Current measurement circuit and method
By introducing switchable gain amplifiers and gain control sub-circuits into the current measurement circuit, the problems of low resolution and high component cost under high current loads are solved, and high accuracy measurement and cost reduction over a wide current range are achieved.
Patent Information
- Application Number
- CN202410768650.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-06-22
- Filing Date
- 2024-06-14
- Publication Date
- 2024-12-24
AI Technical Summary
Existing current measurement circuits are difficult to maintain high resolution when monitoring high current loads, and the components are costly, especially when measuring saturation is prone to occur.
A switchable gain amplifier current measurement circuit is designed to automatically adjust the gain of the amplifier through the gain control sub-circuit and controller, selectively change the current path to increase resolution at low currents and avoid saturation at high currents.
High-precision current measurements over a wide current range are achieved, avoiding measurement saturation, reducing component costs, and optimizing resolution with automatic gain adjustment.
Smart Images
Figure CN119178918A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to a current measurement circuit and a method for controlling a current measurement device. In particular, the present invention relates to a switchable gain amplifier with saturation protection and a current protection device and a load driver including the switchable gain amplifier. Background Art
[0002] In modern vehicles, it is common to have several loads that consume very high currents. For example, in high demand situations (such as in city driving scenarios), the vehicle's electric power steering (EPS) system can draw up to 80 to 100 amps. In contrast, when the vehicle is traveling at higher speeds in highway conditions, the current drawn by the EPS is lower because the steering action is relatively minimal. As vehicles include more automated systems, the range of current demands on load driver circuits continues to increase. For example, a load driver circuit may need to provide current in the range of 1 amp to 800 amps.
[0003] The above current ranges present specific challenges to current monitoring circuits associated with load drivers. Namely, it is often necessary to include shunts or current sensing resistors as current measurement sensors to monitor operation in vehicle systems and detect faults. For example, current monitoring circuits can be used to trigger electronic fuses, so the current must be measured correctly to detect possible overcurrent or short circuits. However, in load drivers that can support very high currents, the gain of the current sensor must be moderated to avoid measurement saturation. However, this reduces the measurement resolution at lower currents.
[0004] In load drivers capable of delivering very high currents, dual drivers are often used to avoid exceeding the technical limits of the MOSFETs. In this case, one configuration that addresses the above issues is to include dual current measurements, with the outputs of the two measurements combined to measure the total current. However, while this allows for lower gain on each channel, thereby improving the overall measurement resolution, it increases component cost because a current amplifier is required for each channel. In addition, the combined measurement requires a microcontroller with several input pins, which adds expense and complexity.
[0005] Therefore, there is a need to solve the above problems and provide a current measurement circuit that has good measurement resolution for low currents while still being able to monitor overcurrent and minimize component costs. Summary of the invention
[0006] According to a first embodiment, a current measurement circuit is provided, the current measurement circuit comprising: an operational amplifier, the operational amplifier comprising two input terminals and an output terminal; an input connector, the input connector being used to connect the two input terminals across a current sensing resistor; a gain control subcircuit, the gain control subcircuit being connected to the output terminal, wherein the gain control subcircuit comprises a switch operable to select a current path from a plurality of current paths; and a measurement output terminal, the measurement output terminal being connected to the gain control subcircuit, for outputting a signal indicating a measured current based on the selected current path, the gain control subcircuit being configured to select a gain across the operational amplifier based on a ratio between the input connector and the selected current path.
[0007] Thus, a switchable gain amplifier may be provided that allows saturation protection by selectively varying its gain. Thus, high resolution current measurement may be achieved at low current levels by selecting a higher gain configuration, while higher currents may be accommodated without saturating the signal by selecting a lower gain configuration.
[0008] In some forms, the gain control subcircuit includes a plurality of output resistors, and the plurality of current paths are connected through one or more of the plurality of output resistors.
[0009] In some forms, the gain control subcircuit includes a high gain current path and a low gain current path, wherein the low gain current path has a lower resistance than the high gain current path, and wherein the switch is operable to selectively connect the output to one of the high gain current path and the low gain current path.
[0010] In some forms, the current measurement circuit further comprises a controller for controlling the switch based on a characteristic indicative of the magnitude of the sensed current. In this way, the controller can automatically vary the gain of the measurement circuit to optimize resolution for the risk of measurement saturation.
[0011] In some forms, the controller controls the switch based on a characteristic exceeding a threshold, and wherein the threshold is selected to indicate a current amplitude below a saturation amplitude associated with the operational amplifier. Thus, by selecting a threshold lower than the current amplitude level at which the measurement will saturate, the risk of measurement saturation can be avoided.
[0012] In some forms, the characteristic includes voltage.
[0013] In some forms, the voltage at the output is measured relative to ground.
[0014] In some forms, the controller includes a comparator for comparing the voltage on the measured output with a threshold value. In this way, the controller can provide a fast response.
[0015] In some forms, the controller further includes a voltage follower connected between the measurement output and the comparator, the voltage follower generating an input signal for the comparator based on the voltage at the measurement output. Thus, the voltage follower can be used as an input buffer to avoid the influence of the comparator on the measurement signal.
[0016] In some forms, the measurement output includes a high gain measurement output and a low gain measurement output, and wherein the switch is operable to select a current path that provides a lower gain signal on the low gain measurement output and a current path that provides a higher gain signal on the high gain measurement output.
[0017] In some forms, the gain control subcircuit includes a first output resistor and a second output resistor connected in series between the output terminal and ground, and the switch is operable to bypass the first output resistor, and wherein the high gain measurement output terminal is connected to ground through the first output resistor and the second output resistor, and the low gain measurement output terminal is connected to ground through the second output resistor.
[0018] According to a second embodiment, there is provided a load driver, comprising the current measurement circuit according to any one of the above aspects.
[0019] According to a third embodiment, a current protection device is provided. The current protection device includes a current measurement circuit according to any one of the above aspects.
[0020] According to a fourth embodiment, there is provided a method of controlling a current measurement circuit according to any one of the above aspects, the method comprising the following steps: identifying a characteristic exceeding a threshold, wherein the threshold is selected to indicate a current amplitude below a saturation amplitude associated with the operational amplifier; and controlling the switch to select a current path that reduces the gain across the operational amplifier.
[0021] In an embodiment, the controller further comprises hysteresis for preventing oscillation of the comparator output. Thus, the threshold value may be supplemented by hysteresis, for example by a feedback resistor from the output to the positive input located below the comparator. Thus, this may avoid oscillation of the output of the comparator where there is a continuous rapid tuning on and off of the switch when there is a low amplitude oscillation of the measured current around the threshold value. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Illustrative arrangements will now be described with reference to the accompanying drawings, in which:
[0023] Figure 1 shows a current measurement circuit according to a first example embodiment;
[0024] Figure 2 shows a current measurement circuit according to a second example embodiment;
[0025] Figure 3 Shows Figure 2 An alternative representation of the current measurement circuit 1 shown;
[0026] Figure 4 shows a current measurement circuit according to a fourth example embodiment; and
[0027] Figure 5 A current measurement circuit according to a fifth example embodiment is shown. DETAILED DESCRIPTION
[0028] Figure 1 A current measurement circuit 1 according to a first exemplary embodiment is shown. The current measurement circuit 1 includes a shunt resistor 21 connected on a line between a power source 11 such as a battery and a load 10. A bypass 2 is connected around the shunt resistor 21 and serves as an input connected to an operational amplifier (op-amp) 3 in a differential amplifier configuration. An input resistor 4 is connected to the inverting input terminal of the operational amplifier 3 on the line.
[0029] The gain control subcircuit 5 is connected to the output line 6 from the operational amplifier 3. The gain control subcircuit 5 includes a first output resistor 51 connected between the output line 9 and ground, and includes a parallel second output resistor 52 switchably connected between the output line 6 and ground. The second output resistor 52 is switchably connected under the control of a switch 53. In this way, the operation of the switch 53 controls the gain of the current sensing circuit based on changing the resistance of the gain control subcircuit 5.
[0030] In this connection, the switch 53 can be implemented as a MOSFET that can be controlled to adjust the gain of the current measurement circuit 1 based on the combination of gain setting resistors used. That is, the overall gain is equal to the resistance provided by the gain control subcircuit 5 divided by the resistance provided by the input resistor 4. Thus, when the switch 53 is closed, the second output resistor 52 is connected, reducing the resistance of the gain control subcircuit 5. In this way, the gain is reduced. This allows higher currents to be measured without saturation. Conversely, when the switch 53 is opened, thereby disconnecting the second output resistor 52, the output resistance increases, thereby providing increased gain. This allows lower currents to be measured with higher resolution.
[0031] The switch 53 is controlled by a controller 54. The controller 54 may be implemented using, for example, a microcontroller or a comparator that provides a signal for controlling the switch 53, such that the switch 53 is opened when the measured voltage exceeds a threshold value and is closed when the measured voltage is below the threshold value. Thus, at higher currents where the voltage exceeds a predetermined threshold value, the gain control subcircuit 5 is set to a lower gain to avoid saturation. Conversely, at lower currents where the voltage is below a predetermined threshold value, the gain control subcircuit 5 is set to a higher gain to improve resolution.
[0032] Figure 2 1 shows a current measurement circuit 1 according to a second exemplary embodiment. This embodiment is similar to the first exemplary embodiment except that the gain control subcircuit 5 includes a first output resistor 51 and a second output resistor 52 connected in series between the output line of the operational amplifier 3 and the ground, and the output line 6 is divided into a high gain measurement output line 61 and a low gain measurement output line 62. In addition, the operation of the switch 53 is used to control the gain of the current sensing circuit 1 based on changing the resistance of the gain control subcircuit 5.
[0033] In this connection, when the switch 53 is open, the output resistance of the gain control subcircuit 5 is the sum of the first output resistor 51 and the second output resistor 52, resulting in a high gain output on the high gain measurement output line 61. In this way, the high gain measurement output line 61 provides a high gain output that can be used to measure low currents. However, as the current increases, saturation will occur. To address this problem, the switch 53 can be closed, thereby bypassing the first output resistor 51. In this way, the gain is based on the resistance of the second output resistor 52 divided by the resistance of the input resistor 4, resulting in a low gain output being applied to the low gain measurement output line 62. Therefore, the closure of the switch 53 is used to disable the high gain, low current measurement chain output on the high gain measurement output line 61.
[0034] The switch 53 in this second example is controlled by the controller 54 similarly to the first example embodiment. Therefore, when the measured voltage is below the threshold, the switch 53 is closed, thereby providing a higher gain. Conversely, when the voltage exceeds the predetermined threshold, the switch 53 is opened, providing a lower gain, thereby avoiding saturation.
[0035] Figure 3 Shows Figure 2An alternative representation of the current measurement circuit 1 is shown, in which the corresponding feature numbers are the same. In this case, the controller 54 operates by comparing the threshold voltage input 55 with the controller input 56 taken from the low gain measurement output line 62. Thus, when the voltage on the controller input 56 exceeds the threshold voltage applied to the threshold voltage input 55, the switch 53 is opened to provide a lower gain in the current measurement circuit. The low gain measurement output line 62 is used for voltage measurement because this is used for high current measurement, and the gain on this low gain measurement output line is stable and therefore is not affected by the gain changes achieved using the switch 53.
[0036] Figure 4 1 shows a current measurement circuit 1 according to a third example embodiment. This embodiment is similar to Figure 3 In this case, the signal applied to the switch input 58 is controlled by a comparator 57, which comprises an operational amplifier with positive feedback for comparing the voltage on the input line 56 with the voltage on the threshold voltage input 55. The input line 56 is connected to a voltage follower 58, which simply follows the voltage on the low gain measurement output line 62, but is used to prevent the comparator 57 from interfering with the signal on the low gain measurement output line 62. In particular, the provision of the voltage follower 58 can be used to mitigate the effects of temperature changes on the switching threshold of the controller 54.
[0037] In addition, the controller 54 in this embodiment also includes hysteresis around the comparison threshold to avoid oscillations. That is, the threshold set by the input 55 of the comparator 57 is supplemented by the feedback resistor 581 from the output 58 to the positive input below the comparator 57. Thus, this provides hysteresis for avoiding oscillations of the output 58 of the comparator 57, and thereby avoids continuous rapid tuning-on and tuning-off of the switch 53 in the presence of low amplitude oscillations of the measured current around the threshold.
[0038] Therefore, with the above-described embodiment, when the voltage exceeds the predetermined threshold, the comparator 57 generates a switch command signal on the switch input 58 to open the switch 53 to provide a lower gain. In this way, saturation of the measurement signal can be avoided.
[0039] It should be understood that the current measurement circuit can be implemented to provide more than two gains. In this regard, Figure 5 A current measurement circuit 1 according to a fourth example embodiment is shown. In this case, the gain control subcircuit 5 comprises two gain control switches 531, 532 independently controlled by a controller 54 in order to vary the output resistance. This provides an additional gain level that can be used to vary the amplification of the current measurement circuit.
[0040] Therefore, using the above-described embodiments, a variable gain current measurement amplifier can be provided, which allows accurate measurement of current over a wide amplitude range. In particular, saturation of the measurement amplifier can be avoided at high currents, while still providing high resolution at lower currents.
[0041] It should be understood that the above embodiments are only for illustrative purposes and show applications. In fact, the embodiments can be applied to many different configurations, the details of which are straightforward for those skilled in the art.
[0042] For example, a microcontroller can be used to monitor the measurement chain and control the switching of the gain control subcircuit. However, if the current changes suddenly, the measurement circuit can go into saturation between two polling cycles of the microcontroller. In this way, using a comparator to control the gain change allows fast gain switching based on a logic function.
[0043] It will also be appreciated that in some arrangements the low gain (high current) measurement line may be continuously monitored by providing a dedicated low gain measurement output line 62 having two output resistors in series.
[0044] Finally, it should be understood that various embodiments can be implemented to combine the above Figure 4 The hysteresis principle described in . Thus, a hysteresis around the comparison threshold can be used to strengthen the controller to avoid oscillations. In an embodiment, this hysteresis can be implemented on an analog comparator with feedback from the output to the positive input, or digitally in a microcontroller by adjusting the threshold accordingly once a crossing of the initial threshold is detected.
Claims
1. A current measurement circuit, comprising: An operational amplifier, the operational amplifier comprising two input terminals and an output terminal; an input connector connecting the two input terminals across a current sensing resistor; a gain control subcircuit connected to the output, wherein the gain control subcircuit includes a switch operable to select a current path from a plurality of current paths; and a measurement output terminal connected to the gain control subcircuit to output a signal indicative of the measured current based on the selected current path, The gain control subcircuit is configured to select a gain across the operational amplifier based on a ratio between the input connector and the selected current path.
2. The current measuring circuit according to claim 1, in, The input connector includes an input resistor, and The gain control circuit includes a plurality of output resistors, and the plurality of current paths are connected through one or more output resistors among the plurality of output resistors.
3. The current measurement circuit according to claim 1 or 2, wherein: The gain control subcircuit includes a high gain current path and a low gain current path, wherein the low gain current path has a lower resistance than the high gain current path, and wherein the switch is operable to selectively connect the output terminal to one of the high gain current path and the low gain current path.
4. The current measurement circuit of any one of claims 1 to 3, further comprising a controller that controls the switch based on a characteristic indicative of the sensed current magnitude.
5. The current measurement circuit according to claim 4, wherein: The controller controls the switch based on the characteristic exceeding a threshold, and wherein the threshold is selected to indicate a current amplitude below a saturation amplitude associated with the operational amplifier.
6. The current measurement circuit according to claim 4 or 5, wherein: The characteristic includes voltage.
7. The current measurement circuit according to claim 6, wherein: The voltage on the output is measured with respect to ground.
8. The current measurement circuit according to any one of claims 4 to 7, wherein: The controller includes a comparator that compares the voltage at the measurement output to a threshold value.
9. The current measurement circuit according to claim 8, wherein: The controller also includes a voltage follower connected between the measurement output and the comparator to generate an input signal to the comparator based on a voltage on the measurement output.
10. The current measurement circuit according to claim 8 or 9, wherein: The controller also includes hysteresis for preventing oscillation of the comparator output.
11. The current measuring circuit according to any one of claims 1 to 10, in, The measurement output terminal includes a high-gain measurement output terminal and a low-gain measurement output terminal, and The switch is operable to select a current path for providing a lower gain signal at the low gain measurement output and a current path for providing a higher gain signal at the high gain measurement output.
12. The current measuring circuit according to claim 11, in, The gain control subcircuit includes a first output resistor and a second output resistor connected in series between the output terminal and ground, and the switch is operable to bypass the first output resistor, and The high-gain measurement output terminal is connected to the ground through the first output resistor and the second output resistor, and the low-gain measurement output terminal is connected to the ground through the second output resistor. 13 . A load driver, comprising the current measurement circuit according to claim 1 .
14. A current protection device, comprising the current measurement circuit according to any one of claims 1 to 12.
15. A method for controlling a current measurement circuit according to any one of claims 1 to 12, the method comprising the following steps: identifying a characteristic that exceeds a threshold, wherein the threshold is selected to indicate a current amplitude that is below a saturation amplitude associated with the operational amplifier; and The switch is controlled to select a current path for reducing the gain across the operational amplifier.