Power conversion system for providing a current to meet operation of an electronic device by varying a leakage inductance thereof and method for providing the current thereof

A power conversion system includes an isolating transformer (30) and an output-controlling device (40). The isolating transformer (30) includes a primary winding (310) and a plurality of secondary windings (320a˜320d) coupled with the primary winding (310), and the isolating transformer (30) has a plurality of coupling distances between the secondary windings (320a˜320d). The output-controlling device (40) includes a controller (420) and a plurality of output-controlling modules (400a˜400d), wherein each one of the secondary windings (320a˜320d) is electrically connected to one of the output-controlling device (400a˜400d). The controller (420) places at least one output-controlling device (400a˜400d) in a conducting state for output a rectified power. An amount of the secondary windings (320a˜320d) coupled with the primary winding (310) is modulated for varying a leakage inductance of the power conversion system.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a power conversion system. More particularly, the present disclosure relates to a power conversion system for providing power to meet operations of an electronic device.

Description of Related Art

Since diode and Schottky diode have designated forward bias, the power loss of the power conversion system having the diode or Schottky diode to rectify power is large. Metal-oxide-semiconductor field-effect transistor (MOSFET) has advantages of low input resistance, short response time, and high input resistance, thus it replaces the diode and Schottky diode to be the main component of the rectifier.

In general, the power conversion system includes a plurality of synchronous rectifiers, which are driven at the same time the rectify power entering thereto. Specifically, when an electronic device electrically connected to the power conversion system is activated, the synchronous rectifiers perform synchronous rectifying procedure, and the MOSFETs of the synchronous rectifiers are switched to rectify the power entering the synchronous rectifiers; however, when the electronic device is inactivated, the synchronous rectifiers does not perform synchronous rectifying procedure. Even if the operation manner of the synchronous rectifier mentioned above is easy, the power provides by the power conversion system is a constant no matter the electronic device during non-light load condition and light load condition, thus the power loss during the electronic device under light load condition is large.

SUMMARY OF THE INVENTION

According to one aspect of the present disclosure, a power conversion system used for providing a power required for an electronic device is provided. The power conversion system includes an isolating transformer and an output-controlling device. The isolating transformer includes a primary winding and a plurality of secondary windings coupled with the primary winding, the isolating transformer has a plurality of coupling distances between the secondary windings. The output-controlling device includes a controller and a plurality of output-controlling modules electrically connected to the controller, wherein each of the secondary windings is electrically connected to one of the output-controlling devices. The controller places at least one output-controlling device in a conducting state for outputting a power. An amount of the secondary windings coupled with the primary winding is modulated for varying a leakage inductance of the power conversion system

According to another aspect of the present disclosure, a method for powering an electronic device includes the following steps: providing the power conversion system comprising a primary winding and a plurality of secondary windings, and there are a plurality of coupling distances between the primary winding and the secondary windings; sensing a current required for the electronic device; and modulating an amount of the secondary windings coupled with the primary winding for varying a leakage inductance of the power conversion system, thus an output current provided by the power conversion system is modulated to meet the current requirement of the electronic device.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made toFIG. 1, which is a circuit block diagram of a power conversion system according to a first embodiment of the present disclosure. InFIG. 1, the power conversion system (its reference numeral is omitted) receives an input voltage Vi and is configured to provide an output voltages Vo. The power conversion system includes a primary side and a secondary side, which are separated by an isolating transformer30. The isolating transformer30includes a primary winding310and a plurality of secondary windings320a˜320dmagnetically coupled to the primary winding310. The power conversion system further includes a switching module10, a resonant module20, an output-controlling device40, and a current sense unit50. The switching module10, the resonant module20, and the primary winding310are arranged at the primary side of the power conversion system, and the secondary windings320a˜320d, the output-controlling device40, and the current sense unit50are arranged at the secondary side of the power conversion system. The output-controlling device40includes a plurality of output-controlling modules400a˜400d, and the controlling modules400a˜400dinclude a plurality of synchronous rectifying units (details are described in the following paragraphs) and a plurality of output switches (details are described in the following paragraphs). The current sense unit50senses a current flowing through a sensing resistor Rs electrically connected to the output-controlling device40and sends a current sensed signal to the controller420for controlling the operation of the output-controlling device40.

Reference is made toFIG. 2, which is a circuit diagram of a power conversion system according to the first embodiment of the present disclosure. The switching module10is electrically connected to the input voltage Vi and includes a first power switch QA, a second power switch QB, a third power switch QC, and a fourth power switch QD. The first to fourth switches QA˜QD are, for example, metal-oxide-semiconductor field-effect transistors (MOSFETs). The drains of the first power switch QA and the third power switch QC are connected to the input voltage Vi, the source of the first power switch QA is connected to the drain of the second power switch QB, and the source of the third power switch QC is connected to the drain of the fourth power switch QD and the primary winding310. The sources of the second power switch QB and the fourth power switch QD are connected to the input voltage Vi.

The switching module10may further includes a plurality of diodes D and a plurality of capacitors C electrically connected to the first to fourth power switches QA˜QD. Specifically, the diodes D are, for example, the body diodes of the first to fourth power switches QA˜QD, and the capacitors C are, for example, parasitic capacitances of the first to fourth power switches QA˜QD; the cathode of each diode D is connected to the drain of one of the first to fourth power switches QA˜QD, the anode thereof is connected to the source of one of the first to fourth power switches QA˜QD, and each of the capacitors C is electrically connected to one of the diodes D in parallel.

The resonant module20includes a resonant inductor Lr, a direct-current (DC) isolating capacitor Cb, and a magnetizing inductor. InFIG. 2, the resonant inductor Lr and the isolating transformer30are shown integrally; nevertheless, they are able to be separated in the practical manufacturing process. The DC isolating capacitor Cb, the resonant inductor Lr, and the primary winding310are electrically connected in series. specifically, one terminal of the DC isolating capacitor Cb is connected to the sources of the first power switch QA and second power switch QB, and the other terminal of the DC isolating capacitor Cb is connected to one terminal of the resonant inductor Lr, and the other terminal of the resonant indictor Lr is connected to the primary winding310.

The first to fourth power switches QA˜QD of the resonant module20are controlled using a zero-voltage-switching (ZVS) scheme to reduce switching loss.

The output-controlling device40includes a first synchronous rectifying unit410a, a second synchronous rectifying unit410b, a third synchronous rectifying unit410c, a fourth synchronous rectifying unit410d, a first output switch SW1, a second output switch SW2, a third output switch SW3, and a fourth power switch SW4. The first synchronous rectifying unit410ais connected to the secondary winding320aand the first output switch SW1, the second synchronous rectifying unit410bis electrically connected to the secondary winding320band the second output switch SW2, the third synchronous rectifying unit410cis electrically connected to the secondary winding320cand the third output switch SW3, and the fourth synchronous rectifying unit410dis electrically connected to the secondary winding320dand the fourth output switch SW4.

The source of the rectifying switch Q1is connected to the source of the rectifying switch Q2, and the drains of the rectifying switches Q1and Q2are respectively connected to the secondary winding320a(the drain of the rectifying switch Q1is connected to one terminal of the secondary winding320a, and the drain of the rectifying switch Q2is connected to the other terminal of the secondary winding320a). The source of the rectifying switch Q3is connected to the source of the rectifying switch Q4, and the drains of the rectifying switches Q3and Q4are respectively connected to the secondary winding320b. The source of the rectifying switch Q5is connected to the source of the rectifying switch Q6, and the drains of the rectifying switches Q5and Q6are respectively connected to the secondary winding320c. The source of the rectifying switch Q7is connected to the source of the rectifying switch Q8, and the drains of the rectifying switches Q7and Q8are respectively connected to the secondary winding320d. The gates SR1˜SR8of the rectifying switches Q1˜Q8are electrically connected to the controller420, and the rectifying switches Q1˜Q8are controlled by the controller420using a synchronous rectifying scheme.

The power conversion system further includes filters L1˜L8, which are, for example, chokes. The filters L1and L2are arranged between the secondary winging320aand the first output switch SW1, the filter L3and L4are arranged between the secondary winding320band the second output switch SW2, the filter L5and L6are arranged between the secondary winding320cand the third output switch SW3, and the filter L7and L8are arranged between the secondary winding320dand the fourth output switch SW4. Specifically, each secondary winding320a˜320dhas two terminals, one terminal of the secondary winding320ais connected to the filter L1, and the other terminal thereof is connected to the filter L2; one terminal of the secondary winding320bis connected to the filter L3, and the other terminal thereof is connected to the filter L4; one terminal of the secondary winding320cis connected to the filter L5, and the other terminal thereof is connected to the filter L6; one terminal of the secondary winding320dis connected to the filter L7, and the other terminal thereof is connected to the filter L8.

The power conversion system still further includes a plurality of output capacitors Co. One terminal of the output capacitor is connected to synchronous rectifying unit410a˜410d, and the other terminal thereof is connected to one of the first to fourth output switch SW1˜SW4.

It should be noted that the power conversion system is configured to provide different powers to meet the power required for the electronic device. Therefore, the controller420may measure the power required for the electronic device by the current sensed signal representing the current flowing through the sensing resistor Rs sent from the current sense unit50and place at least one of the synchronous rectifying units410a˜410dor at least one of the first to fourth output switch SW1˜SW4in a conducting state to conduct the power required for the electronic device to the electronic device. It should be noted that when the synchronous rectifying410a˜410dare in the conducting state, the powers coupled to the secondary winding320a˜320dare conducted to the synchronous rectifying units410a˜410d, and a synchronous rectifying procedure is performed. On the contrary, when the synchronous rectifying units410a˜410dare not in the conducting state (or called the synchronous rectifying units410a˜410dare in a non-conducting state), the power transmitted to the primary winding310cannot conducted to the secondary windings320a˜320d, and the synchronous rectifying procedure is not performed. Besides, when the first to fourth output switches SW1˜SW4are in the conducting state, the first to fourth output switches SW1˜SW4turn on (close), the powers with synchronous rectification are conducted to the output capacitors Co and the output Vo. One the contrary, when the first to fourth output switches SW1˜SW4are in the non-conducting state, the first to fourth output switches SW1˜SW4turn off (open), the powers with synchronous rectification cannot be conducted to the output capacitors Co and the output Vo.

The isolating transformer30and the resonant inductor Lr (if exist) provide a leakage inductance. In order to achieve higher efficiencies and lower electromagnetic interferences (EMI), a zero voltage switching (ZVS) mode is operated. With ZVS mode, during operation, the first to fourth power switches QA˜QD in a switching stage of the power conversion system are activated at zero crossings of their main terminal voltage to minimize turn on losses. An amount of time is required by the first to fourth power switches QA˜QD to turn off (open) and on (close). The overlap between these transitions can be referred to as dead-time (as time points between t2 and t3 and the time points between t4 and t5 shown in theFIG. 4a). A minimum amount of dead-time is needed to avoid having the first power switch QA and second power switch QB (or the third power switch QC and the fourth power switch QD) closed (turned on) at the same time. If the first power switch QA and the second power switch QB (or the third power switch QC and the fourth power switch QD) are closed at the same time, potentially destructive shoot-through current that travels directly from input voltage Vi to electronic device may result. The period of the dead-time is rises gradually as leakage inductance is increased. The gates of the first to fourth power switches QA˜QD are electrically connected to a controlling circuit (not shown), and the first to fourth power switches QA˜QD are turned off and on according to signals sent from the controlling circuit.

Reference is made toFIG. 2andFIG. 4a, whereinFIG. 4ais a timing chart indicating operations of the power conversion system during light load condition. In order to clarify detailed operation of the power conversion system of the present disclosure, the following example is given. It should be noted that the values given in the example are only for clarity. The values can be changed to meet system requirements. During the heavy load condition, the power (including voltage and current) provided by the power conversion system is the largest. As the load lightens, the power is reduced. During the light load condition, the power provided by the power conversion system reduces to, for example, 20%; during the normal load condition, the power provided by the power conversion system reduces to, for example, 50%.

Seven time points t1-t7 are shown in theFIG. 4a. With the second power switch QB and the third power switch QC are closed (placed in conducting states) (wherein the first power switch QA and the fourth power switch QD are opened) to provide a conduction path between time points t1 and t2, a primary current Ip from the input voltage Vi flows through the third power switch QC, the primary winding310, the resonant module20, the second power switch QB to the ground. During this time, energy is stored in the resonant inductor Lr, and the primary current (Ip) is raised.

The second power switch QB is then opened at time point t2 (the third power switch QC is continuously closed), and then a short time duration later, the first power switch QA is closed (at time point t3). During this short duration, the current supported by the energy stored in the isolating transformer's leakage inductance, and optionally in resonant inductor Lr, now flows out of the capacitances C associated with the first power switch QA and the second power switch QB and into the third power switch QC (which is still closed). Specifically, when the second power switch QB is opened, the primary current Ip freewheels through the diode D associate with the first power switch QA, and the capacitor C associated with the second power switch QB is charged, and the capacitor C associated with the first power switch QA is discharged until the potential of the capacitor C associates with the second power switch QB is equal to that of the input voltage Vi.

When a voltage across drain-source of the first power switch QA is lower than a voltage across the forward bias of the diode D associated with the first power switch QA, the diode D associate with the first power switch QA turns on (placed in conducting states). As such, the first power switch QA is closed under zero-voltage condition (i.e., zero voltage switching). Due to that the voltage across drain-source of the first power switch QA is lower than the voltage across the diode D associate with the first power switch QA, the conduction loss is low. At this time, the primary voltage Vp of the power conversion system is zero.

Between time points t4 and t5, the third power switch QC is closed and the current freewheels through the diode D associated with the fourth power switch QD. During this short duration, the current supported by the energy stored in the isolating transformer's leakage inductance, and optionally in resonant inductor Lr, now flows out of the capacitances C associated with the third power switch QC and the fourth power switch QD and into the first power switch QA (which is still closed). Specifically, when the third power switch QC is opened, the primary current Ip freewheels through the diode D associate with the fourth power switch QD, and the capacitor C associated with the third power switch QC is charged, and the capacitor C associated with the fourth power switch QD is discharged until the potential of the capacitor C associates with the third power switch QC is equal to that of the input voltage Vi and a voltage across drain-source of the fourth power switch QD is dropped to zero (as curve VQ4shown).

When a voltage across drain-source of the fourth power switch QD is lower than a voltage across the forward bias of the diode D associated with the fourth power switch QD, the diode D associate with the fourth power switch QD turns on (placed in conducting states). As such, the fourth power switch QD is closed under zero-voltage condition.

Due to the voltage across the resonant inductor Lr is equal to the input voltage Vi, the primary current Ip is linearly decreased between time points t5 and t6. InFIG. 4a, a duty cycle loss appears between time points t5 and t6 since a primary voltage Vp does not drop to negative value at time point t5, which the fourth power switch QD is closed (wherein the fourth power switch QD is closed at time point t6). The more the leakage inductance is, the more duty cycle loss is, and the duty cycle loss is given by

wherein

Lr is the inductance of the resonant inductor;

Ip is the primary current of the power conversion system; and

Vp is the primary voltage of the power conversion system.

FIG. 5ais a timing chart indicating operations of the power conversion system during normal load condition.FIG. 6ais a timing chart indicating operations of the power conversion system during heavy load condition. The function and relative description of the power conversion system during normal load condition and during heavy load condition are the same as that of during light load condition mentioned above and are not repeated here for brevity. It should be noted that the current provided by the power conversion system is increased while the power (current) required for the electronic device is increased, and the duty cycle loss of the power conversion system is increased while the current provided by the power conversion system is increased. As such, a hold-up time depends upon the duty cycle loss is then decreased, that result in lower efficiency. Specifically, if the input voltage Vi falls below the minimum permissible voltage and adversely affects the power conversion system operation, the electronic devices that rely on the power conversion system for power could experience critical failures such as the loss of data. The length of time that the power conversion system can continue to operate in the absence of line voltage is referred to as the hold-up time.

If power conversion system is to provide a better efficiency, then a lower duty cycle loss will be needed. As a result, a distinctive operation of the output-controlling device40is required to meet the duty cycle loss required to keep the efficiency of the power conversion system within acceptable limits.

In general, the power provided by the power conversion system depends upon the power required for the electronic device. More particularly, the power required for the electronic device during heavy load condition is higher than that of during the light load condition. Therefore, the power (such as current) provided by the power conversion system while the electronic device operated under heavy load condition will be higher than that of operated under light load condition.

The output-controlling device40of the present disclosure is controlled to make the current provided by the power conversion system to meet the power required for the electronic device.

The power conversion system may provide the power to meet the required for the electronic device depends upon the operation of the first to fourth synchronous rectifying units410a˜410dof the output-controlling module400a˜400d. Reference is made back toFIG. 2andFIG. 3. In first operation state, when a first current I1is required for the electronic device, the controller420sends signals to gates SR1˜SR8of the rectifying switches Q1˜Q8according to the current sensed signal sent from the current sense unit50for indicating that the first current I1is required by the electronic device, and places one of the first to fourth rectifying unit410a˜410din the conducting state for performing synchronous rectifying procedure, thus the first current I1is provided by the power conversion system. Specifically, the controller420may send pulsating signals to drive the rectifying switches Q1and Q2to interleaved turn off and on (as time points between 0˜t1 shown inFIG. 3), thus a power coupled to the secondary winding320ais synchronous rectified by the first synchronous rectifying unit410aand the rectified power is then conducted to the output terminal (connected to the electronic device) by passing through the filters L1and L2, the first output switch SW1, and the output capacitor Co connected to the first output switch SW1.

In second operation state, when a second current I2is required for the electronic device, the controller420receives the current signal sent from the current sense unit for indicating that the second current I2is required by the electronic device, and sends signals to the gates SR1˜SR8for placing two of the first to fourth synchronous rectifying units410a˜410din the conducting state for performing synchronous rectifying procedure, thus the second current I2is then provided by the power conversion system, the second current I2is larger than the first current I1. Specifically, the controller420may send pulsating signals to drive the rectifying switches Q1˜Q4to interleaved turn off and on (as time points between t1 and t2 shown inFIG. 3), thus powers coupled to the secondary winding320aand320bare synchronous rectified by the first and second synchronous rectifying units410aand the410b, respectively, and the rectified powers are then conducted to the output terminal (connected to the electronic device) by passing through the filters L1˜L4, the first power switch SW1, second output switch SW2, and the output capacitors Co connected to the first power switch SW1and the second output switch SW2.

In third operation state, when a third current I3is required for the electronic device, the controller420receives the current sensed signal sent from the current sense unit50for indicting that the third current is required for the electronic device, and sends signals the gates SR1˜SR8for placing three of the first to fourth synchronous rectifying unit410a˜410din the conducting state for performing synchronous rectifying procedure, thus the third current I3is then provided by the power conversion system, the third current I3is larger than the second current I2. Specifically, the controller420may send pulsating signals to drive the rectifying switches Q1˜Q6to interleaved turn off and on (as time points between t2 and t3 shown inFIG. 3), thus powers coupled to the secondary windings320a˜320care synchronous rectified by the first to third synchronous rectifying units410a˜410c, respectively, and the rectified powers are then conducted to the output terminal (connected to the electronic device) by passing through the filters L1˜L6, the first to third output switch SW1˜SW3, and the output capacitors Co connected to the first to third output switch SW1˜SW3.

In fourth operation state, when a fourth current I4is required for the electronic device, the controller420receives the current sensed signal sent from the current sense unit for indicating that the third current is required for the electronic device, and sends signals to the gates SR1˜SR8for placing all of the first to fourth synchronous rectifying unit410a˜410din the conducting state for perform synchronous rectifying procedure, thus a fourth current I4is then provided by the power conversion system, the fourth current I4is larger than the third current I3. Specifically, the controller420may sent pulsating signals to drive the rectifying switches Q1˜Q8to interleaved turn on and off continuously (after time point t3 shown inFIG. 3), thus powers coupled to the secondary winding320a˜320dare synchronous rectified by the first to fourth synchronous rectifying units, respectively, and the rectified power are then conducted to the output terminal (connected to the electronic device) by passing through the filters L1˜L8, the first to fourth output switch SW1˜SW4and the output capacitors Co.

As such, an effect of energy conservation is provided and the power loss while the electronic device operated under light load condition is reduced since the first to the fourth rectifying unit410a˜410dare separately placed in the conducting state and driven to synchronous rectify the powers coupled to the secondary windings320a˜320d.

The controller420may selectively place the first to fourth switches SW1˜SW4in the conducting state for conducting power required for the electronic device to the output terminal. It should be noted when the controller420places at least one of the first to fourth synchronous rectifying units410a˜410din the conducting state for conducting power require for the electronic device to the output terminal, the first to fourth switches SW1˜SW4are always closed to make the rectified power(s) flowing therethrough; when the controller420places at least one of the first to fourth switch SW1˜SW4in the conducting state for conducting power required for the electronic device to the output terminal, the controller420sends the pulsating signals to the rectifying switches Q1˜Q8to makes the first to fourth synchronous rectifying units410a˜410dperform synchronous rectifying procedure all the time.

Reference is made back toFIG. 2andFIG. 3. The controller420may place the first switch SW1in the conducting state for conducting a power coupled to the secondary winding320aand rectified by the first synchronous rectifying unit410ato the output terminal (connected to the electronic device) in first operation state, therefore the first current I1is provided to the electronic device (as the time points between 0 and t1 shown in theFIG. 3).

In second operation state, the controller420may place the first switch SW1and the second switch SW2in the conducting state for conducting powers coupled to the secondary windings320aand320band rectified by the first synchronous rectifying unit410aand the second synchronous rectifying unit410bto the output terminal (connected to the electronic device), therefore the second current I2is provided to the electronic device (as the time points between t1 and t2 shown in theFIG. 3), wherein the second current I2is larger than the first current I1.

In third operation state, the controller420may place the first to third switches SW1˜SW3in the conducting state for conducting powers coupled to the secondary windings320a˜320cand rectified by the first to third synchronous rectifying units410a˜410cto the output terminal (connected to the electronic device), therefore the third current I3is provided to the electronic device (as the time points between t2 and t3 shown in theFIG. 3), wherein the third current I3is larger than the second current I2.

The controller420places the first to fourth switches SW1˜SW4in the conducting state for conducting powers coupled to the secondary windings320a˜320dand rectified by the first to fourth synchronous rectifying units410a˜410dto the output terminal (connected to the electronic device), therefore the fourth current I4is provided to the electronic device (as the time point t3 shown in theFIG. 3), wherein the fourth current I4is larger than the third current I3.

The arrangement of the primary winding310and the second windings320a˜320dof the present disclosure is further controlled to lower the power loss of the power conversion system.

Reference is made toFIG. 7, which is a cross-sectional view of the isolating transformer according to the first embodiment of the present disclosure. The isolating transformer30further includes a bobbin330and a magnetic core340, and the magnetic core340is assembled with the bobbin330. The primary winding310and the secondary winding320a˜320dare placed on the bobbin330. InFIG. 7, the isolating transformer30includes one primary winding310and four secondary windings320a˜320d, the secondary windings320a˜320dare arranged at the bobbin330with equidistance intervals (such as inserted into slots preset on the bobbin330with equidistance intervals), the primary winding310is wound on the bobbin330(where the secondary windings320a˜320ddoes not placed and across each of the secondary windings320a˜320d). As a result, the primary winding310and the secondary windings320a˜320dare arranged in a staggered manner in a side view direction, i.e., the primary winding310is placed at same side of each secondary winding320a˜320d(wherein inFIG. 7, the primary winding310is wound on the bobbin310and placed at the left side of the secondary winding320a˜320d).

Reference is made back toFIG. 2andFIG. 7, the power conversion system may provide power required for the electronic device by controlling the operation states of the output-controlling modules400a˜400d.

In one of the operation states, the controller420may send pulsating signals to drive the rectifying switches Q1˜Q8to perform synchronous rectifying procedure. As a result, the power coupled to the second windings320a˜32dis synchronously rectified by the first to fourth synchronous rectifying units410a˜410d, and the rectified powers are then conducted to the output terminal (connected to the electronic device) by passing through the conducted first to fourth switches SW1˜SW4. Selectively, the controller420may drive the first to fourth switches SW1˜SW4to close and then conduct the power coupled to the second windings320a˜320dand rectified by the first to fourth synchronous rectifying units410a˜410dto the output terminal (connected to the electronic device). As a result, a leakage inductance based on the magnetic coupling between the primary winding310, the secondary windings320a˜320d, and optionally in resonant inductor Lr is generated.

Reference is made toFIG. 8, the lowest leakage inductance appears at the points that each of the second windings320a˜320dis close to the primary winding310, and the leakage inductance is increased when the coupling distance between each of the secondary windings320a˜320dand the primary winding310is increased. The leakage inductance varies in a fixed range since the primary winding310and the secondary windings320a˜320dare arranged in the staggered manner.

In another operation state, the controller420may send pulsating signals to the rectifying switches Q1˜Q2to drive the first synchronous rectifying unit410aperform synchronous rectifying procedure (wherein the rectifying switches Q3˜Q8are always opened). As a result, only the power coupled to the second windings320ais synchronously rectified by the first synchronous rectifying units410a, and the rectified power is then conducted to the output terminal (connected to the electronic device) by passing through the conducted first to fourth switches SW1˜SW4. Selectively, the controller420may drive the first switch SW1to close and conduct the power coupled to the second windings320aand rectified by the first synchronous rectifying units410ato the output terminal (connected to the electronic device). Another leakage inductance based on the magnetic coupling between the primary winding310, the secondary windings320a, and optionally in resonant inductor Lr is generated.

Reference is made toFIG. 9, the lowest leakage inductance appears at the point between the second winding320aand the primary winding310, and the leakage inductance is increased when the coupling distance between the secondary winding320aand the primary winding310is increased.

In the other state, the controller420may send pulsating signals to the rectifying switches Q3˜Q6to drive the second synchronous rectifying unit410band the third synchronous rectifying unit410cto perform synchronous rectifying procedure (wherein the rectifying switches Q1, Q2, Q7, and Q8are always opened). As a result, only the powers coupled to the second windings320band320care synchronously rectified by the second synchronous rectifying units410band the third synchronous rectifying units410c, and the rectified powers are then conducted to the output terminal (connected to the electronic device) by passing through the conducted first to fourth switches SW1˜SW4. Selectively, the controller420may drive the second switch SW2and the third switch SW3to close and conduct the powers coupled to the second windings320band320cand rectified by the second synchronous rectifying unit410band the third synchronous rectifying units410cto the output terminal (electrically connected to the electronic device). Still another leakage inductance based on the magnetic coupling between the primary winding310, the secondary windings320band320c, and optionally in resonant inductor Lr is generated.

Reference is made toFIG. 10, the lowest leakage inductance appears at the point between the second windings320b,320cand the primary winding310, and the leakage inductance is increased when the coupling distance between the secondary winding320b,320cand the primary winding310is increased.

In sum, the amount of the first to fourth synchronous rectifying units410a˜410dperforming synchronous rectifying procedure and the coupling distance between the secondary winding320a˜320dperforming synchronous rectifying and the primary windings310affects the leakage inductance of the power converting system. As such, by effectively controlling the amount of the first to fourth synchronous rectifying units410a˜410dperforming synchronous rectifying procedure and the coupling distance mentioned above, the power conversion system can accurately provide power required for the electronic device to the electronic device.

It should be noted that the power conversion system provides power to the electronic device only when the synchronous rectifying unit (410a˜410d) connected to the particular secondary winding (320a˜320d) performs synchronous rectifying procedure and the output switch (SW1˜SW4) connected to the synchronous rectifying (410a˜410d) is close. For example, reference is made toFIG. 2, when the first synchronous rectifying unit410aperforms synchronous rectifying procedure and the first switch SW1is close, the power conducted to the primary winding310is coupled to the secondary winding320aconnected to the first synchronous rectifying unit410a, and then the rectified power is conducted to the electronic device by passing through the filters L1and L2. In the meanwhile, a leakage inductance based on the magnetic coupling between the primary winding310and the secondary windings320a˜320dis generated.

The detail data of the leakage inductance in different operation states are shown in Table 1.

In Table 1, “conducting state” means that the synchronous rectifying unit (410a˜410d) is places in the conducting state and performs synchronous rectifying procedure, thus the power conducted to the primary winding310may be coupled to particular secondary winding (320a˜320d) connected to the synchronous rectifying unit (410a˜410d) placed in the conducting state, and a rectified power is then conducted to the electronic device; nevertheless, “non-conducting state” means that the synchronous rectifying unit410a˜410dis places in the non-conducting state and does not perform synchronous rectifying procedure, and the power conducted to the primary winding310does not coupled to the secondary winding320a˜320dconnected to the synchronous rectifying unit410a˜410dplaced in the non-conducting state.

Reference is made toFIG. 4b, which is another timing chart indicating operations of the power conversion system during light load condition. It should be noted that the timing chart shown in theFIG. 4bindicates the power conversion system which the amount of the first to fourth synchronous rectifying units410a˜410dperforming synchronous rectifying procedure and the coupling distance between the secondary winding320a˜320dconnected to the first to fourth synchronous rectifying units410a˜410dperforming synchronous rectifying procedure and the primary windings310are controlled as mentioned above. InFIG. 4b, a duty cycle loss appears between time points t5 and t6′ since a primary voltage Vp does not drop to negative value at time point t5, which the fourth power switch QD is closed. Comparing to theFIG. 4a(the duty cycle loss appears between time points t5 and t6), the duty cycle loss shown in theFIG. 4bis reduced (the period between time points t6′ and t6 shown in theFIG. 4bindicates the duty cycle loss which is eliminated fromFIG. 4a).

FIG. 5bis another timing chart indicating operations of the power conversion system during normal load condition.FIG. 6bis another timing chart indicating operations of the power conversion system during heavy load condition. InFIGS. 5band 6b, the period between time points t5 and t6 indicates duty time loss of the power conversion system which the amount of the synchronous rectifying units performing synchronous rectifying procedure and the coupling distance between the secondary winding320a˜320dand the primary windings310are not controlled (for example, the first to fourth synchronous rectifying units410a˜410dperform synchronous rectifying procedure as the same time). On the contrary, the period between time points t5 and t6′ indicates duty time loss of the power conversion system which the amount of the synchronous rectifying units performing synchronous rectifying procedure and the coupling distance between the secondary winding320a˜320dand the primary windings310are well controlled (wherein the period between time points t6′ and t6 shown in theFIG. 5bandFIG. 6bindicates the duty cycle loss which is eliminated fromFIGS. 5aand 6a).

In order to prevent generated heat that arises at the time of driving from being stored, the first to fourth synchronous rectifying units410a˜410dmay perform synchronous rectifying procedure in sequence. For example, the controller420may progressively increase the amount of the synchronous rectifying units (410a˜410d) performing synchronous rectifying procedure when the power required for the electronic device is gradually increased. In addition, the controller420may drives the synchronous rectifying units (410a˜410d) in a convergence manner when only one of the synchronous rectifying units (410a˜410d) performs synchronous rectifying procedure. More particularly, the convergence manner may first make the synchronous rectifying unit (410a˜410d) far from a central axis of the isolating transformer30shown in theFIG. 7perform synchronous rectifying procedure, and next makes the synchronous rectifying units close to the central axis of the transformer shown in theFIG. 7to prevent generated heat that arises at the time of driving from being stored, i.e., the controller420may makes the first synchronous rectifying units410a, the fourth synchronous rectifying units410d, the second synchronous rectifying units410b, and the third synchronous rectifying units410cshown in theFIG. 7perform synchronous rectifying procedure in sequence. It should be noted that if the distances between two synchronous rectifying units and the central axis are the same, the two synchronous rectifying units interleaved perform synchronous rectifying procedure.

Reference is made back to Table 1, in 1st and 2nd states, they are only one of the synchronous rectifying units is placed in the conducting state and performs synchronous rectifying procedure. As can be shown inFIG. 7, the distance between the synchronous rectifying unit performing synchronous rectifying procedure in 1st state and the central axis of the isolating transformer30is equal to that of in 2nd state, and the leakage inductance in 1st state is close to that of in 2nd state. Therefore, the controller420may interleaved drive the first synchronous rectifying unit410aand the fourth synchronous rectifying unit410dto conduct the power coupled to the secondary winding320aand320dto the electronic device while the electronic device is operated under the same condition (such as light load condition) to prevent generated heat that arises at the time of driving from being stored in particular synchronous rectifying unit (410a˜410d), which is placed in the conducting state and performs synchronous rectifying procedure all the time.

It should be noted that the synchronous rectifying units (410a˜410d) may be interleaved placed in the conducting state (i.e. the first to fourth synchronous rectifying units410a˜410dmay be driven to interleaved perform synchronous rectifying procedure) according to the distance between the central axis and the synchronous rectifying units (410a˜410d), for example, the synchronous rectifying units (410a˜410d) with same distance from the central axis may be interleaved driven to perform synchronous rectifying procedure. However, that the synchronous rectifying units (410a˜410d) may be driven to interleaved perform synchronous rectifying procedure according to inductance in different operation states of the synchronous rectifying units (410a˜410d). For example, the operation states with similar leakage inductance (such as the difference in leakage inductance between the operation states is less than 5 μH) may be interleaved driven to perform synchronous rectifying procedure.

In sum, the power conversion system of the present disclosure performs a power conversion procedure for powering the electronic device includes step as following first, the power conversion system including a primary winding310, a plurality of secondary windings320a˜320d, and a plurality of synchronous rectifying units410a˜410dis provided. There are a plurality of coupling distances between the primary winding310and the secondary windings320a˜320d.

Next, the operation condition (such as light load condition, normal load condition, or heavy load condition) of the electronic device is measured by measuring a current required by the electronic device. Specifically, the current required for the electronic device during light load condition may be smaller than that of during normal load condition, and the current required for the electronic device during heavy load condition may be larger than that of during normal load condition. Thereafter, the synchronous rectifying units (410a˜410d) are selectively placed in a conducting state for varying a leakage inductance of the power conversion system, thus a output current of the power conversion system is modulated to meet the current requirement of the electronic device. The output current is only provided by the synchronous rectifying units410a˜410dwhich is placed in the conducting state, and the power conversion system has a lowest leakage inductance when all of the output-controlling modules400a˜400dare placed in the conducting state, therefore a largest output current is provided.

The power conversion system may vary the leakage inductance by selectively place one of the synchronous rectifying units410a˜410din the conducting state at a time; however, the power conversion system may further selectively place two or more synchronous rectifying units410a˜410dat a time. Besides, the leakage inductance of the power conversion system is varied when an amount of the synchronous rectifying units410a˜410dplaced in the conducting state changes.

Reference is made toFIG. 11, which is a circuit diagram of a power conversion system according to a second embodiment of the present disclosure. InFIG. 11, the power conversion system includes a switching module10, a resonant module20, a transformer30, and an output-controlling device40. The transformer30includes a primary winding310and a plurality of secondary windings320a˜320dcoupled with the primary winding310.

The function and relative description of switching module10and the resonant module20of the power conversion system shown in theFIG. 11are the same as that of first embodiment (shown in theFIG. 2) mentioned above and are not repeated here for brevity, and the switching module10and the resonant module20of the power conversion system shown in theFIG. 11can achieve the functions as power conversion system of the first embodiment does. It should be noted that the transformer30and the output-controlling device40shown in theFIG. 11is different from that of the first embodiment.

InFIG. 11, the transformer30is a center-tapped transformer, which has an advantage of compact. However, the isolating transformer shown inFIG. 2has an advantage of double-current. The output-controlling device40is electrically connected to the secondary winding320a˜320dof the transformer and includes first to fourth synchronous rectifying units410a˜410d, controller420, and first to fourth output switch SW1˜SW4. The first synchronous rectifying unit410ais connected to the secondary winding320a, the second synchronous rectifying unit410bis connected to the secondary winding320b, the third synchronous rectifying unit410cis connected to the secondary winding320c, and the fourth synchronous rectifying unit410dis connected to the secondary winding320d.

The first synchronous rectifying unit410aincludes rectifying switches Q1and Q2, the second synchronous rectifying unit410bincludes rectifying switches Q3and Q4, the third synchronous rectifying unit410cincludes rectifying switches Q5and Q6, and the fourth synchronous rectifying unit410dincludes rectifying switches Q7and Q8. Specifically, the sources of the rectifying switch Q1and Q2are connected to ground, the drains thereof is connected to two taps of the second winding320a, and the filter L1is connected to the center-tap of the second winding320a; the sources of the rectifying switch Q3and Q4are connected to ground, the drains thereof is connected to two taps of the second winding320b, and the filter L2is connected to the center-tap of the second winding320b; the sources of the rectifying switch Q5and Q6are connected to ground, the drains thereof are connected to two taps of the second winding320c, and the filter L3is connected to the center-tap of the second winding320c; the sources of the rectifying switch Q7and Q8are connected to ground, the drains thereof is connected to two taps of the second winding320d, and the filter L4is connected to the center-tap of the second winding320d. The gates SR1˜SR8of the rectifying switch Q1˜Q8and the first to fourth output switch SW1˜SW4are connected to the controller420. The controller420sends signals the rectifying switch Q1˜Q8to drive one of the first to the fourth synchronous rectifying units410a˜410dto perform synchronous rectifying procedure. The controller420further sent signals to the first to fourth output switch SW1˜SW4to makes one of the first to fourth output switch SW1˜SW4to turn off or on, wherein when the first to fourth output switch SW1˜SW4is turned on, the rectified power con be conducted to the electronic device. The center tap of the transformer30is further electrically connected to an output capacitor Co.

The function and relative description of other components of power conversion system of this embodiment are the same as that of first embodiment mentioned above and are not repeated here for brevity, and the power conversion of this embodiment can achieve the functions as the power conversion system of the first embodiment does.

Although the present disclosure has been described with reference to the foregoing preferred embodiment, it will be understood that the invention is not limited to the details thereof. Various equivalent variations and modifications can still occur to those skilled in this art in view of the teachings of the present disclosure. Thus, all such variations and equivalent modifications are also embraced within the scope of the invention as defined in the appended claims.