1996 Jan 03

5

Philips Semiconductors

Product specification

Electronic TL-lamp starter

UBA2000T

During preheating, the integrated circuit draws its supply

current from the buffer capacitor. As a result, the voltage

over the buffer capacitor decreases. When the ignition has

failed after the ignition pulse, the voltage on the buffer

capacitor increases to start level and the external

switching device will be turned on again. This time the

preheat time is reduced to 0.64 seconds because the lamp

electrodes are still warm. An internal counter limits the

number of ignitions attempts to 7. This prevents the lamp

from flickering at end of lamp life.

The UBA2000T has an integrated current protection.

When the current through the sense resistor exceeds the

and the circuit will enter a standby state. Switching the

mains voltage off and on again will reset the circuit.

The flow chart of the starting process is given in Fig.5.

In the following subsections the several blocks of the block

diagram are described in more detail.

IC supply

When the mains power is switched on, the buffer capacitor

is charged and the internal current source is started.

The internal voltage is stabilized, making it independent of

the voltage at the buffer capacitor. An internal zener diode

Voltage detectors

The voltage detectors measure the voltage on the buffer

capacitor and activate the switching device when the start

This time depends on the value of C1, the IC current and

voltage is near its peak value, the switching device is

actually turned on. When the voltage decreases to a value

indicating that the mains supply is interrupted, the starter

is ready to start preheating and igniting the TL-lamp at the

moment the mains supply returns.

Latch

The internal state of the latch represents the state of the

switching device. The setting of the latch depends on the

outputs of the voltage detectors, the number of starts

counter and the standby state. Resetting the latch is

controlled by the timer, the current detector and the current

protection circuit.

Current detector

The current detector detects when the switching device

must be turned off. The current detector also generates the

clock pulses to activate the counter (see Fig.4). For proper

functioning, the preheat current should be within the range

current peaks on the preheat current have no effect on the

counter. Because the current detector has a low-pass

transfer function, it is not influenced by spikes. This

circuitry eliminates the effect of spikes on the preheat time.

Edge detector

The edge detector ensures that the switching device will

be turned off when the rectified preheat current is on the

negative-going edge.

Fig.4 Current detection.

handbook, full pagewidth

MGE007

hysteresis

Iso level

current through

sense resistor

clock signal

(fed to counter)

switch off level at end of preheat

clock generation during preheat