DC current measurement

Abstract

Direct current (DC) current measuring circuit, comprising: a shunt resistor electrically connected in a current path, wherein a current flowing through the current path includes an alternating current (AC) component; a low-pass filter (LPF) electrically connected across the shunt resistor and configured to filter a voltage signal across the shunt resistor and output a filtered voltage signal; and an amplifier electrically connected to the LPF and configured to receive the filtered voltage signal and output a measurement signal, the measurement signal providing a measurement of a DC component of the current.

Description

Area

[0001] The embodiments described here relate to a device and a circuit for measuring current with direct current (DC). Summary

[0002] In some aspects, the techniques described herein relate to a direct current (DC) current measurement circuit comprising: a shunt resistor electrically connected in a current path, wherein a current flowing through the current path includes an alternating current (AC) component; a low-pass filter (LPF) electrically connected across the shunt resistor and configured to filter a voltage signal across the shunt resistor and output a filtered voltage signal; and an amplifier electrically connected to the LPF and configured to receive the filtered voltage signal and output a measurement signal, wherein the measurement signal provides a measurement of a DC component of the current.

[0003] In some aspects, the techniques described herein relate to an electronic device comprising: a power converter electrically connected between a battery system and a load; and a direct current (DC) current measurement circuit electrically connected in a current path of the power converter and including a resistor electrically connected in the current path, wherein a current flowing through the current path includes an alternating current (AC) component; a low-pass filter (LPF) electrically connected across the resistor and configured to filter a voltage signal across the shunt resistor and output a filtered voltage signal; and an amplifier electrically connected to the LPF and configured to amplify the filtered voltage signal and output a measurement signal.

[0004] In some aspects, the techniques described herein relate to a portable power source comprising: a battery system; a power converter electrically connected to the battery system; a direct current (DC) current measurement circuit electrically connected in a current path of the power converter and including a resistor electrically connected in the current path, wherein a current flowing through the current path includes an alternating current (AC) component; a low-pass filter (LPF) electrically connected across the resistor and configured to filter a voltage signal across the shunt resistor and output a filtered voltage signal; and an amplifier electrically connected to the LPF and configured to amplify the filtered voltage signal and output a measurement signal.

[0005] One embodiment provides a DC current measurement circuit comprising a shunt resistor, an LPF, and an amplifier. The shunt resistor is electrically connected in a current path and configured to convert a current flowing through the current path into a voltage signal. The LPF is electrically connected to the shunt resistor and configured to receive the voltage signal from the shunt resistor and output a filtered voltage signal. The amplifier is connected to the LPF and configured to receive the filtered voltage signal and provide a measurement signal. The measurement signal provides a measurement of the current flowing through the current path.

[0006] In particular, the direct current (DC) measurement may include converting a current flowing through the current path into a voltage signal using a shunt resistor electrically connected in a current path, filtering the voltage signal using a low-pass filter (LPF) electrically connected to the shunt resistor, and amplifying the voltage signal using an amplifier electrically connected to the LPF to provide a measurement signal. The measurement signal provides a measurement of the current flowing through the current path.

[0007] Another embodiment provides an electronic device comprising a current converter electrically connected between a battery system and a load, and a DC current measuring circuit electrically connected in a current path of the current converter. The DC current measuring circuit includes a resistor, an LPF, and an amplifier. The resistor is electrically connected in the current path and configured to convert a current flowing through the current path into a voltage signal. The LPF is electrically connected to the resistor and configured to filter the voltage signal. The amplifier is electrically connected to the LPF and configured to amplify the filtered voltage signal.

[0008] Before embodiments are explained in detail, it is to be understood that the embodiments are not limited in their application to the details of the configuration and arrangement of the components set forth in the following description or illustrated in the accompanying drawings. The embodiments may be implemented or carried out in a variety of ways. Furthermore, it is to be understood that the phraseology and terminology used herein is for the purpose of description only and should not be considered limiting. The use of "comprising," "having," or "with," and variations thereof, is intended to include the elements listed thereafter and their equivalents, as well as additional elements. Unless otherwise stated or limited, the terms "mounted," "connected," "supported," and "coupled," and variations thereof, are used broadly to include both direct and indirect mountings, connections, supports, and couplings.

[0009] Unless the context of their use clearly requires otherwise, the articles "ein," "eine," and "der, die das" should not be interpreted as "one" or "only one." Rather, these articles should be interpreted as "at least one" or "one or more." Similarly, when referring to a noun previously introduced by the indefinite article "ein" or "eine," the terms "der," "die," "das," or "besagte / r" mean "at least one" or "one or more," unless the context clearly indicates otherwise.

[0010] Furthermore, it should be understood that embodiments may include hardware, software, and electronic components or modules, which for purposes of explanation may be illustrated and described as if most components were implemented solely in hardware. However, one of ordinary skill in the art would recognize, based on this detailed description, that in at least one embodiment, the electronic aspects may be implemented in software (e.g., stored on a non-transitory, computer-readable medium) that may be executed by one or more processing units, such as a microprocessor and / or application-specific integrated circuits ("ASICs"). Therefore, it should be understood that a variety of hardware- and software-based devices, as well as a variety of different components, may be used to implement the embodiments.For example, “servers,” “computing units,” “controllers,” “processors,” etc., described in the specification may include one or more processing units, one or more computer-readable media modules, one or more input / output interfaces, and various connections (e.g., a system bus) that connect the components.

[0011] Relative terms such as "about," "approximately," "substantially," etc., used in connection with an amount or condition, would be understood by one skilled in the art to include the stated value and to have the meaning given by the context (e.g., the term encompasses at least the degree of error associated with measurement accuracy, tolerances [e.g., manufacturing, assembly, use, etc.] associated with the particular value, etc.). Such terminology should also be considered to disclose the range defined by the absolute values ​​of the two endpoints. For example, the phrase "from about 2 to about 4" also discloses the range "from 2 to 4." Relative terminology can refer to plus or minus a percentage (e.g., 1%, 5%, 10%, or more) of a stated value.

[0012] It should be understood that while certain drawings depict hardware and software in particular devices, these depictions are for illustrative purposes only. Functions described herein as being performed by one component may be performed in a distributed manner by multiple components. Likewise, functions performed by multiple components may be consolidated and performed by a single component. In some embodiments, the depicted components may be combined or separated into separate software, firmware, and / or hardware. For example, rather than being housed in and executed by a single electronic processor, logic and processing may be distributed among multiple electronic processors.Regardless of how they are combined or distributed, hardware and software components may be located on the same computing device or distributed among different computing devices interconnected by one or more networks or other suitable communications links. Likewise, a component described as performing a particular function may also perform additional functions not described herein. For example, a device or structure "configured" in a particular manner is configured at least in that manner, but may also be configured in other ways not explicitly listed.

[0013] Accordingly, in the claims, where an apparatus or system is claimed as comprising, for example, a controller, control unit, electronic processor, computing device, logic element, module, memory module, communications channel or network, or other element configured in a particular way, for example to perform a plurality of functions, the claim or claim element is to be construed to mean one or more such elements, one of the one or more elements being configured as claimed, for example to perform one or more of the recited functions, so that the one or more elements as a whole perform the functions jointly.

[0014] Further aspects of the embodiments will become clear from the detailed description and the accompanying drawings. Brief description of the drawings Fig. 1 is a simplified block diagram of a DC current measurement circuit according to some embodiments. Fig. Figure 2 is a simplified block diagram of an electronic device incorporating the DC current measuring circuit of Fig. 1 according to some embodiments. Fig. 3A-3C are perspective views of examples of electrical devices embodying the DC current measuring circuit of Fig. 1 according to some embodiments. Fig. Figure 4 is a simplified block diagram of a battery-powered flyback converter that incorporates the DC current measurement circuit from Fig. 1 according to some embodiments. Fig. Figure 5 is a graph showing the results of the DC current measurement circuit of Fig. 1 shows when used in the battery-powered flyback converter of Fig. 4 is used according to some embodiments. Fig. Figure 6 is a simplified block diagram of a DC / DC converter that incorporates the DC current measurement circuit of Fig. 1 according to some embodiments. Fig. Figure 7 is a flowchart of a DC current measurement. Detailed description

[0015] Power tools and portable power supplies use various converter circuits, such as DC-to-AC converters, DC / DC converters, AC / AC converters, AC / DC converters, and combinations thereof. A transformer can be used to convert voltage at a first level to a second level desirable for use at a converter output. Transformers are typically used to step up or step down AC voltage. Undesirable core saturation can occur in a transformer when a DC current component flows through the transformer along with the AC current. Even a small amount of DC current can quickly lead to core saturation. However, detecting small DC currents in a signal with a large AC component can be difficult.

[0016] Fig. 1 illustrates a simplified block diagram of an exemplary DC current measuring circuit 100. In the illustrated example, the DC current measuring circuit 100 includes a resistor 110, a low-pass filter (LPF) 120, an amplifier 130, and a post-amplifier filter 140. The DC current measuring circuit 100 may include more or fewer components than in Fig. 1. Resistor 110 is electrically connected in a current path 150 to monitor the current flow along current path 150. The current flowing through the current path may include a DC component, an AC component, or both. In some examples, the DC component may be an undesirable component for the device including DC current sensing circuit 100. In one example, resistor 110 is a current sensing shunt resistor, which may be provided as an integrated circuit or as part of an integrated circuit with two terminals, three terminals, or four terminals. With a two terminal shunt resistor, the two terminals are used both to connect the shunt resistor in current path 150 and to measure the voltage drop across current path 150.In a four-terminal shunt resistor, two terminals are used to connect the shunt resistor to current path 150, and two additional terminals are used to measure the voltage drop across current path 150. Resistor 110 is configured to convert the current flowing through current path 150 into a voltage signal. That is, a voltage drop across resistor 110 is proportional to the current flowing through current path 150, and this voltage drop can be measured as a voltage signal by a component connected across resistor 110. The voltage signal indicates the voltage drop across resistor 110 and is proportional to the current flowing through current path 150.

[0017] The LPF 120 is connected across resistor 110 and receives the voltage signal. The LPF is connected in parallel with resistor 110 and in parallel with current path 150. The voltage signal can include both DC and AC components. The LPF 120 filters out the AC components, allowing only the DC components to exit the LPF 120. The LPF 120 can include one or more stages (e.g., one or more stages) depending on the desired filter characteristics. The LPF 120 can be single-ended or differential, depending on the desired filter characteristics. Additionally, the LPF 120 can be passive or active, depending on the desired filter characteristics. The voltage signal can be a differential signal, so that the difference between two terminals indicates the level of the voltage drop.The LPF 120 may also include a differential circuit such that the input is received at two input terminals and the output is provided to the amplifier 130 at two output terminals.

[0018] Amplifier 130 is electrically connected to the output of LPF 120 and receives a filtered voltage signal from LPF 120. The gain of resistor 110 and LPF 120 is typically less than 1. Amplifier 130 may use external power to amplify the voltage signal to facilitate current measurement. Amplifier 130 may be an inverting or non-inverting amplifier. Amplifier 130 may be an operational amplifier, a discrete differential amplifier, an integrated differential amplifier, a full differential amplifier, an instrumentation amplifier, an isolation amplifier, or a similar amplifier. In one example, amplifier 130 is a differential amplifier and includes additional circuitry (e.g., a level shifter circuit) to shift the output voltage present at zero resistance current to a non-zero value.This shift in the output voltage allows the measurement of the bipolar shunt resistor current with a differential amplifier fed from a single positive voltage rail.

[0019] The post-amplifier filter 140 is electrically connected to the output of the amplifier 130 and receives the amplified voltage signal from the amplifier 130. The post-amplifier filter 140 provides additional filtering functions for the DC current measurement circuit 100. For example, the post-amplifier filter 140 can supplement the LPF 120 to provide additional or redundant filtering of AC components. The post-amplifier filter 140 can also serve as a buffer for a sampling capacitor in an analog-to-digital converter. The post-amplifier filter 140 can further attenuate the noise generated by the amplifier, for example, when a chopper amplifier or a chopper-stabilized amplifier is used for the amplifier 130. The post-amplifier filter 140 can comprise one or more stages, depending on the desired filter characteristics. The post-amplifier filter 140 can be single-ended or differential, depending on the desired filter characteristics.Additionally, the post-amplifier filter 140 can be passive or active depending on the desired filter characteristics. In some examples, the post-amplifier filter 140 may not be required because the LPF 120 can provide sufficient filtering of unwanted signals.

[0020] The amplifier 130 or the post-amplifier filter 140 (if used) outputs a DC current measurement signal. A controller of an electronic device including the DC current measurement circuit 100 may receive the DC current measurement signal and determine the magnitude of current flowing through the current path based on the DC current measurement signal. In some examples, an analog-to-digital converter may be connected between the post-amplifier filter 140 and the controller to convert the DC current measurement signal into a digital signal for the controller. In other examples, the controller may include an analog-to-digital converter, and the DC current measurement signal may be applied directly to the analog-to-digital converter pin of the controller. The inclusion of the filter components, such as the LPF 120 provided between the resistor 110 and the amplifier 130, enables the controller to accurately measure the typically small DC component of currents with significant AC content.As used herein, a controller that determines the DC component of the current based on the DC current measurement signal may determine the DC component directly from the output of amplifier 130 or from the DC current measurement signal passed through other circuitry, e.g., the post-amplifier filter, the analog-to-digital converter, or the like, to condition the DC current measurement signal for input to the controller.

[0021] Fig. Figure 2 shows a simplified block diagram of an electronic device 200 including the DC current measuring circuit 100. The electronic device 200 includes a battery system 210, a power source 220, a load 230, and a bidirectional converter 240. The electronic device may include more or fewer components than in Fig. 2. The bidirectional converter 240 is electrically connected between the battery system 210, the power source 220, and the load 230. The bidirectional converter 240 can be configured to convert DC to DC, DC to AC, AC to DC, or AC to AC. For example, the bidirectional converter 240 converts DC power from the battery system 210 to AC or DC power at a different level for the load 230 and converts AC or DC power from the power source 220 to DC power at an appropriate level to charge the battery system 210.

[0022] Fig. 3A illustrates an example of an electronic device 200 in the form of a portable power source 200A. The portable power source 200A includes a housing 305 for accommodating an internal battery module 310. The housing 305 also includes an input / output board 315. The input / output board 315 includes a power input 320 and a power output 325. The power output 325 is, for example, an AC output for powering AC electronic devices or a DC output (e.g., a USC-C output) for powering DC electronic devices. The internal battery module 310 corresponds to the battery system 210, the power input 320 corresponds to the power source 220, and the power output 325 corresponds to the load 230. Fig. 2. The bidirectional converter 240 is coupled between the internal battery module 310, the power input 320, and the power output 325. The bidirectional converter 240 converts direct current from the internal battery module 310 into alternating current or direct current for the power output jack 325. The bidirectional converter 240 also converts the alternating current or direct current from the power input 320 into direct current at a suitable level for charging the internal battery module 310. The portable power source 200A may include additional components not described and illustrated herein. For example, the portable power source 200A may include additional power outputs 325 (e.g., both AC and DC), a display, and the like.

[0023] Fig. 3B illustrates an example of an electronic device 200 in the form of a portable power source 200B. The portable power source 200B includes a housing 330 having a first battery interface 335A and a second battery interface 335B. The first battery interface 335A and the second battery interface 335B are configured to receive a first removable power tool battery pack 340A and a second removable power tool battery pack 340B, respectively. The first removable power tool battery pack 340A and the second removable power tool battery pack 340B, individually referred to as a removable power tool battery pack 340, are, for example, lithium-ion power tool battery packs having a nominal voltage of 12 volts, 18 volts, 24 volts, 36 volts, 54 volts, 72 volts, 90 volts, 108 volts, or the like.The detachable power tool battery pack 340 can be used to power cordless indoor and outdoor power tools. The portable power source 200B also includes a power input 345 and a power output 350. The power output 350 is, for example, an AC output for powering AC electronic devices or a DC output (e.g., USC-C output) for powering DC electronic devices. The detachable power tool battery packs 340 correspond to the battery system 210, the power input 345 corresponds to the power source 220, and the power output 350 corresponds to the load 230. The bidirectional converter 240 is coupled between the detachable power tool battery packs 340, the power input 345, and the power output 350. The bidirectional converter 240 converts direct current from the removable power tool battery packs 340 into alternating current or direct current for the power output 250.The bidirectional converter 240 also converts the AC or DC power from the power input 345 to DC power at a suitable level for charging the removable power tool battery packs 340. The portable power source 200B may include additional components not described or illustrated herein. For example, the portable power source 200B may include additional power outputs 350 (e.g., both AC and DC), a display, and the like.

[0024] Fig. 3C illustrates an example of an electronic device 200 in the form of a power tool 200C. In the illustrated example, the power tool 200C is a handheld core drill. The power tool 200C may include other types of indoor and outdoor power tools, handheld or mounted, such as drills, saws, hammer drills, lighting equipment, sanders, or the like. The power tool 200C includes a housing 355 that houses a motor (e.g., a brushless direct current (BLDC) motor) and receives a removable power tool battery pack 340. The removable power tool battery pack 340 corresponds to the battery system 210, and the motor corresponds to the load 230. The bidirectional converter 240 is coupled between the removable power tool battery pack 340 and the motor.The bidirectional converter 240 converts direct current from the power tool's removable battery pack 340 into alternating current (e.g., for a BLDC motor) or direct current (e.g., for a DC motor) for the motor. In some examples, the power tool 200C may further include a power cord for receiving alternating current. In these examples, the bidirectional converter 240 also converts the alternating current power from the power input or the motor into direct current power for charging the power tool's removable battery pack 340. The power tool 300C may include additional components not described or illustrated herein.

[0025] Fig. 4 illustrates one embodiment of a flyback converter 400 that may be used in electronic device 200. Flyback converter 400 is connected to battery system 210 to step up or down the voltage from battery system 210. Flyback converter 400 includes a transformer 405 having a primary winding 410 and a secondary winding 415. In one example, transformer 405 is a coupled inductor. Primary winding 410 is electrically connected to battery system 210 via a switch 420. Switch 420 may include a semiconductor switch, such as a metal oxide semiconductor field-effect transistor (MOSFET), a wideband semiconductor FET, a bipolar junction transistor (BJT), or the like. The secondary winding 415 supplies the converted output to, for example, the load 230 or to an intermediate circuit (e.g., an inverter).

[0026] The flyback converter 400 also includes a flyback controller 425 for controlling the switch 420. The flyback controller 425 provides control signals (e.g., at an output pin) to the gate of the switch 420 to turn the switch 420 on or off. The flyback controller 425 controls the switch 420 to convert the DC power at a first voltage from the battery system 210 to DC power at a second voltage provided at the output of the flyback converter 400.

[0027] The DC current measurement circuit 100 is connected in a current path 430 between the battery system 210 and the primary winding 410 of the flyback converter 400. In the illustrative example, the resistor 110 is connected in the current path 430. The flyback controller 425 includes a current measurement pin CS (e.g., an input pin) for receiving an output signal from the resistor 110. The flyback controller 425 measures the current using the current measurement pin CS and controls the switch 420 based on the measured current. In one example, the flyback controller 425 implements a peak current mode control principle to control the switch 420 based on the current sensed at the current measurement pin CS. In other examples, the flyback controller 425 may implement a different control principle to control the switch 420. The same resistor 110 is shared by the DC current sense circuit 100 and the current sense pin CS of the flyback controller 425.Resistor 110 provides a primary peak current measurement to flyback controller 425 via current sense pin CS. Resistor 110 also converts the current drawn from battery system 210 by flyback converter 400 into a voltage used by DC current sense circuit 100.

[0028] In the Fig. In the example illustrated in Figure 4, the LPF 120 is implemented as a passive single-stage differential low-pass filter comprising two resistors 435, 440 and a capacitor 445. The amplifier 130 is implemented as a differential amplifier comprised of an operational amplifier 450, two resistors 455, 460, and two capacitors 465, 470. In some examples, the two capacitors 465, 470 may be removed. The post-amplifier filter 140 is implemented as a single-stage, single-ended, passive RC (resistor-capacitor) filter. In the example illustrated in Fig. 4, the DC current measurement circuit 100 also includes an analog-to-digital converter 475 coupled to the output of the post-amplifier filter 140. The analog-to-digital converter 475 converts the analog DC current measurement signal from the amplifier 130 into a digital value used by a controller (e.g., a second controller), for example, a battery management system, the battery system 210, or the like. The DC current measurement circuit 100 is used in the flyback converter 400 to measure the average DC current that the flyback converter 400 draws from the battery system 210. This average DC current measurement can be used to track how quickly the battery is charging or discharging, a technique known as Coulomb counting. This information can be used to model the state of charge and health of the battery system 100.For example, the second controller uses the measured DC component of the current to determine the state of charge of the battery system 210 and / or the state of health of the battery system 210 using a lookup table stored in a memory of the second controller. In some examples, the analog-to-digital converter 475 may be a part (e.g., a component) of the second controller.

[0029] Fig. 5 shows a graph 500 illustrating the output of each component of DC current sensing circuit 100 when used with flyback converter 400. A first trace 510 of graph 500 shows the voltage signal, which is the output of resistor 110. As can be seen, there is significant switching noise resembling an AC component from switch 420 in the voltage signal. A second trace 520 of graph 500 shows the voltage signal after passing through LPF 120. The filtered voltage signal does not include the switching noise and provides an average value of the DC current flowing through current path 430. A third trace 530 of graph 500 shows the amplified voltage signal from amplifier 130. The voltage signal is amplified to a level sufficient for detection by a controller. A fourth curve 540 of the diagram 500 shows the measurement signal after the amplified voltage signal has passed the post-amplifier filter 140.AC components are further attenuated from the voltage signal as the voltage signal passes post-amplifier filter 140, resulting in the measurement signal. DC current measurement circuit 100 therefore provides an accurate DC current measurement when significant AC components or AC-like noise are present in the current signal.

[0030] Fig. 6 illustrates one embodiment of a DC / DC converter 600 that may be used in electronic device 200. In the illustrated example, DC / DC converter 600 includes a dual active bridge topology with a full bridge 605 (e.g., one or more H-bridge topologies) and a high-frequency transformer 610. Full bridge 605 includes two high-side switches 615A, 615B and two low-side switches 615C, 615D. Switches 615 are, for example, MOSFETs, wide-bandgap semiconductor FETs, BJTs, or the like. The input of full bridge 605 may be connected to battery system 210. High-frequency transformer 610 includes a primary winding 620 and a secondary winding 625. The output of full bridge 605 is supplied to primary winding 620. The secondary winding 625 supplies the converted output to, for example, the load 230 or to an intermediate circuit (e.g., an inverter).In other examples, the DC / DC converter 600 may be a switching converter with different H-bridge topologies.

[0031] In the illustrative example, the DC current measuring circuit 100 is connected in a current path 630 on the primary winding side 620 of the high-frequency transformer 610. In other examples, the DC current measuring circuit 100 may be connected in a current path on the secondary winding side 625 of the high-frequency transformer 610. In the illustrated example, the resistor 110 is connected in the current path 630. The resistor 110 converts the current through the primary winding 620 into a voltage used by the DC current measuring circuit 100. The resistor 110 may consist of one or more shunt resistors and converts the current through the transformer winding into a voltage used by the DC current measuring circuit 100.

[0032] In the Fig. In the example illustrated in Figure 6, the LPF 120 is implemented as a passive, three-stage, differential low-pass filter comprising two resistors 635, 640, and one capacitor 645 per stage. The LPF 120 is configured to strongly attenuate the AC component of the voltage signal, while the DC component can be amplified and measured. The amplifier 130 is implemented as a series of amplifiers including a high-gain differential amplifier 650, an isolation amplifier 655, and a differential-to-single-ended amplifier 660. The high-gain differential amplifier 650 is optimized for sensing the voltage across the resistor 110. The isolation amplifier 655 provides isolation (e.g., galvanic isolation) between different ground reference points. The 660 differential-to-single-ended amplifier converts the differential output of the isolation amplifier into a single-ended output suitable for delivery to a control pin.The differential-to-single-ended amplifier 660 may be constructed from an operational amplifier (op-amp) circuit and may include capacitors in the feedback network to further attenuate the AC component of the voltage signal by filtering.

[0033] The post-amplifier filter 140 is designed as a single-stage, single-ended, passive RC filter (resistor-capacitor). Fig. 6, the electronic device 200 also includes a microcontroller unit (MCU) 665 that receives the single-ended output from the differential-to-single-ended amplifier 660. The single-ended output is received at an analog-to-digital converter pin ADC_IN of the MCU 665. The post-amplifier filter 140 further attenuates any remaining AC components of the measured signal before it is read from the analog-to-digital converter pin ADC_IN. The DC current measurement circuit 100 is used in the DC / DC converter 600 to measure the DC bias current in the winding of a large, high-frequency transformer. The DC current may be measured as part of an active flux compensation strategy, in which control logic may be used to actively limit the DC current through the winding of a transformer.The active flux balancing strategy can be used to prevent or reduce damage to the DC / DC converter 600 from DC current that may flow through the transformer 610.

[0034] Fig. 7 illustrates a flowchart of an example method 700 for DC current measurement using DC current measurement circuit 100. In the depicted example, method 700 includes converting a current flowing through current path 150 into a voltage signal using resistor 110 electrically connected into current path 150 (at block 710). Resistor 110 is, for example, a shunt resistor used for current sensing, which converts the current flowing through resistor 110 into a voltage signal to facilitate current measurement. The voltage signal indicates the voltage drop across resistor 110 caused by the current flowing through current path 150.

[0035] The method 700 includes filtering the voltage signal (in block 720) using the LPF 120, which is electrically connected to the resistor 110. The LPF 120 receives the voltage signal from the resistor 110. The LPF 120 may include an RC (resistor-capacitor) circuit to filter out any AC components from the voltage signal. The LPF 120 may include multiple filter stages to adjust the degree of attenuation.

[0036] The method 700 includes amplifying the voltage signal using amplifier 130 electrically connected to the LPF 120 to provide a measurement signal (at block 730). The amplifier 130 amplifies the voltage to a level suitable for detection by, for example, a controller or control circuit. The measurement signal may be converted to a digital signal by an analog-to-digital converter before being provided to a controller. In some examples, the controller may include an integrated analog-to-digital converter and receive the measurement signal directly from the DC current measurement circuit 100.

[0037] Although the disclosure has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the disclosure as described. Various features and advantages are set forth in the following claims.

Claims

[1] Direct current (DC) current measuring circuit, comprising: a shunt resistor electrically connected in a current path, wherein a current flowing through the current path includes an alternating current (AC) component; a low-pass filter (LPF) electrically connected across the shunt resistor and configured to filter a voltage signal across the shunt resistor and output a filtered voltage signal; and an amplifier electrically connected to the LPF and configured to receive the filtered voltage signal and output a measurement signal, the measurement signal providing a measurement of a DC component of the current. [2] The DC current measuring circuit of claim 1, wherein the LPF is a passive differential filter having one or more stages. [3] The DC current measuring circuit of claim 1, wherein the LPF is a passive three-stage differential filter. [4] The DC current measuring circuit of claim 1, wherein the amplifier comprises a differential amplifier. [5] The DC current measuring circuit of claim 4, wherein the amplifier further comprises: an isolation amplifier electrically coupled to the differential amplifier and configured to provide isolation between different ground reference points; and a differential-to-single-ended amplifier electrically coupled to the isolation amplifier and configured to convert a differential output signal of the isolation amplifier into a single-ended output signal. [6] The DC current measuring circuit of claim 1, further comprising a controller configured to determine the DC component of the current flowing through the current path based on the measurement signal. [7] The DC current measuring circuit of claim 6, further comprising an analog-to-digital converter electrically coupled between the amplifier and the controller and configured to convert the measurement signal into a digital signal and provide the digital signal to the controller. [8] The DC current measurement circuit of claim 1, further comprising a post-amplifier filter electrically coupled to the amplifier and configured to filter the measurement signal. [9] The DC current measuring circuit of claim 1, wherein the LPF is configured to filter the AC component of the current from the voltage signal. [10] Electronic device comprising: a power converter electrically connected between a battery system and a load; and a direct current (DC) current measuring circuit electrically connected in a current path of the current transformer and a resistor electrically connected in the current path, wherein a current flowing through the current path has an alternating current component; a low-pass filter (LPF) electrically connected across the resistor and configured to filter a voltage signal across the resistor and output a filtered voltage signal; and an amplifier electrically connected to the LPF and configured to amplify the filtered voltage signal and output a measurement signal. [11] The electronic device of claim 10, wherein the current converter is a flyback converter. [12] The electronic device of claim 11, wherein the flyback converter comprises a switch, the electronic device further comprising: a flyback converter controller comprising an input pin connected to a terminal of the resistor and an output pin connected to the switch, the flyback converter controller being configured to determines a current value based on a signal at the input pin and provides a control signal at the output pin to control the switch based on the current value; and a second controller configured to determines a DC component of the current using the DC current measuring circuit, and determines a state selected from a group consisting of a battery system state of charge and a battery system state of health based on the DC component of the current. [13] The electronic device of claim 10, wherein the power converter is a DC / DC converter comprising a high frequency transformer and one or more H-bridge topologies, the current path delivering power from the dual active bridge to a winding of the high frequency transformer. [14] The electronic device of claim 13, further comprising: an isolation amplifier having an input side and an output side, configured to provide galvanic isolation between the input side and the output side, wherein the input side is connected to the amplifier to receive the measurement signal, and wherein the output side provides a differential output signal corresponding to the measurement signal; a differential-to-single-ended amplifier connected to the output side of the isolation amplifier and configured to convert the differential output signal into a single-ended output signal; and a microcontroller unit including a digital pin configured to receive the single-ended output signal from the differential-to-single-ended amplifier. [15] The electronic device of claim 12, wherein the LPF is a passive three-stage differential filter. [16] Portable power source comprising: a battery system; a power converter electrically connected to the battery system; and a direct current (DC) current measuring circuit electrically connected in a current path of the current transformer and a resistor electrically connected in the current path, wherein a current flowing through the current path has an alternating current component; a low-pass filter (LPF) electrically connected across the resistor and configured to filter a voltage signal across the resistor and output a filtered voltage signal; and an amplifier electrically connected to the LPF and configured to amplify the filtered voltage signal and output a measurement signal. [17] A portable power source according to claim 16, wherein the power converter is a flyback converter with a switch, the portable power source further comprising: a flyback converter controller comprising an input pin connected to a terminal of the resistor and an output pin connected to the switch, the flyback converter controller being configured to determines a measure of current based on a signal at the input pin and provides a control signal at the output pin to control the switch based on the measure of current; and a second controller configured to using the DC current measuring circuit, a DC component of the current is determined and determines a state selected from a group consisting of a battery system state of charge and a battery system state of health based on the DC component of the current. [18] A portable power source according to claim 17, wherein the DC current measuring circuit further comprises: an analog-to-digital converter electrically connected to the amplifier and configured to convert the measurement signal at an output of the analog-to-digital converter into a digital signal, wherein the output of the analog-to-digital converter is connected to an input pin of the second controller. [19] The portable power source of claim 16, wherein the power converter is a DC / DC converter comprising a high frequency transformer and one or more H-bridge topologies, the current path delivering the current from the dual active bridge to a winding of the high frequency transformer, the portable power source further comprising: an isolation amplifier comprising an input side and an output side and configured to provide galvanic isolation between the input side and the output side, wherein the input side is connected to the amplifier to receive the measurement signal, and wherein the output side provides a differential output corresponding to the measurement signal; a differential-to-single-ended amplifier connected to the output side of the isolation amplifier and configured to convert the differential output signal into a single-ended output signal; and a microcontroller unit including a digital pin configured to receive the single-ended output signal from the differential-to-single-ended amplifier. [20] A portable power source according to claim 16, wherein the LPF is a passive, three-stage differential filter.

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