Abstract: A circuit (100) for driving fluorescent lamps (102, 104, 106) and including: a half-bridge inverter (112) receiving a unidirectional voltage and producing an alternating voltage, and having control inputs (156, 166); a series-resonant oscillator (126) coupled to the inverter output (116) for producing an alternating signal; and a non-saturating feedback transformer (146) having a primary winding (148) coupled in series between the inverter and the oscillator and secondary winding (150, 152) coupled respectively to the control inputs of the inverter. Since the feedback transformer is non-saturating it provides to the inverter control inputs a linear feedback signal from the inverter. This results in safe, stable, predictable and well-defined circuit operation, in which the possibility of the inverter transistors being destroyed by cross-conduction is substantially removed, and the amount of input voltage "ripple" present in the signal applied to the lamps is reduced.

Abstract: A circuit (500) for driving two or more series-connected gas discharge lamps, having: an oscillator (518, 520, 522); and a transformer (524) with a primary winding (526) and a secondary winding (528). The transformer secondary winding has first (129A) and second (129B) points connected respectively to first (508) and second (514) output terminals across the series-connected lamps. A capacitor (532) couples the first point of the transformer secondary winding to an intermediate output terminal (112). The voltage produced by the secondary winding thus drives the lamps in series, while the pre-strike voltage produced across the secondary winding is applied across a single lamp (106) to cause it to strike. After striking, current to the intermediate output terminal (512) is limited by the capacitor (532). In this way, the voltage which needs to be produced across the secondary winding to ensure striking of all of the lamps is reduced.

Abstract: A circuit for dimmably driving fluorescent lamps (102, 104, 106) from a DC supply voltage includes: input nodes (174, 176) having input capacitors (184, 186) connected therebetween; a half-bridge transistor inverter (178, 180) connected between the input terminals; a series-resonant LC oscillator (196, 198) coupled in series between the half-bridge transistors and the input capacitors; an output transformer (212) having a primary winding (214) connected in series with the LC inductor (196) and in parallel with the LC capacitor (198) and a secondary winding (216) for connection to the lamp load; and first and second voltage clamp diodes (215A, 215B) connected between an intermediate point on the primary winding and the input nodes respectively.

Abstract: A drive circuit for driving a capacitive load (4) and for producing a signal (FIG. 2b, 3b, 4b, 5b) indicative of the condition of the load, the circuit comprising: a FET (26) applying current to the load; a resistance (30) sensing the level of the applied current; a differential amplifier (32) detecting when the sensed level exceeds a predetermined threshold; and a bipolar transistor producing a control signal (FIG. 2b, 3b, 4b, 5b) to limit the applied current until the load current falls below the threshold, whereby the control signal is a pulse width modulated signal whose pulse width is indicative of the condition of the load.

Abstract: An optical coupling arrangement comprising: an optical laser emitter (4); an optical fiber (8); mounting means (10, 12, 14) for mounting the laser relative to the optical fiber so as to couple into the optical fiber light emitted by the laser; sensing means (11, 18, 24) for sensing the level of a predetermined proportion of light in the optical fiber; and piezoelectric moving means (10, 14) for moving the laser in orthogonal directions responsive to the sensing means so as to the increase coupling into the optical fiber of light emitted by the laser. The sensing means and the piezoelectric moving means thus form a closed, auto-alignment feedback loop which moves the laser relative to the optical fiber so as to compensate for movement between the laser and the optical fiber, thereby ensuring maximum coupling efficiency between the laser and the optical fiber.