ballast resistor


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ballast resistor

[′bal·əst ri′sis·tər]
(electricity)
A resistor that increases in resistance as current through it increases, and decreases in resistance as current decreases. Also known as barretter (British usage).

Ballast resistor

A resistor that has the property of increasing in resistance as current flowing through it increases, and decreasing in resistance as current decreases. Therefore the ballast resistor tends to maintain a constant current flowing through it, despite variations in applied voltage or changes in the rest of the circuit.

The ballast action is obtained by using resistive material that increases in resistance as temperature increases. Any increase in current then causes an increase in temperature, which results in an increase in resistance and reduces the current. Ballast resistors may be wire-wound resistors. Other types, also called ballast tubes, are usually mounted in an evacuated envelope to reduce heat radiation.

Ballast resistors have been used to compensate for variations in line voltage, as in some automotive ignition systems, or to compensate for negative volt-ampere characteristics of other devices, such as fluorescent lamps and other vapor lamps.

References in periodicals archive ?
Therefore, most applications simply use a fixed bias voltage and ballast resistors, as seen in Figure 1.
It is appropriate for driving LEDs in parallel, using ballast resistors to set the current, in LCD backlighting and color indicator applications.
These devices use ion implanted polysilicon ballast resistors for maximum resistance to current induced hot spot failures.
The drivers are suitable for a broad range of high-brightness, general illumination applications, including signage, architectural, emergency lighting and MR16 lamp replacement, ensuring uniform LED brightness as well as eliminate the need for ballast resistors.
The SiP12401 boost controller IC uses double-cell NiMH or alkaline and Li-ion batteries to drive white LEDs connected in series for uniformly bright backlighting without the need for ballast resistors.
It provides a solution to drive LEDs in parallel, using ballast resistors to set the current, in LCD backlighting and color indicator applications.