Two-Electrode Cold-Cathode Tubes

The characteristics are shown in Fig. 7. Over the region A-B, the current that flows is very minute, and no observable discharge occurs within the tube. At B-C the voltage required to maintain the current falls to a low value, about 75 volts for a typical tube; also, a slight glow appears as a spot on the cathode. As the current through the tube is permitted to increase over the region C-D, the voltage required to maintain the current increases little and the glow gradually increases until at D the cathode is covered entirely. Beyond point D an increase in current is accompanied by an increase in voltage, and, if the current is increased to E, an arc may be formed and the tube will be ruined. This tube is used as a voltage regulator in communication rectifiers.