Abstract: The present invention relates to a converter for transferring power between a first DC system of DC voltage V1 and a second DC system of DC voltage V2, the converter comprising: —a first AC/DC converter for transforming DC voltage V1 into a first single phase AC voltage V1ac, of frequency ?, root mean square line-neutral magnitude V1acm and angle ?1; a second AC/DC converter for transforming DC voltage V2 into a second single phase AC voltage V2ac, of frequency ?, root mean square line-neutral magnitude V2acm and angle ?2; and two inductors L1, L2 and a capacitor C, wherein the first terminals of the inductors and capacitor are connected together, the second terminal of inductor L1 and the second terminal of the capacitor C are connected to the first AC voltage V1ac, and the second terminal of inductor L2 and the second terminal of the capacitor C are connected to the second AC voltage V2ac; wherein the value of the capacitor C, inductor L1 and inductor L2 are selected to enable required power transfer and to

Abstract: Disclosed is a bidirectional DC/DC converter including: a primary side circuit that includes a first DC power source or a first load; a secondary side circuit that includes a second load or a second DC power source; and a power transfer unit that is capable of transferring power bi-directionally between the primary side circuit and the secondary side circuit. Further, the bidirectional DC/DC converter includes a control circuit that controls the primary side circuit and secondary side circuit in such a way that current flows through the power transfer unit from the first DC power source to the second load or from the second DC power source to the first load.

Abstract: This document discusses, among other things, systems and methods to provide an internal supply rail with over voltage protection using a host power source, an external power source, and a switch configured to receive indications of host and external power source validity. In an example, the switch can be configured to provide the internal supply rail using the host power source when the indication of host power source validity indicates a valid host power source and the external power source when the indication of host power source validity indicates an invalid host power source and the indication of external power source validity indicates a valid external power source.

Abstract: An AC-to-DC conversion apparatus is provided, and which includes a first switch-element, an output capacitor and a bridgeless power-factor-correction (PFC) circuit. The bridgeless PFC circuit is coupled to an AC input, and includes a first inductor, a second inductor and a bridge circuit constructed by second to fifth switch-elements. The first switch-element is connected between bridgeless PFC circuit and the output capacitor. Under such circuit configuration and suitable control manner, the common-mode interference in the provided AC-to-DC conversion apparatus is lowered and thus reducing the power loss.

Abstract: The configurations of a bridgeless PFC circuit system and a controlling method thereof are provided. The proposed system includes a bridgeless PFC circuit including a first bridge arm having a first and a second terminals and a first middle point, a second bridge arm having a first and a second terminals and a second middle point, and a bidirectional switch coupled between the first middle point and the second middle point, and an inductor coupled between the first middle point and an AC power source coupled to the second middle point, and a current sensing circuit including a first current transformer sensing a first current flowing through the bidirectional switch, which having a primary side winding coupled to the bidirectional switch and a first and a second secondary side windings, and a switching device coupled to the two secondary side windings.

Abstract: A method and apparatus for power conversion comprising a three-port converter comprising a DC port for coupling to an external DC line, an AC port for coupling to an external AC line, and a storage port, internal to the three-port converter, for storing excess energy and discharging needed energy during power conversion, wherein the storage port is located on a DC-side of the three-port converter and is decoupled from the DC port such that a voltage on the storage port can be controlled independently of a DC voltage on the DC port.

Abstract: A method for operating an electrical power rectifier. The power rectifier comprises at least two branches that are connected in parallel to each other, each of the branches comprising at least two power semiconductor elements that are connected in series. The collector-emitter voltage Vce(t) and/or the collector current Ic(t) of one of the power semiconductor elements is detected by means of the method. Furthermore, it is determined whether at least one of the following conditions is met: dVce(t)/dt<(dVce/dt)crit, and/or dIc(t)/dt<(dIc/dt)crit, and or Ic(t13 ent)<Iccrit. If at least one of the aforementioned conditions has been met, the gate-emitter voltage of at least one of the power semiconductor elements is increased.

Abstract: A power factor improvement circuit is configured with two series circuits each having a switching element and a rectifying element connected in series. Two input terminals of a single-phase AC power source are respectively connected between the switching elements and the rectifying elements in the series circuits. An inductor element is connected between an output terminal of the power factor improvement circuit and two terminals, which are on the other side of the rectifying elements, of the switching elements. A capacitor element is connected between the output terminal and the two terminals. According to the above configuration, it is possible to decrease a loss of a bridge circuit and common-mode noise, and to provide a power factor improvement circuit in a smaller size.

Abstract: Systems, methods and apparatus are disclosed for AC to DC conversion. In one aspect a rectifier circuit for providing DC voltage to a load based at least in part on an AC input from an AC output source having a first and second terminal is provided. The rectifier circuit includes a first transistor and a second transistor, each transistor having a first terminal, a second terminal, and a control terminal. The second transistor is configured to limit a voltage applied to the control terminal of the first transistor. The control terminal of the second transistor is coupled to a voltage source applying a control voltage to the control terminal. The control terminal of the first transistor is coupled to the first terminal of the second transistor. The first and second transistors have their second terminals respectively connected to the second and first terminals of the AC output source.

Abstract: A normally-off bidirectional switch having two gates is connected to a transformer. The transformer has a first winding and a second winding. A first gate bias power supply configured to use power generated at the first winding to supply power for driving one of the gates of the bidirectional switch and a second gate bias power supply configured to use power generated at the second winding to supply power for driving the other gate of the bidirectional switch are provided.

Abstract: A three-phase boost-buck PFC converter including three independent single-phase boost-buck PFC circuits respectively is provided, which are capable of performing PFC on each phase of the three-phase power. The single-phase boost-buck PFC circuit is composed of two single-phase boost-buck converters independently working in a positive and a negative half cycle of an input voltage, and the two single-phase boost-buck converters are connected in parallel at an input side, and are connected in series at an output side, and each of the single-phase boost-buck converters is composed of a front-end boost circuit and a back-end buck circuit connected in cascade. Compared to the existing technique, regardless of a boost mode or a buck mode, the conduction loss is effectively reduced, and the whole system efficiency is effectively improved.

Abstract: A drive system for driving a multi-phase motor (such as a three-phase AC motor) or other load. Where a transformer is used, the transformer may have a disconnected wye configuration on the secondary side. The system may also utilize the average or other combination of DC bus voltages of inverters for each load phase, to provide feedback control.

Abstract: A power converter module including a voltage source current controlled power converter for providing unidirectional current having at least four output voltage levels is provided. The voltage source current controlled power converter includes an input terminal and an output terminal, and a first conductive path and a second conductive path is coupled in parallel to each other between the input terminal and the output terminal. Each of the conductive paths comprises at least one diode and at least one switch coupled in series to the respective conductive path. The at least one diode in the first conductive path are coupled closer to the input terminal and the at least one diode in the second conductive path are coupled closer to the output terminal. The voltage source current controlled power converter further includes at least two energy storage elements coupled between the first conductive path and the second conductive path.

Abstract: A synchronous rectifier circuit rectifies an AC input voltage to produce a DC output voltage. The synchronous rectifier circuit comprises MOSFET (metal-oxide-semiconductor field-effect transistor) switches coupled within secondary transformer windings resulting in a shortened AC current path compared to conventional synchronous rectifier circuits. The shortened current path mitigates skin and proximity effects, substantially improving the power efficiency of the synchronous rectifier circuit. A rectifier assembly integrates one or more synchronous rectifier circuits within a magnetic core.

Abstract: Systems and methods are presented for an improved high power density power adapter. On one potential embodiment, an improved power adapter includes an AC input; a rectifier coupled to the AC input; a power factor correction circuit coupled to the rectifier; and a burst switch circuit coupled to the power factor correction circuit. The burst switch circuit provides power to a DC output via a set of FET drivers, a set of FETs, and a transformer and may provides power exclusively in a burst mode using a feedback input from the DC output. The transformer may be composed of windings coupled to the set of FETs, and additional windings embedded in the PCB and coupled to the first winding. Certain windings may comprise a conductive ribbon that loops around a transformer core. Additional embodiments may include monitoring circuits and multiple outputs.

Abstract: Exemplary embodiments are directed to power conversion. A device may include a controllable switch coupled between an AC network and a DC network. The device may further include control circuitry configured to modify a configuration of the switch based on a detected difference between a reference signal and an output signal at the DC network.

Abstract: A power supply device controls drive of a synchronous rectification switch unit by converting a voltage into a current, and comparing a voltage obtained by current-to-voltage conversion with a predetermined value.

Abstract: There is provided a driver device for a power factor correction circuit including first and second main switches that are switched on and off with a phase difference therebetween, and first and second auxiliary switches that provide conduction paths of surplus voltage in the first and second main switches before the first and second main switches are switched on, the driver device including: an input unit receiving a plurality of input signals; and an output unit outputting a first control signal for the first main switch, a second control signal for the second main switch, a third control signal for the first auxiliary switch, and a fourth control signal for the second auxiliary switch based on a plurality of input signals.

Abstract: A system for testing the existing protection schemes of a power converter. The system simulates the voltage regulator producing a voltage level below an under-voltage threshold. The system simulates the voltage regulator producing a voltage level above an over-voltage threshold. The system simulates a short in the power converter pulling down the input bus. The system simulates a short in the power converter pulling down the output bus. The system measures the system responses to these simulations against responses of a properly operating system and determines if the power converter's protection schemes are operating correctly.

Abstract: Embodiments of the subject invention relate to a method and apparatus for providing a low-power AC/DC converter designed to operate with very low input voltage amplitudes. Specific embodiments can operate with input voltages less than or equal to 1 V, less than or equal to 200 mV, and as low as 20 mV, respectively. Embodiments of the subject low-power AC/DC converter can be utilized in magnetic induction energy harvester systems. With reference to a specific embodiment, a maximum efficiency of 92% was achieved for a 1 V input, and efficiencies exceeding 70% were achieved for a 200 mV input. A specific embodiment functioned properly when connected to a magnetic energy harvester device operating below 200 mV input.

Abstract: A system for increasing parallel rectifier DC power system efficiency. In one embodiment, the system includes: (1) a controller configured to sense and classify a load magnitude change into groups including large load transients and moderate load transients and (2) at least one rectifier coupled to the controller and configured to transition from a stand-by mode to an active mode upon an occurrence of one of a large load transient and a moderate load transient.

Abstract: A flyback converter involves a bipolar transistor (BJT) and a parallel-connected diode as the rectifying element in the secondary side of the converter. The transformer of the converter has a primary winding, a first secondary winding, and a second secondary winding. A first end of the first secondary winding is coupled to the BJT base. A first end of the second secondary winding is coupled to the BJT collector and to the anode of the diode. The first and second secondary windings are wound such that when primary winding current stops, pulses of current flow out of the first ends of the first and second secondary windings. These currents are such that the BJT is maintained in saturation throughout at least most of the time current flows through the rectifying element, thereby achieving a low forward voltage across the rectifying element, reducing conduction loss, and increasing converter efficiency.

Abstract: The multifunctional power converter apparatus and method includes an input power stage configured to receive a DC input voltage from a DC power source and convert the DC input voltage to an AC or DC output voltage. At least one electrical power conversion electronic circuit is connected to an output of the input power stage, a DC output circuit; an AC output circuit; and a controller configured to control the input power stage, the DC output circuit and the AC output circuit. The controller is configured to automatically control the power converter output voltage based on a preselected user input.

Abstract: In controlling switching elements of a current source inverter, a switching loss in the switching element is prevented according to a normal switching operation for a commutation operation, without requiring any particular control. In the commutation operation of the current source inverter, a timing for driving the switching elements is controlled in such a manner that an overlap period is generated, during when both a switching element at the commutation source and a switching element at the commutation target are set to be the ON state, a resonant circuit is controlled based on the control of the switching elements having this overlap period, and resonant current of the resonant circuit reduces the switching loss upon commutation operation of the switching elements.

Abstract: The invention relates to a current-source power converter comprising, in a module thereof , switching legs having normally-on field effect transistors each controlled by a gate control device. A normally-open auxiliary switch is in series with the switching legs and connected to the positive line of the power supply bus. This auxiliary switch can prevent the mains from short-circuiting during start-up or during malfunction of the auxiliary power supply.

Abstract: According to one embodiment, a nitride semiconductor device includes a semiconductor layer, a source electrode, a drain electrode, a first and a second gate electrode. The semiconductor layer includes a nitride semiconductor. The source electrode provided on a major surface of the layer forms ohmic contact with the layer. The drain electrode provided on the major surface forms ohmic contact with the layer and is separated from the source electrode. The first gate electrode is provided on the major surface between the source and drain electrodes. The second gate electrode is provided on the major surface between the source and first gate electrodes. When a potential difference between the source and first gate electrodes is 0 volts, a portion of the layer under the first gate electrode is conductive. The first gate electrode is configured to switch a constant current according to a voltage applied to the second gate electrode.

Abstract: A circuit exhibiting rectification and amplification characteristics. In particular, a full-wave rectifier, wherein the rectifier has the ability to simultaneously amplify and rectify an input voltage. The circuit comprises transconductor circuit, rectifying circuit and amplifying circuit. The transconductor circuit is adapted for receiving an input voltage from at least one voltage source. The input voltage is then converted into intermediate currents by the transconductor circuit. Thereafter, the rectifying circuit rectifies the intermediate currents current to produce a rectified current. Lastly, the amplification circuit amplifies the input voltage to produce the amplified voltage.

Abstract: Embodiments of the disclosure relate to a low drop diode equivalent circuit. Piezoelectric device based vibration energy harvesting requires a rectifier for conversion of input ac to usable dc form. Power loss due to diode drop in rectifier is a significant fraction of the already low levels of harvested power. The low-drop-diode equivalent can replace the rectifier diodes and minimise power loss. The diode equivalent mimics a diode using linear region operated MOSFET. The diode equivalent is powered directly from input signal and requires no additional power supply for its control. Power used by the control circuit is kept at a value which gives an overall output power improvement. The diode equivalent replaces the four diodes in a full wave bridge rectifier, which is the basic full-wave rectifier and is a part of the more advanced rectifiers like switch-only and bias-flip rectifiers.

Abstract: Various circuit configurations and topologies are provided for single and multi-phase, single-level or multi-level, full and half-bridge rectifiers in which diodes are replaced by combinations of voltage-controlled self-driven active switches, current-controlled self-driven active switches and inductors in order to reduce the effects of conduction loss in the diodes.

Abstract: A switching power supply apparatus which receives AC voltage and includes: a transformer including a primary winding and a secondary winding; a first bidirectional switch connected in series with the primary winding; and a Snubber circuit connected in parallel with the primary winding. The AC voltage is applied to a series circuit which includes the primary winding and the first bidirectional switch. The Snubber circuit includes a second bidirectional switch for controlling the first bidirectional switch.

Abstract: A vehicle power converter including a plurality of switching elements having diodes connected thereto in parallel and constituting a multi-phase bridge circuit and a controller for conducting the switching element corresponding to each diode in synchronization with a conduction state of the diode concerned to perform synchronous rectification and is connected between a power generator-motor driven from the external to generate multi-phase AC power and DC equipment, further includes a load state detecting unit for detecting a load state of the power generator-motor when the multi-phase AC power occurs, wherein a shift from diode rectification to synchronous rectification or a shift from the synchronous rectification to the diode rectification is carried out in accordance with an output of the load state detecting unit.

Abstract: An off line resonant converter includes a boost storage inductance circuit coupled to a switcher circuit that includes stacked first and second passive switching devices coupled to the boost storage inductance circuit and stacked first and second active bidirectional switching devices coupled to the stacked first and second passive switching devices. The stacked first and second active bidirectional switching devices generate a square wave signal and alternately store energy in and receive energy from the boost storage inductance circuit such that a pulsating current is conducted between the boost storage inductance circuit and the switcher circuit. The pulsating current is bidirectional and flows in a direction responsive to a polarity of the ac input line voltage. A resonant circuit is coupled to an output of the switcher circuit to receive the square wave signal from the switcher circuit to generate an output of the resonant converter.

Abstract: A transistor-based full-wave bridge rectifier is suitable for low A.C. input voltages such as received by a Radio-Frequency Identification (RFID) device. Voltage drops due to bridge diodes are avoided. Four p-channel transistors are arranged in a bridge across the A.C. inputs to produce an internal power voltage. A comparator receives the A.C. input and controls timing of voltage boost drivers that alternately drive gates of the four p-channel transistors with voltages boosted higher than the peak A.C. voltage. Four diode-connected transistors are connected in parallel with the four p-channel bridge transistors to conduct during initial start-up before the comparator and boost drivers operate. Substrates are connected to the power voltage on the power-voltage half of the bridge and to the A.C. inputs on the ground half of the bridge to fully shut off transistors, preventing reverse current flow. The transistor bridge can be integrated onto system chips.

Abstract: A bridge rectifier operates on low A.C. input voltages such as received by a Radio-Frequency Identification (RFID) device. Voltage drops due to bridge diodes are avoided. Four p-channel transistors are arranged in a transistor bridge across the A.C. inputs to produce an internal power voltage. Another four diode-connected transistors form a start-up diode bridge that generates a comparator power voltage and a reference ground. The start-up diode bridge operates even during initial start-up before the comparator and boost drivers operate. A comparator receives the A.C. input and controls timing of voltage boost drivers that alternately drive gates of the four p-channel transistors in the transistor bridge with voltages boosted higher than the peak A.C. voltage. Substrates are connected to the power voltage on the power-voltage half of the bridge and to the A.C. inputs on the ground half of the bridge to fully shut off transistors, preventing reverse current flow.

Abstract: An inverter comprising: a circuit including arms connected in parallel, each of the arms including a first switch and a second switch connected in series; and a gate drive circuit configured to control, by pulse-width modulation using synchronous rectification, each of the first switch and the second switch to switch to an on-state or an off-state, wherein each of the first switch and the second switch includes: a channel region that is conductive in both a forward direction and a reverse direction in the on-state, and that is not conductive in the forward direction in the off-state; and a diode region that is combined as one with the channel region, and that is conductive only in the reverse direction, the diode region being unipolar, and the gate drive circuit synchronizes a timing at which the gate drive circuit outputs a signal for causing the first switch to switch to the on-state with a timing at which the gate drive circuit outputs a signal for causing the second switch to switch to the off-state, and

Abstract: A shunt regulated permanent magnet alternator voltage source includes a permanent magnet alternator, a shunt regulator, and a pulse width modulation controller. Also included is a load controller capable of detecting a PMA margin.

Abstract: A power converter includes at least one leg with a first string including a plurality of controllable semiconductor switches, a first connecting node, and a second connecting node, wherein the first string is operatively coupled across a first bus and a second bus. The at least one leg also includes a second string operatively coupled to the first string via the first connecting node and the second connecting node, wherein the second string includes a plurality of switching units. The first string includes a first branch and a second branch, wherein the second branch is operatively coupled to the first branch via a third connecting node and the third connecting node is coupled to a ground connection.

Abstract: A rectification circuit includes a first field-effect transistor and a bias voltage generation circuit. The field-effect transistor includes a first gate terminal, a first source terminal, a first source region having a first p-type diffusion layer and connected to the first source terminal, a first drain terminal, and a first drain region having a first n-type diffusion layer and connected to the first drain terminal. The bias voltage generation circuit is configured to apply a DC voltage between the first gate terminal and the first drain terminal.

Abstract: A method and apparatus for bi-directional current sensing for a synchronous rectifier bi-directional converter system is disclosed. A first current is measured through a first synchronous rectifier via a first transformer to provide a first signal. A second current is measured through a second force synchronous rectifier via a second transformer to provide a second signal. The first signal and the second signal are DC restored to provide a first DC restored signal and a second DC restored signal respectively. A first correction current is added to the first DC restored signal to produce a first corrected signal, and a second correction current is added to the second DC restored signal to produce a second corrected signal. The first corrected signal and the second corrected signal are added to produce a combined signal.

Abstract: It is described a high efficiency rectification stage using dynamic threshold MOSFET. The idea is to use the input signal to reduce the threshold voltage when the transistor has to be on, and to increase the threshold when the transistor has to be off. This allows reducing both the resistive losses and the leakage current. A matching network allows the generation of a second higher voltage signal to drive the control gates and the bulk, i.e. the wells, of the transistors. Further, a self-tuned front-end is provided to extend the bandwidth of the high-Q charge pump.

Abstract: In one form, a synchronous rectifier controller includes a drive clamp adjust terminal, a drive terminal, a clamp voltage generator circuit coupled to the drive clamp adjust terminal for measuring a signal at the drive clamp adjust terminal and providing a clamp voltage having a value determined by the signal, and a driver for providing a drive signal to the drive terminal at a voltage related to the clamp voltage during an active period of the drive signal. In an alternate form a power converter includes a rectifier transistor having a first current electrode, a control electrode for receiving a drive signal, and a second current electrode, and a synchronous rectifier controller having a first terminal coupled to the control electrode of the rectifier transistor for providing the drive signal alternately in an active state and an inactive state.

Abstract: A power factor correction booster circuit for connection to an alternating current (AC) power source including a first circuit portion arranged to be active over a first AC half cycle of the power source, the first circuit portion including: a first AC input node in connection with a source node of a first power transistor, a first node of an inductive element in connection with a drain node of the first power transistor, a second node of the inductive element in connection with a drain node of a second power transistor, a second AC input node in connection with a source node of the second power transistor, an anode of a first semiconductor diode element in connection with the second node of the inductive element, a cathode of the first semiconductor diode element in connection with a first node of a first output capacitor element, and a second node of the first output capacitor element in connection with the second AC input node, wherein the first and second power transistors are controllable to switch the f

Abstract: Systems and methods for reducing current imbalance between parallel bridge circuits used in a power converter of a doubly fed induction generator (DFIG) system are provided. A control system can monitor the bridge current of each of the bridge circuits coupled in parallel and generate a feedback signal indicative of the difference in bridge current between the parallel bridge circuits. Command signals for controlling the bridge circuits can then be developed based on the feedback signal to reduce current imbalance between the bridge circuits. For instance, the pulse width modulation of switching devices (e.g. IGBTs) used in the bridge circuits can be modified to reduce current imbalance between the parallel bridge circuits.

Abstract: An example of the current source power conversion circuit is provided with a plurality of half-bridge rectifier circuits which are connected in parallel, each including a serial connection of a first switch circuit having a first self-turn-off element and a first diode which are connected in series to each other, and a second switch circuit having a second self-turn-off element and a second diode which are connected in series to each other. A first current electrode of said first self-turn-off element in one of said half-bridge rectifier circuits and a first current electrode of said first self-turn-off element in other one of said half-bridge rectifier circuits are short-circuited and connected.

Abstract: A circuit arrangement includes a first transistor device and a second transistor device. Each transistor device includes a first load terminal, a second load terminal, a gate terminal, and a control terminal. The first load terminals are electrically connected, and the control terminals are electrically connected. A capacitive storage element is connected between the first load terminals and the control terminals.

Abstract: An active rectification system includes a three-level active rectifier and a pulse with modulation (PWM) control portion. The three-level active rectifier includes at least three switches, the at least three switches are selectively switchable between an upper state, a center state, and a lower state. The PWM control portion is in communication with the at least three switches, the PWM control portion is configured and disposed to create an upper carrier signal and a lower carrier signal, and the PWM control portion is configured and disposed to selectively switch the at least three switches between the upper state, the center state, and the lower state in response to a phase disposition of the upper carrier signal and the lower carrier signal.

Abstract: It is intended to provide a semiconductor device capable to improve a controllability of dv/dt by a gate drive circuit during a turn-on switching period, while maintaining a low loss and a high breakdown voltage. Trench gates are disposed so as to have narrow distance regions and wide distance regions, wherein each of the narrow distance regions is provided with a channel region, and each of the wide distance regions is provided with trenches, each trench having an electrode electrically connected to the emitter electrode. In this manner, even if a floating-p layer is removed, it is possible to reduce a feedback capacity and maintain a breakdown voltage.

Abstract: The invention relates to a method for actuating the switching transistors of a rectifier which is provided for converting the phase voltages that are provided by a vehicle generator into a direct current voltage. Each switching transistor comprises a parasitic diode. An activation signal for initiating the conducting phase and a de-activation signal for ending the conducting phase are supplied to each control terminal of the switching transistors. A timer is started simultaneously with the provision of an activation signal and the de-activation signal is provided once a predetermined time period has passed.

Abstract: Single-phase voltage operation techniques are provided for a three-phase drive system. A drive system may include a rectifier configured to couple to a three-phase AC voltage source. The rectifier may be configured to convert AC voltage from the three-phase AC voltage source to a direct current (DC) voltage. The drive system may also include a controller configured to send a plurality of switching signals to a plurality of switches in the rectifier such that the plurality of switching signals minimizes a current provided to the rectifier when only a single-phase of the three-phase AC voltage source is available.

Abstract: An alternate current rectifier circuit which includes a first diode, a second diode, a first transistor, a second transistor, a third transistor, and a fourth transistor is power saving. The first diode is connected to the first transistor and the fourth transistor; the second diode is connected to the second transistor and the third transistor. During a positive half cycle of the alternate current, the first transistor and the fourth transistor are switched on and the alternate current flows through the first diode, the first transistor, and the fourth transistor; during a negative half cycle of the alternate current, the second transistor and the third transistor are switched on and the alternate current flows through the second diode, the second transistor, and the third transistor.