1996 Jan 03

7

Philips Semiconductors

Product specification

Electronic TL-lamp starter

UBA2000T

Counter

With the counter, which is supplied with pulses with twice

the frequency of the mains supply, the preheat time for the

first preheat and (if necessary) the next six preheats is

defined.

Time select

Number of starts counter

The number of starts are counted by a counter. After seven

ignition attempts the IC is brought into standby state.

Due to the increased current, the buffer capacitor C1 will

discharge faster when the starter is disconnected from the

mains. This makes it possible to automatically reset the

starter the moment a malfunctioning tube is replaced by a

new one.

Current protection

When the current through the sense resistor exceeds its

the first few periods of conduction, the current protection is

do not trigger the current protection. When the current has

exceeded its limit, the switching device is turned off and

the IC enters the standby state that prevents re-activating

the switching device. Only an interruption of the supply

voltage will reset the standby state.

Output driver

The output driver is capable of driving a low input current

trigger device as well as a device controlled by a gate.

During start-up the output is kept low to prevent turning on

the external switching device.

A typical application that uses a low input current trigger

device (such as TN22) as switching device is given in

Fig.7. The resistive divider R1//R2 is not connected to

ground but to the gate of the trigger device.

This has a minimal effect on the voltage division ratio,

since the voltage at the gate of the trigger device is low.

The output driver generates the current pulse, which is

necessary to activate the external switching device TH1.

This current pulse is synchronized with the voltage at pin 4

and R2 is a part of the current needed to activate the

switching device. If necessary, the current pulse is

delivered every half cycle of the mains voltage. When the

switching device must be turned off, the output driver is

capable of sinking the gate turn-off current of the switching

device.

It might be necessary to limit the current peaks, which flow

through the switching device at turn-on, resulting from

discharging the suppressor capacitor (C2). This can be

achieved using a resistor (R3).

A typical application that uses a MOSFET is given in Fig.8.

In this circuit the resistive divider is connected to ground.

The output driver of the IC operates the same way as when

a trigger device is used. The output current pulse will

charge the gate of the MOSFET. As a result, the MOSFET

will be activated.

To keep the MOSFET conductive, a high ohmic pull-up

resistor is connected between the gate of the MOSFET

and the buffer capacitor C1. This is necessary, because

the output current is a pulse and not a continuous signal.

This pull-up resistor increases the current which is drawn

from the buffer capacitor. An internal zener diode in the IC

limits the voltage at the output (and thus at the gate of the

MOSFET) to a typical value of 6.8 V.

Both switching devices require the breakdown voltage

the TL-lamp.