Valve Electric

an electrical device whose conductivity depends to a significant extent on the direction of the electric current; in one direction (forward) the conductivity of the electric valve is greater than in the opposite direction (reverse) by one or more orders of magnitude. This feature has led to the widespread use of the electric valve as a rectifying device.

The valve effect is possible between metal and electrolyte (electrolytic valves), metal and gas (ion valves), metal in a vacuum (electronic, or electrovacuum, valves), and metal and a semiconductor or two semiconductors of different impurities (semiconductor valves). Valves are controlled or noncontrolled. In controlled valves the conductivity is varied at the moment of the input of the control signal. In noncontrolled electric valves the control electrode is absent, and the transfer from a low-conduction state to a high-conduction state depends on input to the valve of a voltage exceeding the connecting voltage.

Electric valves are characterized by power (from a tenth of a watt to tens of kilowatts), rectified current intensity (from a hundredth of an ampere to hundreds of amperes), operating voltage (from fractions of a volt to hundreds of kilovolts), forward voltage drop (from tenths of a volt to several tens of volts), reverse breakdown voltage (from tens of volts to hundreds of kilovolts), connection time and restoration time, size, and mass.

Electronic and semiconductor electric valves are used primarily for electric energy conversion in low-wattage devices such as radio receivers. Ion valves are used mainly in high-power plants, electric transmission lines, and DC power lines. High-power semiconductor control valves (thyristors) are widely used. They have performance characteristics qualitatively similar to those of the ion control valves; however, in electrical and mechanical parameters they have significant advantages over the ion valves and successfully replace the latter in electric power generation.

In automatic and contactless commutating and safety switches, signaling devices, and computer technology, electric valves are used for the stabilization of parameters such as forming elements for the carrying out of logical functions, and so on. Since equipment size and mass are very important in these devices, semiconductor valves are mainly used and electron valves are used less frequently.

Electric valves are also used in ultra-high-frequency engineering and radio circuit devices as detectors, rectifiers, and the like.