Power supply device and method with power limiting mechanism

Abstract

A power supply device with a power limiting mechanism. A switch transistor is controlled by a control voltage to form a path when turned on to allow a power supply unit to provide power to a powered device, wherein the switch transistor has an operating current, an operating voltage and an operating power when turned on. A voltage detection circuit detects the operating voltage. A power limiting circuit performs analog-to-digital conversion on the operating voltage, generates a current limit signal associated with a current limit value according to a preset voltage and current curve based on the operating voltage, and performs digital-to-analog conversion on the current limit signal to generate a reference voltage. A current limiting circuit receives the reference voltage and compares it with a feedback voltage generated according to the operating current to generate the control voltage to control the switch transistor to maintain the operating current at the current limit value.

Description

TECHNICAL FIELD

[0001] The present application relates to power supply technology, and in particular, to a power supply device and method with a power limiting mechanism. BACKGROUND

[0002] Power over Ethernet (PoE) is a technology that utilizes the capability of network cables to deliver power to devices. Traditionally, devices require both network and power cables, but with PoE technology, only network cables are needed, and the network connectors are used to supply power.

[0003] In performing PoE, a switching transistor is often used as a switch to drive the power supply device to supply power to the powered device. The power of the switching transistor must be limited to a certain value or less. However, the common power limiting mechanism cannot accurately control the power, and when the current of the switching transistor is too large and needs to be limited, the on-state of the switching transistor decreases to reduce the current, which in turn increases the on-resistance (Ron) of the switching transistor, and thus the power cannot be reduced. SUMMARY

[0004] In view of the problems of the prior art, one object of the present application is to provide a power supply device and method with a power limiting mechanism to improve the prior art.

[0005] The present application includes a power supply device with a power limiting mechanism, comprising a switching transistor, a voltage detection circuit, a power limiting circuit, and a current limiting circuit. The switching transistor is connected in series with the powered device and is controlled by a control voltage to form a path when turned on so that the power supply unit provides power to the powered device, wherein the switching transistor has an operating current, an operating voltage, and an operating power when turned on. The voltage detection circuit is configured to detect the operating voltage. The power limiting circuit includes an analog-to-digital conversion circuit, an operation circuit, and a digital-to-analog conversion circuit. The analog-to-digital conversion circuit is configured to perform analog-to-digital conversion on the operating voltage. The operation circuit is configured to generate a current limiting signal related to a current limiting value according to the operating voltage and a predetermined voltage and current curve, wherein the predetermined voltage and current curve makes the operating power not greater 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 compare it with a feedback voltage generated according to the operating current feedback to generate a control voltage to control the switching transistor to maintain the operating current at the current limiting value.

[0006] The present application also provides a power supply method with a power limiting mechanism, comprising: controlling a switch transistor in series with a powered device by a control voltage to form a path when turned on so that a power supply unit provides power to the powered device, the switch transistor having an operating current, an operating voltage and an operating power when turned on; detecting the operating voltage by a voltage detection circuit; performing analog-to-digital conversion on the operating voltage by an analog-to-digital conversion circuit of a power limiting circuit; generating a current limiting signal related to a current limiting value according to a preset voltage and current curve based on the operating voltage by an operation circuit of the power limiting circuit, wherein the preset voltage and current curve makes the operating power not greater than a preset value; performing digital-to-analog conversion on the current limiting signal by a digital-to-analog conversion circuit of the power limiting circuit to generate a reference voltage; and comparing the reference voltage with a feedback voltage generated according to the operating current feedback by a current limiting circuit and generating the control voltage to control the switch transistor based on the comparison to maintain the operating current at the current limiting value.

[0007] The features, implementations and effects of the present application are described in detail below with reference to the preferred embodiments and the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 A block diagram of a power supply system in one embodiment of the present application is shown in FIG. 1.

[0009] Figure 2A A schematic diagram of a preset voltage and current curve in one embodiment of the present application is shown in FIG. 3.

[0010] Figure 2B A schematic diagram of a preset voltage and current curve in one embodiment of the present application is shown in FIG. 3.

[0011] Figure 3 A circuit diagram of a switch transistor, a current limiting circuit and a feedback voltage generating circuit in one embodiment of the present application is shown in FIG. 4; and

[0012] Figure 4 A flowchart of a power supply method in one embodiment of the present application is shown in FIG. 5. DETAILED DESCRIPTION

[0013] One object of the present application is to provide a power supply device and method with a power limiting mechanism, generating a current limiting signal according to a preset voltage and current curve based on an operating voltage and controlling the on / off state of a switch transistor to maintain its operating current at a current limiting value, so as to achieve an accurate power limiting mechanism.

[0014] Please refer to Figure 1 . Figure 1A block diagram of a power system 100 is shown in one embodiment of the present application. The power system 100 is configured to power a powered device 190. The power system 100 comprises a power supply unit 105 and a power supply apparatus 110 with a power limiting mechanism.

[0015] The power supply unit (PSU) 105 is a power supply apparatus for providing, for example, but not limited to, 57 volts or 48 volts. The power supply apparatus 110 comprises a switching transistor 120, a voltage detection circuit 125, a power limiting circuit 130, a current limiting circuit 135, and a feedback voltage generation circuit 140.

[0016] The power supply unit 105 is electrically coupled to the powered device 190 for providing power to the powered device 190. The switching transistor 120 is in series with the powered device 190 and is controlled by a control voltage VC for forming a path when turned on so that the power supply unit 105 provides power to the powered device 190.

[0017] In one embodiment, the power system 100 and the powered device 190 perform power transmission according to the Power over Ethernet technology. Therefore, when performing power transmission, the power supply apparatus 110 works as a Power Sourcing Equipment (PSE) and the powered device 190 works as a Powered Device (PD).

[0018] In one embodiment, the switching 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 GND, and the gate receives the control voltage VC. The switching transistor 120 has an operating current IOP, an operating voltage VOP (i.e., the voltage across the drain and the source), and an operating power (not shown) when turned on.

[0019] The voltage detection circuit 125 is configured to detect the operating voltage VOP. It is noted that in Figure 1 , the voltage detection circuit 125 is depicted as being electrically coupled only to the drain of the switching transistor 120, however, in order to detect the voltage across the drain and the source of the switching transistor 120, the voltage detection circuit 125 can actually be electrically coupled to the drain and the source of the switching transistor 120.

[0020] The power limiting circuit 130 comprises an analog-to-digital conversion circuit 150, an operation circuit 155, and a digital-to-analog conversion circuit 160.

[0021] The analog-to-digital conversion circuit 150 is configured to perform analog-to-digital conversion on the operating voltage VOP.

[0022] The operation circuit 155 is configured to generate the current limit signal ILS related to the current limit value according to the preset voltage-current curve based on the operating voltage VOP after analog-to-digital conversion. The preset voltage-current curve is inversely proportional to the current limit value, so that the operating power of the switching transistor 120 is not greater than a preset value.

[0023] Referring to Figure 2A . Figure 2A A schematic diagram of a preset voltage-current curve 200 is shown in one embodiment of the present application. The x-axis (horizontal axis) corresponds to the voltage value, and the y-axis (vertical axis) corresponds to the current value.

[0024] In this embodiment, the preset voltage-current curve 200 is a straight line and can be represented as Y = aX + b, where X and Y are positive numbers, a is a preset negative coefficient, and b is a preset positive coefficient. In one actual numerical example, the preset voltage-current curve 200 can be Y = -X + 5.

[0025] In this case, since the power is the product of the voltage value and the current value, it can be represented as X(aX + b), and the quadratic curve of this power has a maximum value. Therefore, the operation circuit 155 can calculate the required current limit value according to the preset voltage-current curve 200 based on the operating voltage VOP, generate the current limit signal ILS related to the current limit value, and ensure that the operating power of the switching transistor 120 is not greater than the maximum value of the curve.

[0026] Referring to Figure 2B . Figure 2B A schematic diagram of a preset voltage-current curve 210 is shown in one embodiment of the present application. The x-axis (horizontal axis) corresponds to the voltage value, and the y-axis (vertical axis) corresponds to the current value.

[0027] In this embodiment, the preset voltage-current curve 210 is an inverse curve and can be represented as XY = c, where X and Y are positive numbers, and c is a preset positive coefficient. In one actual numerical example, the preset voltage-current curve 210 can be XY = 10.

[0028] In this case, since the power is the product of the voltage value and the current value, it is c. Therefore, the operation circuit 155 can calculate the required current limit value according to the preset voltage-current curve 210 based on the operating voltage VOP, generate the current limit signal ILS related to the current limit value, and ensure that the operating power of the switching transistor 120 is not greater than c.

[0029] It should be noted that the above-mentioned preset voltage-current curve is only an example. In other embodiments, other curves can also be used to achieve the purpose of making the operating power not greater than a preset value.

[0030] The digital-to-analog conversion circuit 160 is configured to digitally-to-analog convert the current limit signal ILS to generate a reference voltage VRF.

[0031] The current limit circuit 135 is configured to receive the reference voltage VRF and a feedback voltage VFE generated according to the operating current IOP feedback, and compare the two voltages and generate a control voltage VC to control the switch transistor 120 to maintain the operating current IOP at the current limit value. The feedback voltage VFE is generated by the feedback voltage generation circuit 140.

[0032] Please refer to Figure 3 . Figure 3 A circuit diagram of the switch transistor 120, the current limit circuit 135, and the feedback voltage generation circuit 140 in one embodiment of the present application is shown. The feedback voltage generation circuit 140 includes a control transistor 300, a comparator 310, and a current mirror 320.

[0033] In one 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, and the gate receives the control voltage VC. The switch transistor 120 has a control current ICP when turned on.

[0034] The comparator 310 has two input terminals and an output terminal. The two input terminals are electrically coupled to the drain of the switch transistor 120 and the drain of the control transistor 300, respectively. The output terminal is electrically coupled to the drain of the control transistor 300. The comparator 310 can make the control current ICP and the operating current IOP present a fixed ratio by comparing the drain voltages of the switch transistor 120 and the control transistor 300 through a feedback mechanism to make the two drain voltages equal. The fixed ratio is related to the channel size (e.g., width-to-length ratio) between the switch transistor 120 and the control transistor 300. In one embodiment, when the channel sizes of the switch transistor 120 and the control transistor 300 are the same, the control current ICP and the operating current IOP are the same.

[0035] The current mirror 320 has a first current output terminal and a second current output terminal, which are electrically coupled to the drain of the control transistor 300 and the output resistor RO, respectively, to mirror the control current ICP to the output resistor RO and generate the feedback voltage VFE at the second current output terminal.

[0036] In one embodiment, the current limit circuit 135 can be a comparator configured to receive the feedback voltage VFE and the reference voltage VRF for comparison to output the control voltage VC to the gates of the switch transistors 120 and the control transistor 300 according to the comparison result.

[0037] Through such feedback mechanism, the current limiting circuit 135 can adjust the size of the control voltage VC according to the comparison result of the received feedback voltage VFE and the reference voltage VRF when the operating current IOP is greater or smaller than the current limit value, change the on degree of the switch transistor 120, and then maintain the operating current IOP at the current limit value, so that the operating power of the switch transistor 120 is not greater than the preset value.

[0038] It should be noted that the architecture of the feedback voltage generating circuit 140 described above is only an example. In other embodiments, other architectures can also be used to achieve the purpose of generating the feedback voltage VFE according to the operating current IOP.

[0039] In some technologies, the power limiting mechanism of the switch transistor is performed by a completely analog comparator. On the one hand, the accuracy and consistency between the voltage value and the current limit value cannot be accurately controlled. On the other hand, such a way can only be linearly adjusted. When the current of the switch transistor is too large to limit the current, in order to reduce the on degree of the switch transistor, the on resistance of the switch transistor will instead rise, and thus the power cannot be reduced. It is difficult to achieve true power limiting by elastically selecting a suitable curve to control the power.

[0040] The power supply device of the present application can control the on state of the switch transistor by converting the operating voltage into a digital form, generating a current limit signal according to a preset voltage and current curve, such as a curve in which the current is inversely proportional to the voltage, and then converting the current limit signal into an analog form to control the on state of the switch transistor so that its operating current is maintained at the current limit value, thereby achieving an accurate power limiting mechanism.

[0041] In one embodiment, the analog-to-digital conversion circuit 150 and the digital-to-analog conversion circuit 160 in the above-mentioned Figure 1 may be selectively shared with other circuits that can work with the switch transistor 120. For example, the analog-to-digital conversion circuit 150 can be shared with a temporary storage circuit (not shown in the figure) configured to temporarily store the operating voltage VOP, and this temporary storage circuit can be accessed by other circuits to perform other operations and processing according to the operating voltage VOP. The digital-to-analog conversion circuit 160 can be shared with an over current protection (OCP) circuit (not shown in the figure). Through such configuration, the power supply device 110 can make more efficient use of circuit area.

[0042] Please refer to Figure 4 . Figure 4 A flowchart of a power supply method 400 in an embodiment of the present application is shown.

[0043] In addition to the aforementioned apparatus, the present application also discloses a power supply method 400, which is applied in, for example, but not limited to Figure 1 the power supply apparatus 110. One embodiment of the power supply method 400, as shown in Figure 4 , comprises the following steps.

[0044] In step S410, the switch transistor 120 in series with the powered device 190 in the power supply apparatus 110 is controlled by the control voltage to form a path when turned on so that the power supply unit 105 provides power to the powered device 190, and the switch transistor 120 has an operating current IOP, an operating voltage VOP and an operating power when turned on.

[0045] In step S420, the voltage detection circuit 125 detects the operating voltage VOP.

[0046] In step S430, the analog-to-digital conversion circuit 150 of the power limiting circuit 130 performs analog-to-digital conversion on the operating voltage VOP.

[0047] In step S440, the operation circuit 155 of the power limiting circuit 130 generates a current limiting signal ILS related to the current limiting value according to the operating voltage VOP according to a preset voltage and current curve, wherein the preset voltage and current curve makes the operating power not greater than a preset value.

[0048] In step S450, the digital-to-analog conversion circuit 160 of the power limiting circuit 130 performs digital-to-analog conversion on the current limiting signal ILS to generate a reference voltage VRF.

[0049] In step S460, the current limiting circuit 135 receives the reference voltage VRF and a feedback voltage VFE generated according to the operating current IOP for comparison and generates a control voltage VC to control the switch transistor 120 to maintain the operating current IOP at the current limiting value.

[0050] It should be noted that the above embodiments are only examples. In other embodiments, those skilled in the art can make changes without departing from the spirit of the present application.

[0051] In summary, the power supply apparatus and method with power limiting mechanism in the present application can control the on-off state of the switch transistor by digital control, generate a current limiting signal according to the operating voltage converted into digital form according to a preset voltage and current curve, and then convert the current limiting signal into analog form to control the on-off state of the switch transistor to maintain its operating current at the current limiting value, achieving accurate power limiting mechanism.

[0052] Although the embodiments of the present application have been described above, these embodiments are not intended to limit the present application, and a person having ordinary skill in the art can make various changes to the technical features of the present application based on the disclosure or implied content of the present application, and such changes can all belong to the scope of the patent protection sought for the present application. In other words, the scope of the patent protection of the present application should be defined by the claims of the present specification.

[0053] BRIEF DESCRIPTION OF DRAWINGS

[0054] 100: power supply system

[0055] 105: power supply unit

[0056] 110: power supply device

[0057] 120: switching transistor

[0058] 125: voltage detection circuit

[0059] 130: power limit circuit

[0060] 135: current limit circuit

[0061] 140: feedback voltage generation circuit

[0062] 150: analog-to-digital conversion circuit

[0063] 155: operation circuit

[0064] 160: digital-to-analog conversion circuit

[0065] 190: power receiving device

[0066] 200, 210: preset voltage and current curve

[0067] 300: control transistor

[0068] 310: comparator

[0069] 320: current mirror

[0070] 400: power supply method

[0071] S410-S460: steps

[0072] GND: ground terminal

[0073] ICP: control current

[0074] ILS: current limit signal

[0075] IOP: operating current

[0076] RO: output resistor

[0077] VC: control voltage

[0078] VFE: feedback voltage

[0079] VOP: operating voltage

[0080] VRF: reference voltage

Claims

1. A power supply device with power limiting mechanism, comprising: a switch transistor connected in series with a load and controlled by a control voltage to form a path when turned on to allow a power supply unit to provide power to the load, wherein the switch transistor has an operating current, an operating voltage and an operating power when turned on; a voltage detection circuit configured to detect the operating voltage; a power limiting circuit, comprising: an analog-to-digital conversion circuit configured to analog-to-digital convert the operating voltage; a calculation circuit configured to generate a current limit signal related to a current limit value according to a preset voltage and current curve of the operating voltage, wherein the preset voltage and current curve makes the operating power not greater than a preset value; and a digital-to-analog conversion circuit configured to digital-to-analog convert the current limit signal to generate a reference voltage; and a current limiting circuit configured to receive the reference voltage and a feedback voltage generated according to the operating current feedback to compare and generate the control voltage to control the switch transistor to maintain the operating current at the current limit value.

2. The power supply device with power limiting mechanism of claim 1, wherein the preset voltage and current curve makes the operating voltage and the current limit value inversely proportional.

3. The power supply device with power limiting mechanism of claim 1, wherein the operating voltage is X, the current limit value is Y, the preset voltage and current curve is Y=aX+b or XY=c, wherein X and Y are positive numbers, a is a preset negative coefficient and b is a preset positive coefficient, and c is a preset positive coefficient.

4. The power supply device with power limiting mechanism of claim 1, further comprising a feedback voltage generation circuit, comprising: a control transistor having a control current when turned on; a comparator having two input terminals and an output terminal, the two input terminals are electrically coupled to the drain of the switch transistor and the drain of the control transistor respectively, and the output terminal is electrically coupled to the drain of the control transistor to make the control current and the operating current in a fixed proportion; and a current mirror having a first current output terminal and a second current output terminal electrically coupled to the drain of the control transistor and an output resistor respectively to mirror the control current to the output resistor and generate the feedback voltage at the second current output terminal.

5. The power supply device with power limiting mechanism of claim 4, wherein the current limiting circuit receives the feedback voltage and the reference voltage to compare and output the control voltage to the gate of each of the switch transistor and the control transistor.

6. A power supply method with power limiting mechanism applied to a power supply device, comprising: controlling a switch transistor connected in series with a load by a control voltage to form a path when turned on to allow a power supply unit to provide power to the load, wherein the switch transistor has an operating current, an operating voltage and an operating power when turned on; ​ detecting the operating voltage by a voltage detecting circuit; analog-to-digital converting the operating voltage by an analog-to-digital converting circuit of a power limiting circuit; generating a current limit signal related to a current limit value according to a preset voltage and current curve of the operating voltage by an operation circuit of the power limiting circuit, wherein the preset voltage and current curve makes the operating power not greater than a preset value; digital-to-analog converting the current limit signal by a digital-to-analog converting circuit of the power limiting circuit to generate a reference voltage; and comparing the reference voltage and a feedback voltage generated according to the operating current feedback by a current limiting circuit and generating the control voltage to control the switch transistor to maintain the operating current at the current limit value.

7. The power supply method with power limiting mechanism as claimed in claim 6, wherein the preset voltage and current curve makes the operating voltage and the current limit value inversely proportional.

8. The power supply method with power limiting mechanism as claimed in claim 6, wherein the operating voltage is X, the current limit value is Y, the preset voltage and current curve is Y=aX+b or XY=c, wherein X and Y are positive numbers, a is a preset negative coefficient, b is a preset positive coefficient, and c is a preset positive coefficient.

9. The power supply method with power limiting mechanism as claimed in claim 6, further comprising: making a control transistor of a feedback voltage generating circuit have a control current when turned on; electrically coupling two input terminals of a comparator of the feedback voltage generating circuit to a drain of the switch transistor and a drain of the control transistor respectively, and electrically coupling an output terminal of the comparator to the drain of the control transistor, so that the control current is in a fixed proportion to the operating current; electrically coupling a first current output terminal and a second current output terminal of a current mirror of the feedback voltage generating circuit to the drain of the control transistor and an output resistor respectively, so as to mirror the control current to the output resistor and generate the feedback voltage at the second current output terminal.

10. The power supply method with power limiting mechanism as claimed in claim 9, further comprising: making the current limiting circuit compare the feedback voltage and the reference voltage to output the control voltage to the gate of each of the switch transistor and the control transistor.

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