Cold cathode
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A cold cathode
Cold-cathode devices
A cold-cathode vacuum tube does not rely on external heating of an electrode to provide thermionic emission of electrons. Early cold-cathode devices included the Geissler tube and Plucker tube, and early cathode-ray tubes. Study of the phenomena in these devices led to the discovery of the electron.
Many types of cold-cathode switching tube were developed, including various types of thyratron, the krytron, cold-cathode displays (Nixie tube) and others. Voltage regulator tubes rely on the relatively constant voltage of a glow discharge over a range of current and were used to stabilize power-supply voltages in tube-based instruments. A Dekatron is a cold-cathode tube with multiple electrodes that is used for counting. Each time a pulse is applied to a control electrode, a glow discharge moves to a step electrode; by providing ten electrodes in each tube and cascading the tubes, a counter system can be developed and the count observed by the position of the glow discharges. Counter tubes were used widely before development of integrated circuit counter devices.
The
Lamps
Cold-cathode lamps include
Cold-cathode fluorescent lamps were used for
In the lighting industry, “cold cathode” historically refers to luminous tubing larger than 20 mm in diameter and operating on a current of 120 to 240 milliamperes. This larger-diameter tubing is often used for interior alcove and general lighting.[3][4] The term "neon lamp" refers to tubing that is smaller than 15 mm in diameter[citation needed] and typically operates at approximately 40 milliamperes. These lamps are commonly used for neon signs.
Details
The cathode is the negative electrode. Any gas-discharge lamp has a positive (anode) and a negative electrode. Both electrodes alternate between acting as an anode and a cathode when these devices run with alternating current.
A cold cathode is distinguished from a hot cathode that is heated to induce thermionic emission of electrons. Discharge tubes with hot cathodes have an envelope filled with low-pressure gas and containing two electrodes. Hot cathode devices include common vacuum tubes, fluorescent lamps, high-pressure discharge lamps and vacuum fluorescent displays.
The surface of cold cathodes can emit
Another mechanism to generate free electrons from a cold metallic surface is field electron emission. It is used in some x-ray tubes, the field-electron microscope (FEM), and field-emission displays (FEDs).
Cold cathodes sometimes have a
Cold-cathode devices typically use a complex
Applications
Cold cathodes are used in
A common cold-cathode application is in
Due to its efficiency, CCFL technology has expanded into room lighting. Costs are similar to those of traditional
Effects of internal heating
In systems using
This aspect is problematic in the case of backlights used for
References and notes
Notes
- field emission.
- Moore lamp.
Citations
- ^ U.S. patent 1,993,187, Cold cathode discharge tube
- ^ D. M. Neale, Cold Cathode Tube Circuit Design, Francis and Taylor, 1964. pp. 1–7.
- ^ "Ifay guide info electric discharge lighting systems, cold cathode".
- ^ "EGL lighting products". Archived from the original on October 26, 2010. Retrieved 9 February 2011.
- ^ U.S. patent 1,860,149, Discharge tube.
- ^ U.S. patent 2,103,033, Electron emissive electrode.
- ^ U.S. patent 1,316,967, Gaseous-conduction lamp.
- ^ Solé Lighting (commercial site advocating CCFLs).