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I have received quite a few questions from people wanting to know more about low voltage fluorescent inverters. If you have a specific question, send me an Email and I will endeavor to assist. |
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These notes apply to low voltage, low wattage inverters. There seem to be two main configurations, Driven and Self-Resonant.
Most small lamps run with an applied voltage of between 50V and 100V, depending on wattage and tube length. To strike the lamp a much higher voltage must be applied, usually between 200V and 600V. Often, to strike the lamp, a series inductor and a capacitor across the lamp form a series resonant circuit that boosts the voltage applied to the lamp. When the lamp is lit the energy passes through the lamp which now has a much lower impedance. For maximum lamp life, the current passed through the lamp should not be too high. The light output is directly related to the current through the lamp. I have read that the lamp efficiency is not greatly affected by frequency. The inverters I have designed and built are all driven, consisting of a switch-mode control IC and two mosfets driving the primary of a transformer. The secondary supplies the lamp. The lamp is struck using the same series resonance principal. I have built quite a few of a PL11 (11 Watt, 4 pin lamp) inverter which runs off 75V DC. This circuit operates at about 170khz and is about 85% efficient. See picture below. I have also produced a variation on this unit that runs an 18W lamp from a 12V DC supply. The currents are much higher, so efficiency in the switching mosfets is slightly lower.
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There is quite a bit of information available on the Internet. Many of the companies making transistors have data sheets and application notes describing these circuits. Have a look at: Motorola and ST: click here for Links |
