Series-resonant electronic ballast circuit

A ballast for a fluorescent lamp, said fluorescent lamp having a pair of thermionic cathodes, each such cathode having a lamp input terminal, said lamp requiring in order to get started the presence of a relatively high-magnitude starting voltage across said pair of cathodes for a relatively brief period of time, said ballast being adapted to be powered from an ordinary electric utility power line and comprising:

• rectifier-means connected in circuit with said power line by way of a pair of power-line-wires and operative to provide a DC voltage;
• inverter-means connected with said DC voltage and operative to provide a high-frequency-voltage across a pair of output terminals, said high-frequency-voltage having a fundamental frequency that is substantially higher than that of the voltage normally present on said power line;
• lamp-connect-means connected in circuit with said pair of output terminals and operable to permit disconnectable connection with each of said lamp input terminals;
• disable-means connected in circuit with said inverter-means and operable, upon the receipt of a disable-signal, to disable the operation of said inverter-means, thereby to remove said high-frequency-voltage from said pair of output terminals;
• voltage-sensing-means connected in circuit with said pair of output terminals and operable to provide said disable-signal to said disable-means whenever the magnitude of said high-frequency-voltage has remained equal to or larger than that of said relatively high-magnitude starting voltage for a length of time that is at least equal to that of said relatively brief period of time;
• and
• current-sensing-means operative to sense the flow of high-frequency-current through said pair of power-line-wires and to provide said disable-signal to said disable-means whenever said high-frequency-current has been flowing for longer than a certain short length of time, said high-frequency-current being of a frequency substantially the same as that of said high-frequency-voltage.

A ballast for a gas discharge lamp, said ballast adapted to be powered from a voltage source and comprising:

• voltage-conversion-means connected in circuit with said voltage source and operable to provide a current-limited AC voltage across a pair of output terminals;
• connect-means connected with said pair of output terminals and operative to permit connection thereto of a gas discharge lamp, said gas discharge lamp requiring a starting voltage of relatively high magnitude for a relatively brief period of time in order to initiate proper lamp operation;
• disable-means operative, upon the receipt of a disable-signal, to remove said AC voltage from said output terminals;
• voltage-sensing-means connected in circuit with said pair of output terminals and operative to provide said disable-signal to said disable-means whenever the magnitude of said AC voltage has remained equal to or larger than that of said starting voltage for longer than a relatively brief period of time;
• and
• current-sensing-means operative to sense the flow of ground-fault-current between said pair of output terminals and said voltage source, and to provide said disable-signal to said disable-means after said ground-fault-current has been flowing for longer than a very short period of time.