There are many types of ballasts. In principle, they ca […]
There are many types of ballasts. In principle, they can be composed of resistors, capacitors, inductors, and leakage transformers independently, or they can be combined with these devices or composed of other electronic components.
1, resistance ballast
Resistive ballast relies on the relationship between the voltage on the resistor and the current to adjust the lamp current. The application of the resistor ballast in the DC-powered gas discharge light source circuit is simple and easy to install. When taking into account the circuit efficiency and the working stability of the lamp, when VLAMP=0.6Vn, η=60%, it can be seen that the power consumption of the ballast resistor is very large, and the working efficiency of the circuit is very low.
Resistive ballast has a small number of applications in AC power supply. For example, self-ballasted high-pressure mercury lamps use tungsten wires as ballast devices, and many high-frequency reference ballasts are also made of resistors. The use of a resistive ballast in an AC circuit will affect the waveform of the lamp current, the luminous efficiency of the lamp will also decrease, and the stability of the circuit 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, it will produce a lamp current with a high peak value, which causes serious distortion of the lamp current waveform, which has a very harmful effect on the electrode of the lamp, shortens the life of the lamp, and causes the lamp to flash. Therefore, capacitive ballast is rarely used in low frequency AC circuits.
3, inductive ballast
Inductive ballast works by using the inductor's self-inductance principle, that is, it regulates the lamp current through the voltage on the inductor which is proportional to the time rate of change of the current. Since the lamp current lags behind the power supply voltage for a positioning phase (so it is also called a hysteresis ballast), the power factor of the circuit is low, generally around 0.5. Inductive ballast is more sensitive to changes in supply voltage, and the ballast effect is not stable. Inductive ballast has the advantages of simple circuit, low specific resistance ballast loss, improved lamp current waveform and stable operation, and is widely used in various gas discharge lamps.
In high pressure gas discharge lamps, in order to obtain a higher ignition voltage, a magnetic leakage transformer can be used as an inductive ballast. Magnetic flux leakage transformer is a hysteresis type ballast. Although it is bulky and noisy, it can obtain a higher open circuit voltage than the power supply voltage. It is used for gas discharge lamps whose tube voltage is higher than the power supply voltage (such as neon lamps, cold Cathode lamp, ultraviolet lamp, etc.), can significantly improve the starting performance.
4, inductance, capacitance (LC) ballast
There are two types of LC ballasts. One is a ballast composed of inductance and capacitance in series. It is usually designed so that the capacitive reactance is larger than the inductive reactance, so that the circuit is generally capacitive. When the capacitive reactance is 2.76 times the inductive reactance, the constant current characteristics of the circuit are the most stable. The lamp current of this ballast circuit leads the power supply voltage by a certain phase, and belongs to the advanced ballast.
LC lead type ballast has low power consumption, has better steady current characteristics, and has good short-circuit characteristics when the lamp is started. When used in conjunction with a hysteresis type inductive ballast, it can better improve the power factor of the circuit. However, when the lamp current crosses zero, the peak value of the power supply voltage is opposite to the direction of the lamp voltage, and the repeated ionization voltage is low, resulting in poor repeated ignition capability.
5, electronic ballast
Electronic ballast is a new type of ballast composed of electronic components. It is essentially a power converter, which converts the power frequency AC into an AC voltage of 20-100kHz to start and light the fluorescent lamp. The use of high-frequency AC electronic ballasts can improve the luminous efficiency of the lamp tube, avoid power frequency noise, reduce the volume and weight of the ballast, improve the power factor, and facilitate intelligent control. In principle, it is suitable for all kinds of gas discharge lamps, but the application of fluorescent lamps, especially compact fluorescent lamps, has developed more rapidly.