Abstract: An electronic ballast circuit for fluorescent or other gaseous discharge lamps includes a resonant half-bridge inverter circuit. The source voltage to the inverter is a full-wave rectified line voltage together with a DC carry-over voltage for supplying power in the inter-cusp period of the recitified line voltage. A negative feedback circuit is responsive to lamp current to vary the inverter drive frequency and thereby regulate lamp current. The frequency response of the feedback loop is high enough and the gain-versus-frequency response of the inverter is such that lamp current and voltage are regulated to reduce the crest factor of lamp current to compensate for variation in the amplitude of the voltage across the semi-conductor switches.

Abstract: A thyristor/capacitor inverter bridge energizes the lamp circuit with a high frequency oscillating voltage derived from full-wave rectified line voltage. Lamp current is regulated by a commutation circuit which is synchronized with zero crossings of the thyristor current. When power is first applied, an initialization circuit initiates a time delay to permit lamp warm up and then enables the high frequency inverter to begin energizing the lamp load. A re-strike circuit generates pulses coupled to the commutation circuit to re-start it when the rectified line voltage falls below that which is necessary to sustain oscillation of the inverter. Fault detection circuits are included for detecting faults such as loss of primary power, thyristor over-voltage, and thyristor over-current for taking corrective action, such as inhibiting the inverter and commencing a new initialization sequence.

Abstract: A fault protection system for a balanced thyristor capacitor/inverter half-bridge which generates a high frequency oscillating voltage from full-wave rectified line voltage is disclosed. Following the detection of thyristor over-current and the removal of transformer-coupled, alternating, gated drive signals from the thyristors by means of logic and control circuitry, the natural ringing of a charged resonant circuit coupled across the inverter half-bridge causes thyristor commutation and inverter shutdown. The resonant circuit and inverter half-bridge are isolated from the line voltage source during the fault recovery cycle by means of an inductance, the size of which is selected to greatly exceed the total inductance in the inverter bridge-resonant circuit system to avoid saturation until the power thyristors have been given sufficient time to turn off.

Abstract: Circuitry for providing high voltage DC power from commercially available 60 hertz AC utility power. The incoming 60 hertz AC voltage is rectified to a DC voltage. This DC voltage is then converted to a high frequency AC voltage by means of a sine wave inverter. This high frequency sine wave voltage is then converted to a different voltage and rectified by a voltage doubler. The inversion and rectification are under the control of logic circuitry which includes means for sensing line faults to provide circuit protection.