Abstract: An arrangement for converting an AC supply to a DC supply comprising an inverter circuit and a boost power factor correction stage. The inverter circuit comprises switchable components and utilizes a pulsed waveform indicative of power factor correction for causing some at least of the components repeatedly to adopt a condition permitting the boost power factor correction stage to draw current from the AC supply.

Abstract: A lamp driver circuit for a discharge lamp in which a high frequency is used to initiate a discharge and a lower frequency is used to sustain the discharge. A tuned circuit boosts the voltage at the starting frequency. In addition, a transformer is connected to the tuned circuit to provide a further boost to the starting voltage. The transformer core may be made of a different material from that of the inductor of the tuned circuit, and is preferably selected to saturate during starting, to enhance the voltage spikes available for starting the lamp.

Abstract: A laser system comprises an optical head, a power supply and a computer for controlling the power supply. The optical head comprises a pair of mirrors and four pumping sections. Each pumping section comprises a pair of gas discharge lamps pumping an Nd:YAG laser element. The power supply provides the lamps with alternating current at 25 kHz so that the laser system produces a continuous, modulated or pulsed output light beam. The power supply comprises three boost converters connected in parallel for converting three phase mains supply to direct current and four DC-AC converters. Each DC-AC converter converts the DC output from the boost converters to an AC supply for the lamps of a respective one of the pumping sections.

Abstract: A resonant inverter has transistor switches (20, 30) arranged to conduct current from a d.c. source (10) alternately in one direction and the other through an inductor (40) and capacitor (42). The transistor switches (20, 30) are turned on alternately by signals from secondary windings (24, 34) of a drive transformer (44) having a primary winding (45) in series with the inductor (40) and capacitor (42). To control the output power of the inverter, a control circuit (50) senses reversal of current in through the inductor (40) and capacitor (42) and turns off one of the transistor switches (30 ) a predetermined time after current reversal. Current reversal is sensed by an additional transformer (60) having a primary winding (61) in series with the inductor (40) and capacitor (42). The control circuit (50) includes a timer (52) controlling the predetermined time, which may be varied to vary the power output of the inverter. A load (80) is connected across the inductor (40 ) or capacitor (42 ) .

Abstract: A magnetron is powered via an output transformer TR whose primary winding (a) is connected in series with a resonant converter oscillator circuit comprising an inductor (L) and a capacitor (C3) and switching transistors (T.sub.1, T.sub.2) which are connected to positive and negative power supply terminals and are switched by respective current transformers (CT1, CT2). The switching points of the switching transistors are varied so as to vary the output of the circuit by varying the positive and negative flux excursions in the cores of the transformers (CT1, CT2) such that the net flux excursions are sufficient to saturate the transformers and switch off the switching transistors at a predetermined point in each half cycle. The relative positive and negative flux excursions in the transformer cores are controlled by providing additional windings (g) which are connected to a control circuit whcih rectifies the output of these windings and controls the rectified DC voltage appearing across them.

Abstract: The power supply circuit has an inductor connected to a DC source through a regulating circuit arranged to maintain a constant current in the inductor. A MOSFET is connected to the inductor and to the spark gap so that when the MOSFET is conducting, current is diverted from the inductor to the spark gap. The frequency and mark-space ratio of switching of the switching device is controlled to control the machining process. A second switching device (40) is arranged to conduct when the voltage across a capacitor (34) exceeds a reference voltage. A diode (46) is used to return excess energy to the DC source.

Abstract: A high frequency converter of push-pull form comprises a center tapped D.C. input supply 16, 17, 18, two solid state switching devices (20, 21) connected in series across the D.C. input terminals, a load circuit including a supersonic frequency transformer 30 and an output rectifier 35, and an oscillatory circuit including at least one capacitor 40 and a parallel inductor 34 connected in parallel with the primary winding 37 of the transformer between the center tapping 19 of the supply and the junction 25 of the switching devices. The switching devices are synchronized to the oscillation of the oscillatory circuit to allow the circuit to oscillate freely for part of a cycle to transfer energy from the inductor 34 to the capacitor 40 to charge the latter to a certain condition in which the voltage across the parallel inductor is substantial and that across the switching device is negligible and only then connect the parallel inductor across the D.C.

Abstract: An alternator for an internal combustion engine driven vehicle comprises a permanent magnet rotor mounted in operation for rotation with the engine crankshaft, a wound stator within which the rotor extends, rectifying means connected to the output of the stator, and a pulse controlled DC chopper regulator supplied from the output of the rectifier means and adapted to control the output from the rectifier and to supply the so controlled output to the vehicle battery for charging thereof.

Abstract: A converter includes a resonant oscillatory tank circuit comprising a capacitor and an inductor, at least one switching circuit including a solid state switching device in parallel with a diode connected to apply a predetermined potential difference from a DV supply to the inductor, and synchronizing means responsive to the oscillation of the oscillatory circuit for switching on the switching means for a fraction of a cycle when the instantaneous value of the oscillatory potential difference across the inductor is already not less than a predetermined value, to delay the fall of the said oscillating potential difference and inject energy from the supply into the oscillatory circuit, and a load circuit coupled or connected to the tank circuit in series with the inductor.

Abstract: A converter includes a resonant oscillatory tank circuit comprising a capacitor and an inductor, at least one switching circuit including a solid state switching device in series with a diode connected to apply a predetermined potential difference from a DV supply to the inductor, and synchronizing means responsive to the oscillation of the oscillatory circuit for switching on the switching means for a fraction of a cycle only when the instantaneous value of the oscillatory potential difference across the inductor is already not less than a predetermined value, to delay the fall of the said oscillating potential difference and inject energy from the supply into the oscillatory circuit, and a load circuit coupled or connected to the tank circuit.

Abstract: A control circuit is provided for a d.c. motor for sensing the temperature of the field winding and automatically reducing the temperature of the field winding when the temperature exceeds a preselected value.

Abstract: A pulse controller for controlling the current supply to a plurality of d.c. loads through a respective main thyristor for each load is provided with digital circuitry operable to maintain the mark-space ratios of voltage applied to the loads in a relationship to one another which is set by a differential control circuit while the mark-space ratios are simultaneously varied in response to a drive control circuit. The controller may be used to control two d.c. motors respectively driving right-hand and left-hand traction wheels of a battery-electric vehicle, to provide differential drive when the vehicle negotiates a curve.

Abstract: A pulse controller for a reversible d.c. series motor is provided, in place of the conventional freewheel diode across the armature and field and plugging diode across the armature, with a unidirectional current path connected across the armature and field and containing sufficient impedance to prevent build-up of motor current in interpulse periods when the motor is in a plugging mode, and switch means for shorting out the impedance during normal motoring.

Abstract: In electrical circuit means having a load, an SCR pulse controller in series with the load and including a commutation capacitor, a transmission line connected to the load and pulse controller to supply the load from a D.C. source, and, a reservoir capacitor shunting the transmission line, the provision of control means which during interpulse periods of the controller by repeatedly discharging the reservoir capacitor limit the voltage to which the reservoir capacitor charges above the voltage of the source.

Abstract: A thyristor pulse controller in which current supply to each of a plurality of d.c. loads is controlled by respective main thyristors and a single commutating capacitor common to all the main thyristors is provided, the capacitor being connected across the main thyristors to commutate them one at a time at intervals not less than the time required to forward charge the commutating capacitor from the d.c. source and to reverse the charge on the capacitor.

Abstract: A separately excited speed-controlled D.C. motor which has constant armature current and pulse-controlled field current has its armature connected by way of a bridge rectifier and an inductor to an A.C. source of substantially greater r.m.s. voltage than the rated supply voltage of the armature, the inductor serving to regulate the armature current. The field winding is connected to a field excitation supply and to a thyristor chopper and the mean current through the field winding controlled by the thyristor chopper thereby to control the armature torque and therefore the speed. The field winding may comprise two field coils arranged to produce opposing magnetic fields, the thyristor chopper serving to control the net magnitude and direction of the motor field. A thyristor chopper may be provided in the armature circuit to maintain a constant armature current during plugging of the motor.

Abstract: A thyristor pulse controller having an electromagnetically actuated shorting contactor comprising an actuating coil and an armature which moves on energization of the actuating coil to close the contactor tips and which moves on de-energization of the coil to open the contactor tips and to create an air-gap in the magnetic circuit of the coil, is provided with an interlock circuit comprising a voltage sensing circuit connected in parallel with the contactor actuating coil, the voltage sensing circuit being adapted to provide an output signal when the modulus of the voltage across the actuating coil exceeds a predetermined value which is lower than the modulus of the voltage across the coil at the instant when the contactor tips open. A unidirectional current path, which may be provided by the interlock circuit itself, is connected across the actuating coil to discipate inductive energy in the coil when the contactor opens.