Classification and Working Principle of Ballast Resistor

Catalog

Ⅰ Introduction

A ballast resistor is a device that limits current and generates an instantaneous high voltage on fluorescent lamps. It is made by winding enameled wire on an iron core made of silicon steel. When such a coil with an iron core turns on/off in an instant, it will self-induce and generate high voltage, which is applied to the electrodes (filaments) at both ends of the fluorescent tube. This action is performed alternately. When the starter (jumping bulb) is closed, the filament of the lamp tube passes through the current limit of the ballast and conducts heat; when the starter is open, the ballast will self-induct and generate a high voltage on the filaments at both ends of the tube. The filament emits electrons to bombard the fluorescent powder on the tube wall to emit light. The starter is repeatedly turned on and off several times, and this action will be repeated several times to open the tube. When the lamp tube emits light normally, the internal resistance becomes smaller, and the starter always keeps an open circuit state. The current will stably pass through the lamp tube and the ballast to work so that the lamp tube emits light normally. Since the ballast always has current passing through when the fluorescent lamp is working, it is easy to produce vibration and heat. Ballast resistors are divided into electronic ballasts and inductance ballasts.

Ⅱ History and development

In the late 1980s, the United States applied toroidal inductive ballasts to compact energy-saving fluorescent lamps. In 1988, Midwest Toriod began mass production.

There was a worldwide energy crisis in the 1970s. The urgency of saving energy made many companies devote themselves to the research of energy-saving light sources and electronic ballasts for fluorescent lamps. With the rapid development of semiconductor technology, various high back-pressure power switching devices continue to emerge, providing conditions for the development of electronic ballasts. At the end of the 1970s, manufacturers took the lead in launching the first generation of electronic ballasts, which was a major innovation in the history of lighting development. Because of its many advantages such as energy-saving, it has attracted great attention and interest all over the world. It is considered to be an ideal product to replace inductive ballasts. Later, some famous enterprises have invested considerable manpower and material resources to carry out higher-level research and development. Due to the rapid advancement of microelectronics technology, the development of electronic ballasts in the direction of high performance and high reliability has been promoted. Many semiconductor companies have introduced a series of dedicated power switching devices and control integrated circuits. In 1984, Siemens developed TPA4812 active power factor correction electrical IC whose power factor reaches 0.99. Subsequently, some companies have successively introduced integrated electronic ballasts. In 1989, Helvali, Finland, successfully launched dimmable monolithic integrated circuit electronic ballasts. Electronic ballasts have been promoted and applied throughout the world, especially in developed countries.

Ⅲ Classification and working principle

1 Classification of the ballast resistor

From the working principle, it can be divided into inductive ballast and electronic ballast; according to the installation mode, it can be divided into independent, built-in, and integral types; from the starting method, it can be divided into preheating start, cold start (or Instant start) types.

2 Inductive ballast

As shown in the figure below, when 220V 50HZ AC power is applied to the switch closed circuit, the current flow through the ballast, and the lamp filament starter heats the filament. The starter is disconnected at the beginning. Because an AC voltage greater than 190V is applied, the gas arc discharge in the jumping bubble in the starter. Then the two metal sheets deformed by heat, and the two electrodes are close together to form a path to heat the filament. When the two electrodes of the starter are close together, because there is no arc Discharge, bimetallic cooling, and the two poles are separated. Because the inductive ballast is inductive, when the circuit is suddenly interrupted, a pulse voltage of 600V-1500V with a duration of about 1ms will be generated at both ends of the lamp. The exact voltage value depends on the lamp. In the case of discharge, the voltage across the lamp drops immediately. At this time, the ballast resistor limits the lamp current. And on the other hand, the ballast resistor makes a phase difference of 55 to 65 between the power supply voltage and the lamp operating current. The phase difference of the lamp can maintain the secondary starting voltage of the lamp so that the lamp can work more stably.

Due to its simple structure, inductive ballast, as the first type of ballast resistor to work with fluorescent lamps, has a relatively large market share. Due to its low power factor, poor low-voltage starting performance, heavy energy consumption, stroboscopic, and many other shortcomings. Its market share is gradually being replaced by electronic ballasts. The energy loss of inductive ballasts: 40W (lamp power) + 10W (inductive ballast self-heating loss) is equal to the total power consumption of the whole set of lamps and lanterns which is 50W.

3 Electronic ballast

The electronic ballast is a converter that converts power frequency AC power to high-frequency AC power. Its basic working principle is:

As shown in the figure below, after the industrial frequency power supply passes through the radio frequency interference (RFI) filter, full-wave rectification, and passive (or active) power factor corrector (PPFC or APFC), it becomes a DC power supply. Through the DC/AC converter, the output of high-frequency AC power of 20K-100KHZ is added to the LC series resonant circuit connected to the lamp to heat the filament, but the lamp is "discharged" into the "on" state, and then enters the light-emitting state. The high-frequency inductor plays a role in limiting the increase of current, ensuring that the lamp tube obtains the lamp voltage and lamp current required for normal operation. In order to improve reliability, various protection circuits are often added, such as abnormal protection, surge voltage, and current protection, temperature protection, and so on.

Schematic diagram of electronic ballast

Detailed schematic diagram of electronic ballast