EFS Datasheet, PDF (7/14 Pages) STMicroelectronics – STARLIGHT-KIT

Present solutions work with a unidirectional
switch, like MOS transistors or GTO (Gate Turn
Off thyristor). As a starter is a bi-directional switch,
it is necessary to use a rectifier bridge (4 diodes of
1500V ). More, 2 or 3 diodes in series with the
GTO are required to get the necessary switch off
effect, and the whole is controlled with an analog
timer built around a small SCR.
The interest of a bi-directional switch arises itself:
a drastic reduction of the number of components,
and of course, a reduction of power losses (only 1
forward voltage instead of 5).
EFS
Conventional discrete circuit (minimal version)
1500V
GTO
SCR
3/ LAMP IGNITION FEATURE:
A lamp requires a minimum energy level to be ignited, but this energy depends especially on the lamp
temperature. The lower the temperature is, the more energetic the lamp strike is.
This energy stored in
In other words, the
the ballast is directly proportional to the Switched
required energy and of course the I_SO level,
Off current I _SO
are maximum
(E =
L.I _SO
2
).
for the m2inimum
temperature. Results based on experiments show that it is necessary to switch off a current of 350 mA to
strike a 58W tube at -30°C (with a voltage amplitude clamped at 1200V and starting aid).
Therefore, the best way to strike a tube independently of the temperature is to keep the maximum I_SO level
for all the temperature range. Unfortunately, the solution is not so simple to implement because the energy
level at ambient or warm temperature would be much important: the lamp would be ignited, but the lamp
lifetime would be shortened. This is why one of the innovations of the ASD™ is to modulate the striking
energy versus temperature (see feature hereafter).
350mA
I.S.O.
Switched off current
versus ambient temperature
200mA
A.S.D.™ FEATURE
For freezing temperatures, the I_SO level is maintained at 350 mA, and for positive temperatures, the I_SO
level decreases slowly.
7/14