UBA2028 データシートの表示（PDF） - NXP Semiconductors.
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UBA2028 Datasheet PDF : 23 Pages
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NXP Semiconductors
UBA2028
600 V dimmable power IC for compact fluorescent lamps
8.5 Preheat state
After starting at fmax, the frequency decreases until the momentary value of the voltage
across sense resistor R21 (see Figure 8) or R5 (Figure 9) reaches the internally fixed
preheat voltage level (pin PCS). Detection of the preheat voltage occurs during the end of
the ‘on-time’ of the low-side switch TR2 when the internal preheat fixed voltage reference
level is exceeded. Once detection has occurred the output current of the Preheat Current
Sensor (PCS) circuit discharges the capacitor CCSW, thus raising the frequency. The
internal preheat control is reset during each “on-time’ of the high-side switch TR1, thus
CCSW is charged, and the frequency decreases. It remains in this condition when no
detection occurs. The preheat time begins at the moment that the circuit starts oscillating.
During the preheat time the Average Current Sensor (ACS) circuit is disabled. An internal
filter of 30 ns is included at pin PCS to increase the noise immunity.
8.6 Ignition state
After the preheat time the ignition state is entered and the frequency will sweep down due
to charging of the capacitor at pin CSW with an internally fixed current; see Figure 4.
During this continuous decrease in frequency, the circuit approaches the resonant
frequency of the load. This will cause a high voltage across the load, which normally
ignites the lamp. The ignition voltage of a lamp is designed above the Vlamp(fail) level. If the
lamp voltage exceeds the Vlamp(fail) level the ignition timer is started.
8.7 Burn state
If the lamp voltage does not exceed the Vlamp(max) level the voltage at pin CSW will
continue to increase until the clamp level at pin CSW is reached; see Figure 4. As a
consequence the frequency will decrease until the minimum frequency is reached.
When the frequency reaches its minimum level it is assumed that the lamp has ignited
and the circuit will enter the burn state. The Average Current Sensor (ACS) circuit will be
enabled. As soon as the averaged voltage across sense resistor R21 (see Figure 8) or R5
(Figure 9), measured at pin CSN, reaches the reference level at pin CSP, the average
current sensor circuit will take over the control of the lamp current. The average current
through R21 or R5, is transferred to a voltage at the voltage controlled oscillator and
regulates the frequency and, as a result, the lamp current.
8.8 Lamp failure mode
8.8.1 During ignition state
If the lamp does not ignite, the voltage level increases. When the lamp voltage exceeds
the Vlamp(max) level, the voltage will be regulated at the Vlamp(max) level; see Figure 5.
When the Vlamp(fail) level is crossed the ignition timer has already started. If the voltage at
pin LVS is above the Vlamp(fail) level at the end of the ignition time the circuit stops
oscillating and is forced into the Power-down mode. The circuit will be reset only when the
supply voltage is powered down.
8.8.2 During burn state
If the lamp fails during normal operation, the voltage across the lamp will increase and the
lamp voltage will exceed the Vlamp(fail) level; see Figure 6. At that moment the ignition
timer is started. If the lamp voltage increases further it will reach the Vlamp(max) level. This
forces the circuit to re-enter the ignition state and results in an attempt to reignite the
UBA2028
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 02 — 19 July 2010
© NXP B.V. 2010. All rights reserved.
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