The ballast resistor sits between the power source and one or more discharge lamps. Its main job is to keep the lamp’s current at the right level. It might also include things that adjust the supply voltage or frequency and boost the power factor. You can use it alone or along with the starter to make sure the lamp can start up properly.
Ⅰ Introduction
A ballast resistor basically controls the current and creates a quick, high voltage for fluorescent lamps. It’s made by winding enameled wire around an iron core, which is usually made from silicon steel. When this coil with the iron core switches on or off quickly, it creates a high voltage (through self-induction) that goes to the electrodes (or filaments) at both ends of the fluorescent tube. This process repeats. When the starter (or “jumping bulb”) is closed, current flows through the ballast, heating the lamp’s filament. Then, when the starter opens, the ballast induces that high voltage across the tube, causing the filaments to shoot out electrons, which hit the fluorescent coating inside the tube and make it light up. The starter will open and close several times before the tube fully lights up. Once the tube is glowing normally, the internal resistance drops, and the starter stays open. The current flows steadily through the tube and ballast, keeping the light on. Since the ballast always carries current while the lamp is on, it tends to vibrate and heat up over time. There are two main types of ballast resistors: electronic and inductive ballasts.
Ⅱ History and Development
In the late ’80s, the U.S. started using toroidal inductive ballasts for compact, energy-saving fluorescent lamps. By 1988, Midwest Toriod was mass-producing them.
Back in the 1970s, during the global energy crisis, saving energy became a huge focus. Many companies started working on energy-saving light sources and electronic ballasts for fluorescent lamps. As semiconductor technology advanced, new high-power switching devices started popping up, setting the stage for electronic ballasts. By the late ’70s, the first generation of electronic ballasts was released, a big innovation in the lighting industry. These ballasts became super popular because they were energy-efficient, and everyone was looking for ways to save power. Many major companies jumped into the game, pouring resources into higher-level R&D. Thanks to fast-moving microelectronics tech, electronic ballasts started to get even more reliable and high-performing. Around this time, semiconductor companies began releasing specialized power-switching devices and control integrated circuits. In 1984, Siemens came out with the TPA4812, a power factor correction IC with a power factor of 0.99. After that, more companies began releasing integrated electronic ballasts. By 1989, Helvali in Finland developed dimmable monolithic integrated circuit ballasts. Electronic ballasts spread worldwide, especially in more developed countries.
Ⅲ Types and Working Principle
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Classification of the Ballast Resistor
Based on how it works, there are two main types of ballast resistors: inductive ballasts and electronic ballasts. Depending on how they’re installed, you can divide them into independent, built-in, and integral types. When it comes to how they start, there are preheating start, cold start (also called instant start) types.
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Inductive Ballast
Here’s how it works: when you apply 220V, 50Hz AC power to a closed circuit, the current flows through the ballast and heats up the lamp’s filament starter. At first, the starter is disconnected. But since the AC voltage is higher than 190V, a gas arc discharge happens inside the starter’s little “jumping bubble.” Then, because of the heat, the two metal plates inside bend and get close enough to form a path that heats the filament. When those two metal plates touch, there’s no more arc discharge, the bimetal plates cool down, and the two poles move apart again.
Since the inductive ballast is, well, inductive, when the circuit gets interrupted suddenly, it generates a pulse voltage (between 600V and 1500V) at both ends of the lamp. This voltage only lasts for about 1 millisecond, and the exact number depends on the type of lamp you’re using. Once the discharge happens, the voltage across the lamp drops quickly. At this point, the ballast resistor kicks in to limit the current flowing through the lamp. Plus, the ballast creates a phase difference of about 55 to 65 degrees between the supply voltage and the current in the lamp. This phase difference helps maintain a secondary starting voltage, which keeps the lamp running more steadily.
Inductive ballasts have been around the longest and were the first type used with fluorescent lamps. They’ve got a pretty simple structure, which helped them capture a big chunk of the market early on. But they’ve got some drawbacks, like a low power factor, poor performance when starting under low voltage, high energy consumption, and the fact that they cause flickering (stroboscopic effect). Because of these issues, electronic ballasts are gradually replacing them. Here’s the breakdown of energy loss for inductive ballasts: if the lamp is 40W, the ballast itself loses about 10W to heat. So, the total power consumption for the whole setup is around 50W.
- Electronic Ballast
An electronic ballast is a kind of converter that changes the regular power frequency AC into high-frequency AC. Here’s how it works:
As shown in the diagram, the industrial frequency power supply first passes through a radio frequency interference (RFI) filter, then gets full-wave rectified and corrected by a passive or active power factor corrector (PPFC or APFC). After that, it becomes DC power. This DC power goes through a DC/AC converter, which cranks out high-frequency AC power (between 20KHz and 100KHz) that’s fed into an LC series resonant circuit connected to the lamp. This heats up the filament, gets the lamp to “discharge,” and flips it to the “on” state, after which it enters the light-emitting phase. The high-frequency inductor’s job is to keep the current in check, making sure the lamp gets just the right voltage and current to run smoothly. To make sure things stay reliable, various protection circuits are often added, like for abnormal conditions, surge voltage, current, and temperature protection.
Schematic diagram of electronic ballast
Detailed schematic diagram of electronic ballast
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