Recently, the operation of discharge lamps at frequencies
in the several tens kHz range has been a matter of great
interests for the reduction of the size, weight, and power
consumption of the ballast. However, for high intensity
discharge (HID) lamps, acoustic resonance (AR) has been
observed especially when they are operated at high frequency.
Such AR phenomenon causes various problems such as arc
instability, light output fluctuation, color temperature
variation, and in the worst case, may crack arc tubes. On the
other hand, high voltage stress may be caused due to the arc
extingushing , which is very dangerous to the ballast.
In order to eliminate the AR in HID lamps, a reasonable
criterion for AR must be determined first. Many efforts have
been made. Witting['] considered arc instability as a unique
criterion of AR which consumers concem most. However, for
the ballast designers, it is necessary to reflect such instability
into a certain electrical signal which can be used to eliminate
AR through some feedback control strategy. A reliable testing
method was proposed by R.Schafer[*].I n hs experiment, a
precision phonometer was adopted to measure the sound
intensity from the arc tube. Although the measured resonance
points coincided with the estimated ones well, it is incredible
for a ballast containing such an expensive phonometer. As a
matter of fact, the testing and eliminating AR of HID lamps is
now becoming one of the toughest task for designers of
electronic ballasts.
This paper presented a novel testing method for AR.
The line voltage feed forward (LVFF) method was adopted to
increase the testing precision. The experimental results show
that the proposed scheme makes the examination of AR
simple and reliable.