Power supply circuit

Abstract

A power supply circuit adapted to an electronic device is provided. The power supply circuit includes a first power interface terminal, a system power terminal, a first switch circuit, a first sense resistor, a second power interface terminal, a buck-boost circuit, a second switch circuit, a battery interface terminal, and a second sense resistor and a third switch circuit. The first sense resistor and the first switch circuit are connected in series between the first power interface terminal and the system power terminal. The buck-boost circuit is coupled between the second power interface terminal and a first node. The second switch circuit is coupled between the first node and a second node. The second sense resistor is coupled between the second node and the battery interface terminal. The third switch circuit is coupled between the system power terminal and the first node.

Description

Technical Field

[0001] This invention relates to a power supply circuit capable of accurately controlling a battery. Prior Technology

[0002] Traditionally, paralleling hybrid charger architectures with narrow voltage direct current (NVDC) charger architectures can lead to inherent circulating current issues. This can affect the voltage across the sensing resistor at the NVDC charger terminal, distorting the fed-back current parameters. Consequently, it becomes difficult to accurately measure battery charging energy and control the charging current, resulting in longer charging times and a negative impact on the user experience. Summary of the Invention

[0003] This invention provides a power supply circuit suitable for electronic devices. The power supply circuit includes a first power interface terminal, a system power terminal, a first switching circuit, a first sensing resistor, a second power interface terminal, a buck-boost circuit, a second switching circuit, a battery interface terminal, a second sensing resistor, and a third switching circuit. The first power interface terminal is configured to receive a first power supply voltage. The first switching circuit is coupled between the first power interface terminal and the system power terminal. The first sensing resistor and the first switching circuit are connected in series between the first power interface terminal and the system power terminal. The second power interface terminal is configured to receive a second power supply voltage. The buck-boost circuit is coupled between the second power interface terminal and a first node. The second switching circuit is coupled between the first node and the second node. The battery interface terminal is configured to receive a battery voltage. The second sensing resistor is coupled between the second node and the battery interface terminal. The third switching circuit is coupled between the system power terminal and the first node.

[0004] Based on the above, the power supply circuit in this case can solve the inherent circulating current problem. This allows for accurate battery control, preventing excessively long charging times and providing a better user experience.

[0005] To make the above-mentioned features and advantages of this case more apparent and understandable, specific embodiments are provided below, along with detailed descriptions in conjunction with the accompanying drawings. Simple Explanation of the Diagram

[0006] Figure 1 is a block diagram of a power supply circuit according to an embodiment of the present invention. Figure 2 is a circuit diagram of a power supply circuit according to an embodiment of the present invention. Figures 3A and 3F are schematic diagrams illustrating the operation of a power supply circuit according to an embodiment of the present invention. Implementation

[0007] Please refer to Figures 1 and 2 simultaneously. The power supply circuit 100 of this embodiment is applicable to electronic devices such as notebook computers, mobile phones, and tablet computers. The power supply circuit 100 can be regarded as a circuit architecture formed by connecting a hybrid charger architecture and a narrow voltage DC charger architecture in parallel. It includes a first power interface terminal TADP, a system power terminal TSYS, a first switching circuit 110, a first sensing resistor 112, a second power interface terminal TPADP, a buck-boost circuit 114, a second switching circuit 116, a battery interface terminal TBAT, a second sensing resistor 118, a third switching circuit 120, a buck circuit 122, and a control circuit 124.

[0008] The first power interface terminal TADP is for connection to a first power adapter, such as an AC adapter. The first power interface terminal TADP is used to receive a first power supply voltage Vps1 (e.g., 20 volts) from the first power adapter.

[0009] The system power supply terminal TSYS can be used to transmit the received power supply voltage, for example via a voltage regulator, to the central processing unit (CPU), graphics processing unit (GPU), and other various system components on the motherboard, and to transmit the unused remaining power supply voltage Vrps to the buck circuit 122.

[0010] The first switching circuit 110 is coupled between the first power interface terminal TADP and the system power terminal TSYS. The first sensing resistor 112 is connected in series with the first switching circuit 110 between the first power interface terminal TADP and the system power terminal TSYS. As shown in FIG2, the first switching circuit 110 includes two first switches SW1_1 and SW1_2 connected in series and two first diodes D1_1 and D1_2 connected in parallel with the first switches SW1_1 and SW1_2, respectively. The anodes of the two first diodes D1_1 and D1_2 are coupled to each other, the cathode of the first diode D1_1 is coupled to the first power interface terminal TADP, and the cathode of the first diode D1_2 is coupled to the first sensing resistor 112. The voltage across the first sensing resistor 112 can be used, for example, by a portion of the Hybrid charger chip in the control circuit 124 to detect the current parameter value flowing through the first sensing resistor 112.

[0011] The second power interface terminal TPADP allows connection to a second power adapter, such as a PD adapter (powered via USB Type-C PD). The second power interface terminal TPADP is used to receive a second power supply voltage Vps2 (e.g., 5~20 volts) from the second power adapter.

[0012] The buck-boost circuit 114 is coupled between the second power interface terminal TPADP and the first node N1. In this embodiment, the buck-boost circuit 114 operates depending on whether the second power supply voltage Vps2 is supplied to the second power interface terminal TPADP. For example, when the second power supply voltage Vps2 is supplied to the second power interface terminal TPADP, the buck-boost circuit 114 will be turned on, and will boost or buck the received second power supply voltage Vps2 and output it. When the second power supply voltage Vps2 is not supplied to the second power interface terminal TPADP, the buck-boost circuit 114 will be turned off.

[0013] The second switching circuit 116 is coupled between the first node N1 and the second node N2. As shown in Figure 2, the second switching circuit 116 includes a second switch SW2 and a second diode D2 connected in parallel with the second switch SW2. The anode of the second diode D2 is coupled to the second node N2, and the cathode of the second diode D2 is coupled to the first node N1.

[0014] When the battery BAT is installed in an electronic device, the battery interface terminal TBAT is coupled to the battery BAT and is used to receive the battery voltage Vbat (e.g., 12~16 volts) from the battery BAT.

[0015] The second sensing resistor 118 is coupled between the second node N2 and the battery interface terminal TBAT. The voltage across the second sensing resistor 118 can be used, for example, by a portion of the NVDC charger chip in the control circuit 124 to detect the current parameter value flowing through the second sensing resistor 118 (equivalent to the charging current of the battery BAT). Incidentally, in this embodiment, only one sensing resistor is used for the NVDC charger chip, which achieves optimization by reducing the total number of components.

[0016] The third switching circuit 120 is coupled between the system power supply terminal TSYS and the first node N1. As shown in Figure 2, the third switching circuit 120 includes a third switch SW3 and a third diode D3 connected in parallel with the third switch SW3. The anode of the third diode D3 is coupled to the first node N1, and the cathode of the third diode D3 is coupled to the system power supply terminal TSYS.

[0017] The step-down circuit 122 is coupled between the system power supply terminal TSYS and the second node N2. In this embodiment, the step-down circuit 122 operates depending on whether the battery BAT, which provides the battery voltage Vbat to the battery interface terminal TBAT, has a charging requirement. For example, when the battery BAT has a charging requirement, the step-down circuit 122 will conduct, step down the received power supply voltage Vrps, and output it. When the battery BAT does not have a charging requirement, the step-down circuit 122 will be turned off.

[0018] The control circuit 124 can be implemented, for example, using multiple independent charger chips (including a hybrid charger chip and an NVDC charger chip) and logic circuits designed by those skilled in the art. The information it uses may come from an embedded controller (EC), a battery gauge IC, and the system. The control circuit 124 can provide a first control signal Sc1, a second control signal Sc2, and a third control signal Sc3 to the first switch circuit 110, the second switch circuit 116, and the third switch circuit 120, respectively, based on the power connection status of the first power interface terminal TADP, the second power interface terminal TPADP, and the battery interface terminal TBAT. Accordingly, the first switch SW1_1 and SW1_2 in the first switch circuit 110, the second switch SW2 in the second switch circuit 116, and the third switch SW3 in the third switch circuit 120 are turned on or off (disconnected).

[0019] It should be noted that, since the system power supply terminal TSYS and the second node N2 are not connected through any switch in the power supply circuit 100 of this embodiment, the inherent circulating current problem can be solved compared with the conventional circuit architecture.

[0020] The following examples illustrate the operational details of the power supply circuit 100. Table 1 lists the eight operational configurations of the power supply circuit 100. In Table 1, a "0" for the first power interface terminal TADP and the second power interface terminal TPADP indicates no voltage input, while a "1" for both terminals indicates voltage input (Vps1 or Vps2). A "0" for the battery interface terminal TBAT indicates no voltage input from the battery BAT (equivalent to no voltage output to the system, including situations where the battery BAT is in a dead battery state or has been removed), while a "1" for the battery interface terminal TBAT indicates voltage input (Vbat) from the battery BAT (equivalent to voltage output to the system). When the first switching circuit 110, the second switching circuit 116, and the third switching circuit 120 are "ON", it means that the switches (SW1_1, SW1_2, SW2, or SW3) in the switching circuit are turned on. When the first switching circuit 110, the second switching circuit 116, and the third switching circuit 120 are "OFF", it means that the switches (SW1_1, SW1_2, SW2, or SW3) in the switching circuit are turned off. Operation configuration TADP TPADP TBAT 110 116 120 1 0 0 0 OFF OFF OFF 2 0 0 1 OFF ON ON 3 0 1 0 OFF ON: Battery Activation OFF: Battery not activated ON 4 0 1 1 OFF ON: Charging required. OFF: No charging required ON 5 1 0 0 ON ON: Battery Activation OFF: Battery not activated OFF 6 1 0 1 ON ON OFF 7 1 1 0 ON ON: Battery Activation OFF: Battery not activated OFF 8 1 1 1 ON OFF OFF Table 1

[0021] When no voltage is supplied to the first power interface terminal TADP, the second power interface terminal TPADP, and the battery interface terminal TBAT (i.e., operation configuration 1, TADP / TPADP / TBAT=0 / 0 / 0), the first switches SW1_1 and SW1_2 in the first switch circuit 110, the second switch SW2 in the second switch circuit 116, and the third switch SW3 in the third switch circuit 120 are turned off. At this time, no switches are conducting and the system has no power.

[0022] When no voltage is supplied to the first power interface terminal TADP and the second power interface terminal TPADP, and the battery voltage Vbat is supplied to the battery interface terminal TBAT (i.e., operation configuration 2, TADP / TPADP / TBAT=0 / 0 / 1), the first switches SW1_1 and SW1_2 in the first switching circuit 110 are turned off, and the second switch SW2 in the second switching circuit 116 and the third switch SW3 in the third switching circuit 120 are turned on. Specifically, as shown in Figure 3A, at this time only the battery voltage Vbat is supplied to the battery interface terminal TBAT. The Hybrid charger chip in the control circuit 124 is recognized as DC mode, so the first switches SW1_1 and SW1_2 in the first switching circuit 110 are turned off, so the buck circuit 122 does not operate (is turned off). The NVDC charger chip in the control circuit 124 is also recognized as DC mode, so the second switch SW2 in the second switching circuit 116 is turned on, so the buck-boost circuit 114 does not operate. The third switch SW3 in the third switching circuit 120 is turned on because no voltage is supplied to the first power interface terminal TADP. In this case, the energy of the system power terminal TSYS is supplied by the battery BAT, as shown in path R1, and the energy is transferred to the system power terminal TSYS via the battery interface terminal TBAT, the second switching circuit 116 and the third switching circuit 120.

[0023] When no voltage is supplied to the first power interface terminal TADP and the battery interface terminal TBAT, and the second power supply voltage Vps2 is supplied to the second power interface terminal TPADP (i.e., operation configuration 3, TADP / TPADP / TBAT=0 / 1 / 0), the first switches SW1_1 and SW1_2 in the first switching circuit 110 are turned off, and the third switch SW3 in the third switching circuit 120 is turned on. The second switch SW2 in the second switching circuit 116 continuously switches between on and off for a predetermined period of time. Specifically, as shown in Figure 3B, at this time only the second power supply voltage Vps2 is supplied to the second power interface terminal TPADP, and the Hybrid charger chip in the control circuit 124 partially recognizes it as DC mode, so the first switches SW1_1 and SW1_2 in the first switching circuit 110 are turned off, so the buck circuit 122 does not operate. In the control circuit 124, the NVDC charger chip is partially in AC mode, and since there is no voltage input from the battery BAT, the NVDC charger chip enters trickle charging mode and continuously switches the second switch SW2 in the second switching circuit 116 between on and off to attempt to charge the battery BAT with a low current to remove it from the depleted battery state. If a battery voltage Vbat is supplied to the battery interface TBAT within a predetermined time, the second switch SW2 in the second switching circuit 116 is turned on. If no battery voltage Vbat is supplied to the battery interface TBAT after the predetermined time, the second switch SW2 in the second switching circuit 116 remains off. In other words, the switching state of the second switching circuit 116 depends on whether the battery BAT can be activated by charging energy.

[0024] The third switch SW3 in the third switching circuit 120 is turned on because no voltage is supplied to the first power interface terminal TADP. In this case, the energy of the system power terminal TSYS is supplied by the second power supply voltage Vps2, and as shown in path R2, the energy is transferred to the system power terminal TSYS via the second power interface terminal TPADP and the third switching circuit 120. In addition, path R3 represents the energy path that attempts to activate the battery BAT.

[0025] When no voltage is supplied to the first power interface terminal TADP, and the second power supply voltage Vps2 is supplied to the second power interface terminal TPADP, and the battery voltage Vbat is supplied to the battery interface terminal TBAT (i.e., operation configuration 4, TADP / TPADP / TBAT=0 / 1 / 1), the first switches SW1_1 and SW1_2 in the first switching circuit 110 are turned off, the third switch SW3 in the third switching circuit 120 is turned on, and the second switch SW2 in the second switching circuit 116 is turned on or off depending on whether the battery BAT, which supplies the battery voltage Vbat to the battery interface terminal TBAT, has a charging requirement. Specifically, as shown in Figure 3C, at this time, the second power supply voltage Vps2 is supplied to the second power interface terminal TPADP, and the battery voltage Vbat is also supplied to the battery interface terminal TBAT. The Hybrid charger chip in the control circuit 124 is partially recognized as DC mode, so the first switches SW1_1 and SW1_2 in the first switching circuit 110 are turned off, so that the buck circuit 122 does not operate. The NVDC charger chip in control circuit 124 is partially recognized as AC mode, and the battery voltage Vbat is normally input from battery BAT. Therefore, the second switch circuit 116 is controlled according to whether battery BAT has a charging demand. If there is a charging demand, the second switch SW2 in the second switch circuit 116 is turned on; if there is no charging demand, the second switch SW2 in the second switch circuit 116 is turned off.

[0026] The third switch SW3 in the third switching circuit 120 is turned on because no voltage is supplied to the first power interface terminal TADP. In this case, similar to operation configuration 3, the energy of the system power terminal TSYS is supplied by the second power supply voltage Vps2. As shown in path R2, the energy is transferred to the system power terminal TSYS via the second power interface terminal TPADP and the third switching circuit 120. In addition, path R4 represents the energy path when the battery BAT has a charging requirement.

[0027] When the first power supply voltage Vps1 is supplied to the first power interface terminal TADP, and no voltage is supplied to the second power interface terminal TPADP and the battery interface terminal TBAT (i.e., operation configuration 5, TADP / TPADP / TBAT=1 / 0 / 0), the first switches SW1_1 and SW1_2 in the first switch circuit 110 are turned on, the third switch SW3 in the third switch circuit 120 is turned off, and the second switch SW2 in the second switch circuit 116 is turned on or off depending on whether the battery BAT used to supply the battery voltage Vbat to the battery interface terminal TBAT is activated. Specifically, as shown in Figure 3D, at this time only the first power supply voltage Vps1 is supplied to the battery interface terminal TBAT. The Hybrid charger chip in the control circuit 124 is partially recognized as being in AC mode, so the first switches SW1_1 and SW1_2 in the first switch circuit 110 are turned on. Since there is no voltage input from the battery BAT, the step-down circuit 122 is activated, and the Hybrid charger chip enters trickle charging mode to attempt to charge the battery BAT with a low current to remove it from the depleted battery state until a predetermined time has elapsed.

[0028] If battery voltage Vbat is supplied to the battery interface TBAT within the predetermined time period, the NVDC charger chip in control circuit 124 partially recognizes DC mode, thus turning on the second switch SW2 in the second switch circuit 116 (but its current path will not be established), and preventing the buck-boost circuit 114 from operating. If battery voltage Vbat is not supplied to the battery interface TBAT after the predetermined time period, the NVDC charger chip in control circuit 124 partially recognizes no power, thus turning off the second switch SW2 in the second switch circuit 116, and preventing the buck-boost circuit 114 from operating.

[0029] The third switch SW3 in the third switching circuit 120 is turned off because the first power supply voltage Vps1 is supplied to the first power interface terminal TADP. In this case, the energy of the system power terminal TSYS is supplied by the first power supply voltage Vps1, and as shown in path R5, the energy is transferred to the system power terminal TSYS via the first power interface terminal TADP and the first switching circuit 110. In addition, path R6 represents the energy path that attempts to activate the battery BAT.

[0030] When the first power supply voltage Vps1 is supplied to the first power interface terminal TADP, the battery voltage Vbat is supplied to the battery interface terminal TBAT, and no voltage is supplied to the second power interface terminal TPADP (i.e., operation configuration 6, TADP / TPADP / TBAT=1 / 0 / 1), the first switches SW1_1 and SW1_2 in the first switching circuit 110 and the second switch SW2 in the second switching circuit 116 are turned on, and the third switch SW3 in the third switching circuit 120 is turned off. Specifically, as shown in Figure 3E, at this time, the first power supply voltage Vps1 is supplied to the first power interface terminal TADP, and the battery voltage Vbat is also supplied to the battery interface terminal TBAT. The Hybrid charger chip in the control circuit 124 is partially recognized as AC mode, so the first switches SW1_1 and SW1_2 in the first switching circuit 110 are turned on, and the battery voltage Vbat is normally input from the battery BAT. Therefore, the buck circuit 122 operates depending on whether the battery BAT, which supplies the battery voltage Vbat to the battery interface terminal TBAT, has a charging requirement. If battery BAT requires charging, buck circuit 122 is turned on, and the power supply voltage Vrps received from the system power supply terminal TSYS is stepped down and output. If battery BAT does not require charging, buck circuit 122 is turned off.

[0031] The third switch SW3 in the third switching circuit 120 is turned off because the first power supply voltage Vps1 is supplied to the first power interface terminal TADP. In this case, similar to operation configuration 5, the energy of the system power terminal TSYS is supplied by the first power supply voltage Vps1. As shown in path R5, the energy is transferred to the system power terminal TSYS via the first power interface terminal TADP and the first switching circuit 110. In addition, path R7 represents the energy path when the battery BAT has a charging requirement.

[0032] When the first power supply voltage Vps1 is supplied to the first power interface terminal TADP and the second power supply voltage Vps2 is supplied to the second power interface terminal TPADP (i.e., operation configurations 7 and 8, TADP / TPADP / TBAT=1 / 1 / 0, 1 / 1 / 1), regardless of whether the battery voltage Vbat is supplied to the battery interface terminal TBAT, the second power supply voltage Vps2 will be removed from the second power interface terminal TPADP through circuit design. Therefore, the operation details of operation configuration 7 are the same as those of operation configuration 5, and the operation details of operation configuration 8 are the same as those of operation configuration 6, and will not be repeated here.

[0033] In addition, the above eight operation configurations are for the steady-state part, but special attention needs to be paid to the timing of the transfer of control in the transient part. Since the control weight of the first power supply voltage Vps1 is higher than that of the second power supply voltage Vps2 and the battery voltage Vbat, regardless of the original system state, as long as the first power adapter providing the first power supply voltage Vps1 is plugged into the first power interface terminal TADP, the transfer of control will occur. At this time, it is important to note that the third switch SW3 in the third switch circuit 120 must be turned off before the first switches SW1_1 and SW1_2 in the first switch circuit 110 are turned on, otherwise a voltage conflict (short circuit) problem will occur.

[0034] For example, when the second power supply voltage Vps2 is supplied to the second power interface terminal TPADP, the energy of the system power terminal TSYS is supplied by the second power supply voltage Vps2, as shown in Figure 3F. The energy is transferred to the system power terminal TSYS via the second power interface terminal TPADP and the third switching circuit 120. At this time, if the first power supply voltage Vps1 is supplied to the first power interface terminal TPADP, the third switch SW3 in the third switching circuit 120 is turned off before the first switches SW1_1 and SW1_2 in the first switching circuit 110 are turned on, so as to avoid the first power supply voltage Vps1 and the second power supply voltage Vps2 from conflicting at the system power terminal TSYS.

[0035] Furthermore, during the brief period when the third switch SW3 in the third switching circuit 120 is off but the first switches SW1_1 and SW1_2 in the first switching circuit 110 are not yet on, as shown in path R8, the second power supply voltage Vps2 will still supply energy to the system power supply terminal TSYS through the third diode D3 in the third switching circuit 120. Only after the first switches SW1_1 and SW1_2 in the first switching circuit 110 are on will the second power supply voltage Vps2 be removed from the second power interface terminal TPADP.

[0036] On the other hand, when the second power supply voltage Vps2 was originally supplied to the second power interface terminal TPADP and the battery voltage Vbat was supplied to the battery interface terminal TBAT, the second power adapter supplying the second power supply voltage Vps2 was suddenly disconnected from the second power interface terminal TPADP. At this time, as shown in path R9, although the second switch SW2 in the second switching circuit 116 does not turn on so quickly, the battery BAT can immediately supply energy to the system power terminal TSYS with the help of the second diode D2.

[0037] In summary, the power supply circuit of this invention can solve the inherent circulating current problem and reduces the sensing resistor used in the NVDC charger chip to a single resistor. This allows for accurate battery control, preventing excessively long charging times and optimizing the overall component count.

[0038] 100: Power supply circuit 110: First switching circuit 112: First sensing resistor 114: Buck-boost circuit 116: Second Switching Circuit 118: Second sensing resistor 120: Third Switching Circuit 122: Step-down circuit 124: Control Circuit BAT: Battery D1_1, D1_2: First Dipolar Body D2: Second Dipolar Body D3: Third Dipolar Body N1: First node N2: Second node Paths R1~R9 Sc1: First control signal Sc2: Second control signal Sc3: Third control signal SW1_1, SW1_2: First switches SW2: Second switch SW3: Third switch TADP: First power interface terminal TBAT: Battery Interface TPADP: Second Power Interface Terminal TSYS: System power supply terminal Vbat: Battery voltage Vps1: First power supply voltage Vps2: Second power supply voltage Vrps: Power supply voltage

Claims

1. A power supply circuit suitable for an electronic device, the power supply circuit comprising: A first power interface terminal, configured to receive a first power supply voltage; A system power supply terminal; A first switching circuit is coupled between the first power interface terminal and the system power terminal; a first sensing resistor is connected in series with the first switching circuit between the first power interface terminal and the system power terminal; a second power interface terminal is configured to receive a second power supply voltage; a buck-boost circuit is coupled between the second power interface terminal and a first node; a second switching circuit is coupled between the first node and a second node; a battery interface terminal is configured to receive a battery voltage; a second sensing resistor is coupled between the second node and the battery interface terminal; and a third switching circuit is coupled between the system power terminal and the first node.

2. The power supply circuit as described in claim 1, further comprising: A step-down circuit is coupled between the power supply terminal of the system and the second node.

3. The power supply circuit as described in claim 1, further comprising: A control circuit is configured to provide a first control signal, a second control signal, and a third control signal to a first switch circuit, a second switch circuit, and a third switch circuit respectively, based on a power connection state of the first power interface terminal, the second power interface terminal, and the battery interface terminal, thereby turning the first switch circuit, the second switch circuit, and the third switch circuit on or off.

4. The power supply circuit as claimed in claim 1, wherein the buck-boost circuit operates depending on whether the second power supply voltage is supplied to the second power interface terminal.

5. The power supply circuit as claimed in claim 1, wherein the first switching circuit, the second switching circuit, and the third switching circuit are turned off when no voltage is supplied to the first power interface terminal, the second power interface terminal, and the battery interface terminal.

6. The power supply circuit as claimed in claim 1, wherein when no voltage is supplied to the first power interface terminal and the second power interface terminal, and the battery voltage is supplied to the battery interface terminal, the first switching circuit is turned off, and the second switching circuit and the third switching circuit are turned on.

7. The power supply circuit as claimed in claim 1, wherein when no voltage is supplied to the first power interface terminal and the battery interface terminal, and the second power supply voltage is supplied to the second power interface terminal, the first switching circuit is turned off, the third switching circuit is turned on, and the second switching circuit continuously switches between on and off for a predetermined period of time.

8. The power supply circuit as claimed in claim 7, wherein if no battery voltage is supplied to the battery interface after the predetermined time has elapsed, the second switching circuit remains off.

9. The power supply circuit as claimed in claim 1, wherein when no voltage is supplied to the first power interface terminal, and the second power supply voltage is supplied to the second power interface terminal, and the battery voltage is supplied to the battery interface terminal, the first switching circuit is turned off, the third switching circuit is turned on, and the second switching circuit is turned on or off depending on whether a battery supplying the battery voltage to the battery interface terminal has a charging requirement.

10. The power supply circuit as claimed in claim 2, wherein when the first power supply voltage is supplied to the first power interface terminal and no voltage is supplied to the second power interface terminal and the battery interface terminal, the first switching circuit is turned on and the third switching circuit is turned off, and the second switching circuit is turned on or off depending on whether a battery used to supply the battery voltage to the battery interface terminal is activated.

11. The power supply circuit as claimed in claim 2, wherein when the first power supply voltage is supplied to the first power interface terminal, the battery voltage is supplied to the battery interface terminal, and no voltage is supplied to the second power interface terminal, the first switching circuit and the second switching circuit are turned on, and the third switching circuit is turned off.

12. The power supply circuit as claimed in claim 11, wherein the step-down circuit operates depending on whether a battery supplying the battery voltage to the battery interface terminal has a charging requirement.

13. The power supply circuit as claimed in claim 1, wherein when the first power supply voltage is supplied to the first power interface terminal and the second power supply voltage is supplied to the second power interface terminal, the second power supply voltage is removed from the second power interface terminal.

14. The power supply circuit as claimed in claim 1, wherein when the second power supply voltage is supplied to the second power supply interface, if the first power supply voltage is supplied to the first power supply interface, the third switching circuit is turned off before the first switching circuit is turned on.

15. The power supply circuit as claimed in claim 14, wherein the second power supply voltage is removed from the second power interface terminal after the first switching circuit is turned on.

16. The power supply circuit as claimed in claim 1, wherein the first switching circuit includes two first switches connected in series and two first diodes connected in parallel with the two first switches, the anodes of the two first diodes being coupled to each other, the cathode of one of the two first diodes being coupled to the first power interface terminal, and the cathode of the other of the two first diodes being coupled to the first sensing resistor.

17. The power supply circuit as claimed in claim 1, wherein the second switching circuit includes a second switch and a second diode connected in parallel with the second switch, the anode of the second diode being coupled to the second node and the cathode of the second diode being coupled to the first node.

18. The power supply circuit as claimed in claim 1, wherein the third switching circuit includes a third switch and a third diode connected in parallel with the third switch, the anode of the third diode being coupled to the first node and the cathode of the third diode being coupled to the system power supply terminal.

19. The power supply circuit as claimed in claim 1, wherein the first power interface receives the first power supply voltage from a first power adapter, the second power interface receives the second power supply voltage from a second power adapter, and the battery interface receives the battery voltage from a battery.

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