Constant current supply for gas discharge lamps - uses relaxation oscillator and is independent of number or length of discharge tubes in circuit

TLDR: In this article, a relaxation oscillator is used for illuminated letters, where a constant intensity is required, and a current discriminator detects when a particular current in the transistor has been attained and then forces it into the cut off condition.

Abstract: The current supply is used for illuminated letters, where a constant intensity is required. The circuit consists of a relaxation oscillator, containing a transistor (1), a transformer (4, 5, 10) a timing circuit and a current discriminator. The transistor in the oscillator switches repeatedly from fully conducting to fully cut off and vice versa, with the lengths of time in either state defined by the discriminator and timing circuit respectively. The discriminator detects when a particular current in the transistor has been attained and then forces it into the cut off condition. This defines the current in the transformer secondary circuit (10) which in turn feeds the gas discharge lamp (11) or lamps.