UBA2024

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© NXP B.V. 2010. All rights reserved.

Product data sheet

Rev. 6.2 — 1 November 2010

4 of 17

NXP Semiconductors

UBA2024

Half-bridge power IC for CFL lamps

7.

Functional description

7.1 Supply voltage

The UBA2024 does not require an external low-voltage supply as the mains supply

voltage applied to pin HV powers it. The IC derives its own low supply voltage from this for

its internal circuitry.

7.2 Start-up state

With an increase of the supply voltage on pin HV, the IC enters the start-up state. In the

start-up state the high-side power transistor is not conducting and the low-side power

transistor is switched on. The internal circuit is reset and the capacitors on the bootstrap

7.3 Sweep mode

(1)

During the sweep time the current flowing through the lamp electrodes performs some

preheating of the filaments. See Figure 5.

7.4 Reset

A DC reset circuit is incorporated in the high-side driver. The high-side transistor is

7.5 Oscillation

The oscillation is based upon the 555-timer function. A self oscillating circuit is made with

To realize an accurate 50

% duty cycle, an internal divider is used. This reduces the bridge

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:

(2)

An overview of the oscillator signal, internal LS and HS drive signals and the output is

given in Figure 4.

t

sweep

C

SW

nF

() 10.3 ms

×

=

f

osc

1

kR

OSC

×

C

OSC

×

-----------------------------------------

=