Abstract: The present invention describes a method and apparatus for a swept frequency switching gas discharge tube supply which produces a "crawling effect" in gas discharge tubes containing neon, argon or mercury gases or other gases and which has a means for eliminating the "bubble effect". To produce the "crawling effect", the driving frequency of the switching supply is swept from a higher frequency to a lower frequency thereby causing the excitation point to move from the electrodes on both ends of the dual electrode gas discharge tube to the center of the gas discharge tube. By varying the base switching frequency of the supply, the bubble effect which plagues some displays can be eliminated.

Abstract: An overvoltage shutdown circuit for use with high voltage excitation supplies for gas discharge tubes is described. In one embodiment, a spark gap is placed between the secondary output windings of a resonant conversion output transformer. In a second embodiment, a sense conductor is placed in proximity to the high voltage output windings of the resonant conversion transformer to receive a spark in the event of overvoltage on the output. A sensed spark causes a latching circuit to stop the resonant conversion thereby protecting the power supply from a potentially damaging overvoltage situation.

Abstract: The present invention uses a variable frequency oscillator to drive a primary resonant converter output transformer circuit for exciting gas discharge tubes. The combination of the impedance of the resonant conversion circuit along with the impedance of the driven gas discharge tube taken in combination with the frequency of the variable oscillator will determine the output voltage of the circuit. By varying the frequency of the oscillator, the optimal output voltage and hence the optimal brightness of the gas discharge tube may be selected. At the optimal output voltage, the frequency of the switching supply may create an undesirable or desirable "bubble effect" in the gas discharge tube. An optional secondary frequency may be combined with the frequency of the variable frequency oscillator to create or eliminate the bubble effect according to the esthetic desires of the user.