A ballast resistor is an electronic component that is often used to regulate current in a circuit. Certain devices, such as fluorescent lamps, may have a quality known as negative resistance, in which an increase in current can result in a decrease in voltage. This negative resistance can damage the power supply or destruction of the device. The resistors ballast generally are wired in series with a negative charge, and take advantage of the fact that all components of a series circuit receive the same amount of electric current. Some ballasts are simply series resistors, while others make use of more complex capacitors and components .
There are several different types of ballast resistance, including fixed, variable, and reactive. While the most common use of a ballast resistor is to regulate current flow to a negative resistor load, they can also be used in other situations. Fixed ballast resistors are commonly used in low power devices such as light emitting diodes (LEDs) and neon lamps. LEDs are an example of a positive resistance load that can benefit from ballast resistance.
Another example of a fixed ballast resistor used with a positive charge is in the ignition systems of older vehicles. Ballast resistors were useful in these applications because of the ignition systems, which were designed to operate at the low voltages available during startup. Without ballast resistors, these systems could be damaged by the higher voltages present after startup. Later solid-state ignition systems removed ballast resistors as they were better able to operate below starting and operating voltage levels.
Variable resistors work similarly to incandescent lamps, as their resistance tends to increase in response to increased current flow. Some mercury vapor lamps include an incandescent filament that can act as an internal ballast. These types of variable ballasts have certain advantages over fixed resistors because they can dynamically respond to changes in current flow. Higher wattage lamps will often use a reactive ballast, such as an inline inductor .
Electronic ballasts involve the use of solid state components to increase efficiency. Using an electronic ballast in an item such as a fluorescent lamp can also have other benefits, such as reducing or eliminating the flicker effect that can be caused by changes in power frequency. Electronic ballasts are also used in a variety of other products, such as LCD monitors.