Power control system and method thereof

A power control system is electrically connected to a power function circuit including a power circuit, a coil module, a switch, and a load circuit, and includes at least one timer, a zero-current trigger unit, a status control unit, and a driver unit. The status control unit has a first status interval, a second status interval, a third status interval and a fourth status. The power control method triggers the status control unit to change the status interval when a counting time reaches one specific time interval corresponding one status interval. When a coil voltage of the coil module drops to zero from a voltage larger than a positive threshold voltage in the third status interval or the fourth status interval, the status control unit triggers to change the status interval, re-enters the first status interval, resets the timer, and triggers the driver unit to open the switch.

This application claims the benefit of Taiwan Patent Application Serial No. 104137518, filed Nov. 13, 2015, the subject matter of which is incorporated herein by reference.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates to a power control system and a power control method, and more particularly to the power control system and the power control method that can be applicable to various operation modes.

2. Description of the Prior Art

Currently, typical portable electronic devices such as notebook computers, tablet computers, personal digital assistants, video games, video cameras and so on, can transform a DC (direct current) signal of a voltage level to a DC signal of another voltage level (a DC/DC transformer for example), an AC (alternate current) signal to a DC signal (an AC/DC transformer), a DC signal to an AC signal (a DC/AC transformer for example), or an AC signal to another AC signal (an AC/AC transformer for example). The classification of the forgoing transformers of the AC or DC power control system is based on the current status of the induction-storage elements. If a switch element is controlled to reach a conduction status prior to a zero-current point, then the operation of the power system is defined as a continuous conduction mode (CCM). If the switch element is controlled to reach the conduction status right at the zero-current point, then the operation of the power system is defined as a boundary (or critical) conduction mode (BCM/CrM). If the switch element is controlled to reach the conduction status after a delay time posterior to the zero-current point, then the operation of the power system is defined as a non-continuous conduction mode (DCM).

However, none of the current power control systems can fulfill all of the aforesaid operation modes, and thus the instant power control system cannot be switched to a proper operation mode in correspondence to the load status. Thereupon, various disadvantages to the power control system would be inevitable, such as a high input peak current, high frequency switch loss, entrance of the low-frequency intermittent burst mode, bias in current waveform, occurrence of audio noise while in entering an audio frequency and so on. Hence, any improvement upon the conventional power control system is definitely welcome to the art.

SUMMARY OF THE INVENTION

In view of the prior art of the power control system can't be switched to a relevant operation mode with respect to a particular load status, thus, accordingly, it is the primary object of the present invention to provide a power control system and a power control method that include a status control unit to divide the status of the switch into four status intervals, by which the object of fulfilling different operation modes can be achieved.

In the present invention, the power control system is electrically connected to a power function circuit further having a power circuit, a coil module, a switch and a load circuit. The coil module is electrically connected to the power circuit, the switch is electrically connected to the coil module, the load circuit is electrically connected to the coil module, and the power circuit is to provide a supply voltage for having a detection coil of the coil module to generate an auxiliary winding voltage. The power control system includes at least one timer, a zero-current trigger unit, a status control unit and a driver unit. The at least one timer is to count a first counting time, a second counting time, a third counting time and a fourth counting time. The zero-current trigger unit, electrically connected to the coil module, is to transmit a zero-current trigger signal upon when the auxiliary winding voltage drops to zero from a voltage larger than a positive detected threshold voltage. The status control unit, electrically connected to the timer and the zero-current trigger unit, has a first status interval, a second status interval, a third status interval and a fourth status interval. The first status interval is corresponding to a first time interval, the second status interval is corresponding to a second time interval, the third status interval is corresponding to a third time interval, and the fourth status interval is corresponding to a fourth time interval. An switching-on interval of the switch is defined to the first status interval, while a switching-off interval of the switch is divided to define the second status interval, the third status interval and the fourth status interval. The driver unit is electrically connected to the status control unit and the switch.

In the present invention, initially when the status control unit enters the first status interval, the timer begins to count the first counting time; when the first counting time reaches the first time interval, the status control unit enters the second status interval, and the timer counts the second counting time; when the second counting time reaches the second time interval, the status control unit enters the third status interval, and the timer counts the third counting time; when the third counting time reaches the third time interval, the status control unit enters the fourth status interval, and the timer counts the fourth counting time; and, when the fourth counting time reaches the fourth time interval, the status control unit re-enters the first status interval and triggers the timer to recount. Further, when the status control unit in one of the third status interval and the fourth status interval receives the zero-current trigger signal, the first status interval is re-entered, the timer is triggered to recount, and the driver unit is triggered to open the switch.

In one embodiment of the present invention, the power control system further includes an arithmetic unit electrically connected to the load circuit and the status control unit. The supply voltage generates a load voltage in the load circuit, and the arithmetic unit bases on the load voltage to calculate the first time interval, the second time interval, the third time interval and the fourth time interval. In addition, the power control system further includes a zero-current recording unit electrically connected to the zero-current trigger unit and the status control unit. The zero-current recording unit records and transmits a zero-current recording signal upon when the zero-current trigger unit transmits the zero-current trigger signal. When the status control unit enters the fourth status interval and detects the zero-current recording signal, the first status interval is re-entered, the timer is triggered to recount, and the driver unit is triggered to open the switch. In addition, when the status control unit is in the second status interval, the switch is maintained to be switched off.

In another aspect of the present invention, the power control method, applicable to the aforesaid power control system, includes: a step (a) of determining whether or not the first counting time reaches the first time interval; a step (b) of, if a judgment of the step (a) is positive, the status control unit entering the second status interval; a step (c) of determining whether or not the second counting time reaches the second time interval; a step (d) of, if a judgment of the step (c) is positive, the status control unit entering the third status interval; a step (e) of determining whether or not the auxiliary winding voltage drops to zero from a voltage larger than the positive detected threshold voltage (namely, a corresponding zero-current trigger signal is generated); a step (f) of, if a judgment of the step (e) is positive, the status control unit re-entering the first status interval, triggering the timer to recount, and triggering the driver unit to open the switch; a step (g) of, if the judgment of the step (e) is negative, determining further whether or not the third counting time reaches the third time interval; a step (h) of, if a judgment of the step (g) is positive, the status control unit entering the fourth status interval; a step (i) of determining whether or not the auxiliary winding voltage drops to zero from the voltage larger than the positive detected threshold voltage; a step (j) of, if a judgment of the step (i) is positive, the status control unit re-entering the first status interval, triggering the timer to recount, and triggering the driver unit to open the switch; a step (k) of, if the judgment of the step (i) is negative, determining further whether or not the fourth counting time reaches the fourth time interval; and, a step (l) of, if a judgment of the step (k) is positive, the status control unit re-entering the first status interval, triggering the timer to recount, and triggering the driver unit to open the switch.

In one embodiment of the present invention, between the step (j) and the step (k), the power control method further includes a step (j0) of determining whether or not the zero-current recording signal is zero. In addition, if a judgment of the step (j0) is positive, the status control unit re-enters the first status interval, triggers the timer to recount, and triggers the driver unit to open the switch.

In one embodiment of the present invention, the supply voltage generates a load voltage in the load circuit. In addition, prior to the step (a), the power control method further includes a step (a0) of basing on the load voltage to calculate the first time interval, the second time interval, the third time interval and the fourth time interval. Also, between the step (b) and the step (c), the switch is maintained to be switched off, and the step (b) further includes a step (b0) of determining whether or not the auxiliary winding voltage is zero (i.e. the zero-current trigger signal is active). If the judgment is positive, a zero-current occurrence event is recorded and a zero-current recording signal is transmitted.

By providing the power control system and the power control method of the present invention, since the four status intervals are introduced so as to have the system and the method applicable to various operation modes, thus the preferred operation mode can be determined and selected according to the practical load status. Thereupon, the conventional shortcomings in the high input peak current, the high frequency switch loss, the entrance of the low-frequency intermittent burst mode, the bias in current waveform, the occurrence of audio noise while in entering an audio frequency and so on, can be effectively resolved.

All these objects are achieved by the power control system and the method thereof described below.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention disclosed herein is directed to a power control system and a method thereof. In the following description, numerous details are set forth in order to provide a thorough understanding of the present invention. It will be appreciated by one skilled in the art that variations of these specific details are possible while still achieving the results of the present invention. In other instance, well-known components are not described in detail in order not to unnecessarily obscure the present invention.

Refer now toFIG. 1andFIG. 2; whereFIG. 1is a schematic view showing electrical connection of a preferred power control system in accordance with the present invention and a first power function circuit, andFIG. 2is a schematic view showing electrical connection of the preferred power control system ofFIG. 1and a second power function circuit.

As shown, the preferred power control system1of the present invention is electrically connected to a first power function circuit2and a second power function circuit2a, respectively, inFIG. 1andFIG. 2. The power function circuit2/2aincludes individually a power circuit21/21a, a coil module22/22a, a switch23/23aand a load circuit24/24a. The coil module22/22ais electrically connected to the power circuit21/21a. The switch23/23ais electrically connected to the coil module22/22a. The load circuit24/24ais electrically connected to the coil module22/22a. It shall be noted that the first power function circuit2ofFIG. 1is (but not limited to) a topology of a flyback circuit, while the second power function circuit2ais (but not limited to) a topology of a boost power factor correction (PFC) circuit. The combination of the power circuit21/21a, the coil module22/22a, the switch23/23aand the load circuit24/24ais determined simply per practical requirements. For concise explanations of the present invention, the first power function circuit2(i.e.FIG. 1) would be adopted as the typical embodiment for the following descriptions.

The power control system1includes at least one timer11, a zero-current trigger unit12, a status control unit13, a driver unit14, an arithmetic unit15and a zero-current recording unit16. Though only one timer11is shown in the preferred embodiment ofFIG. 1, yet the other embodiment may includes more than one timer11. However, since the timer11is already mature in the art, and thus details thereabout would be omitted herein.

The zero-current trigger unit12is electrically connected to a detection coil221of the coil module22. The status control unit13is electrically connected to the zero-current trigger unit12and the timer11. Particularly, the status control unit13includes a first status interval (ON interval), a second status interval (OFF interval), a third status interval (Soft-window interval, i.e. SW interval) and a fourth status interval (Hard-window interval, i.e. HW interval). The first status interval is respective to a first time interval, the second status interval is respective to a second time interval, the third status interval is respective to a third time interval, and the fourth status interval is respective to a fourth time interval. Any of the aforesaid four time intervals is an interval of time. An switching-on interval (also called as a conduction interval) of the switch23is defined to the first status interval, while a switching-off interval of the switch23is divided to define the second status interval, the third status interval and the fourth status interval. Namely, while the switch23is opened, it is in the first status interval; and, while the switch23is switched off, it is in the second status interval, the third status interval or the fourth status interval. Details would be followed lately.

The driver unit14is electrically connected to the status control unit13. The arithmetic unit15is electrically connected to the load circuit24and the status control unit13. The zero-current recording unit16is electrically connected to the zero-current trigger unit12and the status control unit13. In the present invention, each of the zero-current trigger unit12, the status control unit13, the driver unit14, the arithmetic unit15and the zero-current recording unit16can be embodied as an analog circuit or a digital circuit. For example, the zero-current trigger unit12and the zero-current recording unit16can be embodied as, but not limited to, a combination of a gate and an SR latch.

In the preset invention, the power circuit21can provide a supply voltage generally processed by wave filtration and bridge rectification. While the supply voltage is transmitted to the coil module22, an auxiliary winding voltage (VZCD) is generated in a detection coil221of the coil module22. Generally, the detection coil221is a secondary coil for sensing a current of a first coil. Details about the auxiliary winding voltage would be elucidated lately. In addition, while the supply voltage is transmitted to the load circuit24, a load voltage would be generated in the load circuit24. In the present invention, the load voltage can be, but not limited to, a voltage across a resistor or an optical coupler.

The timer11is to count a first counting time t1, a second counting time t2, a third counting time t3and a fourth counting time t4. Practically, the timer11counts in an order of the first counting time t1, the second counting time t2, the third counting time t3and, finally, the fourth counting time t4. Namely, as soon as the first counting time t1has been counted, then the second counting time t2begins to count, etc.

The zero-current trigger unit12is to transmit a zero-current trigger signal S1upon when the auxiliary winding voltage VZCDis dropped to zero from a positive detected threshold voltage Vzcd_th. It shall be noted that, when the switch23is switched off, the detection coil221would generate the aforesaid auxiliary winding voltage VZCD. Also, the detected threshold voltage, generally a positive voltage, is the lowest detection capability of the circuit with respect to the voltage (as shown fromFIG. 4toFIG. 6). The auxiliary winding voltage VZCDwould experience an oscillating interval (also called as an oscillation frequency), and then decay to zero.

The arithmetic unit15is to base on the load voltage of the load circuit24to calculate the first time interval, the second time interval, the third time interval and the fourth time interval with respect to the first status interval, the second status interval, the third status interval and the fourth status interval of the status control unit13, respectively. Refer now toFIG. 3, where a schematic waveform plot showing the time intervals and the load voltages of the preferred power control system ofFIG. 1is illustrated. As shown, the curve100stands for the time value of the first time interval, the curve200stands for the time value of the second time interval, the curve300stands for the time value of the fourth time interval. InFIG. 3, the relationships of the load voltage to the first time interval, the second time interval and the fourth time interval are clearly demonstrated.

More precisely, the first time interval is proportional to the instant value of the load voltage, the second time interval is inversely proportional to the mean value of the load voltages at different timing (for example, the mean value of the output voltages at the 1st, 2ndand 3rdseconds), the third time interval is 1.5˜2 times of the aforesaid oscillating interval, and the fourth time interval is the lowest preset operating frequency (a constant) if the mean value of the load voltages at different timing is lower than a specific preset threshold voltage (for example, the threshold voltage at A ofFIG. 3). In addition, if the mean value of the load voltages at different timing is larger than the specific preset threshold voltage, the fourth time interval is inversely proportional to the mean value of the load voltages at different timing. In the present invention, the definitions for different time intervals are not limited to the aforesaid examples.

The zero-current recording unit16is to record and transmit a zero-current record signal (not shown in the figure) upon when the zero-current trigger unit12transmits the zero-current trigger signal S1, and to reset to the first status interval for another trigger upon when the status control unit13enters the fourth status interval and detects the existence of the zero-current record signal. The method for recording a zero-current occurrence event can be a step of assigning “1” to the digital signal for the system.

In practice, when the situation of the auxiliary winding voltage VZCDdropping to zero from a voltage larger than the detected threshold voltage Vzcd_th is not considered, the initial status of the switch23is opened, and, if the status control unit13enters the first status interval, the timer11is synchronous to count the first counting time t1. In addition, when the first counting time t1reaches the first time interval, the status control unit13would be triggered to enter the second status interval. At this time, the timer11would synchronously count the second counting time t2, and then the status control unit13would be triggered to enter the third status interval if the second counting time t2reaches the second time interval. Thus, the timer11would immediately count the third counting time t3. When the third counting time t3reaches the third time interval, the status control unit13would be triggered to enter the fourth status interval, and the timer11would synchronously count the fourth counting time t4. Further, when the fourth counting time t4reaches the fourth time interval, the status control unit13would reset to enter the first status interval and trigger the timer11to recount. Namely, the status control unit13would enter the next counting of time orderly if the counting time reach the instant time interval.

On the other hand, when the possible situation of the auxiliary winding voltage VZCDdropping to zero from a voltage larger than the detected threshold voltage Vzcd_th is considered, if the status control unit13in the second status interval receives the zero-current trigger signal S1issued by the zero-current trigger unit12, the switch23is maintained at the switching-off status. Namely, even upon receiving of the zero-current trigger signal S1, the switch23is not opened. In addition, when the fourth counting time t4reaches the fourth time interval, the status control unit13would reset to enter the first status interval, to trigger the timer11to recount, and to trigger the driver unit14to open the switch23.

If the status control unit13in any of the third status interval and the fourth status interval receives the zero-current trigger signal S1, then status control unit13would reset to enter the first status interval, to trigger the timer11to recount, and to trigger the driver unit14to open the switch23. Namely, as long as the zero-current trigger signal S1is received in either the third status interval or the fourth status interval, then the first status interval is directly entered, and the switch23is opened. When the fourth counting time t4reaches the fourth time interval and the zero-current record signal is detected, the first status interval is re-entered, the timer11is triggered to recount, and the driver unit14is triggered to open the switch23.

In order to clearly explain the present invention to the art, following example is adopted. Referring now toFIG. 4, a schematic waveform plot of the preferred power control system ofFIG. 1applied to a boundary conduction mode is illustrated. As shown, in the initial open status of the switch23, the timer11begins to count the first counting time t1. At this time, the status control unit13is in the first status interval. While the first counting time t1reaches the first time interval corresponding to the first status interval, the status control unit13would be triggered to enter the second status interval, and the switch23would be switched to the switching-off status. Then, the trigger timer11would begin to count the second counting time t2. While the second counting time t2reaches the second time interval corresponding to the second status interval, the status control unit13would be triggered to enter the third status interval. Then, the trigger timer11would be immediately to count the third counting time t3. InFIG. 4, while in the third status interval, as the auxiliary winding voltage approaches the end of the third status interval, the auxiliary winding voltage would drop to zero from a voltage larger than the detected threshold voltage Vzcd_th in an oscillating manner. At this time, the zero-current trigger unit12would be triggered to issue the zero-current trigger signal S1, the zero-current recording unit16would be triggered to record the zero-current occurrence event (by assigning “1” to the corresponding digital logic signal), the status control unit13is triggered to reset the timer11by assigning “1” to the corresponding digital logic signal), and the driver unit14is triggered to open the switch23and to re-enter the first status interval. It shall be noted that, in the boundary conduction mode, the fourth time interval corresponding to the fourth status interval is far smaller than the other time intervals and thus omitted in the figure. In other embodiments, the definition of the fourth time interval corresponding to the fourth status interval can be the sum of the first time interval through the third time interval. Namely, the fourth time interval defined for the fourth status interval can be an interval following the third time interval, or a sum of the first time interval through the third time interval.

Referring now toFIG. 5, a schematic waveform plot of the preferred power control system ofFIG. 1applied to a non-continuous conduction mode is illustrated. As shown, the first status interval ofFIG. 5is resembled to that ofFIG. 4, and thus details thereabout are omitted herein. In the second status interval, the auxiliary winding voltage drops to zero from a voltage larger than the detected threshold voltage Vzcd_th in an oscillating manner. However, at this interval, the switch is maintained at the switching-off status. Till the second counting time t2reaches the second time interval corresponding to the second status interval, the status control unit13would be triggered to enter the third status interval, and the timer11is triggered to begin the counting of the third counting time t3. As shown, when the third status interval ends (the fourth status interval is neglected as explained above), and though the auxiliary winding voltage does not drop to zero from a voltage larger than the detected threshold voltage Vzcd_th, yet, at this time, the status control unit13would keep detecting the existence of the zero-current record signal, the first status interval is re-entered, the timer11is triggered to recount, and the driver unit14is triggered to open the switch23.

Referring now toFIG. 6, a schematic waveform plot of the preferred power control system ofFIG. 1applied to a light-duty fixed-frequency mode is illustrated. As shown, in the light-duty fixed-frequency mode (GM), if the situation of dropping the auxiliary winding voltage to zero from a voltage larger than the detected threshold voltage Vzcd_th is not detected in either the second status interval or the third status interval so that the fourth counting time t4is the same as the fourth time interval corresponding to the fourth status interval, then the status control unit13is directly triggered to reset the timer11, and the driver unit14is triggered to open the switch23so as to re-enter the first status interval.

Referring now toFIG. 7, a schematic waveform plot of the preferred power control system ofFIG. 1applied to a continuous conduction mode is illustrated. As shown,FIG. 7is resembled toFIG. 6for the light-duty fixed-frequency mode. InFIG. 7, if the situation of dropping the auxiliary winding voltage to zero from a voltage larger than the detected threshold voltage Vzcd_th is not detected in either the second status interval or the third status interval so that the fourth counting time t4is the same as the fourth time interval corresponding to the fourth status interval, then the status control unit13is directly triggered to reset the timer11, and the driver unit14is triggered to open the switch23so as to re-enter the first status interval.

As described above, in any of the boundary conduction mode, the non-continuous conduction mode and the light-duty fixed-frequency mode, the situation of dropping the auxiliary winding voltage to zero from a voltage larger than the detected threshold voltage Vzcd_th is commonly used to determine the opening of the switch23at the trough of the corresponding waveform. The only differences are the delay of the triggering and the management at the situation that the dropping of the auxiliary winding voltage to zero from a voltage larger than the detected threshold voltage Vzcd_th is not detected. In the present invention, if the oscillation intensity of the auxiliary winding voltage is remarkable (for example, larger than the detected threshold voltage Vzcd_th plotted inFIG. 4toFIG. 6), then the switch23is immediately opened as long as the zero current is detected in either the third status interval or the fourth status interval. Or, while the situation of dropping the auxiliary winding voltage to zero from a voltage larger than the detected threshold voltage Vzcd_th is detected in the second status interval, then the zero-current occurrence event is recorded, and the switch23is triggered to directly open at the end of the third status interval. Hence, a user can simply control the length of each individual time interval corresponding to the specific status interval, and then he/she can switch easily to a preferred operation of the power control system.

In the present invention, the power control system can control the operating frequency as well. For example, in the boundary conduction mode (BCM/CrM), the period is the sum of the first counting time and a natural discharge time of the coil module (tzcd). The natural discharge time of the coil module22is smaller than the sum of the second counting time, the third counting time and the fourth counting time. Hence, when the load is decreased, the second counting time can be selectively controlled to increase (as shown inFIG. 3). In the fixed-frequency mode, the period is the sum of the first counting time to the fourth counting time. While in an extreme light duty, the second counting time is far larger than the sum of the first counting time, the third counting time and the fourth counting time. Hence, the ratio of the period to the frequency is about equal to the second counting time.

In addition, in the heavy duty, the first counting time is increased, the second counting time is dropped to almost zero, and the fourth counting time is decreased as well. When any of the aforesaid counting times is larger than the sum of the second counting time, the third counting time and the fourth counting time, then the system is in the continuous conduction mode. Thus, simply based on the curves ofFIG. 3, the operating frequency of each interval can be selectively controlled.

It shall be noted that the preferred system of the present invention introduces the second status interval to limit the highest switching frequency, so as to avoid an excessive high switching frequency in the situation of a too short open time of the switch23and a too short zero-current time. Thereupon, the switch loss can be reduced. The inclusion of the fourth status interval is to overcome the situation that the auxiliary winding voltage is too low to affect the detection of the zero-current trigger unit12and the zero-current recording unit16of the power control system1while an unexpected short open time of the switch23in the light-duty status is met. Hence, through arranging properly the second status interval, the third status interval and the fourth state interval, the switch23can be forced to open at the end of the fourth status interval.

In addition, when the system is operated under a medium load, the auxiliary winding voltage is usually detectable to the power control system1. Thus, the fourth status interval is negligible. In the heavy-duty status as shown inFIG. 3, as the load voltage rises to a level, the fourth status interval can be set so as to have the sum of the second counting time, the third counting time and the fourth counting time to be smaller than the previous sum of the second counting time, the third counting time and the fourth counting time. Then, even the zero-current status is not met, the switch23can be still opened at the end of the fourth status interval, and then the system is switched from the boundary conduction mode to the continuous conduction mode.

Refer now fromFIG. 1throughFIG. 8A, whereFIG. 8andFIG. 8Aare integrally to show a flowchart of a preferred power control method in accordance with the present invention. As shown, the power control method includes the following steps.

Step S101: Base on the load voltage to calculate the first time interval, the second time interval, the third time interval and the fourth time interval.

Step S102: The status control unit13enters the first status interval and opens the switch23.

Step S103: Determine whether or not the first counting time t1reaches the first time interval.

Step S104: The status control unit13enters the second status interval and switches off the switch23;

Step S105: Determine whether or not the auxiliary winding voltage drops to zero from a voltage larger than the positive detected threshold voltage; such that a corresponding zero-current trigger signal of the zero-current trigger unit12is active.

Step S106: The switch23is maintained to be switched off, and a zero-current occurrence event is recorded.

Step S107: Determine whether or not the second counting time t2reaches the second time interval.

Step S108: The status control unit13enters the third status interval.

Step S109: Determine whether or not the zero-current trigger signal is active.

Step S110: The status control unit13re-enters the first status interval, triggers the timer11to recount, and triggers the driver unit14to open the switch23.

Step S111: Determine whether or not the third counting time t3reaches the third time interval.

Step S112: The status control unit13enters the fourth status interval.

Step S113: Determine whether or not a zero-current record event is met.

Step S114: Determine whether or not the zero-current trigger signal is active.

Step S115: Determine whether or not the fourth counting time t4reaches the fourth time interval.

In this embodiment, if the judgment in any of the aforesaid step S109, step S113, step S114and step S115is positive, then step S110is performed to re-open the switch23. In other embodiments, step S105and step S106can be skipped, and step S107is performed directly. However, all the other steps are still prevailed in these embodiments, and thus details thereabout are omitted herein. In addition, in step S113, the zero-current record event is corresponding to the zero-current occurrence event in step S106, or to an instant zero-current occurrence event in the fourth status interval.

Accordingly, by providing the power control system and the power control method of the present invention, since the four status intervals are introduced so as to have the system and the method applicable to various operation modes, thus the preferred operation mode can be determined and selected according to the practical load status. Thereupon, the conventional shortcomings in the high input peak current, the high frequency switch loss, the entrance of the low-frequency intermittent burst mode, the bias in current waveform, the occurrence of audio noise while in entering an audio frequency and so on, can be effectively resolved.