UBA2024 データシートの表示（PDF） - Philips Electronics

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UBA2024

Half-bridge power IC for CFL lamps

Philips Electronics 

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

pin FS and low-voltage supply pin VDD are charged. Pins RC and SW are switched to

ground. The start-up state is defined until VDD = VDD(startup).

7.3 Sweep mode

The IC enters the sweep mode when the voltage on pin VDD > VDD(startup). The capacitor

on pin SW is charged by ISW and the half-bridge circuit starts oscillating. The circuit enters

the start-up state again when the voltage on pin VDD < VDD(stop).

The sweep time (tsweep) is determined by the charge current (Ich(sw)) and the external

capacitor (CSW). Typical the total sweep time set by CSW is:

tsweep = CSW (nF) × 10.3 ms

(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

switched off when the voltage on pin FS is below the high-side lockout voltage Vfloat(UVLO).

7.5 Oscillation

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

the external resistor ROSC and the capacitor COSC (see Figure 4).

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:

fosc

=

--------------------1---------------------

k × ROSC × COSC

(2)

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

given in Figure 4.

UBA2024

Product data sheet

All information provided in this document is subject to legal disclaimers.

Rev. 6.2 — 1 November 2010

© NXP B.V. 2010. All rights reserved.

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