Bulletin 2007

01/08/2007

The ballast circuit drives the gas discharge lamps with a slew angle controlled power waveform and a means for providing a digital reference value to control the power waveform; this also ensures that the correct current is also fed to the lamp depending on the age and type of lamp.

The major advantage of this innovation/invention is:

The power waveform current and shape is controlled by a micro controller, this ensures a quick zero current to positive current and a defined current controlled current slew rate, this minimises the time that the arc is extinguished. This ensures that the new arc will be identical to the original arc as this will deliver solid arc stability, the gradual transition on increasing current, a controlled rise over time to peak current and then a controlled decay over time provides a suitable slew rate. This ensures a number of benefits, benefits that will extend lamp life and lumens throughout lamp life with the elimination of lamp sputtering, there is no possibility of lamp acoustic harmonics which causes the lamps mechanically assembly to “ring” which can in a very short time cause the mechanically assembly of the lamp itself to fail. As it also provides a flat top power waveform crest factor the ratio of peak value to the RMS value is minimised, which also adds to ensuring maximum lamp life and improved lumen output through its life. (This method is patented)

The very important benefit of this innovation is: that it achieves a quick zero cross transition to minimise the time for which the arc is extinguished while at the same time compensating for acoustic harmonics especially during various transitions of dimming. Different shapes of waveforms can be accommodated and the percentage rise in current instantaneously can vary depending on the particular constructions of gas discharge lamps as this can vary from 25% to 75% depending on the different type of lamps peak currents and the particular gas fill.

Another patented innovation is the technique where at a (which is beneficial to control and monitoring and predicting when the lamp fails) certain voltage before cycling or rectification is reached the Selc ballast can cut off the power to the lamp. This is because of the above and the ability to accurately measure the voltage and current fed to the lamp. If the voltage and current was not controlled then not alone would the lamp fail but the ballast could fail aswell and this happens more that is realised. Eventually there arrives a stage when a circuit cannot deliver the drive to the lamp and it is important that the ballast can detect this and switch off the lamp before it gets to that stage. This innovation allows us to set predetermined levels along the lamp life cycle and feed this information to the ballast control circuit to turn of the power to the lamp before the critical stage, as a further benefit we can forward this information to a monitoring and control tele-management system to inform maintenance of possible lamp failure within a number of hours.

For all discharge lamps to operate correctly it is necessary for the lamp ignition to be controlled in a smart and correct way. The lamps need the correct train of high voltage pulses for the correct period of time and depending on the type of lamp and the length of time the lamp is operating: be able in a smart way to increase the voltage levels of the pulses depending on the type of lamps connected and the changing characteristics through life of the lamps. This is necessary especially for the powering of ageing CDM lamps, as we increase burning hours we must increase the voltage of the ignition pulse aswell, thousands of volts maybe necessary to ignite those lamps as they age, we must ignite them very fast aswell and this again is very necessary especially if we are constantly dimming the lamps.

None of our competitors drive the lamps with this type of innovation; they just supply a square wave voltage waveform to drive the lamps. A number of our competitors drive them at very high frequencies so as to reduce the selling cost. Driving them at high and very frequencies leads to high lamp failure rates especially when they attempt to dim the lamps and even more so as the lamps age. Any oscillations in the arc have the effect of reducing the lamps life and they will find it difficult to control lamp sputtering. Lamp sputtering leads to blackening of the arc tube walls and this leads to a constant decrease in light output as the lamp ages.

Especially now as we are beginning to introduce dimming after initial lamp switch “on” the power waveform is critical especially if we want to maintain colour temperature aswell.

The Selc electronic ballasts are now actively powering and dimming all types of discharge lamps now with over eight years and no catastrophic lamp failure or rapid reduction of light output has ever been reported. Furthermore it powers and dims all the present new Metal Halide lamps with no degradation or as with most other types of electronic ballasts no arc tube destruction.

The Selc Smart Electronic Ballast delivers to the lamp:

Instant Turn-on and fast warm up
Non destructive lamp dimming
Enhanced lamp life
Better lumen maintenance throughout the lamps life
The correct electrical breakdown
The perfect cold cathode glow discharge
The perfect thermionic arc or hot cathode glow discharge

Because:

All HID Lamps Need Higher Current During The Thermionic Arc Phase Especially Metal Halide Lamps
The lamp needs the correct high voltage pulses to initiate the Cold Cathode Glow Discharge

As:

Breakdown formation is subject to formative and statistical lag times
Formative lag time is controlled by the gas dielectric properties
By the type of gas or mixture of gas and by the field strength and the neutral particle density
The formative lag time can be microseconds or milliseconds depending on the lamps depending on the lamp type
Statistical lag time depends on the presence of free electrons inside the arc tube their volume and reduced field

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