The Gas-Filled Diode

Author: E.E. Kimberly

In the high-vacuum type of diode, the voltage drop between elements is high. That high voltage drop may be greatly reduced by the introduction of a small amount of gas.

Fig. 27-3. Elemental Circuit of Tungar Battery Charger

If an electron, in its journey from the cathode to the plate, collide with a gas atom with sufficient velocity, one or more electrons will be detached from that atom and will be caused to join those in migration. The gas atom, having been robbed of one or more electrons, exhibits a positive charge and is said to be ionized. Thus, the gas atoms contribute electrons over and above those starting their migration from the cathode because of plate potential, and the resulting current flow is increased in that way because of the presence of gas and because the slow-moving ions tend to neutralize the space charge. Diodes of the gas type are used extensively in battery-charging service. In Fig. 27-3 (a) and (6) are shown simple circuits for battery charging by half-wave and by full-wave rectification. Fig. 27-4 shows an industrial type of diode charger. Overloads are liable to destroy the active surface of the cathode by bombardment from gas atoms which have lost one or more electrons by ionization and, being positively charged, are attracted to the cathode.

Fig. 27-4. Diode Battery-Charger