Current Sensing Circuit

Abstract

A current sensing circuit includes a sensing resistor, a current monitor, a variable resistor, and a processor. The sensing resistor is arranged in a circuit to be tested and coupled between a first voltage terminal and a second voltage terminal of the circuit to be tested. The current monitor has a first terminal and a second terminal. The first winding is coupled between the first terminal and the first voltage terminal, and the second winding is coupled between the second terminal and the second voltage terminal. The variable resistor and the first winding are connected in series between the first terminal and the first voltage terminal. The current monitor obtains a sensing current according to a first voltage on the first terminal, a second voltage on the second terminal, and an impedance of the sensing resistor and generates a sensing signal according to the sensing current. The processor determines whether to adjust the impedance of the variable resistor according to the sensing signal.

Description

Technical Field

[0001] The present invention relates to a current sensing circuit, and more particularly to a current sensing circuit which can adjust the impedance on a sensing path according to a sensed current. Background Art

[0002] Generally speaking, in order to protect the components in the electronic device from being affected by excessive current, a current monitor is set to monitor the current between two nodes / terminals on a specific circuit or device, and the electronic device further performs a protection operation based on the sensed current. For example, in a notebook computer, when a large current is sensed to flow through a specific circuit or device, it means that the temperature of the specific circuit or device is increased due to the large current. At this time, the notebook computer can start a fan pen or reduce operating performance to reduce the temperature of the specific circuit or device. However, the equivalent impedances of at least two windings used to sense the current path on the circuit board of the electronic device may not match each other, resulting in errors in the sensed current, so that the electronic device cannot correctly perform operations corresponding to the actual current. If the operation corresponding to the actual current cannot be performed correctly, in a vehicle electronic device, since each data of the vehicle electronic device is related to human life safety, it is very important for the vehicle electronic device to accurately sense the current on a specific circuit or device. Summary of the invention

[0003] In view of this, the present invention proposes a current sensing circuit for an electronic system. The electronic system includes a circuit to be tested. A first voltage terminal of the circuit to be tested is coupled to a first winding, and a second voltage terminal of the circuit to be tested is coupled to a second winding. The current sensing circuit includes a sensing resistor, a current monitor, a first variable resistor, and a processor. The sensing resistor is arranged in the circuit to be tested and coupled between the first voltage terminal and the second voltage terminal. The current monitor has a first terminal and a second terminal. The first winding is coupled between the first terminal and the first voltage terminal, and the second winding is coupled between the second terminal and the second voltage terminal. The first variable resistor and the first winding are connected in series between the first terminal and the first voltage terminal. The processor is coupled to the current monitor. The current monitor obtains a sensing current according to a first voltage on the first terminal, a second voltage on the second terminal, and the impedance of the sensing resistor, and generates a sensing signal according to the sensing current. The processor receives the sensing signal and determines whether to adjust the impedance of the first variable resistor according to the sensing signal.

[0004] According to the above embodiment, by adjusting the impedance of the variable resistor, the total equivalent impedance of the first winding and the variable resistor can be matched with the equivalent impedance of the second winding. Based on the impedance matching, the sensed current obtained by the current monitor can accurately represent the actual current flowing through the sense resistor, that is, the current difference between the sensed current and the actual current flowing through the sense resistor is linear or nearly linear over time. Even when the environment of the electronic system changes and causes the equivalent impedance of the first or second winding to change, the sensed current can still accurately represent the actual current flowing through the sense resistor, thereby enabling the electronic system to correctly and instantly perform specific operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 FIG. 4 is a schematic diagram of an electronic system with a current sensing circuit according to an embodiment of the present invention.

[0006] Figure 2 It is the change of the current difference between the sensed current and the actual current in the ideal situation and in actual operation over time.

[0007] Figure 3 FIG. 4 is a schematic diagram of an electronic system with a current sensing circuit according to another embodiment of the present invention.

[0008] Figure 4 FIG. 4 is a schematic diagram of an electronic system with a current sensing circuit according to another embodiment of the present invention.

[0009]

Explanation of symbols

[0010] 1, 3, 4: Electronic system

[0011] 10: Processor

[0012] 11: Current monitor

[0013] 12: Operation circuit (circuit to be tested)

[0014] 13: Digital variable resistor

[0015] 14: Sense resistor

[0016] 15N: Second winding

[0017] 15N-1: The third winding section

[0018] 15N-2: Fourth winding section

[0019] 15P: First winding

[0020] 15P-1: First winding section

[0021] 15P-2: Second winding section

[0022] 20, 21: Curve

[0023] 30: Digital variable resistor

[0024] 100: Current sensing circuit

[0025] 110: First terminal

[0026] 111: Second terminal

[0027] 120: first voltage terminal

[0028] 121: second voltage terminal

[0029] GND: Ground voltage

[0030] S10: Control signal

[0031] S11: Sensing signal

[0032] S30: Control signal

[0033] VDD: Operating voltage

[0034] VN: Second voltage

[0035] VP: First voltage DETAILED DESCRIPTION

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, a preferred embodiment is given below and described in detail with reference to the accompanying drawings.

[0037] Figure 1 FIG. 2 is an electronic system according to an embodiment of the present invention. Figure 1 The electronic system 1 includes a processor 10, a current monitor 11, at least one operating circuit 12, a digital variable resistor 13, and a sensing resistor 14. Figure 1 In the embodiment of the present invention, the processor 10, the current monitor 11, at least one operating circuit 12, the digital variable resistor 13, and the sensing resistor 14 are located on the same circuit board. In other embodiments, the current monitor 11, at least one operating circuit 12, the digital variable resistor 13, and the sensing resistor 14 are located on one circuit board, and the processor 10 is located on another circuit board.

[0038] The electronic system 1 may include a plurality of operating circuits to perform a plurality of specific operations or functions. Figure 1In the embodiment of the present invention, an operating circuit 12 is taken as an example. When the current monitor 11 performs a current sensing operation, the operating circuit 12 serves as a circuit to be tested. The current monitor 11 has a first terminal 110 and a second terminal 111. The circuit to be tested 12 has a first voltage terminal 120 and a second voltage terminal 121. The sensing resistor 14 has a fixed impedance, which is disposed on the circuit to be tested 12 and coupled between the first voltage terminal 120 and the second voltage terminal 121 of the circuit to be tested 12. Figure 1 In the embodiment, when the electronic system 1 is powered on, the first voltage terminal 120 receives an operating voltage VDD of the circuit under test 12, and the second voltage terminal 121 receives a ground voltage GND. The first terminal 110 of the current monitor 11 is connected to the first voltage terminal 120 of the circuit under test 12 via a first winding 15P on the circuit board, and the second terminal 111 of the current monitor 11 is connected to the second voltage terminal 121 of the circuit under test 12 via a second winding 15P on the circuit board.

[0039] Assume that the digital variable resistor 13 is not connected in series to the first winding 15P. After the circuit board of the electronic system 1 is laid out, ideally, the equivalent impedance of the first winding 15P matches the equivalent impedance of the second winding 15N (for example, the length and width of the first winding 15P are respectively equal to the length and width of the second winding 15). Therefore, the sensing current I can accurately represent the actual current flowing through the resistor 14, that is, the current difference ΔI between the sensing current I and the actual current flowing through the sensing resistor 14 has a linear characteristic (or a nearly linear characteristic) over time, as shown in FIG. Figure 2 As shown in the curve 20. However, in actual operation, due to the layout of the circuit board, the process of the circuit board, or the environmental changes, the equivalent impedance of the first winding 15P and the equivalent impedance of the second winding 15N may become mismatched (for example, the length of the first winding 15P is not equal to the length of the second winding 15, or the width of the first winding 15P is not equal to the width of the second winding 15). At this time, the sensed current I obtained cannot accurately represent the actual current flowing through the sense resistor 14, that is, the sensing operation of the current monitor 11 has an error, which makes the current difference ΔI between the sensed current I and the actual current flowing through the sense resistor 14 become nonlinear over time, as shown in FIG. Figure 2 As shown in curve 21.

[0040] In order to eliminate the above-mentioned error, the present application connects a digital variable resistor 13 in series to the first winding 15P or the second winding 15N, and the variable resistor 13 has an initial impedance.

[0041] exist Figure 1 In the embodiment, it is assumed that after the circuit board of the electronic system 1 is arranged, the length of the first winding 15P is shorter than the length of the second winding 15N, and the digital variable resistor 13 is connected in series with the first winding 15P. Figure 1The first winding 15P and the second winding 15N shown are only used to illustrate the connection between the circuit to be tested 12 and the current monitor 11. Figure 1 The length and configuration shown are not the actual conditions on the circuit board. Figure 1 Specifically, the first winding 15P is divided into a first winding section 15P-1 and a second winding section 15P-2, and the digital variable resistor 13 is coupled between the first winding section 15P-1 and the second winding section 15P-2.

[0042] The impedance of the digital variable resistor 13 can be adjusted by the control signal S10 generated by the processor 10. The voltage level of the control signal S10 can determine the adjustment direction of the impedance of the digital variable resistor 13. For example, when the control signal S10 has a high voltage level, the impedance of the digital variable resistor 13 increases (the adjustment direction is from low impedance to high impedance), and conversely, when the control signal S10 has a low voltage level, the impedance of the digital variable resistor 13 decreases (the adjustment direction is from high impedance to low impedance).

[0043] exist Figure 1 In the embodiment of the present invention, the processor 10, the current monitor 11, the variable resistor 13, and the sense resistor 14 constitute the current sensing circuit 100. The operation of the current sensing circuit 100 will be described in detail below. The current sensing circuit 100 can operate in different modes, such as a test mode and an operation mode.

[0044] In one embodiment, the test mode occurs when the circuit board layout of the electronic system 1 is completed but before it leaves the factory. The operation mode occurs after the electronic system 1 leaves the factory and the electronic device used in the electronic system 1 is enabled. In one embodiment, the electronic device may be, for example, transportation equipment, such as an aircraft, a car, a motorcycle, etc.

[0045] In the test mode, the digital variable resistor 13 initially has a reference impedance. When the electronic system 1 is powered on, the current monitor 11 detects the first voltage VP on the first terminal 110 and the second voltage VN on the second terminal 111. According to the above, the sensing resistor 14 has a fixed impedance (R14). The current monitor 11 stores the impedance R14 in a storage device therein. Figure 1, the current sensing path passes through the first terminal 110, the first winding 15P (15P-1 and 15P-2), the digital variable resistor 13, the sensing resistor 14, the second winding 15N, and the second terminal 111. The voltage difference (VP - VN) between the first voltage VP and the second voltage VN can represent whether the total equivalent impedance of the first winding 15P and the digital variable resistor 13 (the sum of the equivalent impedance of the first winding 15P and the reference impedance of the digital variable resistor 13) matches the equivalent impedance of the second winding 15N. Based on Ohm's law, the current monitor 11 performs operations using the impedance R14 and the sensed voltages VP and VN to obtain a sensed current. The current monitor 11 generates a sensing signal S11 based on the obtained sensed current I, which represents the value of the sensed current I.

[0046] When the current monitor 11 generates the sensing signal S11, the processor 10 receives the sensing signal S11 and determines whether the value of the sensed current I is within a preset current range (IR) according to the sensing signal S11. In an embodiment of the present invention, the processor 10 predefines a preset current value IPRE and defines the above preset current range according to the tolerance of the electronic system 1 for current detection. The preset current range has an upper limit value THH and a lower limit value THL, and the preset current value IPRE is within the preset current range IR, that is, THL < IPRE < THH.

[0047] When the processor 10 determines that the value of the sensed current I falls within the preset current range IR (i.e., THL < I < THH), it means that the total equivalent impedance of the first winding 15P and the digital variable resistor 13 matches the equivalent impedance of the second winding 15N or the difference between the two is within an acceptable range, that is, the obtained sensed current I can accurately represent the actual current flowing through the sensing resistor 14. At this time, the processor 10 does not adjust the impedance of the digital variable resistor 13, that is, the impedance of the digital variable resistor 13 remains at the reference impedance. The test mode then ends.

[0048] When the processor 10 determines that the value of the sensed current I does not fall within the preset current range IR (i.e., I < THL or I > THH), it indicates that the total equivalent impedance of the first winding 15P and the digital variable resistor 13 does not match the equivalent impedance of the second winding 15N or the difference between the two is beyond the allowable range, that is, the obtained sensed current I does not accurately represent the actual current flowing through the sensing resistor 14. At this time, the processor 10 knows from the judgment result that the impedance of the digital variable resistor 13 needs to be adjusted. Therefore, the processor 10 generates a control signal S10 to adjust the impedance of the digital variable resistor 13. Through the above operations, the total equivalent impedance of the first winding 15P and the digital variable resistor 13 is adjusted to match the equivalent impedance of the second winding 15N or the difference between the two returns to the allowable range. At this time, the obtained sensed current I gradually changes towards the preset current value IPRE and finally maintains equal to or close to the preset current value IPRE. After that, the test mode ends.

[0049] Through the operation of the current detection circuit 100 in the test mode, it can ensure before leaving the factory that the total equivalent impedance of the first winding 15P and the digital variable resistor 13 matches the equivalent impedance of the second winding 15N or the difference between the two is within the allowable range, so that the sensed current I can accurately represent the actual current flowing through the sensing resistor 14, that is, the current difference ΔI between the sensed current I and the actual current flowing through the sensing resistor 14 has a linear characteristic or a characteristic close to linear with time.

[0050] The reference impedance of the digital variable resistor 13 or the last adjusted impedance of the digital variable resistor 13 before the end of the test mode is used as an initial impedance for the operation mode.

[0051] After the electronic system 1 leaves the factory and during the period when the electronic device applied by the electronic system 1 is enabled, the equivalent impedances of the first winding 15P and the second winding 15N may change due to changes in the operating environment of the electronic device (for example, temperature changes), resulting in a mismatch between the total equivalent impedance of the first winding 15P and the digital variable resistor 13 and the equivalent impedance of the second winding 15N.

[0052] Therefore, when the electronic device is enabled, the current sensing circuit 100 enters the operation mode. In the operation mode, the digital variable resistor 13 has the above-mentioned initial impedance. At this time, the electronic system 1 is powered on. The current monitor 11 detects the first voltage VP on the first terminal 110 and the second voltage VN on the second terminal 111, and based on Ohm's law, uses the impedance R14 and the sensed voltages VP and VN for calculation to obtain the sensed current The current monitor 11 generates a sensing signal S11 according to the obtained sensed current I, which represents the value of the sensed current I.

[0053] When the current monitor 11 generates the sensing signal S11 , the processor 10 receives the sensing signal S11 and determines whether the variation range of the value of the sensing current I within a preset time length is greater than a critical value according to the sensing signal S11 .

[0054] When the processor 10 determines that the change range of the value of the sensing current I within the preset time length is not greater than a critical value, it means that the total equivalent impedance of the first winding 15P and the digital variable resistor 13 matches the equivalent impedance of the second winding 15N or the difference between the two becomes within an allowable range, that is, the obtained sensing current I can accurately represent the actual current flowing through the sensing resistor 14. At this time, the processor 10 does not adjust the impedance of the digital variable resistor 13, that is, the impedance of the digital variable resistor 13 is maintained at the initial value.

[0055] When the processor 10 determines that the change amplitude of the value of the sensing current I within the preset time length is greater than the critical value, it means that due to the change in the environment of the electronic device, the total equivalent impedance of the first winding 15P and the digital variable resistor 13 does not match the equivalent impedance of the second winding 15N or the difference between the two exceeds the allowable range, that is, the obtained sensing current I becomes unable to accurately represent the actual current flowing through the sensing resistor 14. At this time, the processor 10 knows that the impedance of the digital variable resistor 13 must be adjusted according to the judgment result. Therefore, the processor 10 generates a control signal S10 to adjust the impedance of the digital variable resistor 13. Through the above operation, the total equivalent impedance of the first winding 15P and the digital variable resistor 13 is adjusted to match the equivalent impedance of the second winding 15N or the difference between the two returns to the allowable range.

[0056] According to the above, in the operation mode, even if the operation environment of the electronic device changes and causes the equivalent impedance of each winding on the circuit board to change, the current detection circuit 100 can adjust the impedance of the digital variable resistor 13 so that the total equivalent impedance of the first winding 15P and the digital variable resistor 13 becomes matched with the equivalent impedance of the second winding 15N or the difference between the two returns to the allowable range. Therefore, the sensed current I obtained by the current monitor 11 can accurately represent the actual current flowing through the sense resistor 14, that is, the current difference ΔI between the sensed current I and the actual current flowing through the sense resistor 14 is linear or nearly linear over time. The electronic device can correctly and instantly perform a specific operation based on the sensed current I obtained.

[0057] exist Figure 1 In the embodiment of the present invention, the digital variable resistor 13 is connected in series with the first winding 15P. In other embodiments, after the circuit board of the electronic system 1 is arranged, the length of the second winding 15N is shorter than the length of the first winding 15P. At this time, the digital variable resistor 13 is not connected in series with the first winding 15P, but a digital variable resistor is connected in series with the second winding 15N.

[0058] See also Figure 3 , electronic system 3 and Figure 1 The electronic system 1 is substantially the same as the electronic system 1 of FIG. The difference between the electronic systems 1 and 3 is that a digital variable resistor 30 is connected in series with the second winding 15N, while the first winding 15P is not connected in series with any digital variable resistor. In this embodiment, the processor 10, the current monitor 11, the variable resistor 30, and the sensing resistor 14 constitute the current sensing circuit 100.

[0059] like Figure 3 Specifically, the second winding 15N is divided into a third winding section 15N-1 and a fourth winding section 15N-2, and the digital variable resistor 30 is coupled between the third winding section 15N-1 and the fourth winding section 15N-2. The impedance of the digital variable resistor 30 can be adjusted by the control signal S30 generated by the processor 10.

[0060] exist Figure 3 In the embodiment of the present invention, the operation of the current monitor 11 and the processor 10 is similar to Figure 1 The same as the embodiment of FIG. 1 , the description is omitted here. It should be noted that Figure 3 In the embodiment of the present invention, the processor 10 generates a control signal S30. The mechanism for generating the control signal S30 is similar to Figure 1 The mechanism for generating the control signal S10 in the embodiment is the same and its description is omitted here.

[0061] In other embodiments, the first winding 15P and the second winding 15N are each connected in series with a digital variable resistor. Figure 4 , the electronic system 4 is substantially the same as the electronic system 1 and the electronic system 3. The difference between the electronic system 4 and the electronic system 1 and 3 is that a digital variable resistor 13 is connected in series with the first winding 15P, and a digital variable resistor 30 is connected in series with the second winding 15N. In other words, the electronic system 4 is a combination of the electronic systems 1 and 3. In this embodiment, the processor 10, the current monitor 11, the variable resistors 13 and 30, and the sensing resistor 14 constitute the current sensing circuit 100. For the serial connection of the digital variable resistors 13 and 30 with the windings 15P and 15N, respectively, please refer to the relevant description of Figures 1 and 3, and the description is omitted here.

[0062] In the electronic system 4, the sensing operation of the current monitor 11 and the determination operation of the processor 10 are Figure 1The same as the embodiment of the present invention, the description is omitted here. In one embodiment, in the test mode, when the processor 10 determines that the value of the sensing current I does not fall within the preset current range IR, the processor 10 can generate one of the control signals S10 and S30 to adjust the impedance of the corresponding digital variable resistors 13 and 30; in the operation mode, when the processor 10 determines that the value of the sensing current I changes within a preset time length The amplitude is greater than the critical value, the processor 10 can generate one of the control signals S10 and S30 to adjust the impedance of the corresponding digital variable resistors 13 and 30. In other words, the processor 10 adjusts the impedance of the digital variable resistors 13 and 30 at different times according to the judgment result.

[0063] In other embodiments, the processor 10 can adjust the impedance of the digital variable resistors 13 and 30 simultaneously according to the judgment result. Specifically, in the test mode, when the processor 10 determines that the value of the sensing current I does not fall within the preset current range IR, the processor 10 can generate control signals S10 and S30 to adjust the impedance of the digital variable resistors 13 and 30 simultaneously; in the operation mode, when the processor 10 determines that the value of the sensing current I changes by more than a critical value within a preset time length, the processor 10 can generate control signals S10 and S30 to adjust the impedance of the digital variable resistors 13 and 30 simultaneously.

[0064] In the case of adjusting the impedance of the digital variable resistors 13 and 30 at the same time, the adjustment directions of the digital variable resistors 13 and 30 are opposite. In detail, one of the control signals S13 and S30 generated by the processor 10 has a high voltage level to increase the impedance of the corresponding digital variable resistor, and the other of the control signals S13 and S30 has a low voltage level to reduce the impedance of the corresponding digital variable resistor. By adjusting the impedance of the digital variable resistors 13 and 30 at the same time, the total equivalent impedance of the first winding 15P and the digital variable resistor 13 can be changed to match the total equivalent impedance of the second winding 15N and the digital variable resistor 30 in a short time.

[0065] Although the present invention has been disclosed as above in terms of preferred embodiments, it is not intended to limit the present invention. Those skilled in the art may make changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope defined in the attached claims.

Claims

1. A current sensing circuit for an electronic system, the electronic system comprising a circuit to be tested, a first voltage terminal of the circuit to be tested coupled to a first winding, and a second voltage terminal of the circuit to be tested coupled to a second winding, the current sensing circuit comprising: A sensing resistor is disposed in the circuit to be tested and coupled between the first voltage terminal and the second voltage terminal; A current monitor having a first terminal and a second terminal, wherein the first winding is coupled between the first terminal and the first voltage terminal, and the second winding is coupled between the second terminal and the second voltage terminal; A first variable resistor is connected in series with the first winding between the first terminal and the first voltage end; and a processor coupled to the current monitor; The current monitor obtains a sensing current according to a first voltage on the first terminal, a second voltage on the second terminal, and an impedance of the sensing resistor, and generates a sensing signal according to the sensing current; and The processor receives the sensing signal and determines whether to adjust the impedance of the first variable resistor according to the sensing signal.

2. The current sensing circuit of claim 1, wherein: The processor determines whether the value of the sensed current is within a preset current range according to the sensed signal; as well as When the processor determines that the value of the sensing current is not within the preset current range, the processor adjusts the impedance of the first variable resistor so that the value of the sensing current is close to a preset current value within the preset current range.

3. The current sensing circuit of claim 1 , wherein: The processor determines, based on the sensing signal, whether a change range of the value of the sensing current within a preset time length is greater than a critical value; When the processor determines that the variation amplitude is greater than the critical value, the processor adjusts the impedance of the first variable resistor.

4. The current sensing circuit as claimed in claim 1, wherein: One of the first voltage terminal and the second voltage terminal receives an operating voltage of the circuit under test, and the other of the first voltage terminal and the second voltage terminal receives a ground voltage of the circuit under test.

5. The current sensing circuit of claim 1 , further comprising: A second variable resistor is connected in series with the second winding between the second terminal and the second voltage end; The processor determines whether to adjust the impedance of the second variable resistor according to the sensing signal.

6. The current sensing circuit of claim 5, wherein: The processor determines whether the value of the sensed current is within a preset current range according to the sensed signal; When the processor determines that the value of the sensing current is not within the preset current range, the processor adjusts the impedance of at least one of the first variable resistor and the second variable resistor so that the value of the sensing current is close to a preset current value within the preset current range.

7. The current sensing circuit of claim 6, wherein: When the processor simultaneously adjusts the impedance of the first variable resistor and the impedance of the second variable resistor, the processor increases the impedance of one of the first variable resistor and the second variable resistor and decreases the impedance of the other of the first variable resistor and the second variable resistor.

8. The current sensing circuit of claim 5, wherein: The processor determines, based on the sensing signal, whether a change range of the value of the sensing current within a preset time length is greater than a critical value; When the processor determines that the variation amplitude is greater than the critical value, the processor adjusts the impedance of at least one of the first variable resistor and the second variable resistor.

9. The current sensing circuit of claim 8, wherein: When the processor simultaneously adjusts the impedance of the first variable resistor and the impedance of the second variable resistor, the processor increases the impedance of one of the first variable resistor and the second variable resistor and decreases the impedance of the other of the first variable resistor and the second variable resistor.

10. The current sensing circuit of claim 1, wherein: The electronic system is used in transportation equipment.

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