Common Ballast Methods for Gas Discharge Lamps

Most Gas discharge lamps are made by using the characteristics of arc discharge, and have the negative resistance characteristic that the voltage decreases as the current increases. In order to make the discharge stable, a ballast device must be set between the power supply and the discharge lamp to limit the working current of the lamp and ensure that the lamp works stably. This ballast device is usually called a ballast. A ballast is a device that makes the gas discharge lamp discharge stably. There are many types of ballasts. In principle, it can be composed of resistors, capacitors, inductors and leakage transformers, or it can be composed of these devices or other electronic components. Common ballast methods for gas discharge lamps 1. Resistor ballast Resistor ballast relies on the relationship that the voltage on the resistor is proportional to the current to adjust the lamp current. The resistor ballast is applied in the gas discharge light source circuit powered by DC. The circuit is simple and easy to install. When taking into account the circuit efficiency and the working stability of the lamp, it can be seen that the power consumption of the ballast resistor is large and the working efficiency of the circuit is very low. Resistor ballast has a small number of applications in AC power supply, such as self-ballasted high-pressure mercury lamps using tungsten filaments as ballast devices, and many high-frequency reference ballasts are also made of resistors. Using a resistor ballast in an AC circuit will affect the waveform of the lamp current, the luminous efficiency of the lamp will also decrease, and the circuit stability will deteriorate, but the power factor of the circuit is relatively high. 2. Capacitor ballast When the capacitor works in a low-frequency AC circuit, the lamp voltage waveform is approximately a square wave. Since the capacitor cannot limit the instantaneous current, a lamp current with a very high peak value will be generated, which seriously distorts the lamp current waveform and has a very harmful effect on the lamp electrodes, resulting in a shortened lamp life and flickering lamps. Therefore, capacitor ballast is rarely used in low-frequency AC circuits. 3. Inductive ballast Inductive ballast works on the principle of self-inductance of the inductor, that is, it adjusts the lamp current by the voltage on the inductor being proportional to the time rate of change of the current. Since the lamp current lags the power supply voltage by a certain phase (so it is also called a lagging ballast), the power factor of the circuit is low, generally around 0.5. Inductive ballast is sensitive to changes in the supply voltage, and the ballast effect is not very stable. Inductive ballast has the advantages of simple circuit, lower loss than resistor ballast, improved lamp current waveform and stable operation, and is widely used in various types of gas discharge lamps. In high-pressure gas discharge lamps, in order to obtain a higher ignition voltage, a leakage transformer can be used as an inductive ballast. The leakage transformer is a lagging ballast. Although it is bulky and noisy, it can obtain an open-circuit voltage higher than the power supply voltage. When it is used for gas discharge lamps (such as neon lamps, cold cathode lamps, ultraviolet lamps, etc.) with a lamp tube voltage higher than the power supply voltage, it can significantly improve the starting performance. 4. Inductive and capacitor (LC) ballast LC ballast has two forms. One is a ballast composed of an inductor and a capacitor in series. It is usually designed to have a larger capacitive reactance than an inductive reactance, making the circuit capacitive overall. When the capacitive reactance is 2.76 times the inductive reactance, the constant current characteristic of the circuit is most stable. The lamp current of this ballast circuit leads the power supply voltage by a certain phase, which belongs to a leading ballast. The leading ballast has low power consumption, good current stabilization characteristics, and good short-circuit characteristics when the lamp is started. When used in conjunction with the lagging inductive ballast, it can improve the power factor of the circuit. However, because the peak value of the power supply voltage is exactly opposite to the direction of the lamp voltage when the lamp current passes through zero, the voltage of repeated ionization is low, resulting in poor repeated ignition ability. 5. Electronic ballast Electronic ballast is a new type of ballast composed of electronic components. It is essentially a power converter that converts industrial frequency AC into 20~100kHz AC voltage to start and light up fluorescent lamps. The use of high-frequency AC electronic ballast can improve the luminous efficiency of the lamp tube, avoid industrial frequency noise, reduce the size and weight of the ballast, improve the power factor, and facilitate intelligent control. In principle, it is suitable for all types of gas discharge lamps, but the application of fluorescent lamps, especially compact fluorescent lamps, is developing more rapidly. Electronic ballasts have the following advantages: 1) High power factor, reducing reactive power loss, improving the capacity utilization of power supply equipment, and reducing line loss 2) Energy saving, the power loss of the electronic ballast itself is low, only about 40% of the inductive ballast 3) High luminous efficiency, the luminous efficiency of fluorescent lamps at a high frequency of about 30KHZ is increased by 20% 4) Extended lamp life. No need to start repeatedly, and the lamp will not blacken prematurely 5) Good low temperature and low voltage starting performance Lighting Engineer Community. 6) No flicker, when the lamp works at high frequency, the light is stable, and the human eye cannot feel the flicker of light 7) Avoid power frequency noise, which is conducive to working and studying in a quiet environment 8) Small size and light weight 09) Easy to achieve intelligent control, including dimming, remote monitoring and other technologies.