Abstract: A DC-DC converter is provided with a control circuit 6 which comprises a drive signal generator 11 for producing on-off signals to a control terminal of a MOS-FET 3 in synchronization with pulse signals VOSC from an oscillator 10; an intermittent controller 12 for producing a control signal VC1 to drive signal generator 11 in response to the level of detection signal from an output voltage detector 5 to convert MOS-FET 3 to the intermittent operation during the light load period; and a power control circuit 16 for ceasing power supply VCC to oscillator 10 in response to control signal VC1 from intermittent controller 12 to stop production of pulse signal VOSC from oscillator 10 for the cessation term of MOS-FET 3 during the intermittent operation.

Abstract: A switching regulator that performs voltage regulation using synchronous rectification in step-up and step-down modes includes input and output terminals, an inductor, first through fourth transistors, an overcurrent detection unit, and a control unit. The input terminal receives an input voltage. The inductor generates an output voltage. The output terminal provides the output voltage. The first and second transistors perform switching in the step-down mode. The third and fourth transistors perform switching in the step-up mode. The overcurrent detection unit detects an overcurrent condition. The control unit controls operation of the transistors, causes the first and third transistors to be off and the second and fourth transistors to be on when the overcurrent condition is detected in a first state, and causes the first and fourth transistors to be on and the second and third transistors to be off when the overcurrent condition is detected in a second state.

Abstract: A switching control circuit is provided for measuring and regulating an output current of a power converter. The power converter is operated under continuous current mode. A detection circuit generates a continuous-current signal and a peak-current signal by detecting a switching current of an inductive device. An integration circuit generates an average-current signal in response to the continuous-current signal, the peak-current signal and an off time of a switching signal. The switching control circuit generates the switching signal in response to the average-current signal. The switching signal is coupled to switch the inductive device and regulate the output current of the power converter. A time constant of the integration circuit is correlated to the switching period of the switching signal, therefore the average-current signal will be proportional to the output current.

Abstract: Embodiments include controllable voltage device drivers adapted to generate driver output voltages. A device driver includes a direct current (DC) voltage source adapted to receive a voltage level command that indicates a commanded voltage, and to generate a DC transformer input voltage having a voltage level corresponding to the commanded voltage. The device driver also includes a step-up transformer adapted to receive the DC transformer input voltage and to convert the DC transformer input voltage into an alternating current (AC) transformer output voltage. The device driver also includes at least one processing element, adapted to receive one or more control inputs, and to generate an alternating current through a primary transformer winding based on the one or more control inputs. Other embodiments include methods for a controllable voltage device driver to generate a driver output voltage, and optical systems having an electro-optical device and an electro-optical device driver subsystem.

Abstract: The present invention is a system for providing power from solar cells whereby each cell or cell array is allowed to produce its maximum available power and converted by an operatively connected DC/DC converter. Each cell or cell array has its own DC/DC converter.

Abstract: A switching power supply device has a boost power converter which converts a wide range of AC input voltages into a DC voltage larger than an amplitude of the AC input voltage to supply to a DC-DC converter. The switching power supply device includes a load detection circuit, an input voltage detection circuit, and a power conversion controller for the boost power converter. The power conversion controller corrects the determination reference value in accordance with the AC input voltage detected in the input voltage detection circuit. When a light load is detected based on a comparison between the corrected determination reference value and the detection value output from the load detection circuit, the controller disables the boost power converter.

Abstract: An inductive element for transforming and/or regulating voltage input from a multi-phase, interleaved power supply system into an output voltage to a load is disclosed. The multi-phase, interleaved power supply system includes a plurality of pulsed power sources, each of which is adapted to provide voltage at a discrete phase. The inductive element includes a magnetic core having, for each power supply, a distinct area of relatively-high magnetic reluctance, which is surrounded by areas of relatively-low magnetic reluctance, and a pair of windings. Each of the pair of windings includes a first, phase winding that is electrically coupled to an output of one of the pulsed power source and to the load, and a second, loop winding that is operatively coupled and proximate to the first, phase winding. Each of the second, loop windings is disposed serially on a closed loop.

Abstract: A reduced cost energy transfer element for power converter circuits. In one embodiment, an energy transfer element according to an embodiment of the present invention includes a magnetic element having an external surface with at least a first winding and a second winding wound around the external surface of the magnetic element without a bobbin. As such, energy to be received from a power converter circuit input is to be transferred from the first winding to the second winding through a magnetic coupling provided by the magnetic element to a power converter circuit output.

Abstract: A three-phase AC voltage regulator is for adjusting a line voltage on transmission lines. The three-phase AC voltage regulator includes a sampling circuit, a reference-voltage circuit, a comparator, a switch, a power supply, and a compensator. The sampling circuit is for sampling the line voltage. The reference-voltage circuit is for receiving a line-to-line voltage from the transmission lines and generating a standard voltage. The comparator is for comparing the line voltage and the standard voltage to obtain a signal. The switch is for being turned on or off based on the signal. The power supply is for supplying various electric powers to the compensator. The compensator is for receiving the electric power and generating compensating voltages. The compensating voltages are used to compensate the line voltage.

Abstract: A current sensor includes a sensing circuit for sensing current and supplying indications thereof. The current sensor also includes two or more output terminals coupled to the sensing circuit that alternately supply respective indications of the sensed current according to control signals supplied to the current sensor.

Abstract: The present invention is directed at circuit for controlling a voltage applied to an output voltage terminal from a first voltage level supplied by an input voltage terminal comprising a first switch and a second switch connected in series between said input voltage terminal and a common terminal; a transformer, having a primary side and a second side, connected with said first switch on the primary side and to said output terminal on the secondary side; wherein when said first switch is closed and said second switch open, said first voltage level is supplied to said output voltage terminal; and wherein when said first switch is open and said second switch is closed, a second voltage level is supplied to said output voltage terminal.

Abstract: A circuit for providing power factor correction includes a boost converter circuit with a boost inductance and a power factor correction switch and a control circuit. The control circuit provides a pulse width modulated signal to control the on time of a PFC switch, and also includes a power factor correction pulse width modulated device receiving as inputs a rectified AC input voltage, a DC bus voltage, a signal proportional to the current through the inductor and a reference current signal. The power factor correction pulse width modulated device also includes a pulse width modulated generator operable to provide the pulse width modulated signal to control the on time of the PFC circuit and a pulse width modulated blanking device operable to provide an enable/disable signal to disable the pulse width modulated generator when predetermined conditions are met.

Abstract: A circuit for providing power factor correction comprising a boost converter circuit having a boost inductance and a power factor correction switch coupled in series with the boost inductance, the boost inductance and power factor correction switch being coupled across the output of a rectifier being supplied with AC power from an AC line, the boost converter circuit further comprising a boost diode coupled to a junction between the inductor and the switch, an output of the boost diode coupled to an output capacitor, a DC bus voltage being provided across the output capacitor, further comprising a control circuit receiving as inputs a rectified AC input voltage from the rectifier, a signal proportional to current through the inductor and the DC bus voltage across the capacitor, and wherein the control circuit provides a pulse width modulated signal to control the on time of the PFC switch, further comprising an enable/disable circuit receiving as inputs the rectified AC input voltage and the DC bus voltage, t

Abstract: In those conventional arts, a power supply with a voltage holdup circuit generates a peak voltage in output voltage when a switching operation is occurred, and so the quality of the output voltage is decreased and a risk of operating fault in a load apparatus. The present invention employs a feed forward circuit to immediately generate a forward feedback signal when a switching operation is occurred. Hence, the output voltage can be faster corrected to a accurate output voltage and so the peak voltage can be reduced.

Abstract: A motor controller includes a motor-position detector, a motor driver and a power cable having a pair of electric lines (two lines) which feeds power from the driver to the detector. The detector superimposes serial information about the motor-position to the power cable via windings of a transformer or a coupling capacitor. The serial information is obtained by converting parallel information about the motor-position. The serial information superimposed travels to the driver via the power cable. The driver receives the serial information via windings of the transformer or a coupling capacitor, and converts it to parallel information. The driver drives the motor according to this parallel information. The information necessary for driving the motor is superimposed to the power cable and transmitted through the power cable, so that a number of electric lines between the detector and the driver can be minimized.

Abstract: A power regulation system is coupled to an AC power source outputting an input voltage. The system has a first transformer to receive the input voltage and generate a control voltage. The system also has a second transformer that has a primary coil and a secondary coil. The primary coil and secondary coil of the second transformer are electromagnetically coupled to each other and so arranged that when the control voltage from the first transformer is applied to the primary coil, an output voltage is generated between a first end and a second end of the secondary coil, wherein the output voltage is substantially 180° out of phase from the input voltage so as to generate an effective voltage applied to the load, and wherein the effective voltage is less than the input voltage and substantially equals to the difference between the input voltage and the output voltage, resulting a reduction in power consumption of the load.

Abstract: A power regulation system is coupled to an AC power source outputting an input voltage. The system has a first transformer to receive the input voltage and generate a control voltage. The system also has a second transformer that has a primary coil and a secondary coil. The primary coil and secondary coil of the second transformer are electromagnetically coupled to each other and so arranged that when the control voltage from the first transformer is applied to the primary coil, an output voltage is generated between a first end and a second end of the secondary coil, wherein the output voltage is substantially 180° out of phase from the input voltage so as to generate an effective voltage applied to the load, and wherein the effective voltage is less than the input voltage and substantially equals to the difference between the input voltage and the output voltage, resulting a reduction in power consumption of the load.

Abstract: A low power mode and feedback arrangement for a switching power converter. Two or more main power switches, such as transistors, transfer energy from a supply to load by their opening and closing. When the load requires a relatively low power level, this condition is detected. In response, one or more of the transistor switches is disabled from switching and the reduced power requirements of the load are handled by the remaining one or more transistor switches. As a result, switching losses are reduced. This is because parasitic gate capacitance and on-resistance associated with the disabled switches no longer consume power from the power source. The invention provides significant efficiency advantages during periods when the load draws a low level of power. This is especially useful for battery-powered devices which may operate in a low power mode for extended periods of time, such as standby mode as in a portable telephone.

Abstract: A primary winding of a first insulating transformer for balance-to-unbalance transformation is connected between the central electrode and the outer electrode of an input terminal, and windings of a noise eliminating transformer are provided within balanced lines on the side of a secondary winding of the first insulating transformer. A primary winding of a second insulating transformer for balance-to-unbalance transformation is connected between the central electrode and the outer electrode of an output terminal, and balanced lines on the side of the secondary winding of the second insulating transformer is connected to the noise eliminating transformer. One end of each of the primary windings, which is grounded to the ground line, is connected to the middle print of the secondary winding of each insulating transformer.

Abstract: A power flow transformer implements power flow control in a transmission line of an n-phase power transmission system, where each phase of the power transmission system has a transmission voltage. The transformer has n secondary windings, where each secondary winding is on a core. The transformer also has n primary windings on the core of each secondary winding for a total of n2 primary windings, where one primary winding from each core is assigned to each phase. For each phase, the primary windings assigned to the phase are coupled in series, and the in-series primary windings receive the transmission voltage of the respective phase of the power transmission system. For each core, each primary winding thereon induces a voltage in the secondary thereon. The induced voltages are summed by the secondary to result in a summed induced voltage. Such summed induced voltage is a compensating voltage for a respective phase.

Abstract: A method for limiting a switching current and limiting a voltage drop across a circuit includes the steps of limiting a current sent from a power source to a switching device during a turn on time of the switching device by disposing an inductor device in series between the power source and said switching device and returning flux energy stored in said inductor device to the power source during a turn off time of the switching device.

Abstract: An uninterruptable power supply system for producing an AC voltage from at least one of a DC power source or an AC power source includes an input terminal configured to receive an AC voltage from an AC power source, and an inverter operative to produce an AC voltage at an output thereof from a DC power source. A ferroresonant transformer circuit includes a transformer having an input winding, a output winding, and a third winding that forms part of a resonant circuit that produces saturation in the output winding when an AC voltage on the input winding exceeds a predetermined amplitude. A transformer input control circuit is coupled to the input terminal and to the inverter output and is operative to couple at least one of the input terminal and the inverter output to the input winding.

Abstract: An excitation controller includes a reactive current detector for detecting a reactive current output from a synchronous machine connected, by way of a tap-changer-equipped transformer including a tap changer for changing taps of the transformer under load conditions, to a transmission system, a tap controller for setting a tap ratio of the tap-changer-equipped transformer according to an output terminal voltage of the synchronous machine, and a voltage setter for setting a reference voltage for an output voltage of the synchronous machine based on a second reference voltage of the tap-changer-equipped transformer at a side connected to the transmission system, the tap ratio set by the tap controller, and the reactive current detected by the reactive current detector. The excitation controller further includes a control unit for controlling an excitation system for exciting the synchronous machine according to the first reference voltage set by the voltage setter.

Abstract: A static voltage regulator consists of a booster transformer, a regulator transformer, an electronic switching system and a control system. The booster transformer includes a booster primary winding and a booster secondary winding. The booster secondary is provided in series with the input and output terminals of the regulator so as to produce an output voltage. The regulator transformer includes a regulator primary winding and a regulator secondary winding. The regulator primary is electrically coupled to the output. The electronic switching system is coupled between the regulator secondary and the booster primary for providing a voltage to the booster primary. The control system includes a voltage sensor for sensing a voltage at the input, and a gating system coupled to the switching system for switching the output voltage in response to changes in the sensed input voltage.

Abstract: A voltage booster device for increasing the voltage level of power received by a recreational vehicle (RV) from a separate 120-volt power source includes an electrical box, a power cord and female outlet on the box, and an encapsulated transformer within the box. The transformer (e.g., an autotransformer) is adapted to increase the actual voltage level of the separate 120-volt power source a predetermined amount. A relay is provided for switching the transformer, the power cord, and the female outlet between (i) a first circuit configuration that couples power from the power cord to the female outlet via the transformer so that the transformer increases the voltage level by the predetermined amount, and (ii) a second circuit configuration that bypasses the transformer so that the transformer does not increase the voltage level by the predetermined amount.

Abstract: A power supply circuit has: a power supply filter including a coil which is inserted in series into an input line; a DC--DC converter which is connected to an output of the power supply filter and which converts an input voltage into an arbitrary output voltage; a detecting section which detects a potential difference between ends of the coil; and a control section which controls the output voltage of the DC--DC converter based on the detected potential difference.

Abstract: A circuit that senses a current signal in a secondary winding of a transformer by monitoring a current signal in a primary winding of the transformer. The monitored current signal contains an effective current component and a magnetization current component. The magnitude of the effective current signal is related to the magnitude of the current signal in the secondary winding by the turns ratio of the transformer. The magnetization current signal produces flux in the transformer core and does not contribute to producing current in the secondary winding of the transformer. In addition, the magnetization current is 90 degrees out of phase with the effective current signal in the primary winding. The effective current signal in the primary winding is in phase with the voltage signal applied to the primary winding. The invention integrates the monitored current signal over 0 degrees to 180 degrees of the effective current signal waveform.

Abstract: A solid state voltage regulator and methods therefore are shown to include a transformer having a secondary coil, the secondary coil having a plurality of taps. A first solid state switch is connected between the regulator output and a first tap. The first switch need only have the capability of being turned on in response to a gate signal. A second solid state switch is connected between the regulator output and a second tap. The second switch has the capability of being turned on and turned off in response to gating signals. The output voltage resulting from the second tap is greater than the first tap. A controller, connected to the input, the output, the first switch and the second switch, senses the voltage present at the regulator input and output and generates gating signals in response to the sensed voltage. The voltage regulator may include several switches similar in construction and operation to the first switch.

Abstract: An inductive load drive device using a DC--DC converter circuit with which a high voltage is obtained by the discharge of electromagnetic energy stored in a coil to a capacitor, in which a bias is applied to the magnetic core of a coil (L) with the use of a permanent magnet (Mg) in the direction opposite to the magnetic flux induced by a current so as to increase the electromagnetic energy stored in the coil (L) and make it possible to perform efficient discharge with a small coil.

Abstract: An uninterrupted power supply with improved circuit arrangement includes a controller, a detecting circuit and a control circuit. When the incoming AC voltage is normal and in a positive half-wave cycle, an input pin of the controller detects the actual voltage level of the secondary voltage of a transformer. When the incoming AC voltage is in a negative half-wave cycle, the input pin of the controller receives a sinusoidal input waveform voltage based on the voltage Vcc which acts as a reference voltage, and the controller processes the sinusoidal input waveform voltage by subtracting the secondary voltage of the transformer from the voltage reference Vcc to obtain a sinusoidal half-wave voltage with positive half-wave cycle. The controller combines the positive and negative half-wave cycle signals to obtain a composite voltage, and then calculates the RMS value of the composite voltage so as to determine the changing situation of the incoming AC voltage.

Abstract: A control system for a microwave oven having a magnetron unit, a microwave oven using such a control system and methods of making the same are provided, the system being adapted to interconnect a power source to a transformer unit of the magnetron unit to operate the same, the system comprising a unit for determining the actual voltage level of said power source to be utilized at that time and being adapted to interconnect the power source to a particular tap of the transformer unit if the determined power level is above a certain value and to interconnect the power source to another tap of the transformer unit if the determined power level is below the certain value.

Abstract: Adaptors are provided for use with electrosurgical bipolar instruments and standard commercially available electrosurgical generators that reduce coagulum buildup and sticking on electrosurgical instruments. A first type of adaptor converts a high voltage, high crest factor output voltage waveform typical of conventional electrosurgical generators to a more desirable lower voltage, lower crest factor regime. A second type of adaptor limits the peak open-circuit voltage supplied by a conventional electrosurgical generator to an electrosurgical instrument.

Abstract: A system for providing a constant current to airport or airfield signs is disclosed. The system receives input currents of varying amperages which also supply, and allow dimming of, runway or taxiway lights. According to various exemplary embodiments of the present invention, a high power factor is achieved which provides greater cost efficient operation of the signs.

Abstract: A microwave oven driving circuit for stably driving a microwave oven wherein a certain output of a magnetron can be generated by controlling a microcomputer. First and second comparing portions control a voltage supplied from a power supply portion and an output of the magnetron to increase in stages so as to obtain a normal output of the magnetron. Also, the output of the magnetron is gradually decreased without being too abrupt even if the output of the generating portion must be decreased as cooking is completed, thereby improving durability and cooking efficiency of the microwave oven.

Abstract: A high frequency heating apparatus includes a casing, an inverter enclosed in the casing, a magnetron supplied with high frequency voltage from the inverter, and three attachment plugs each connected to one of external power supplies of different output voltages. The attachment plugs are connected to the inverter input side via respective power supply selecting switches. The apparatus further includes three display panels one of which is selectively attached to the apparatus. Each display panel has an indicia indicative of one of the power supply voltages used and two projections selectively turning off the other two power supply selecting switches when attached to the apparatus.

Abstract: A protective device for an electric control circuit having first and second input buses to be applied with a source voltage of low level from a commercially available source of electricity and an electrical load of low rating voltage connected between the input buses. The protective device is in the form of a switchover relay disposed between the input buses and the electrical load for maintaining the electrical load in connection to the input buses when applied with the source voltage of low level and for disconnecting the elecrical load from the input buses when applied with a source of high level from the source of electricity. The operating voltage of the switchover relay is determined to be higher than a maximum allowable voltage of the electrical load and to be lower than a lower limit value of the source voltage of high level.

Abstract: An automatic input switching circuit for a power supply includes a transformer with two primary windings, normally connected in series and connectible in parallel by relay contacts for operation in a doubler mode. The secondary winding supplies a rectifier for developing a DC output voltage and a voltage doubler for developing a higher voltage than the output voltage. The voltage doubler charges a capacitor that stores energy for operating the relay when a transistor switch is closed. The transistor switch is normally held in a nonconductive state by an inhibit transistor driven from a comparator that switches states when the voltage across the capacitor reached a predetermined level. A voltage sensing arrangement compares the rectifier output voltage with a reference voltage and when it reaches a certain level, another comparator switches states to activate a disable transistor.

Abstract: A voltage controlling transformer circuit comprises a setting unit to the input terminals of which an alternating input voltage is applied and the output terminals of which provide an alternating output voltage the amplitude of which can selectively be changed. For this purpose the setting unit comprises a transformer having a first winding connecting one of the input terminals with one of the output terminals while the other input terminal and the other output terminal are directly connected by a conductor. The transformer also comprises at least one further winding the number of turns of which is greater than the number of turns of the first winding, and to which different control voltages can be applied by means of switches in order to induce in the first winding a voltage the amplitude of which is, in dependence on the winding sense of the further winding, either additionally or subtractively imposed on the amplitude of the input voltage.

Abstract: A power supply includes a plurality of transformers with individual primary windings, having one end connected in common, respectively, the transformers sharing a secondary winding; a switching network for (1) applying alternate polarity DC voltages to the commonly connected ends of the primary windings over each half-cycle of a clock signal, and relative to these commonly connected ends of the primary windings, (2) applying the same or opposite polarity DC voltages individually to the other ends of the primary windings, over each half-cycle of the clock signal, and in different combinations dependent upon the amplitude or level of a command signal at any given switching time, for producing a pulsed AC waveform in the secondary winding that is amplitude modulated by the command signal.

Abstract: A battery charging system including a plurality of transformers each having a primary winding, a secondary winding, and a tertiary windings, the primary windings being connected in series forming a "shared primary", a first switching network for connecting a DC voltage across the shared primary winding, in alternating polarity over successive half-cycles of a clock signal, for causing voltage pulses to be induced into the secondary and tertiary windings of the transformers, a second switching network responsive to the magnitude of primary current for shorting the same or different combinations of the tertiary windings, thereby shorting the associated transformers, over each half-cycle of a clock signal, for controlling the magnitude of charging current to the batteries, and a plurality of rectifiers for rectifying the AC voltages developed in each secondary winding, respectively, for providing charging current to the battery.

Abstract: An arrangement for controlling an A.C. voltage supplied to a load, such as a fluorescent lamp emitting germicidal ultraviolet radiation in a water-purifying apparatus. The load is connected to the secondary winding of a transformer, the primary winding of which has a number of taps which are selectively connectable to an exterior A.C. voltage source. An electronic control device is arranged in dependence on the magnitude of the terminal voltage of the exterior A.C. voltage source to automatically connect that tap which causes the voltage applied to the load to be of a predetermined value.

Abstract: A power supply for providing an output voltage amplitude modulated by a command signal, includes a rectifier for rectifying the command signal, a comparator network for comparing the instantaneous rectified level of the command signal with a plurality of predetermined reference voltages, for producing a plurality of phasing signals, respectively, for operating a switching network to (1) alternately and successively connect positive and negative polarity DC voltages to the one ends of a primary windings of a plurality of transformers, and to (2) connect either the positive or the negative DC voltage to the other ends of the primary windings in different combinations, over each half-cycle of a clock signal, for producing in a common secondary winding for the transformers the amplitude modulated output voltage. Another rectifier may be provided for rectifying the AC output voltage, for producing a DC output voltage amplitude modulated by the command signal.

Abstract: A voltage regulator capable of maintaining the output voltage of a unit, such as a power supply, incorporating said voltage regulator within, for example, .+-.5 percent of say, 115 volts, a.c., without any interruptions in the power supply output voltage and without any distortion of the a.c. sine wave.This is accomplished through the monitoring of varying secondary transformer output voltages according to the primary input voltage variations by means of a comparator processing a signal to power relays which switch to specific secondary transformer taps without causing interruptions of the output power and without distortions of the a.c. sine wave, respectively. Various additional devices are provided to enhance the described regulated a.c. power supply performance.

Abstract: A feed forward AC voltage regulator utilizes a step-up, step-down transformer to apply adjustment voltages to an unregulated AC line. Analog circuitry periodically samples the unregulated AC line input and compares it with a scaled representation of the desired line voltage. Digital circuitry converts the information from the analog sampling and comparison to an instruction command which activates an appropriate solid state switch associated with a tap on a multitap transformer connected to the regulated AC output line. The taps are successively located on the multitap transformer to provide selectable adjustment voltages of various values. The switched-in adjustment voltage is provided the proper polarity and applied to the primary of the step-up, step-down transformer, thereby applying to the secondary the adjustment voltage needed to move the regulated AC output line to the desired level.

Abstract: A passive control network for connection between a pair of load output level setting terminals, as on a ballast for a dimmable fluorescent lamp in a lighting system, to provide a required variable impedance, where the magnitude of the impedance establishes the load output level. The passive control network includes an isolation transformer for coupling a periodic waveform at the load input terminals to the variable impedance component, the magnitude of which impedance is reflected through the transformer to provide the load level-setting impedance.

Abstract: An adjustable current source comprises a choke (1) and a capacitor (2) whose reactive impedances are equal at the frequency of a variable voltage source (3), as well as a load current matching and adjusting unit made as a magnetic amplifier (4). Some outputs of the choke (1), the capacitor (2) and a primary winding (6, 7) of the magnetic amplifier (4) are coupled to respective phases of the variable voltage source (3). Other outputs of the choke (1), the capacitor (2) and the primary winding (6,7) of the magnetic amplifier (4) are joined in a star connection. The secondary winding (9, 10) of the magnetic amplifier (4) is coupled to the load (11). The control winding (13) of the magnetic amplifier (4) is coupled to a constant voltage source (14).