Thyratron

Thyratron ( altgr. art word about gating ) is the name for a controllable over a grid gas-filled tube rectifier with a thermionic cathode, a triode is similar in structure. As a filling gas are mercury vapor, xenon, neon, krypton, or hydrogen is used.

Function

Between the anode and the cathode, a high voltage is applied, which is part of the working circuit. Ignition ( = conductivity not burn-out) of the fill gas can be prevented by applying a sufficient negative voltage is applied to the control grid. In case of positive grid potential (or unconnected grid ), there is an ignition of the filling gas, which draws an arc discharge between the anode and cathode by itself and transforms the entire space into a conductive plasma. The anode current can assume, depending on the specification of a value of a few to several thousand amperes, and the voltage drop between anode and cathode, the so-called lamp voltage is approximately 10 to 15 V.

The grid is thereby surrounded by a coating of the plasma ions and thus loses its influence on the gas discharge. Also, by reducing the lattice potential can not be prevented or more of the anode current can be controlled arc discharge. The deletion of the plasma in the thyratron is only possible by reducing the anode voltage drops below the arc voltage or by interrupting the anode circuit.

If you put in the anode circuit such as a sinusoidal AC voltage, and controls the grid voltage in accordance with, it can be the ignition timing of the thyratron in the positive half sine wave and therefore control the current flowing in the central anode current. The thyratron is extinguished then independently in the negative half-cycle and re-ignites at the next positive half-wave. This arrangement then operates as a phase control, as it is implemented today with thyristors or triacs.

Hydrogen thyratron 25 kV/1000 A, Russia, TGI-1000/25 type ( see the anode side)

Cathode side

Law a hydrogen filled thyratron wholesale from a radar installation. To the left of the comparatively tiny thyratron from a jukebox.

Application

Thyratrons were used until the 1960s for the realization of controllable rectifiers and phase controls. They were now almost completely replaced by thyristors, triacs and IGBT.

Hydrogen thyratron pulse, however, made ​​until today, because this very quickly very high powers can switch. They are used in pulse generators, among others, used in excimer lasers to control the pump discharge and may only be by 2004 partly replaced by semiconductors there.

A special application was the common structure consisting of several thyratrons in mercury vapor rectifiers.

The musician, composer and designer Oskar Sala used Thyratronröhren in his Mixturtrautonium, with which he made many movies and industrial films set to music in 1960.

Related components

Cold cathode thyratron

There are also thyratrons with unheated cathode, so-called cold-cathode thyratrons. These are also referred to as a relay tube. They contain an inert gas filling and differ from the heated thyratrons in their ignition behavior: During a heated thyratron with sufficient voltage between anode and cathode, even when de-energized grid or grid voltage ignites zero, the relay tube needs to ignite a positive voltage to its ignition electrode ( the "Starter " ): only if this results in a glow discharge between ignition electrode and cathode, these spreads also to the anode from there and closes the power circuit. Before lighting this start discharge current does not flow into the ignition electrode - in the off state relay bulbs have a very high input resistance. Ignition occurs at a certain positive voltage to the ignition electrode. Therefore, and due to their small size, they found earlier in large numbers in time relays and telephone systems use. Your work condition they signal optically by the glow discharge.

Due to the operation in the range of a glow discharge, the anode current is only a few mA, the operating voltage remains at relatively high values ​​of about 100 V.

Since relay tubes do not need to be heated, they are immediately ready and have not before ignition energy consumption. Have relay tubes, as they have no thermionic cathode, a great life.

Ignitron

Ignitrons work with a mercury pool cathode, require very high ignition currents and can turn in the megawatt range permanent services.

Thyristor

The thyristor is a semiconductor device that has a similar characteristic as the thyratron.