and this causes a high voltage across the load, which ignites the
lamp. 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. See
f
Fig 4.
osc
OSC
=
and C
----------------------------------------- -
k x R
Figure
Oscillator, drivers and output signals
OSC
OSC
1
4.
. During the sweep mode the amplitude of the RC oscillator on pin RC, will
Figure
x C
trip(osc)low
OSC
Rev. 04 — 17 September 2009
OSC
5.
bridge
V
drive
drive
and V
and the capacitor C
V
OUT
half
HS
RC
LS
duty cycle, an internal divider is used. This reduces the bridge
0
0
0
0
SW
SW
+ 0.4V
SW
+ 0.4V
= 0 V), the bridge oscillator starts at 2.5 times the
trip(osc)high
trip(osc)high
OSC
(see
= V
Half-bridge power IC for CFL lamps
. The amplitude of the RC oscillator
trip(osc)high
Figure
014aaa658
time
time
time
time
4).
, this determines the end
UBA2024
© NXP B.V. 2009. All rights reserved.
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