Power supply circuit, DALI module, lighting device and control method

Abstract

A power supply circuit, a digital addressable lighting interface (DALI) module, a lighting device, and a control method are disclosed. The power supply circuit includes: a power supply circuit (100); an regulating transistor (Q161) configured to be connected between the power supply circuit and a first output port (DA+); a first controller (U160) configured to control the regulating transistor (Q161) to be turned on or off; and a current regulating controller (A) configured to be connected between the power supply circuit and a second output port (DA-), the current regulating controller (A) also being connected between the regulating transistor (Q161) and the first controller (U160), wherein when the current at the second output port (DA-) is greater than a preset value, the current regulating controller (A) reduces the current flowing through the regulating transistor (Q161).

Description

Technical Field

[0001] The embodiments disclosed herein relate generally to the field of lighting, and more specifically to power supply circuits, DALI (Digital Addressable Lighting Interface) modules, lighting equipment, and control methods. Background Technology

[0002] This section provides information to aid in a better understanding of aspects of this disclosure. Therefore, the statements in this section should be read in this light and should not be construed as an admission of anything that is in the prior art or not in the prior art.

[0003] DALI (Digital Addressable Lighting Interface) is a data transmission protocol that defines a digital communication method between lighting fixtures and controllers. A DALI system is an intelligent lighting control system that can be used not only for room lighting control but also for connecting to a building management system (BMS). The most important feature of a DALI system is that each lighting fixture has an independent address, and precise dimming of the fixtures can be achieved through the DALI system. These lighting fixtures are, for example, LEDs (Light Emitting Diodes).

[0004] The DALI circuitry provides a DALI communication bus, which may include a data bus and a power bus. Lighting fixtures and peripheral devices can be connected to the communication bus. Summary of the Invention

[0005] A DALI circuit employing a 50mA constant current source can drive more peripheral devices on the DALI communication bus, thus making the DALI lighting system more powerful. Peripheral devices can include dimmers, sensors, controllers, safety devices, etc.

[0006] The DALI circuit may include an NTC (negative temperature coefficient) resistor, which is used to compensate for the temperature drift of the PN junction in the DALI circuit, so that a constant current can be obtained during the operation of the DALI circuit.

[0007] The inventors discovered that in DALI circuits, NTC resistors always struggle to compensate for the temperature drift of the PN junction, resulting in low accuracy of the current output by the DALI circuit.

[0008] Typically, embodiments of this disclosure provide a power supply circuit, a DALI (Digital Addressable Lighting Interface) circuit, a lighting device, and a control method. In the above embodiments, a current regulation controller is provided in the power supply circuit, which reduces the current flowing through the regulating transistor (Q161) when the current at the second output port (DA-) exceeds a preset value. Therefore, higher current accuracy can be obtained.

[0009] In a first aspect, a power supply circuit is provided, the power supply circuit comprising:

[0010] Power supply circuit (100);

[0011] A regulating transistor (Q161) is configured to be connected between the power supply circuit and the first output port (DA+);

[0012] A first controller (U160) is configured to control the adjustment transistor (Q161) to be turned on or off; and

[0013] A current regulator (A) is configured to be connected between the power supply circuit and the second output port (DA-), and the current regulator (A) is also connected between the regulating transistor (Q161) and the first controller (U160).

[0014] When the current at the second output port (DA-) is greater than a preset value, the current regulation controller (A) reduces the current flowing through the regulation transistor (Q161).

[0015] According to one embodiment, the current regulating controller (A) includes:

[0016] A first resistor (R162) is configured to be connected between the control terminal of the regulating transistor (Q161) and the first controller (U160);

[0017] A first transistor (Q160) is configured to be connected between the power supply circuit and the control terminal of the regulating transistor (Q161);

[0018] Voltage reference circuit (U1);

[0019] The second resistor (R164); and

[0020] The third resistor (R170),

[0021] The voltage reference circuit (U1), the second resistor (R164), and the third resistor (R170) are connected in series between the power supply circuit and the ground terminal.

[0022] The control terminal of the first transistor (Q160) is connected to the connection node of the second resistor (R164) and the third resistor (R170).

[0023] The anode of the voltage reference circuit (U1) is connected to the ground terminal.

[0024] The cathode of the voltage reference circuit (U1) is connected to the third resistor (R170).

[0025] The reference terminal of the voltage reference circuit (U1) receives the voltage corresponding to the current of the second output port (DA-).

[0026] According to one embodiment, the current regulating controller (A) further includes:

[0027] The fourth resistor (R174) and the first capacitor (C161),

[0028] The fourth resistor (R174) and the first capacitor (C161) are connected in series between the power supply circuit and the reference terminal of the voltage reference circuit (U1).

[0029] According to one implementation scheme, the power supply circuit also includes:

[0030] A current stage selection circuit (B) is configured to be connected between the first output port (DA+) and the second output port (DA-).

[0031] The current stage selection circuit (B) includes:

[0032] Fifth resistor (R171);

[0033] The sixth resistor (R168); and

[0034] The second transistor (Q162),

[0035] The fifth resistor (R171) and the sixth resistor (R168) are connected in series between the second output port (DA-) and the ground terminal.

[0036] The second transistor (Q162) is connected in parallel with the sixth resistor (R168).

[0037] According to one implementation, the second transistor (Q162) is disconnected when the first output port (DA+) is short-circuited to the second output port (DA-).

[0038] According to one implementation, the current stage selection circuit (B) further includes:

[0039] The seventh resistor (R161);

[0040] The eighth resistor (R163); and

[0041] Ninth resistor (R172),

[0042] The seventh resistor (R161), the eighth resistor (R163), and the ninth resistor (R172) are connected in series between the first output port (DA+) and the ground terminal.

[0043] The control terminal of the second transistor (Q162) is connected to the connection node of the eighth resistor (R163) and the ninth resistor (R172).

[0044] In a second aspect, a Digital Addressable Lighting Interface (DALI) module is provided, the DALI module including a DALI interface circuit and a power supply circuit according to the first aspect, the power supply circuit providing power to the DALI interface circuit and peripheral devices via a DALI communication bus.

[0045] In a third aspect, a lighting device is provided, the lighting device including a lighting apparatus, a digitally addressable lighting interface (DALI) module according to the second aspect, and a driver, the DALI circuit controlling the driver to drive the lighting device.

[0046] In a fourth aspect, a control method for a power supply circuit according to the first aspect is provided, the control method comprising:

[0047] When the current at the second output port (DA-) is greater than a preset value, the current regulation controller (A) reduces the current flowing through the regulation transistor (Q161).

[0048] According to one implementation scheme, the method further includes:

[0049] When the first output port (DA+) is short-circuited to the second output port (DA-), the second transistor (Q162) is turned off.

[0050] According to various embodiments of this disclosure, a current regulating controller is provided in the power supply circuit. When the current at the second output port (DA-) exceeds a preset value, the current regulating controller reduces the current flowing through the regulating transistor (Q161). Therefore, higher precision current can be obtained. Attached Figure Description

[0051] The above and other aspects, features, and benefits of various embodiments of the present disclosure will become more apparent by way of example and through the following detailed description with reference to the accompanying drawings, wherein similar reference numerals or letters are used to denote similar or equivalent elements. The drawings are shown for the purpose of better understanding embodiments of the present disclosure and are not necessarily drawn to scale, wherein:

[0052] Figure 1 This is a diagram of a power supply circuit according to a first aspect of the embodiments of this disclosure;

[0053] Figure 2 This is a diagram showing the current output of the power supply circuit before and after a short circuit at the DALI interface.

[0054] Figure 3This is a flowchart of the control method for the power supply circuit 10;

[0055] Figure 4 This is a diagram of the DALI module, which is the third aspect of the implementation plan;

[0056] Figure 5 This is a diagram of the lighting equipment for the fourth aspect of the implementation plan. Detailed Implementation

[0057] This disclosure will now be discussed with reference to several exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement this disclosure, and not to impose any limitation on the scope of this disclosure.

[0058] As used herein, the terms “first” and “second” refer to distinct elements. Unless the context clearly indicates otherwise, the singular forms “an” and “a” are intended to include the plural forms as well. As used herein, the terms “comprising,” “including,” “having,” and / or “containing” specify the presence of the stated features, elements, and / or components, but do not exclude the presence or addition of one or more other features, elements, components, and / or combinations thereof. The term “based on” should be understood as “at least partially based on.” The terms “one embodiment” and “implementation” should be understood as “at least one embodiment.” The term “another embodiment” should be understood as “at least one other embodiment.” Other explicit and implicit definitions may be included below.

[0059] The first aspect of the implementation plan

[0060] In the first embodiment, a power supply circuit is provided.

[0061] Figure 1 This is a diagram of a power supply circuit according to an embodiment of this disclosure.

[0062] like Figure 1 As shown, the power supply circuit 10 includes a power supply circuit 100, a regulating transistor Q161, a first controller U160, and a current regulating controller A.

[0063] The power supply circuit 100 can provide direct current (DC) power. For example, the power supply circuit 100 may include an inductor L60-a, a diode D160, and two capacitors C160 and C66. The power supply circuit 100 can convert alternating current (AC) power into DC power.

[0064] The regulating transistor Q161 is configured to be connected between the power supply circuit 100 and the first output port DA+. For example, the regulating transistor Q161 is a PNP bipolar transistor with its emitter connected to resistor R167 and its collector connected to the anode of diode D161. Resistor R167 is connected between the cathode of diode D160 and the emitter of regulating transistor Q161. The cathode of diode D161 is connected to the first output port DA+.

[0065] A first controller U160 is configured to control the switching on or off of the regulating transistor Q161. For example, the first controller U160 is an optocoupler (OC). A first resistor R162 is connected between the control terminal (e.g., the base) of the regulating transistor Q161 and the first controller U160. When an "enable" signal is provided to the resistor R100, the transistor Q102 turns on, and the first controller U160 pulls down the voltage at the control terminal of the regulating transistor Q161, thereby turning on the regulating transistor Q161.

[0066] The current regulator A is configured to be connected between the power supply circuit 100 and the second output port DA-. The current regulator A is further connected between the regulating transistor Q161 and the first controller U160.

[0067] In one implementation, when the current at the second output port DA- exceeds a preset value, the current regulation controller A reduces the current flowing through the regulating transistor Q161. This achieves feedback control and enables higher current accuracy.

[0068] like Figure 1 As shown, the current regulation controller A includes: a first resistor R162, a first transistor Q160, a voltage reference circuit U1, a second resistor R164, and a third resistor 170.

[0069] As described above, the first resistor R162 is configured to be connected between the control terminal of the regulating transistor Q161 and the first controller U160.

[0070] The first transistor Q160 is configured to be connected between the power supply circuit and the control terminal of the regulating transistor Q161. The first transistor Q160 may be a PNP bipolar transistor. The emitter of the first transistor Q160 is connected to the cathode of the diode D160 via resistor R173.

[0071] The voltage reference circuit U1, the second resistor R164, and the third resistor R170 are connected in series between the power supply circuit 100 and the ground terminal (GND).

[0072] The control terminal (e.g., base) of the first transistor Q160 is connected to the connection node of the second resistor R164 and the third resistor R170.

[0073] The anode (1) of the voltage reference circuit U1 is connected to the ground terminal (GND_DaliPS), the cathode (2) of the voltage reference circuit U1 is connected to the third resistor R170, and the reference terminal (3) of the voltage reference circuit U1 receives the voltage corresponding to the current of the second output port DA-. The voltage reference circuit U1 can be a TL431.

[0074] The current regulation controller A further includes a fourth resistor R174 and a first capacitor C161. The fourth resistor R174 and the first capacitor C161 are connected in series between the power supply circuit and the reference terminal of the voltage reference circuit U1.

[0075] When the reference terminal (3) of the voltage reference circuit U1 receives a voltage higher than a threshold (e.g., the voltage threshold corresponds to a preset current value), the voltage reference circuit U1 is turned on, and current flows through resistor R173, the second resistor R164, the third resistor R170, the voltage reference circuit U1, and to the ground terminal. The voltage drop across the second resistor R164 turns on the first transistor Q160. Additionally, the voltage received at the reference terminal (3) of the voltage reference circuit U1 is applied to the emitter of the first transistor Q160. The turn-on of the first transistor Q160 increases the current flowing through the first resistor R162, thereby increasing the voltage at the control terminal of the regulating transistor Q161 and reducing the conductive current flowing through the regulating transistor Q161. Therefore, the conductive current can be kept constant, and an accuracy of 1% can be easily achieved.

[0076] like Figure 1 As shown, the power supply circuit 10 further includes a current stage selection circuit B. The current stage selection circuit B is configured to be connected between the first output port DA+ and the second output port DA-.

[0077] For example, the current stage selection circuit B may include a fifth resistor R171, a sixth resistor R168, and a second transistor Q162.

[0078] The fifth resistor R171 and the sixth resistor R168 are connected in series between the second output port DA- and the ground terminal (GND_DAliPS). The second transistor Q162 is connected in parallel with the sixth resistor R168. For example, the second transistor Q162 can be a MOS FET, such as 2N7002. The source of the second transistor Q162 is connected to the ground terminal, and the drain of the second transistor Q162 is connected to the connection node between the fifth resistor R171 and the sixth resistor R168. The resistance of the sixth resistor R168 can be twice that of the fifth resistor R171; for example, the resistance of the sixth resistor R168 can be 150Ω, and the resistance of the fifth resistor R171 can be 50Ω.

[0079] When the first output port DA+ and the second output port DA- are not short-circuited, the second transistor Q162 is turned on, and current flows from the second output port DA- through the fifth resistor R171 to the ground terminal (GND_DAliPS), for example, the current is 50mA. When the first output port DA+ and the second output port DA- are short-circuited (e.g., the DALI interface is short-circuited), the second transistor Q162 is turned off, and current flows from the second output port DA- through the fifth resistor R171 and the sixth resistor R168 to the ground terminal (GND_DAliPS). The current flowing from the second output port DA- to the ground terminal (GND_DAliPS) decreases, for example, to 10mA-11mA.

[0080] In at least one implementation, such as Figure 1 As shown, the current stage selection circuit B further includes: a seventh resistor R161, an eighth resistor R163, and a ninth resistor R172. The seventh resistor R161, the eighth resistor R163, and the ninth resistor R172 are connected in series between the first output port DA+ and the ground terminal. The control terminal (e.g., the gate) of the second transistor Q162 is connected to the connection node of the eighth resistor R163 and the ninth resistor R172.

[0081] The current stage selection circuit B may further include: diode D163 and Zenar diode Z161. The cathode of diode D163 is connected to the cathode of Zenar diode Z161, the anode of diode D163 is connected to the anode of diode D161, and the anode of Zenar diode Z161 is connected to the anode of the seventh resistor R161.

[0082] In at least one embodiment, when the first output port DA+ and the second output port DA- are not short-circuited, the Zenar diode Z161 breaks down in reverse, and current flows through the seventh resistor R161, the eighth resistor R163, and the ninth resistor R172. The voltage drop across the ninth resistor R172 provides Vgs, which turns on the second transistor Q162, and current flows from the second output port DA- through the fifth resistor R171 to the ground terminal (GND_DAliPS). In this case, the fifth resistor R171 functions as a current-sensing resistor.

[0083] In at least one embodiment, when the first output port DA+ and the second output port DA- are short-circuited, no current flows through the seventh resistor R161, the eighth resistor R163, and the ninth resistor R172, thus turning off the second transistor Q162. Current flows from the second output port DA- through the fifth resistor R171 and the sixth resistor R168 to the ground terminal (GND_DAliPS). In this case, the fifth resistor R171 and the sixth resistor R168 function as current-sensing resistors.

[0084] Figure 2 This is a diagram showing the current output of the power supply circuit before and after a short circuit at the DALI interface. Figure 2 In the diagram, the horizontal axis represents time, and the vertical axis represents the current value. For example... Figure 2 As shown, the current was 50mA before the DALI interface was short-circuited. During the delay period after the DALI interface was short-circuited, the current decreased linearly to 11mA. Finally, the current stabilized at 11mA.

[0085] According to the first aspect of the implementation plan, the accuracy of the current output from the power supply circuit 10 is improved by employing a current regulation controller A.

[0086] According to a first aspect of the implementation scheme, by using the current stage selection circuit B, when the first output port DA+ and the second output port DA- are short-circuited, the current of the power supply circuit 10 is reduced, thereby saving energy when the DALI interface is short-circuited.

[0087] The second aspect of the implementation plan

[0088] A control method for a power supply circuit is provided. In a first aspect of the embodiment, a power supply circuit is provided. Content identical to that in the first aspect of the embodiment is omitted.

[0089] Figure 3 A flowchart of the control method for the power supply circuit 10 is shown.

[0090] like Figure 3 As shown, method 30 includes:

[0091] Block 31: When the current at the second output port (DA-) is greater than a preset value, the current regulation controller (A) reduces the current flowing through the regulation transistor (Q161).

[0092] like Figure 3 As shown, method 30 also includes:

[0093] Block 32: When the first output port (DA+) is short-circuited to the second output port (DA-), the second transistor (Q162) is disconnected.

[0094] According to the second aspect of the implementation plan, the accuracy of the current output by the power supply circuit 10 is improved, and energy is saved when the DALI interface is short-circuited.

[0095] The third aspect of the implementation plan

[0096] In one implementation, a Digital Addressable Lighting Interface (DALI) module is provided.

[0097] Figure 4 This is a diagram of the DALI module, which is the third aspect of the implementation plan. (See diagram for example.) Figure 4 As shown, the DALI module 40 includes a power supply circuit 10 and a DALI interface circuit 30. In a first aspect of the embodiment, the power supply circuit 10 is described.

[0098] The power supply circuit 10 provides power to the DALI interface circuit 30 and peripheral devices via the DALI communication bus.

[0099] Peripheral devices can be dimmers, sensors, controllers, safety devices, etc.

[0100] The diagram of the DALI interface circuit 30 is as follows: Figure 4 As shown. Figure 4 As shown, the DALI interface circuit 30 may include resistors R142, R143, R145, R147, R148, R149, and R150; capacitors C03, C142, C140, C144, C146, C147, and C148; transistors Q140, Q141, Q142, Q143, and Q145; Zenar diode Z140; diode bridge D140; and optocouplers U140 and U141.

[0101] Fourth aspect of the implementation plan

[0102] In one embodiment, a lighting device is provided.

[0103] Figure 5 This is a diagram of a lighting device. For example... Figure 5As shown, the lighting device 50 includes a lighting fixture (not shown), a Digital Addressable Lighting Interface (DALI) module 40, and a driver 60. The DALI module 40 is provided according to a third aspect of the embodiment. For example, the DALI module 40 includes a power supply circuit 10 and a DALI interface circuit 30.

[0104] The driver 60 can supply direct current (DC) power to the lighting device. The driver 60 can be an LED driver, and the lighting device can be an LED device. The DALI interface circuit 30 controls the driver 60 to drive the lighting device.

[0105] The output power, output voltage, or output current of the lighting device can be varied between a minimum and a maximum value based on a dimming signal (e.g., 1V-10V) received via DALI (Digital Addressable Lighting Interface), NFC (Near Field Communication), Bluetooth, etc. Preferably, the DC-DC converter supplies the lighting device to change its output parameters (current and / or voltage) according to the dimming signal.

[0106] Furthermore, although the operations are shown in a specific order, this should not be construed as requiring such operations to be performed in the shown specific order or in a sequential order, or as requiring all shown operations to achieve the desired result. In some cases, multitasking and parallel processing may be advantageous. Similarly, while several specific implementation details are included in the foregoing discussion, these specific implementation details should not be construed as limiting the scope of this disclosure, but rather as descriptions of features that may be specific to a particular implementation. Certain features described in the context of individual embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually or in any suitable sub-combination in multiple embodiments.

[0107] Although this disclosure has been described in language specific to structural features and / or methodological actions, it should be understood that this disclosure, as defined by the appended claims, is not necessarily limited to the specific features or actions described above. Rather, the specific features and actions described above are disclosed as exemplary forms for implementing the claims.

Claims

1. A power supply circuit, the power supply circuit comprising: Power supply circuit (100); A regulating transistor (Q161) is configured to be connected between the power supply circuit and the first output port (DA+); A first controller (U160) is configured to control the adjustment transistor (Q161) to be turned on or off; and A current regulating controller (A) is configured to be connected between the power supply circuit and the second output port (DA-), and the current regulating controller (A) is also connected between the regulating transistor (Q161) and the first controller (U160). When the current at the second output port (DA-) is greater than a preset value, the current regulation controller (A) reduces the current flowing through the regulation transistor (Q161). The current regulation controller (A) includes: A first resistor (R162) is configured to be connected between the control terminal of the regulating transistor (Q161) and the first controller (U160); A first transistor (Q160) is configured to be connected between the power supply circuit and the control terminal of the regulating transistor (Q161); Voltage reference circuit (U1); The second resistor (R164); and Third resistor (R170). The voltage reference circuit (U1), the second resistor (R164), and the third resistor (R170) are connected in series between the power supply circuit and the ground terminal. The control terminal of the first transistor (Q160) is connected to the connection node of the second resistor (R164) and the third resistor (R170). The anode of the voltage reference circuit (U1) is connected to the ground terminal. The cathode of the voltage reference circuit (U1) is connected to the third resistor (R170). The reference terminal of the voltage reference circuit (U1) receives the voltage corresponding to the current at the second output port (DA-).

2. The power supply circuit according to claim 1, wherein, The current regulation controller (A) further includes: The fourth resistor (R174) and the first capacitor (C161). The fourth resistor (R174) and the first capacitor (C161) are connected in series between the power supply circuit and the reference terminal of the voltage reference circuit (U1).

3. The power supply circuit according to claim 1, wherein the power supply circuit further comprises: A current stage selection circuit (B) is configured to be connected between the first output port (DA+) and the second output port (DA-). The current stage selection circuit (B) includes: Fifth resistor (R171); The sixth resistor (R168); and Second transistor (Q162). The fifth resistor (R171) and the sixth resistor (R168) are connected in series between the second output port (DA-) and the ground terminal. The second transistor (Q162) is connected in parallel with the sixth resistor (R168).

4. The power supply circuit according to claim 3, wherein, When the first output port (DA+) is short-circuited to the second output port (DA-), the second transistor (Q162) is disconnected.

5. The power supply circuit according to claim 3, wherein, The current stage selection circuit (B) further includes: Seventh resistor (R161); The eighth resistor (R163); and Ninth resistor (R172). The seventh resistor (R161), the eighth resistor (R163), and the ninth resistor (R172) are connected in series between the first output port (DA+) and the ground terminal. The control terminal of the second transistor (Q162) is connected to the connection node of the eighth resistor (R163) and the ninth resistor (R172).

6. A Digital Addressable Lighting Interface (DALI) module, the DALI module comprising a DALI interface circuit and a power supply circuit according to any one of claims 1 to 5, wherein, The power supply circuit provides power to the DALI interface circuit and peripheral devices via the DALI communication bus.

7. A lighting device, the lighting device comprising a lighting unit, a Digital Addressable Lighting Interface (DALI) module according to claim 6, and a driver, wherein, The Digital Addressable Lighting Interface (DALI) module controls the driver to drive the lighting device.

8. A control method for a power supply circuit, the power supply circuit comprising: Power supply circuit; A regulating transistor (Q161) is configured to be connected between the power supply circuit and the first output port (DA+); A first controller (U160) is configured to control the adjustment transistor (Q161) to be turned on or off; and A current regulating controller (A) is configured to be connected between the power supply circuit and the second output port (DA-), and the current regulating controller (A) is also connected between the regulating transistor (Q161) and the first controller (U160). The current regulation controller (A) includes: A first resistor (R162) is configured to be connected between the control terminal of the regulating transistor (Q161) and the first controller (U160); A first transistor (Q160) is configured to be connected between the power supply circuit and the control terminal of the regulating transistor (Q161); Voltage reference circuit (U1); The second resistor (R164); and Third resistor (R170). The voltage reference circuit (U1), the second resistor (R164), and the third resistor (R170) are connected in series between the power supply circuit and the ground terminal. The control terminal of the first transistor (Q160) is connected to the connection node of the second resistor (R164) and the third resistor (R170). The anode of the voltage reference circuit (U1) is connected to the ground terminal. The cathode of the voltage reference circuit (U1) is connected to the third resistor (R170). The reference terminal of the voltage reference circuit (U1) receives the voltage corresponding to the current of the second output port (DA-); The control method includes: When the current at the second output port (DA-) is greater than a preset value, the current regulation controller (A) reduces the current flowing through the regulation transistor (Q161).

9. The control method for a power supply circuit according to claim 8, wherein, The power supply circuit mentioned above also includes: A current stage selection circuit (B) is configured to be connected between the first output port (DA+) and the second output port (DA-). The current stage selection circuit (B) includes: Fifth resistor (R171); The sixth resistor (R168); and Second transistor (Q162). The fifth resistor (R171) and the sixth resistor (R168) are connected in series between the second output port (DA-) and the ground terminal. The second transistor (Q162) is connected in parallel with the sixth resistor (R168). The method further includes: When the first output port (DA+) is short-circuited to the second output port (DA-), the second transistor (Q162) is disconnected.

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