Abstract: A circuit for driving a gas discharge lamp load and including an EMI and transient supply filter coupled to an input source, a rectifier coupled to the filter, a power inverter coupled to the rectifier, a load including a transformer coupled to the power inverter, and a control circuit coupled to the power inverter and the load. A feedback circuit couples the load transformer to the AC side of the rectifier to create a path for transferring a feedback voltage over the rectifier to cause the rectifier to conduct current over a substantive portion of each cycle of the AC input voltage.

Abstract: The present invention provides a method and circuit for controlling the flow of current through a load. In a preferred embodiment, an oscillator generates a pulse signal of constant frequency. A pulse width modulator adjusts the duty cycle of the pulse signal in response to a dimming level signal input indicative of the desired level of current flow through the load. A converter receives the pulse signal as an input and converts it into an AC signal, the frequency of which follows the frequency of the pulse signal and the symmetry of which varies with the duty cycle of the pulse signal. The load is connected into a resonant circuit tuned such that a change in the symmetry of the AC signal changes the level of current flowing through the load.

Abstract: A circuit for driving gas discharge lamps has a bandpass filter coupled between the output of the inverter and the inverter control. The bandpass filter provides protection against the diode operation of the gas discharge lamps. The bandpass filter is composed of a capacitor and the permeance inductance of a transformer.

Abstract: For driving gas discharge lamps (102, 104) having heatable filaments (102A, 102B, 104A, 104B), a circuit (100) has an inverter (132, 134) and a series-resonant LC oscillator (150, 158, 170) forming a self-oscillating inverter. The oscillator output provides filament-heating current through the filaments in series, and drives arc current serially through the lamps. A feedback transformer (174) with a winding (172) connected serially in the filament-heating current path controls the operation of the inverter. A voltage clamp (180, 182) limits the voltage applied to the lamps. The circuit does not require an output-coupling transformer to couple the output of the self-oscillating inverter to lamps, thus avoiding the added cost that the use of such a transformer would bring, while providing efficient, substantially fixed frequency operation of a wide variety of lamp loads, together with the ability to address a number of lamp fault modes. Alternatively, the lamps may be driven in parallel.

Abstract: A circuit for driving one or more gas discharge lamps (102, 104, 106) from a nominal-level voltage supply includes: a voltage boost IC (144); a self-oscillating, series-resonant oscillator (196, 198, 178, 180) for producing a high-frequency output voltage for application to the lamps via an output-coupling transformer (212); and a voltage clamp (215A, 215B) coupling the transformer to the oscillator input (174, 176). The voltage boost IC is arranged to regulate the power drawn by the circuit to a constant level if the supply voltage is greater than 95% of its nominal value. If the supply voltage falls to less than 95% of its nominal value, regulation is lost and the circuit draws less power in proportion to the fall in the supply voltage. If the supply voltage falls to less than 90% of its nominal value the clamp operates to reduce the power drawn by the circuit at a rate greater than that of the fall in the supply voltage.

Abstract: A driving circuit for one or more gas discharge lamps (102, 104, 106) having heatable filaments (102A&B, 104A&B, 106A&B) includes: a self-oscillating, series-resonant oscillator (196, 198, 178, 180) for producing a high-frequency output voltage for application to the lamps via an output-coupling transformer (212); a resistive-capacitive divider (190, 192) for starting-up the oscillator after a first delay; a voltage boost IC (144) for causing the oscillator to produce a boosted output voltage when the voltage boost IC is activated and an unboosted output voltage when the voltage boost IC is unactivated; and a resistive-capacitive divider (170, 172) for starting-up the voltage boost IC after a second delay.

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 circuit (100) for driving a gas discharge lamp load (102, 104, 106) and including: an inverter (112) receiving a unidirectional voltage output and producing an alternating voltage, and having a control input (156, 166); a series-resonant oscillator (126) coupled to the inverter output (116) and having an inductance (128) and a capacitance (130) in series for producing an alternating current; an output transformer (134) coupling the lamp load to the oscillator in series with the inductance and in parallel with the capacitance; and a feedback transformer (146) having a primary winding (148) coupled in parallel with the output transformer and coupled in series with the capacitance and a secondary winding (150, 152) coupled to the control input of the inverter. Since the feedback transformer primary winding carries only capacitive current (I.sub.C), the frequency of the circuit is substantially independent of the load.

Abstract: A circuit (100) for driving a plurality of gas discharge lamps (102, 104), and having: input terminals (126, 130) for connection to a source of voltage supply; output terminals (134, 136, 140) for connection to the lamps in series; an oscillator (124, 132) connected between the input terminals and the output terminals for producing a high-frequency drive voltage at the output terminals; a transformer (106) having a primary winding (108) coupled to the input terminals and having a secondary winding (114) coupled to the output terminals, the transformer secondary winding being coupled at its ends (116, 118) and at an intermediate point (120) to respective ones of the output terminals and the intermediate point (120) of the transformer secondary winding being coupled to its respective output terminal (140) by a capacitor.

Abstract: Alternating current signals are differentially coupled between a two wire communications line and a telecommunications facility by a line interface circuit. The line interface circuit differentially drives signals destined for the two wire communications line, with a predetermined source impedance, via tip and ring amplifiers and tip and ring feed resistors. An amplifier circuit differentially receives signal voltages being developed by currents traversing the tip and ring feed resistors, and detects signals destined for the telecommunications facility by subtracting a representation of the signals destined for the two wire communications from a representation of the differentially received signals.

Abstract: A telephone line interface circuit includes a transformer with tip and ring windings connected between tip and ring feed resistors and tip and ring leads of a telephone line, for feeding energizing current from a telephone facility to the telephone line. A secondary winding in combination with the tip and ring windings couples a.c. signals between the facility and the telephone line. A capacitance device is connected in combination with the secondary winding to simulate a function of a capacitance device as would normally be connected between the tip and ring windings in prior art circuits. The telephone line interface circuit is particularly useful in association with battery reversal responsive telemetry devices as any tendency for false ringer activation, in a connected telephone set, is reduced.

Abstract: A telephone line interface circuit includes a transformer with tip and ring windings connected between tip and ring feed resistors and tip and ring leads of a telephone line for feeding energizing current from telephone facility to the telephone line. A secondary winding in combination with the tip and ring windings couples a.c. signals between the facility. A capacitance is connected in combination with the secondary winding to simulate a function of a capacitance as would normally be connected between the tip and ring windings in prior art circuits, but without the problem of feed resistor interference at lower voice band frequencies. Network and component values are inserted between the secondary winding and an electronic hybrid circuit whereby the line circuit is precisely tailored for anyone of several national telephone line standards.

Abstract: A telephone line circuit transformer couples tip and ring leads of a telephone line to a telephone facility. Tip and ring transformer windings are connected in series with the respective tip and ring leads, tip and rings feed resistors and terminals of a battery power source for supplying energizing current to the telephone line. A capacitor is connected between a junction of the tip winding and the tip feed resistor and a junction of the ring winding and the ring feed resistor. A compensating circuit is connected to drive a compensating winding in current opposing relationship with respect to differential alternating current signals in the tip and ring windings and being within a range of voice frequencies within which an impedance of the capacitor is significantly shunted by the feed resistors.

Abstract: A handsfree communication terminal apparatus includes a transit switch being controllable for passing signals from a microphone to a transmission interface, during a transmit mode of operation, and a receive switch being controllable for passing signals from the transmission interface to a loudspeaker, during a receive mode of operation. A transmit signal processing circuit followed by a converter circuit generate transmit binary signal assertions in response to syllable-like characteristics in the signals from the microphone. A receive signal processing circuit followed by a converter circuit generate receive binary signal assertions in response to syllable-like characteristics in the signals from the transmission interface. A controller includes transmit and receive bistable circuits, each being clock setable by the respective binary signal assertions and being jam reset in response to the opposite binary signal assertions.