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.