An inverter and inverter driving method enable slow start of a load by gradually increasing the lamp current within a range less than a predetermined maximum level, thereby preventing improper operation of the inverter. The inverter includes a transformer for converting a DC input voltage into an AC output voltage, an inverter control unit for controlling a level of the AC output voltage from the transformer in response to a feedback current from a load driven by the AC output voltage, and a kick-off control unit for adjusting the feedback current during a kick-off period for starting the load.

An inverting apparatus comprises: a capacitor input type rectifying circuit consisting of a full-wave rectifier and a smoothing capacitor; a single-phase bridge inverter having four semiconductor switches; and a driving control unit for opening and closing the semiconductor switches, wherein the smoothing capacitor is provided with a switch to open and close the smoothing capacitor.

A start-up delay circuit for an electronic ballast for "instant-start" type fluorescent lamps of the type having an electronic converter powered by an active electronic preregulator. The converter is an inductive-capacitive parallel-resonant push-pull circuit or other type of current-fed power-resonant circuit. The preregulator may be a boost-type. The start-up circuit may be either a resistor and zener diode or resistor, capacitor and diac network or programmable unijunction transistor circuit connected between the preregulator output and an oscillation-enabling input of the converter.

A converter of electric power at a first value of voltage and frequency produces a voltage at a second value and at a higher value of frequency by means of an inverter oscillator circuit having two serially connected transistors. An output power transformer is coupled to the transistors for receiving current excitation from alternate ones of the transistors during alternate half-cycles of the output voltage. Incoming voltage is converted by a diode bridge circuit to a DC voltage which drives the transistors. Serially connected capacitors bypass the bridge circuit to couple high frequency current from a primary winding of the transformer through the transistors. Additional windings of the transformer are coupled in the base-emitter circuit of each transistor for inducing states of saturation during conduction phases of each transistor so as to minimize power dissipation within each of the transistors. The transformer has a saturating reactor core which is made to saturate at the end of each half cycle of the output current, the intervals of current saturation resulting in a flux change which reverses the polarities of the windings in the base emitter circuits to alternate the states of conduction of the transistors.

A direct drive electronic ballast circuit suitable for a fluorescent lamp load includes a high frequency oscillator inverter circuit having a tuned output circuit coupled to a load and to a drive circuit series connected to the load and dependent upon current flow therein. The high frequency oscillator inverter circuit is also coupled to a pulsed DC potential source which is shunted by a charge storage and isolating circuit energized by a feedback rectifier circuit which supplies energy whenever the potential from the pulsed DC potential source decreases below a given reference level. A relaxation type oscillator is coupled to the high frequency oscillator inverter circuit and provides a starting capability therefore.