Abstract: A control circuit for a switching power supply reacts to an over current condition in the switching power supply to bring its operating point to a safe condition. The control circuit senses both the direction and the magnitude of the load current in the switching power supply, and then uses this sensed information to control the active power switches in the switching power supply. In an over current condition, the switches are controlled to actively drive the load current toward zero, even if the sensed information is delayed or heavily filtered, or the switch signals from the control circuit are delayed in reaching the switches. The resulting operation of the switching power supply is more resistant to abnormal load conditions and is maintained in the presence of transient short circuits or arcs. The switching power supply hardware is also better protected.

Abstract: Techniques are disclosed to limit the current in a switch of a switching power supply. An example switching regulator circuit includes a switch to be coupled to an energy transfer element. A controller is coupled to the switch to control switching of the switch. A current sensor is included in the controller. The current sensor includes first and second comparators coupled to compare a current in the switch with first and second current limits, respectively. The controller is to open the switch for a remainder of a current switching cycle of the switch until a next switching cycle of the switch in response to the first or second comparators. A frequency adjuster is also included in the controller and coupled to the second comparator. The frequency adjuster is to adjust an oscillating frequency of an oscillator included in the controller in response to the second comparator.

Abstract: A protection device for a converter includes at least one power switch that operates for a first time period from the time the overload or short-circuit in the converter has been detected. The protection device includes circuitry to control the power switch to minimize the power deliverable by the converter for a second time period from the end of the first operating time period, as well as circuitry to shut down the converter after the second time period.

Abstract: A DC-AC converter for converting DC voltage to AC voltage. The converter includes a conversion circuit for converting DC voltage to voltage having a polarity corresponding to AC voltage. A filter circuit receives the converted voltage, smoothes the converted voltage, and outputs the smoothed voltage as AC voltage. A first switch operably connects the voltage conversion circuit and filter circuit. A second switch is arranged between input terminals of the filter circuit. An output current detection circuit detects overcurrent that is greater than a predetermined first threshold. When overcurrent that is greater than the first threshold is detected, the protection circuit stops the supply of power in the voltage conversion circuit, deactivates the first switch, and activates the second switch.

Abstract: An electric power control apparatus outputs output from a power generation apparatus to a power system has a power converter that converts power output from the power generation apparatus and a power storage apparatus that stores output from the power generation apparatus or output from the power converter as well as discharges stored electric power as necessary detects an amount of electric power generated at the power generation apparatus within a predetermined time period, sets an output pattern of the electric power control apparatus in a next predetermined time period based on the amount of electric power of each predetermined time period, and controls the output of the electric power control apparatus in accordance with the output pattern.

Abstract: Techniques are disclosed to detect a fault in the feedback circuit of a switching power supply while the power supply operates in a mode where the output is below its regulated value. The power supply delivers maximum power at a given switching frequency without a feedback signal while the output is below its regulated value. A fault protection circuit substantially reduces the average output power if there is no feedback signal for the duration of a fault time. When there is no feedback signal, the power supply increases the maximum output power by increasing the switching frequency before the end of the fault time to increase the output to a regulated value. The presence of a feedback signal when the output reaches a regulated value restores the original switching frequency and returns the output to its unregulated value. The absence of a feedback signal at the end of the fault time engages the fault protection circuit to substantially reduce the output power.

Abstract: A controller for a driving circuit of power source comprises a frequency generator, a pulse width modulator, and a driving device. The frequency generator comprises a latch circuit. The frequency generator provides a pulse signal at a first frequency after the controller is started. After the frequency generator receives an indicating signal, the frequency generator changes the frequency of pulse signal from the first frequency to a second frequency and locks the frequency of pulse signal at the second frequency. The pulse width modulator provides a PWM signal according to the pulse signal and a feedback signal which indicates a status of electric power supply of the driving circuit. The driving device controls semiconductor switches according to the PWM signal.

Abstract: The present invention relates to a protection circuit for protecting a half-bridge circuit. The protection circuit detects an incorrect response of the half-bridge by monitoring the current of a first switch at a series resistor of a second switch. The protection circuit has a detector for detecting the voltage across the resistor and an evaluation circuit which is designed in such a manner that it evaluates an output signal from the detector after the first switch has been switched on and provides a fault signal at an output when the voltage across the resistor is greater than the threshold voltage.

Abstract: An inverter (100) comprises first and second input terminals (102,104), an inverter output terminal (106), a series arrangement of a first inverter transistor (110) and a second inverter transistor (120), a driver circuit (130), a primary current sensing circuit (150,154,156), and an auxiliary current sensing circuit (160). Primary current sensing circuit (150,154,156) is coupled between second inverter transistor (120) and a current-sense input (132) of driver circuit (130). Auxiliary current sensing circuit (160) is coupled between second inverter transistor (120) and a frequency control input (134) of driver circuit (130). During operation, if the current flow through inverter transistors (110,120) exceeds a predetermined peak limit, auxiliary current sensing circuit (160) provides an auxiliary signal to frequency control input (134) of driver circuit (130), thereby increasing a drive frequency at which driver circuit (130) commutates inverter transistors (110,120).

Abstract: An overcurrent protective device has a current detecting section and a control section. The current detecting section detects the amount of a current flowing through switching elements of an inverter device. The control section determines whether the inverter device is held in a first state or a second state in correspondence with an input from the current detecting section. When it is determined that the inverter device is held in the first state, the control section performs a flywheel operation. When it is determined that the inverter device is held in the second state, the control section performs a regenerative operation. Accordingly, the overcurrent protective device prevents generation of whine when performing overcurrent protective operation.

Abstract: A converter circuit is disclosed for switching of a multiplicity of switching voltage levels, which have n first switching groups for each phase (R, S, T), with the n-th first switching group being formed by a first drivable bidirectional power semiconductor switch and a second drivable bidirectional power semiconductor switch, and with the first switching group to the (n?1)-th switching group each being formed by a first drivable bidirectional power semiconductor switch and a second drivable bidirectional power semiconductor switch, and by a capacitor which is connected to the first and second drivable bidirectional power semiconductor switches with each of the n first switching groups being connected in a linked form to the respectively adjacent first switching group, and with the first and the second drivable bidirectional power semiconductor switches in the first switching group being connected to one another.

Abstract: A device corrects the power factor in forced switching power supplies and includes a converter and a control device to obtain a regulated voltage on an output terminal. The control device comprises an error amplifier having an inverting terminal (Vout) and a non-inverting terminal receiving a reference voltage. The device includes first and second resistances coupled in series with a conduction element positioned between the first resistance and the inverting terminal of the error amplifier and a fault detector suitable for detecting the electrical connection of the conduction element with the output terminal and suitable for detecting an output signal of the second resistance. The fault detector is suitable for supplying a malfunction signal upon detecting an electric disconnection of the conduction element from the output terminal or when the output signal of the second resistance tends to zero.

Abstract: An insulated gate bipolar transistor and a protective circuit are incorporated. The protective circuit has first and second Zener diodes connected in series in directions opposite to each other between the gate and the current sense terminal of the insulated gate bipolar transistor, and third and fourth Zener diodes connected in series in directions opposite to each other between the gate and the emitter of the insulated gate bipolar transistor.

Abstract: A driving circuit has a p-channel transistor and an n-channel transistor. A power switching element is set at an on state each time the p-channel transistor sets a charging line at a conductive state in response to a leading edge of an output pulse to supply a positive charge to a gate of the element through the charging line. The element is set at an off state each time the n-channel transistor sets a discharging line at a conductive state in response to a trailing edge of the output pulse to discharge the supplied charge through the discharging line. A through current occasionally flows through the transistors set at the on state together. The driving circuit has resistors between the transistors to suppress the through current.

Abstract: The present invention provides an inverter with a simple configuration capable of preventing occurrence of excessive rush current. A current detection circuit detects an AC output current flowing out from an output filter circuit. When the absolute value of the AC output current becomes equal to or larger than a threshold, a reset control unit and a drive pulse generation circuit control a DC/AC inverter so as to re-start operation after the AC output voltage becomes 0V. For example, even in the case where a capacitive load is connected during operation of the inverter or in the case where the load includes a standby circuit, excessive rush current is prevented.

Abstract: A converter circuit is specified for switching a large number of switching voltage levels, which has n first switching groups for each phase, with the n-th first switching group being formed by a first power semiconductor switch and a second power semiconductor switch, and with the first first switching group to the-th switching group each being formed by a first power semiconductor switch and a second power semiconductor switch and by a capacitor, which is connected to the first and second power semiconductor switches, with each of the n first switching groups being connected in series to the respectively adjacent first switching group, and with the first and the second power semiconductor switches in the first first switching group being connected to one another.

Abstract: An electrical power supply system including an engine driven permanent magnet generator (11) operable to produce a variable voltage and high frequency output which is converted by a series train AC/AC conversion circuit (14) into a fixed voltage and relatively low frequency AC output for supply through a trip switch (56-58) to an external load (53-55). A bypass circuit including a pair of normally-closed parallel connected oppositely biased thyristors (66-68) is connected between the generator output and the output of the AC/AC conversion circuit (14).

Abstract: A current-source sine-wave voltage inverter for converting a direct current (DC) voltage to an alternating (AC) voltage includes a DC source for providing a DC voltage, a current source circuit having a primary side inductance of a transformer, a clamping circuit, an inverting circuit, and a control and driving circuit. The clamping circuit includes a first switch cascaded with a first diode, a second diode cascaded with a second switch, a first capacitor connected between an anode of the first diode and a cathode of the second diode, a secondary side inductance of the transformer cascaded with a third diode, the secondary side inductance of the transformer and the third diode connected to two ends of the DC source, and a cathode of the third diode connected to an anode of the DC source. The present invention also provides a fuel cell system.

Abstract: In the current detection circuit that detects the output currents of a switching power supply circuit, an improved current detection circuit makes it possible to detect the output current directions of power supplies solves the malfunction of the power supplies vibrating or diverging during changes in load state and during parallel operation, and thus implements stable operation. The direction of an output current I2 can be detected by using the current detection circuit 8 that has multiple switching elements S1 to S4 each operating synchronously with an inverter circuit.

Abstract: A current averaging circuit for averaging a piecewise linear switching current waveform of a PWM power converter including first, second and third sample and hold circuits and a sample averaging circuit. The first sample and hold circuit samples a short duration of the current waveform for each PWM cycle and provides corresponding short samples. The second sample and hold circuit samples a long duration of each PWM cycle and provides corresponding long samples. The sample averaging circuit is coupled to the first and second sample and hold circuits, averages corresponding ones of the short and long samples and provides corresponding average values. The third sample and hold circuit samples each average value and provides a current average signal. The waveform may include ramp-on-a-step voltage pulses representing switching current. The current average signal is updated after each current pulse.

Abstract: The present invention discloses a control circuit of power supply with selectable current-limiting modes, wherein the control circuit which maintains the power-output circuit of the power supply within the energy-limiting standard is performed with automatic detection mode. In the present invention, a current-limiting set unit of the control circuit is coupled to the power-output circuit and provides a current-limiting set value according to power-output levels of the power-output circuit and outputs a current-limiting set signal to a current-limiting switch unit. The current-limiting set unit sets up switch junctions on the power-output levels of the power-output circuit, and the current-limiting switch unit receives the current-limiting set signal to determine the state of the switch junctions in order to provide current-limiting detect values of single set or multiple sets of power-output levels for the current-limiting set unit.

Abstract: According to one embodiment, a computer system is disclosed. The computer system includes an integrated circuits (IC), a power supply that supplies power to the IC and an over-current protection (OCP) circuit. The OCP circuit prevents the exceeding a predetermined power threshold during a short circuit condition while the IC is enabled to receive a greater power level.

Abstract: A fault handling system for short circuit recovery in three-phase multiple-level inverter bridges, used to drive inductive loads, which waits for either desaturation of switches or expiration of a delay period based upon an amount of time before saturated switches are damaged before commanding off switches that are saturated, and which artificially creates a dead-short across the three-phase output to force switches conducting a fault current to desaturate. By delaying the switching-off of the inverter bridge during a fault, waiting for desaturation to occur, the statistical likelihood of switch survival is improved.

Abstract: The object is to reliably detect a ground fault of a solar battery. To detect a ground fault position to take an efficient measure against the ground fault, DC power input from a solar battery is converted into AC power and supplied to a system. In a system interconnection inverter (utility connected inverter) having non-insulated input and output, the input voltage of a converter circuit and/or the intermediate voltage between the converter circuit and an inverter circuit are varied to control the potential to ground at each portion of the solar battery to a value other than a value close to zero.

Abstract: The invention relates to a circuit arrangement for operating electric lamps (5), in particular dielectric barrier discharge lamps, having an input stage (1) in the form of a voltage-increasing converter, in particular a step-up converter, and at least one subsequent further circuit stage (2), for example a flyback converter in the form of a pulse stage. An intermediate circuit overcurrent protection device (3) is connected between the step-up converter (1) and the flyback converter (2) and protects the flyback converter (2) in the event of a fault, specifically in particular if the input overcurrent protection device (1) does not respond.

Abstract: FA ballast (20) for powering a gas discharge lamp (70) comprises an inverter (200) and an arc protection circuit (600). Arc protection circuit (600) monitors an electrical signal within the ballast. In response to occurrence of a disturbance in the signal, such as what occurs during output arcing, arc protection circuit (600) disables the inverter (200) for a timed shutdown period. Arc protection circuit (600) provides a timed starting period for igniting the lamp, during which time any disturbance in the electrical signal is essentially ignored and inverter (200) is allowed to continue to operate. Arc protection circuit (600) also provides a restart function for periodically attempting to ignite and operate the lamp. Arc protection circuit (600) is preferably realized using a timer integrated circuit (U1) with associated discrete circuitry, and may be adapted for use with ballasts having self-oscillating or driven type inverters.

Abstract: It is an object of the invention to provide a multilevel PWM inverter control apparatus capable of safely carrying out switching from a normal operation to a protecting operation and performing a reset from the protecting operation to the normal run safely and smoothly without requiring a complicated control algorithm. In the invention, if a current value I which is measured is set to have a level which is equal to or higher than the level of a first reference value I1 and is lower than the level of a second reference value I2, a zero vector to be started from an OOO state in which an intermediate potential is output for all of phases is output (Step 22). If the current value I is set to have a level which is equal to or higher than the level of the second reference value I2 and is lower than the level of a third reference value I3, a base block operation for bringing all of switching units into an OFF state is carried out after outputting the zero vector (Step 28).

Abstract: A switching power supply apparatus is provided that is not thermally destroyed even if the load remains short-circuited for a long time when the voltage of the commercially distributed alternating-current power supplied thereto is high. When the load connected between a positive and a negative output terminal is short-circuited, the short-circuited state is detected by an output voltage detection circuit, and a switching control circuit stops operating. At start-up, a current from a bridge rectifier circuit is fed, as a startup current, through a constant current circuit to the switching control circuit. Thus, even when the voltage of the commercially distributed alternating-current power is high, a constant current flows through the switching control circuit. This permits the power consumed with the load short-circuited when the input voltage from the commercially distributed alternating-current power is high to be approximated to that consumed when the input voltage is low.

Abstract: The invention relates to a converter provided with a resonant circuit (16), which converter comprises a device (31) for measuring the derivative (dI/dt) of the current through the current valves 82, 3) and a detection device (32) co-operating with said measuring device (31) for detecting a short-circuit in the converter, the detection device (32) being adapted to detect a short-circuit current when the current derivative (dI/dt) measured by the measuring device (31) is equal to or exceeds a stipulated current derivative limit value (dI/dtlim) during a length of time exceeding a stipulated time limit value (tlim). The invention also relates to a method for controlling such a converter.

Abstract: A half-bridge-type control signal generating circuit outputs two control signals to control directly and drive switching actions of two electronic switches of a half-bridge-type circuit architecture. The half-bridge-type control signal generating circuit comprises an AND-gate logic unit, a NAND-gate logic unit, a circuit protection unit, a function generator, a clock generator, a soft boot unit connected to the clock generator, a sample and hold unit, a first comparator connected to the soft boot unit and the function generator, an OR-gate logic unit connected to the soft boot unit, the first comparator, the AND-gate logic unit and the NAND-gate logic unit, a second comparator connected to the sample and hold unit, the function generator, the AND-gate logic unit and the NAND-gate logic unit, and a dead time control unit connected to the function generator, the AND-gate logic unit and the NAND-gate logic unit.

Abstract: A power supply protecting the electric device circuit when over-voltage is applied, is provided. The power supply has a rectifying unit rectifying AC power externally supplied, into first and second DC power and outputting the first and the second DC power; a main power supply transformer boosting the first DC power and supplying the boosted first DC power to the electric device circuit; a switching controlling unit driven by the second DC power, performing the operation on the main power supply transformer that causes the first DC power to be boosted when the second DC power is received; and a controlling unit determining whether the second DC power is to be supplied to the switching controlling unit, wherein the controlling unit senses the voltage supplied to the electric device circuit and interrupts supplying the second DC power to the switching controlling unit if the sensed voltage exceeds a given value.

Abstract: An apparatus for electrical protection of an electrical system includes a protection circuit for detecting when silicon controlled rectifier (SCR) or other control elements in an engine driven generator of a welding-type power source have failed. In such an apparatus, a shorted rectifying control element detection device has an input stage connected to an engine driven generator that supplies power for a welding-type process and a filtering stage to bandpass current signals acquired by the input stage from the engine driven generator. The apparatus further has an output stage connected to the filtering stage that at least indicates a fault condition if fundamental frequency components present in the current signals exceed a threshold.

Abstract: The invention describes a method of regulating a rectifier inverter system (1), whereby electrical power is generated and/or supplied via a power source (6) and is transmitted from at least one d.c.-to-d.c. converter (3) to an intermediate circuit (4), from where it is fed via a d.c.-to-a.c. converter (5) to an alternating voltage supply (8) and/or delivered to a consumer. The d.c.-to-d.c. converter (3) is regulated in such a way that a virtually constant current flow is applied from the input of the d.c.-to-d.c. converter (3), in other words from the power source (6), to the output of the d.c.-to-d.c. converter (3), in other words the intermediate circuit (4), during a pre-settable period irrespective of the power drawn off from the intermediate circuit (4), whereas during this same period power is drawn off from the intermediate circuit (4) to feed it to the alternating voltage supply (8) or deliver it to the consumer. A controller or a control system of the d.c.-to-d.c.

Abstract: To perform a miniaturization and weight reduction of an electric power conversion apparatus, and in extension, the miniaturization of an inverter apparatus itself. In the inverter apparatus which converts a DC voltage into an AC voltage, a semiconductor device for electric power conversion, and a drive and protection circuit which drives and protects this semiconductor device for electric power conversion, and a power supply circuit which supplies power to this drive and protection circuit are integrated in the same module.

Abstract: The present invention provides a switching power supply which has an overcurrent protection characteristic with a small number of components. The switching power supply includes a regulator from a drain and an auxiliary winding VCC, a drain current detection circuit for detecting a current applied to a switching element, an oscillation circuit for outputting a clock signal of a constant frequency, a feedback signal control circuit for detecting a control signal from the secondary side and controlling current applied to the switching element, a clamping circuit for controlling the maximum value of current applied to the switching element, and a clamp voltage variable circuit for changing a clamp voltage of the clamping circuit and an oscillation frequency of the oscillation circuit according to a voltage of VCC.

Abstract: A solar cell array having an exposed electroactive portion is connected to a system power supply through an insulation transformer, a ground-fault interrupter is provided between the solar cell array and the system power supply, and a ground-fault detector is provided at the grounded line of the solar cell array. A set current value at which the ground-fault detector judges a ground-fault is larger than an amount of a set current value at which the ground-fault interrupter interrupts a circuit. The insulation transformer is provided between the solar cell array and the system power supply.

Abstract: It is an object of the invention to provide an inverter apparatus capable of instantaneously limiting a current to prevent the breakdown of a device and operating an electric motor efficiently and stably.

Abstract: A drive transformer and associated circuitry for providing power and appropriate delays to primary switches and synchronous rectifiers in switch-mode power converters in a full-bridge topology. The invention takes advantage of the leakage inductances of the drive transformer windings as well as the input capacitance of the primary switches (MOSFETs) to provide the delays. No separate circuitry is needed to provide such delays, thereby providing reliability. Exemplary embodiments further disclose means to disable or enable the primary winding from a condition sensed on the secondary side even with a control and feedback circuit located on the secondary side. The invention further discloses means to use one drive transformer winding to control two switches completely out of phase.

Abstract: Method and system for providing current transient control for N electrical devices, numbered (N≧2), where each device has an associated current transient I(n) upon power-up or power-down. Q subsets (preferably mutually exclusive) of devices are provided, where the sum of current transients (in-rush, etc.) for all devices in subset number q (q=1, . . . , Q; Q≧2) is no greater than a selected current value, such as (i) a maximum current that can be supplied by a current source or the maximum current that can be passed through a front end component associated with at least one device without injuring the device and (ii) a maximum current that can be supplied by a current source for power-up. A device may be redundantly assigned to more than one subset, to improve reliability. A time delay is implemented between power-up (or powerown) of any two distinct device subsets. Within an activated subset, a time delay is optionally implemented between any two distinct devices in the subset.

Abstract: A three phase alternating current generator-motor that serves as a starter motor or the alternator includes switching elements for controlling current. When the three phase alternating current generator-motor generates electricity, current flowing to the switching elements is suppressed by current control units in accordance with quantity of generated electricity. A plurality of rectifying diodes are provided in the three-phase alternating current generator-motor are connected in parallel with the corresponding switching elements.

Abstract: If an interturn short-circuit occurs in a stator coil winding of a permanent magnet excited electric machine, a short-circuit current is produced there that results in an electrically induced magnetic alternating flux which corresponds in its value to the permanent magnetic alternating flux flowing through the respective winding and which is opposite in phase. Such a sort-circuit current could lead to burn-off of the turn due to its considerable strength and the loss associated therewith. To prevent this, the invention suggests in case of detection of an interturn short-circuit, to entirely short-circuit at least the coil affected by the short-circuit or to apply thereto a corresponding in-phase current and to reduce the excessive short-circuit current in the individual turn or in the individual turn section by way of this overall short-circuit current in the coil. It is thus possible to prevent burn-off of the respective turn part.

Abstract: A low noise, multiple output power supply circuit featuring a plurality of efficient linear regulators comprises a transformer having a primary circuit with a primary transformer input winding and a plurality of secondary circuits. Each secondary circuit has a secondary transformer output winding having the same number of turns of secondary windings. A saturable reactor core is placed in series with at least one selected output winding of at least one selected secondary circuit to subtract a small amount of average voltage, volt-seconds, from the output voltage of the selected output winding to allow different rectified DC voltages to be obtained from different output windings which have the same number of turns.

Abstract: A power semiconductor device includes a half bridge circuit, a control circuit and a noise removal circuit. The half bridge circuit includes a switching element on a low voltage side and a switching element on a high voltage side, those switching elements serially connected. The control circuit controls a switching operation of the switching element on a low voltage side in the half bridge circuit. The control circuit has a supply-voltage receiving terminal connected to a high voltage side of a power supply for driving the control circuit. The noise removal circuit including, for example, a zener diode, is interposed between the supply-voltage receiving terminal of the control circuit and the low voltage side terminal of the switching element on a low voltage side, to remove noise generated on a conductor connected to a low voltage side terminal of the switching element on a low voltage side.

Abstract: The present invention relates to a system and method for compensating the voltage distortion and minimizing the available voltage range loss both caused by switching dead-time of solid-state switch components in power conversion devices. As a result, the power quality supplied from the power conversion devices can be improved and the output voltage of such devices can be increased.

Abstract: A power supply for performing arc-machining operation includes a primary rectifier connected to the commercial AC power source and an inverter coupled to the rectifier. A switching device is provided between the rectifier and the inverter. By controlling the power supplied from the rectifier to the inverter, the switching device prevents a large switching loss from occurring in the inverter.

Abstract: A device which can be supplied with a given DC voltage and with a current of limited strength via a supply line. A capacitor is connected to an input of the device.

Abstract: A power converter apparatus comprises a detection circuit, a control circuit and a time period generating circuit. The detection circuit detects whether a power device is in a short-circuit state. The control circuit sets, when the detection circuit has detected that the power device is in the short-circuit state, the power device in an inoperable state for a predetermined time period, and restores the power device to an operable state after the passing of the predetermined time period. The time period generating circuit defines the predetermined time period for setting the power device in the inoperable state, by measuring a time from the detection of the short-circuit state by the detection circuit.

Abstract: A digital electric power inverter comprising: a CPU, a PWM driving circuit, a PWM converting circuit, a rectifying circuit, an AC driving circuit, a DC/AC inverting circuit, an overload detecting circuit, a current detecting circuit and an alarm circuit, the power inverter is characterized by that: the entire circuitry of the electric power inverter is designed to be controlled by the CPU; with the CPU, the overload detecting and inductive load distinction ability, the output of the power inverter can be accurately controlled.

Abstract: A switching power supply unit includes first and second switching elements which are alternately turned on/off so as to perform self-excited oscillation. An inductor and a capacitor resonate during an OFF-period of the first switching element. After the second switching element is turned on, a resonance current applied to a series circuit including the second switching element and the indictor is interrupted before energy is completely emitted from a secondary winding. Accordingly, a voltage is generated at the inductor and a voltage at a transformer is reversed. The switching power supply unit also includes an ON-time control circuit in which a time constant is set so as to turn off the second switching element accordingly.

Abstract: A power supply for performing arc-machining operation includes a primary rectifier connected to the commercial AC power source and an inverter coupled to the rectifier. A switching device is provided between the rectifier and the inverter. By controlling the power supplied from the rectifier to the inverter, the switching device prevents a large switching loss from occurring in the inverter.