Electronic Ballast—High Frequency Power Adapter for Fluorescent Lamps

　　The power adapter used in the lighting is 60Hx AC, and a ballast or current limiting element is needed to connect the lamp in series. The current-limiting element must be used because the lighting has a negative input impedance characteristic in its working area. The electromagnetic ballast is equivalent to an inductor or the increased leakage inductance of the transformer secondary.

　　In the preheating lamp tube, the switch quickly closes to preheat the filament, and then opens immediately after lighting. The current on the inductor generates a sharp voltage to ignite the lamp.

　　The quick-start lamp always uses a self-heating filament when starting and after lighting. The instant-started lamp does not heat the filament when it is started, but relies on field emission to provide an electron cloud to start the lamp. This saves preheating energy, but requires a higher starting voltage, which will cause the cathode material to fall off and shorten the lamp life.

　　The series inductance is necessary as a lossless current-limiting element because the lighting exhibits negative input impedance characteristics. Its characteristic is that when the lamp input current increases, the voltage across the lamp tube drops. Therefore, if a power adapter with low output impedance is used to supply power to the lighting, any momentary increase in the input current of the lamp will cause the voltage on the lamp to drop, and the current will become larger. This process will continue until the lamp tube is damaged due to excessive current, or the voltage across the lamp drops below the minimum maintenance voltage and goes out.

　　From 1938 to the mid-1980s, the sales of lighting required the same amount of cheap electromagnetic ballasts. The main disadvantage of using low-cost electromagnetic ballasts was the low efficiency due to the loss of the inductor coil and the iron core magnetic sheet. At the same time, due to the zero-crossing point of the 60Hz power adapter waveform, the lamp will be repeatedly extinguished and produce significant flicker, which will reduce the average brightness of the lamp, which is dangerous for rotating machines based on the gate effect. Secondly, due to the vibration of the iron core magnet pieces, it is necessary to seal them in the jar with asphalt or varnish, which will cause fire and assembly problems. In the end, its typical weight reached 4 pounds. Although this is allowed in the industry, it is still a big disadvantage.

　　These shortcomings make us turn our attention to using a high-frequency 12V power adapter to drive the lighting. The advantage is that it improves the efficiency of the lamp (the output power of the lamp per watt of input power), and is smaller and lighter.

　　Early experience shows that the efficiency of capacitive lighting will increase as the frequency increases, and it will stabilize at 14% around 20kHz (pictured), and the capacitive ballast is smaller and lighter, and does not emit audible noise. It is also relatively low. At the same time, under high frequency, the lamp will not flicker, and the conducted and radiated electromagnetic interference is easier to suppress.

　　These significant advantages of the lamp working at high frequencies must rely on the use of practical and inexpensive high-frequency power adapter circuits. It can be considered to equip each lamp with a small SCR inverter, and the lamp group in a large factory or a large office building can consider using a larger SCR, or even a high-frequency rotating alternator. With the rapid decline in the prices of power transistors and ferrite cores, local DC/AC inverters have replaced large-scale centralized massage fitness equipment power adapter generators. It has become possible to directly supply power to one lamp or two to four lamps in each group with an AC rectifier converted power adapter.

　　When the electronic ballast is adopted, most of the performance indicators can be achieved, but its price is still higher than that of the electromagnetic ballast. But when it is considered that it will save electricity costs and extend the life of the lamp, this has prompted high-frequency electronic ballasts to continuously replace electromagnetic ballasts in the installation of new buildings. It is not necessary to replace the lamp tube when reinstalling the electronic ballast to replace the electromagnetic ballast. Therefore, this kind of replacement has great market potential in large office buildings and large factories.

　　According to estimates, the cost of replacing the electronic ballast can be covered by the electricity saved after the replacement in about one year. If all factories use new electronic ballasts, a total of 20%-25% of the cost of electricity can be saved. The realization of low energy consumption is attributed to the high frequency operation which eliminates the flicker of the lamp, increases the working current, makes the lamp work in a more efficient range, and the use of capacitive ballasts achieves lower losses than electromagnetic ballasts .

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