Abstract: Drift in the zero or datum reference point of a circuit (such as that forming part of a measuring device) is corrected by sensing the rate of change of the signal provided by the circuit and distinguishing between a rate of change characteristic of that due to a valid signal indicative of a measurement and a rate of change characteristic of that due to drift in the circuit.In one embodiment, a window comparator 18 senses the rate of change of the signal output from circuit 10 by periodically sampling in sample/ hold 16 and then comparing with the current value of the signal. A signal circulating path 20, 21, 22 holds a drift compensating value which is updated when comparator 18 senses a rate of change below a threshold value which is indicative of drift in circuit 10. The drift compensating value is added to the signal from circuit 10 in summing amplifier 15 thereby correcting the signal for drift.

Abstract: A forward converter circuit (FIG. 1) is provided with a transformer reset sensing circuit (FIG. 2) whereby base drive to the switching transistor TR1 is inhibited until after reset of the transformer T1. The reset sensing circuit includes a sensing winding T1d provided on the transformer for sensing the waveform at the primary winding T1a, a comparator IC1 and diodes D5, D4 connected in such a way that one input of the comparator is high when the waveform changes in one direction, and the other input of the comparator is high when the waveform changes in the other direction. The output of the comparator inhibits switching of the transistor before reset and thus allows the use of a maximum switching duty cycle of 50% without risk of transformer saturation.

Abstract: An a.c. regulator is disclosed including series and shunt choppers connected between a source of alternating current and an output, each chopper including a pair of unidirectional controlled rectifying paths connected in parallel opposition. The invention is characterized by the provision of a control circuit including a load current sensor for sensing the direction of flow of load current, the control being connected to render conductive a selected one of the transistors in the shunt chopper alternately with a selected one of the transistors in the series chopper, the alternation occurring at a frequency that is high relative to the supply voltage frequency.

Abstract: Power supply apparatus is disclosed including an inverter, such as a half-bridge inverter, and control means for controlling the frequency of operation of the inverter. The control means includes a further control winding on the transformer of the invertor, and means for applying a short circuit of one or other or both polarities to the control winding in order to activate a switching transition of the inverter. In one embodiment, the control means is used to fix the frequency of operation of a free-running inverter; in another embodiment, short circuits of both polarities are applied to the control winding for an overlap period in order to provide a "dwell" period between switch-off of one inverter transistor and switch-on of the other, this method of operation providing pulse width modulation control of the output waveform of the inverter.

Abstract: Voltage converter apparatus is disclosed having circuitry for regulating the output voltage to maintain it at a regulated value. Use is made of switching devices that switch between their alternative states in a cyclic manner and at a particular frequency which is determined by the circuit constants. An inductance is provided for modifying the waveform of the current fed to the output transformer, so that at certain periods of the cycle there is a lesser contribution to the integrated output--i.e., the output is not a true 1:1 square wave. Then, by changing the switching intervals, the integrated output can be controlled. A current transformer is provided for sensing current changes occurring in the output transformer, and a short circuit arrangement is provided for short circuiting a control winding of the converting transformer to control the instants of switching of the switching devices.

Abstract: A regulated power supply system is disclosed including a source of unidirectional electric current, and at least one switch device including a saturable reactor controlled between a saturated condition and an unsaturated condition in a duty cycle such that the load voltage tends to remain constant with varying load current. In one embodiment, a pair of switch devices are coupled, respectively, between the ends of a center-tapped secondary winding of a transformer having a primary winding fed from an inverter, and a pair of rectifier devices coupled to provide the unidirectional current to the load. Control of the switch devices is effected by applying an appropriately varying control voltage to like electrodes of respective inverted control diodes each coupled to the junction between a respective switch device and its associated rectifier device. The control diodes are driven from the output of a comparator amplifier responsive to the difference between the load voltage and a reference voltage.

Abstract: A power supply apparatus is disclosed including a device for producing an oscillatory signal, and an output circuit for producing from said oscillatory signal an alternating-current output voltage, characterized by the provision of a regulating unit connected in series with the output circuit for producing a controllable voltage drop. The regulating unit includes a control device operable in response to a signal derived from the output circuit for controlling the voltage drop in response to a change in an output parameter of the output circuit.

Abstract: An alternating-current voltage regulator including a pair of input terminals adapted for connection with an alternating current supply voltage, a pair of output terminals adapted for connection with a load, a series-connected first switching device, a parallel-connected second switching device, an inductor connected in series with the first switching device, and a control device connected between the regulator output terminals and the switching devices for switching the switching devices at a second frequency which is high with respect to the frequency of the supply voltage. Consequently, a quantity of energy stored in the inductance during one part of a cycle of the second frequency is transferred to the output as an increase in voltage of the output with respect to the input during another part of the cycle.

Abstract: A converter power supply apparatus includes a direct current power supply and an oscillator circuit comprising a feedback transformer and two semiconductor switching devices arranged to be turned on alternately to produce alternating currents in primary winding means of the feedback transformer and in a load circuit. Circuit means couple the load circuit to secondary winding means of the feedback transformer so as to augment control currents fed to the switching devices. Circuit means may be provided to generate a starting pulse and to feed this pulse to the oscillator circuit to cause oscillation to recommence after disconnection of the load circuit. The direct-current source may be provided by rectification of an A.C. input and this input may be controlled in accordance with output voltage of the converter to stabilize the output voltage.