Gas-discharge tubes (electrical oscillation's frequency)


In cold cathode tubes, the electric discharge in gas has three regions, with distinct current-voltage characteristics: a)Townsend discharge, below the breakdown voltage. b) Glow discharge ( occurs once the breakdown voltage is reached) and the Arc discharge (occurs in the ampere range of the current). The Townsend discharge is a gas ionization process where free electrons, accelerated by a sufficiently strong electric field, give rise to electrical conduction through a gas by avalanche multiplication caused by the ionization of molecules by ion impact. A gas-filled tube, also known as a discharge tube, is an arrangement of electrodes in a gas within an insulating, temperature-resistant envelope. Gas-filled tubes exploit phenomena related to electric discharge in gases, and operate by ionizing the gas with an applied voltage sufficient to cause electrical conduction by the underlying phenomena of the Townsend discharge. The occurrence of Townsend discharge, leading to glow discharge breakdown shapes the current-voltage characteristic of a gas discharge tube such as a neon lamp in a way such that it has a negative differential resistance region of the S-type. The negative resistance can be used to generate electrical oscillations and waveforms. The sawtooth shaped oscillation generated has frequency depended on the Townsend discharge breakdown voltage and the glow discharge breakdown voltage.

Related formulas


fFrequency of the electrical oscillation (sec-1)
R1Resistance of the circuit (ohm)
C1Capacitance of the circuit (F)
V1 The supply voltage of the circuit (V)
VGLOWThe glow discharge breakdown voltage (V)
VTWNThe Townsend discharge breakdown voltage (V)