Patent Publication Number: US-2023132775-A1

Title: Power supply apparatus and method having power limiting mechanism

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power supply apparatus and a power supply method having power limiting mechanism. 
     2. Description of Related Art 
     Power over Ethernet (PoE) is a technology using network connections to transfer power to powered device. In conventional design, an electronic device requires different connections to access network and power simultaneously. Power over Ethernet technology allows a single network connection for the electronic device to supply power through the network connector to the electronic device. 
     When Power over Ethernet technology is used, a switch transistor is required to drive the switch that allows the power supply device to supply power to the powered device. The power of the switch transistor needs to be limited under a certain value. However, conventional power-limiting technologies are difficult to provide an accurate control mechanism. Furthermore, when a current of the switch transistor is too large such that a current-limiting operation is required, the operation that lowers the conduction degree of the switch transistor in order to lower the current results in the raise of the on-resistance (Ron) of the switch transistor. The power of the switch transistor cannot be lowered. 
     SUMMARY OF THE INVENTION 
     In consideration of the problem of the prior art, an object of the present invention is to supply a power supply apparatus and a power supply method having power limiting mechanism. 
     The present invention discloses a power supply apparatus having power limiting mechanism that includes a switch transistor, a voltage detection circuit, a power-limiting circuit and a current-limiting circuit. The switch transistor is electrically coupled in series with a powered device and is controlled by a control voltage to form a conduction path when being conducted such that a power supply unit supplies a power to the powered device, wherein the switch transistor has an operation current, an operation voltage and an operation power when being conducted. The voltage detection circuit is configured to detect the operation voltage. The power-limiting circuit includes an analog-to-digital conversion circuit, a calculation circuit and a digital-to-analog conversion circuit. The analog-to-digital conversion circuit is configured to perform analog-to-digital conversion on the operation voltage. The calculation circuit is configured to generate a current-limiting signal related to a current-limiting value according to the operation voltage based on a predetermined voltage-current curve, wherein the predetermined voltage-current curve limits the operation power to be not larger than a predetermined value. The digital-to-analog conversion circuit is configured to perform digital-to-analog conversion on the current-limiting signal to generate a reference voltage. The current-limiting circuit is configured to receive the reference voltage and perform comparison with a feedback voltage generated according to the operation current to generate the control voltage accordingly to control the switch transistor, so as to keep the operation current at the current-limiting value. 
     The present invention also discloses a power supply method having power limiting mechanism used in a power supply apparatus that includes steps outlined below. A switch transistor electrically coupled in series with a powered device is controlled by a control voltage to form a conduction path when being conducted such that a power supply unit supplies a power to the powered device, wherein the switch transistor has an operation current, an operation voltage and an operation power when being conducted. The operation voltage is detected by a voltage detection circuit. Analog-to-digital conversion is performed on the operation voltage by an analog-to-digital conversion circuit of a power-limiting circuit. A current-limiting signal related to a current-limiting value is generated by a calculation circuit of the power-limiting circuit according to the operation voltage based on a predetermined voltage-current curve, wherein the predetermined voltage-current curve limits the operation power to be not larger than a predetermined value. Digital-to-analog conversion is performed on the current-limiting signal to generate a reference voltage by a digital-to-analog conversion circuit of the power-limiting circuit. The reference voltage is received and comparison is performed with a feedback voltage generated according to the operation current by a current-limiting circuit to generate the control voltage accordingly to control the switch transistor, so as to keep the operation current at the current-limiting value. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art behind reading the following detailed description of the preferred embodiments that are illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a block diagram of a power system according to an embodiment of the present invention. 
         FIG.  2 A  illustrates a diagram of a predetermined voltage-current curve according to an embodiment of the present invention. 
         FIG.  2 B  illustrates a diagram of a predetermined voltage-current curve according to an embodiment of the present invention. 
         FIG.  3    illustrates a circuit diagram of the switch transistor, the current-limiting circuit and the feedback voltage generation circuit according to an embodiment of the present invention according to an embodiment of the present invention. 
         FIG.  4    illustrates a flow chart of a power supply method according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An aspect of the present invention is to provide a power supply apparatus and a power supply method having power limiting mechanism to generate a current-limiting signal according to an operation voltage based on a predetermined voltage-current curve and control a conduction state of a switch transistor accordingly, such that the operation current thereof is kept at a current-limiting value to obtain an accurate power-limiting mechanism. 
     Reference is now made to  FIG.  1   .  FIG.  1    is a block diagram of a power system  100  according to an embodiment of the present invention. The power system  100  is configured to supply power to a powered device  190 . The power system  100  includes a power supply unit  105  and a power supply apparatus  110  having power limiting mechanism. 
     The power supply unit (PSU)  105  is a power supply device configured to supply a power of such as, but not limited to 57 volts or 48 volts. The power supply apparatus  110  includes a switch transistor  120 , a voltage detection circuit  125 , a power-limiting circuit  130 , a current-limiting circuit  135  and a feedback voltage generation circuit  140  (abbreviated as FVG in  FIG.  1   ). 
     The power supply unit  105  is electrically coupled to the powered device  190  to supply power to the powered device  190 . The switch transistor  120  is electrically coupled in series with the powered device  190  and is controlled by a control voltage VC to form a conduction path when being conducted such that the power supply unit  105  supplies the power to the powered device  190 . 
     In an embodiment, the power is transmitted between the power system  100  and the powered device  190  according to Power over Ethernet (PoE) technology. As a result, when the power is transmitted, the power supply apparatus  110  operates as a power sourcing equipment (PSE) and the powered device  190  operates as a powered device (PD). 
     In an embodiment, the switch transistor  120  is an N-type transistor having a drain, a source and a gate. The drain is electrically coupled to the powered device  190 . The source is electrically coupled to a ground terminal GND. The gate receives the control voltage VC. The switch transistor  120 , when being conducted, has an operation current IOP, an operation voltage VOP (the cross voltage between the drain and the source) and an operation power (not illustrated in the figure). 
     The voltage detection circuit  125  is configured to detect the operation voltage VOP. It is appreciated that in  FIG.  1   , the voltage detection circuit  125  is illustrated to be only electrically coupled to the drain of the switch transistor  120 . However, in order to detect the cross voltage between the drain and the source of the switch transistor  120 , the voltage detection circuit  125  can actually be electrically coupled to both the drain and the source of the switch transistor  120 . 
     The power-limiting circuit  130  includes an analog-to-digital conversion circuit  150 , a calculation circuit  155  and a digital-to-analog conversion circuit  160 . 
     The analog-to-digital conversion circuit  150  is configured to perform analog-to-digital conversion on operation voltage VOP. 
     The calculation circuit  155  is configured to generate a current-limiting signal ILS related to a current-limiting value according to the operation voltage VOP after the analog-to-digital conversion based on a predetermined voltage-current curve. The predetermined voltage-current curve sets the operation voltage and the current-limiting value to be inversely proportional such that the operation power of the switch transistor  120  is limited to be not larger than a predetermined value. 
     Reference is now made to  FIG.  2 A  at the same time.  FIG.  2 A  illustrates a diagram of a predetermined voltage-current curve  200  according to an embodiment of the present invention. The x-axis corresponds to voltage values and the y-axis corresponds to current values. 
     In the present embodiment, the predetermined voltage-current curve  200  is a straight line and is expressed as Y=aX+b, wherein X and Y are positive numbers, a represents a predetermined negative coefficient and b represents a predetermined positive coefficient. In an actual numerical example, the predetermined voltage-current curve  200  can be Y=−X+5. 
     Under such a condition, since the power is the product of the voltage value and the current value, the power can be expressed as X(aX+b). Such a power corresponding to a curve of second order has a maximum value. As a result, the calculation circuit  155  can calculate the required current-limiting value according to the operation voltage VOP based on the predetermined voltage-current curve  200  to generate the current-limiting signal ILS related to the current-limiting value that guarantees the operation power of the switch transistor  120  to be not larger than the maximum value of such a curve. 
     Reference is now made to  FIG.  2 B  at the same time.  FIG.  2 B  illustrates a diagram of a predetermined voltage-current curve  200  according to an embodiment of the present invention. The x-axis corresponds to voltage values and the y-axis corresponds to current values. 
     In the present embodiment, the predetermined voltage-current curve  210  is an inverse proportional curve and is expressed as XY=c, wherein X and Y are positive number and c represents a predetermined positive coefficient. In an actual numerical example, the predetermined voltage-current curve  200  can be XY= 10 . 
     Under such a condition, since the power is the product of the voltage value and the current value, the power can be expressed as c. As a result, the calculation circuit  155  can calculate the required current-limiting value according to the operation voltage VOP based on the predetermined voltage-current curve  200  to generate the current-limiting signal ILS related to the current-limiting value that guarantees the operation power of the switch transistor  120  to be not larger than the coefficient c. 
     It is appreciated that the predetermined voltage-current curves described above are merely an example. In other embodiments, other curves can be used to accomplish the object to keep the operation power from being larger than the predetermined value. 
     The digital-to-analog conversion circuit  160  is configured to perform digital-to-analog conversion on the current-limiting signal ILS to generate a reference voltage VRF. 
     The current-limiting circuit  135  is configured to receive the reference voltage VRF and perform comparison with a feedback voltage VFE generated according to the operation current IOP to generate the control voltage VC accordingly to control the switch transistor  120 , so as to keep the operation current IOP at the current-limiting value. The feedback voltage VFE is generated by the feedback voltage generation circuit  140 . 
     Reference is now made to  FIG.  3   .  FIG.  3    illustrates a circuit diagram of the switch transistor  120 , the current-limiting circuit  135  and the feedback voltage generation circuit  140  according to an embodiment of the present invention. The feedback voltage generation circuit  140  includes a control transistor  300 , a comparator  310  and a current mirror  320 . 
     In an embodiment, the control transistor  300  is an N-type transistor having a drain, a source and a gate. The drain is electrically coupled to the comparator  310  and the current mirror  320 . The source is electrically coupled to the source of the switch transistor  120 . The gate receives the control voltage VC. The switch transistor  120 , when being conducted, has a control current ICP. 
     The comparator  310  has two input terminals and an output terminal. The two input terminals are respectively electrically coupled to the drain of the switch transistor  120  and the drain of the control transistor  300 . The output terminal is electrically coupled to the drain of the control transistor  300 . By using a feedback mechanism to compare the voltages at the drains of the switch transistor  120  and the control transistor  300  to keep the voltages at the drains equal, the comparator  310  can make the control current ICP and the operation current IOP have a fixed ratio therebetween. Such a fixed ratio is related to the channel sizes (e.g., W/L ratio) of the switch transistor  120  and the control transistor  300 . In an embodiment, when the switch transistor  120  and the control transistor  300  have the same channel size, the control current ICP and the operation current IOP are the same. 
     The current mirror  320  has a first current output terminal and a second current output terminal respectively electrically coupled to the drain of the control transistor  300  and an output resistor RO, so as to mirror the control current ICP to the output resistor RO and generate the feedback voltage VFE at the second current output terminal 
     In an embodiment, the current-limiting circuit  135  can be a comparator and is configured to receive the feedback voltage VFE and the reference voltage VRF to perform comparison and output the control voltage VC according to the comparison result to the gate of each of the switch transistor  120  and the control transistor  300 . 
     By using the feedback mechanism described above, the current-limiting circuit  135  adjusts the amount of the control voltage VC, when the operation current IOP is either larger than or smaller than the current-limiting value, according to the comparison result of the feedback voltage VFE and the reference voltage VRF. The conduction degree of the switch transistor  120  can therefore be adjusted to keep the operation current IOP at the current-limiting value such that the operation power of the switch transistor  120  is not larger than the predetermined value. 
     It is appreciated that the configuration of the feedback voltage generation circuit  140  described above is merely an example. In other embodiments, other configurations can be used to generate the feedback voltage VFE according to the operation current IOP. 
     In some approaches, the power-limiting mechanism of the switch transistor is accomplished by using fully analog comparator. Under such a condition, the accuracy and the consistency between the voltage value and the current-limiting value cannot be controlled accurately. Further, only a linear adjusting approach can be used such that under the condition the current of the switch transistor is too large and is required to be limited, the drop of the conduction degree of the switch transistor causes the raise of the on-resistance (Ron) of the switch transistor. The power thereof cannot be decreased. The power-limiting is hard to implement when an elastic selection of an appropriate curve is not able to be performed to control the power. 
     The power supply apparatus of the present invention can convert the operation voltage to a digital form and perform digital control according to a predetermined voltage-current curve to generate the current-limiting signal, in which such a curve can (but not limited to) make the current and the voltage inversely proportional. The current-limiting signal is further converted to an analog form to control the conduction state of the switch transistor to keep the operation current thereof at the current-limiting value. An accurate power-limiting mechanism can be accomplished. 
     In an embodiment, the analog-to-digital conversion circuit  150  and the digital-to-analog conversion circuit  160  in  FIG.  1    can be selectively shared with other circuits that cooperate with the switch transistor  120 . For example, the analog-to-digital conversion circuit  150  can be shared with a storage circuit (not illustrated in the figure) configured to store the operation voltage VOP, in which such a storage circuit can be accessed by other circuits to perform other calculations and processing according to the operation voltage VOP. The digital-to-analog conversion circuit  160  can be shared with an over-current protection (OCP) circuit (not illustrated in the figure). By using such a configuration, the power supply apparatus  110  can make more efficient usage of the circuit area. 
     Reference is now made to  FIG.  4   .  FIG.  4    illustrates a flow chart of a power supply method  400  according to an embodiment of the present invention. 
     In addition to the apparatus described above, the present disclosure further provides the power supply method  400  that can be used in such as, but not limited to, the power supply apparatus  110  in  FIG.  1   . As illustrated in  FIG.  4   , an embodiment of the power supply method  400  includes the following steps. 
     In step S 410 , the switch transistor  120  electrically coupled in series with the powered device  190  is controlled by the control voltage to form the conduction path when being conducted such that the power supply unit  105  supplies the power to the powered device  190 , wherein the switch transistor  120  has the operation current IOP, the operation voltage VOP and the operation power when being conducted. 
     In step S 420 , the operation voltage VOP is detected by the voltage detection circuit  125 . 
     In step S 430 , analog-to-digital conversion is performed on the operation voltage VOP by the analog-to-digital conversion circuit  150  of the power-limiting circuit  130 . 
     In step S 440 , the current-limiting signal ILS related to the current-limiting value is generated by the calculation circuit  155  of the power-limiting circuit  130  according to the operation voltage VOP based on the predetermined voltage-current curve, wherein the predetermined voltage-current curve limits the operation power to be not larger than a predetermined value. 
     In step S 450 , digital-to-analog conversion is performed on the current-limiting signal ILS to generate the reference voltage VRF by the digital-to-analog conversion circuit  160  of the power-limiting circuit  130 . 
     In step S 460 , the reference voltage VRF is received and comparison is performed with the feedback voltage VFE generated according to the operation current IOP by the current-limiting circuit  135  to generate the control voltage VC accordingly to control the switch transistor  120 , so as to keep the operation current IOP at the current-limiting value. 
     It is appreciated that the embodiments described above are merely an example In other embodiments, it should be appreciated that many modifications and changes may be made by those of ordinary skill in the art without departing, from the spirit of the disclosure. 
     In summary, the present invention discloses the power supply apparatus and the power supply method having power limiting mechanism to convert the operation voltage to a digital form and perform digital control according to a predetermined voltage-current curve to generate the current-limiting signal. The current-limiting signal is further converted to an analog form to control the conduction state of the switch transistor to keep the operation current thereof at the current-limiting value. An accurate power-limiting mechanism can be accomplished. 
     The aforementioned descriptions represent merely the preferred embodiments of the present invention, without any intention to limit the scope of the present invention thereto. Various equivalent changes, alterations, or modifications based on the claims of present invention are all consequently viewed as being embraced by the scope of the present invention.