UM10564 datasheet(7/21 Pages) PHILIPS

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UM10564

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User manual

Rev. 1 — 20 August 2012

7 of 21

NXP Semiconductors

UM10564

UBA2017DB1064 2 x 28 W T5 demo board

5.2.2 Mains harmonics

The Continuous Input Current (CIC) circuit manages the IEC mains harmonics class-C

requirements. The CIC circuit consists of Dcic1, Dcic2, Lcic, Ccic. Dcic1 is a fast diode in

series with the diode bridge. Dcic1 ensures a fast switch off behavior of the bridge diodes.

5.2.3 Lamp current crest factor

To meet the lamp current crest factor for IEC requirements, the lamp current control loop

is used. The lamp current control loop reduces the peak of the lamp current when the

mains voltage it at the maximum. The lamp current is sensed using resistor Rsense. Below

50 kHz the quasi-peak conducted emission requirements of IEC is 110 dB

V. Therefore

the half-bridge frequency is kept below 50 kHz, so there is headroom to allow some HF

ripple in the mains current.

5.2.4 Small and low-cost half-bridge coil

If a lamp cannot ignite, the ballast generates a voltage of 750 V (RMS) which is sufficient

to ignite any T5 lamp. The ignition voltage is maintained over approximate 150 ms to

guarantee ignition of cold and old lamps. In this ignition phase, the LC tank inductor is

saturating. The UBA2017 controller increases the half-bridge frequency instantaneously

when the saturation current occurs. The level of saturation is set using a sense resistor in

the source of the low side switch. Figure 7 shows the saturating current and the open

lamp voltage during ignition.

(1) C1 = Vbus

(2) C2 = anode VD5

(3) F1 = VC4

(4) C4 = connector Vlamp

Fig 6.

Bus voltage during open lamp ignition

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