TN22

3/7

This thyristor has been designed for use as a fluo-

rescent tube starter switch.

An electronic starter circuit provides :

current is applied to the cathode heaters.

s One or several high voltage striking pulses

across the lamp.

TN22

R

S

STARTER CIRCUIT

CONTROLLER

(TIMER)

INDUCTANCE

BALLAST

FLUORESCENT

TUBE

AC

VOLTAGE

BASIC APPLICATION DIAGRAM

PRINCIPLE OF OPERATION

1/ Pre-heating

At rest the switch S is opened and when the mains

voltage is applied across the circuit a full wave rec-

tified current flows through the resistor R and the

TN22 gate : at every half-cycle when this current

tor turns on.

When the device is turned on the heating current,

limited by the ballast choke, flows through the tube

heaters.

The pre-heating time is typically 2 or 3 seconds.

2/ Pulsing

At the end of the pre-heating phase the switch S is

turned on. At this moment :

If the current through the devices is higher than the

off.

If the current is equal or lower than the holding cur-

rent the thyristor turns off instantaneously.

When the thyristor turns off the current flowing

through the ballast choke generates a high voltage

pulse. This overvoltage is clamped by the thyristor

If the lamp is not struck after the first pulse, the sys-

tem starts a new ignition sequence again.

3/ Steady state

When the lamp is on the running voltage is about

150V and the starter switch is in the off-state.

IMPLEMENTATION

The resistor R must be chosen to ensure a proper

triggering in the worst case (minimum operating

temperature) according to the specified gate trig-

gering current and the peak line voltage.

Switch S : This function can be realized with a gate

sensitive SCR type : P0130AA 1EA3

This component is a low voltage device (< 50V)

and the maximum current sunk through this switch

can reach the level of the thyristor holding current.

The pre-heating period can be determined by the

time

constant of

a

capacitor-resistor circuit

charged by the voltage drop of diodes used in se-

ries in the thyristor cathode.