UBA2021 datasheet(5/20 Pages) PHILIPS

5 / 20 page

2001 Jan 30

Philips Semiconductors

Product speciﬁcation

630 V driver IC for CFL and TL lamps

UBA2021

FUNCTIONAL DESCRIPTION

Introduction

The UBA2021 is an integrated circuit for electronically

ballasted compact fluorescent lamps and their derivatives

operating with mains voltages up to 240 V (RMS). It

provides all the necessary functions for preheat, ignition

and on-state operation of the lamp. In addition to the

control function, the IC provides level shift and drive

functions for the two discrete power MOSFETs, T1 and T2

(see Fig.7).

Initial start-up

Initial start-up is achieved by charging capacitor CS9 with

the current applied to pin RHV. At start-up, MOSFET T2

conducts and T1 is non-conducting, ensuring Cboot

becomes charged. This start-up state is reached for a

supply voltage VVS(reset) (this is the voltage level at pin VS

at which the circuit will be reset to the initial state) and

maintained until the low voltage supply (VVS) reaches a

value of VVS(start). The circuit is reset in the start-up state.

Oscillation

When the low voltage supply (VVS) has reached the value

of VVS(start) the circuit starts oscillating in the preheat state.

The internal oscillator is a current-controlled circuit which

generates a sawtooth waveform. The frequency of the

sawtooth is determined by the capacitor CCF and the

current out of pin CF (mainly set by RRREF). The sawtooth

frequency is twice the frequency of the signal across the

load. The IC brings MOSFETs T1 and T2 alternately into

conduction with a duty factor of approximately 50%.

Figure 4 represents the timing of the IC. The circuit block

'non-overlap' generates a non-overlap time tno that

ensures conduction periods of exclusively T1 or T2. Time

tno is dependent on the reference current IRREF.

Operation in the preheat mode

The circuit starts oscillating at approximately 2.5

× fB

(108 kHz). The frequency gradually decreases until a

defined value of current Ishunt is reached (see Fig.5). The

slope of the decrease in frequency is determined by

capacitor CCI. The frequency during preheating is

approximately 90 kHz. This frequency is well above the

resonant frequency of the load, which means that the lamp

is off; the load consists of L2, C5 and the electrode

resistance only. The preheat time is determined by

capacitor CCP. The circuit can be locked in the preheat

state by connecting pin CP to ground. During preheating,

the circuit monitors the load current by measuring the

voltage drop over external resistor Rshunt at the end of

conduction of T2 with decision level VRS(ctrl). The

frequency is decreased as long as VRS >VRS(ctrl). The

frequency is increased for VRS <VRS(ctrl).

handbook, halfpage

MGS991

time

start-up

V(G1-S1)

V(G2)

tno

internal

clock

VCF

Fig.4 Oscillator timing.

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