Test device, overcurrent protector and method for testing overcurrent protector

Abstract

The present disclosure relates to a test device, an overcurrent protector, and a method for testing an overcurrent protector. A first switch and a second switch are configured to connect a first terminal and a second terminal of the overcurrent protector (4) to a first capacitor (15) and a second capacitor (16), respectively. The first capacitor (15) and the second capacitor (16) are precharged to a first voltage and a second voltage, wherein the second voltage is lower than the first voltage. A controller (18) switches the first switch (15) and the second switch (16) to their test positions, which establishes a current path from the first capacitor (15) through the overcurrent protector (4) to the second capacitor (16). The first voltage and the second voltage are selected so that a peak current generated in the current path is greater than an overcurrent threshold of the overcurrent protector (4).

Description

Technical Field

[0001] The present disclosure relates to a test device for an overcurrent protector and an overcurrent protector incorporating the test device. Specifically, the present disclosure relates to a self-test circuit and overcurrent protector for power supplies used in multi-domain controllers and other vehicle electronic control units. The present disclosure also relates to a method for testing an overcurrent protector. Background Art

[0002] Safety-critical electronic devices used in autonomous road vehicles, such as multi-domain controllers, require safety devices to identify fault conditions and take action to protect components and operations. This requirement applies not only to the operation of the CPU and controllers, but also to the power supplies that drive these components. Therefore, power supply units in automotive applications often have an overcurrent protector (OCP) circuit that is used to protect the load from abnormal current conditions caused by, for example, a short circuit. For example, a short circuit that causes a failure of the regulated power supply to the battery voltage may cause electrical overstress in the circuits that supply the load. However, such overcurrent protectors themselves usually need to be tested when the system is powered on to confirm that they are operating properly. Therefore, overcurrent protectors usually include or are associated with self-test circuits that subject the overcurrent protector to simulated overcurrent events to verify that it is operating properly.

[0003] US2013 / 0214806 discloses a conventional self-test circuit for an overcurrent protector. In this configuration, a capacitor is charged and discharged using high-side and low-side switches, with the test current measured using a high-side shunt resistor and actively monitored by a monitoring circuit during the test. However, this configuration has several drawbacks. First, it requires the power supply to be capable of delivering sufficiently high peak current to serve as the test current. This significantly increases the complexity of the power supply, as it not only requires additional control but also requires consistent circuit design and implementation for high output currents. Furthermore, the test current and voltage across the output capacitor must be actively monitored and limited to their maximum current and voltage ratings. The presence of the high-side shunt resistor also causes losses during normal operation. Finally, the overcurrent protector device under test is also shorted to ground via the low-side switch. This limits the application of this type of circuit, as some overcurrent protectors are too sensitive to operate when the circuit contains a hard short to ground.

[0004] Therefore, the present disclosure is directed to solving these problems. Summary of the Invention

[0005] According to a first aspect, a test device for testing an overcurrent protector is provided, which provides an electrical connection between a first terminal and a second terminal, and the electrical connection is interrupted when the current between the first terminal and the second terminal exceeds an overcurrent threshold. The test device includes: a first switch, which can be switched to a test position to connect the first terminal to a first capacitor; a second switch, which can be switched to a test position to connect the second terminal to a second capacitor; a pre-charging circuit, which charges the first capacitor to a first voltage and charges the second capacitor to a second voltage, wherein the second voltage is lower than the first voltage; and a controller, which switches the first switch and the second switch to their test positions to establish a current path from the first capacitor through the overcurrent protector to the second capacitor, wherein the first voltage and the second voltage are set to generate a peak current greater than the overcurrent threshold in the current path.

[0006] In this way, the difference between the voltages of the two capacitors can be used to simulate an overcurrent event. Therefore, an overcurrent protector used to protect a load can be self-tested by subjecting the overcurrent protector to a simulated event. Importantly, a sufficiently high peak current can be generated to trigger the overcurrent protector without requiring a conventional power supply for powering the load to provide this function. At the same time, the structure also avoids the need to short-circuit the overcurrent protector to ground. That is, the current flow is generated by the balancing effect between the voltages of the two capacitors on both sides of the overcurrent protector. Therefore, instead of a hard short circuit to ground, the current flows to the lower second voltage of the second capacitor. Therefore, this allows the test device to be used with a wider range of overcurrent protectors that otherwise may be too sensitive to ground circuit configurations.

[0007] In an embodiment, a first capacitor is connected to the first terminal and a second capacitor is connected to the second terminal. In this manner, the test device circuit can be configured as a unit including capacitors. Alternatively, an embodiment can reuse existing capacitors from adjacent circuits by switchably connecting them to the overcurrent protector to generate a balancing current between the existing capacitors.

[0008] In an embodiment, at least one of the first and second capacitors is grounded. This stabilizes the potential of the ground plate and simplifies charging of the positive plate. In an embodiment, at least one of the first and second capacitors is polarized. This allows for a higher capacity energy storage unit.

[0009] In one embodiment, the test device further includes a resistor connected along the current path to limit the current. This thereby regulates the balancing current in the current path. Advantageously, in this configuration, the resistor is placed in the test current path, rather than in the conventional power line to the load. Therefore, the resistor does not cause losses during normal operation of the device under test.

[0010] In an embodiment, a resistor is connected between the first capacitor and the first switch.

[0011] In an embodiment, the first switch and the second switch are switchable to an operating position, in which the first switch and the second switch connect the first terminal and the second terminal to the power supply and the load, respectively. In this manner, the test device can switch the overcurrent protector between an operating position, in which the normal power line is connected to the load, and a test position, in which the overcurrent protector is disconnected from the normal power supply and load and connected to the capacitor. Thus, a simulated overcurrent event can be generated in a test current path that is independent of the normal current path used to power the load during normal operation.

[0012] In an embodiment, the precharge circuit includes one or more precharge switches that connect the first capacitor and the second capacitor to a precharge power supply to charge to a first voltage and a second voltage, respectively. In this manner, the capacitors can be precharged as part of a test sequence, where the capacitors are first connected to the precharge power supply for charging and then connected to the overcurrent protector. A controller can control the switching of the associated switches to implement the test sequence.

[0013] In an embodiment, the controller switches the first and second switches to their test positions for a predetermined test duration, wherein the predetermined test duration is longer than a specified maximum reaction time of the overcurrent protector. In this manner, if the overcurrent protector is functioning properly, it will interrupt the flow of current within its specified maximum reaction time. Conversely, a defective overcurrent protector will allow the balancing current between the capacitors to flow for a period exceeding the specified maximum reaction time.

[0014] In an embodiment, the testing device further includes an evaluation module that identifies a fault in the overcurrent protector based on a voltage across one of the first capacitor and the second capacitor after a predetermined test duration. Thus, a fault condition of the overcurrent protector may be determined based on a voltage level across any one of the plurality of capacitors at the end of the predetermined test duration.

[0015] According to a second aspect, an overcurrent protector is provided, comprising a test device according to any one of the above statements. In this way, a combined device is provided for overcurrent protection and for performing a self-test to verify its working state.

[0016] According to a third aspect, a method for testing an overcurrent protector is provided, which provides an electrical connection between a first terminal and a second terminal, and the electrical connection is interrupted when the current between the first terminal and the second terminal exceeds an overcurrent threshold. The method includes the following steps: using a precharging circuit to precharge the first capacitor to a first voltage and precharge the second capacitor to a second voltage, wherein the second voltage is lower than the first voltage; and using a controller to control the first switch and the second switch to switch to a test position to connect the first terminal to the first capacitor and the second terminal to the second capacitor to establish a current path from the first capacitor through the overcurrent protector to the second capacitor, wherein the first voltage and the second voltage are set to generate a peak current greater than the overcurrent threshold in the current path.

[0017] In this way, a test method is provided in which an overcurrent event is simulated using a balancing current generated by the difference between the voltages of two capacitors. This allows the generation of a sufficiently high peak current for triggering an overcurrent protector without requiring the conventional power supply used to power the load to provide this function or without shorting the overcurrent protector to ground.

[0018] In an embodiment, the step of controlling the first switch and the second switch includes switching the first switch and the second switch from a working position to a test position. In the working position, the first switch and the second switch connect the first terminal and the second terminal to the power supply and the load, respectively.

[0019] In an embodiment, the precharging step includes switching one or more precharging switches to connect the first capacitor and the second capacitor to a precharging power source to charge to the first voltage and the second voltage, respectively.

[0020] In an embodiment, the step of controlling the first switch and the second switch comprises switching the first switch and the second switch to their test positions for a predetermined test duration, wherein the predetermined test duration is longer than a specified maximum reaction time of the overcurrent protector.

[0021] In an embodiment, the step of controlling the first switch and the second switch includes: using an evaluation module to identify a fault in the overcurrent protector based on the voltage of one of the first capacitor and the second capacitor after a predetermined test duration. In this way, if the change in the voltage of either capacitor exceeds a threshold value (the threshold value corresponds to the expected voltage change caused by the balancing current within the specified maximum reaction time of the overcurrent protector), a fault can be identified. For example, if the voltage of the second capacitor is higher than the maximum expected voltage at the end of the test, the overcurrent protector must have failed to interrupt the balancing current within the specified maximum reaction time. Similarly, if the voltage of the first capacitor is lower than the minimum expected voltage at the end of the test, the same fault can also be identified. The expected voltage can be predetermined or dynamically applied. In addition, the threshold value can be set to take into account tolerances and circuit losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Example embodiments will now be described with reference to the accompanying drawings, in which:

[0023] Figure 1 shows a schematic diagram of a power supply including a self-test circuit;

[0024] Figure 2 A schematic circuit diagram showing a first embodiment of a test circuit;

[0025] Figure 3 shows a graph illustrating the variation of current flowing through a test circuit during an example test;

[0026] Figure 4 and Figure 5 shows a graph illustrating changes in voltage at a first capacitor and a second capacitor during an example test;

[0027] Figures 6 to 10 A schematic circuit diagram showing a test circuit according to a second embodiment through the steps of a test sequence; and

[0028] Figure 11 A schematic circuit diagram of a test circuit according to a third embodiment is shown. DETAILED DESCRIPTION

[0029] Figure 1An exemplary structure of a power supply 2 that powers a multi-domain safety controller 9 is shown. Power supply 2 receives power from a battery 1 and includes a protection circuit 3 and a DC / DC converter 7, which may be part of a power management integrated circuit (PMIC). Protection circuit 3 includes an overcurrent protector 4, which includes a switch 5 that provides a circuit breaker for protecting safety controller 9 from overcurrent events. In this example, protection block 3 is positioned before the preregulator of DC / DC converter 7. However, it will be appreciated that protection block 3 may be positioned after the preregulator.

[0030] In an overcurrent event (such as a short circuit 8 around the preregulator high side transistor), the sensor 6 within the overcurrent protector 4 will detect the rising input current, which then prompts the switch 5 to open the circuit, thereby stopping the current flow.

[0031] In order to comply with the requirements of the Automotive Safety Integrity Level (ASIL), the protection block 3 is provided with a self-test circuit 10 , which tests the working state of the overcurrent protector 4 .

[0032] Figure 2 A self-test circuit 10 according to an exemplary embodiment is shown. The self-test circuit 10 is switchably connected to a first terminal 12 and a second terminal 13 of the overcurrent protector 4 via switches 11 and 14. In this embodiment, the switches are configured as back-to-back NMOSFETs. The switches 11 and 14 switch between a working position and a test position during operation. In the working position, the first terminal 12 and the second terminal 13 are connected to the battery 1 and the PMIC 7 and the safety controller 9, respectively. In the test position, the first terminal 12 is connected to the first capacitor 15 and the second terminal 13 is connected to the second capacitor 16 to perform a test. Therefore, when in the test position, the device under test (i.e., the overcurrent protector 4) is disconnected from its normal power supply (i.e., the battery 1) and the load (the safety controller 9), and is connected to the self-test circuit.

[0033] A first capacitor 15 can be connected to the first terminal 12, and a second capacitor 16 can be connected to the second terminal 13. A balancing resistor 17 is also provided between the first capacitor 15 and the first terminal 12. A pre-charge circuit (not shown) is also provided to pre-charge the first and second capacitors before initiating a test sequence.

[0034] When the test sequence is initiated, the controller 18 switches the first switch 11 and the second switch 14 to connect the first terminal 12 to the first capacitor 15 and the second terminal 13 to the second capacitor 16. This establishes a current balancing configuration between the precharged capacitors 15 and 16 and through the overcurrent protector 4. By precharging the first capacitor 15 to a higher voltage than the second capacitor 16, a balanced current is established through the overcurrent protector 4. For example, the first capacitor 15 and the second capacitor 16 can be precharged with voltages V1 and V2, respectively, where, for example, V1 = 2·V2. The component values ​​of the resistor 17 and the first and second capacitors 15 and 16, as well as the precharge voltages V1 and V2, are selected so that during the test, the balanced current between the capacitors remains above the overcurrent detection threshold for a period of time longer than the maximum specified reaction time of the overcurrent protector.

[0035] In this regard, if the overcurrent protector 4 is operating normally, then at the end of the test period, the voltage levels of the capacitors 15 and 16 will not reach equilibrium because the overcurrent protector 4 will open the circuit. Therefore, a pass or fail decision regarding the operating status of the overcurrent protector can be made based on the voltage level across any of the multiple capacitors at the end of the test. This configuration thus avoids the need to actively monitor current during testing, while the maximum voltage and current levels are limited by the inherent characteristics of the components used, without requiring complex control.

[0036] Since the test current is neither directly measured nor controlled, the described architecture also eliminates the need for a high-side current monitor. Furthermore, the input power source (i.e., battery 1 in this embodiment) does not need to provide the instantaneous peak energy required for the test current, as this is provided by the precharged first capacitor 15, which acts as a buffer. Furthermore, the elimination of the shunt resistor reduces losses in the main current path during normal operation. Furthermore, since all signals are predefined by component selection, neither voltage nor current regulation is required.

[0037] As an illustrative example, the following specifications can be used to Figure 2 The circuit shown is configured:

[0038] First capacitor 15 = second capacitor 16 = 20 μF ± 30%

[0039] The voltage of the first capacitor 15 at the beginning of the test = 10V ± 5%

[0040] The voltage of the second capacitor 16 at the beginning of the test = 5V ± 5%

[0041] Resistor 17 = 0.5Ω ± 5%

[0042] Overcurrent protector 4 current threshold = 4A

[0043] Maximum specified reaction time (t react.DUT.spec.max )=2μs±100ns

[0044] Test duration (t test.dur )=3μs

[0045] Based on the above test parameters, the following calculated voltage and current levels will apply:

[0046] Peak current = 10A

[0047] 2μs after the test starts (t react.DUT.spec.max ) current ≈ 6.7A

[0048] At the end of the test, the voltage of the first capacitor 15 is ≈9.2V

[0049] At the end of the test, the voltage of the second capacitor 16 is ≈5.8V

[0050] Based on the above specifications, the expected voltage tolerance of the second capacitor 16 at the end of the test can be calculated as:

[0051] V tolerance at the end of the test ≈ 0.61V

[0052] V tolerance at the end of the test ≈ 10.3%

[0053] The additional reduction in the expected voltage of the second capacitor 16 at the end of the test, caused by the losses due to the resistor 17 and the voltage drop of the test current across the circuit components of the overcurrent protector 4, can also be estimated as:

[0054] R tot =R Bal +ESR c1 +ESR c2 +R DUT (≈100mΩ)

[0055] Among them, R tot is the total resistance, R Bal is the resistance of resistor 17 (500 mΩ in this example), ESR c1 and ESR c2 is the equivalent series resistance value of the first capacitor and the second capacitor, and R DUT is the internal resistance of the device under test (ie, the overcurrent protector 4).

[0056] Figures 3 to 5 Graphs illustrating the changes in current and voltage across various capacitors during example testing are shown. Figure 3 As shown in Figure 1, once the capacitor is connected to the overcurrent protector, the generated current will exceed the detection threshold of the overcurrent protector. Figure 4and Figure 5 As shown, this is consistent with the voltage discharge from the first capacitor 15 to the second capacitor 16. If the overcurrent device 4 works normally, the current will be interrupted by the specified maximum reaction time, such as Figure 3 As shown, the voltage of each capacitor is fixed at the expected level. However, if the overcurrent device 4 does not work properly, the current will continue to flow beyond the specified maximum reaction time, as shown in FIG. Figure 3 As shown. This results in a larger variation in the voltage of each of the multiple capacitors, with first capacitor 15 discharging to a lower-than-expected voltage level and second capacitor 16 charging to a higher-than-expected voltage. Therefore, a fault can be identified by evaluating the voltage level of one of the multiple capacitors at the end of the test. Furthermore, because first and second switches 11 and 14 can disconnect capacitors 15 and 16 at the end of the test, a very rapid evaluation of the capacitor voltages is not required.

[0057] Figures 6 to 10 FIG2 shows a self-test circuit according to a second exemplary embodiment, with the figure illustrating a switching sequence through various stages of the test. This embodiment is substantially the same as the first embodiment, except that the first switch 11 and the second switch 14 are three-way switches, and the circuit 10 further includes a first pre-charge power supply 19 and a second pre-charge power supply 21, the first pre-charge power supply being switchably connected to the first capacitor 15 via a first pre-charge switch 20, and the second pre-charge power supply being switchably connected to the second capacitor 16 via a second pre-charge switch 22. The first pre-charge switch 20 and the second pre-charge switch 22 operate under the control of the self-test controller 18.

[0058] exist Figure 6 In the pre-charge configuration, the circuit is in a pre-charge configuration, in which the first pre-charge switch 20 connects the first capacitor 15 and the second pre-charge switch 22 connects the second capacitor 16 to charge the first capacitor and the second capacitor to voltages V1 and V2, respectively. Once the capacitors 15 and 16 are charged, the first pre-charge switch 20 and the second pre-charge switch 22 disconnect the pre-charge power supplies 19 and 21, as shown in FIG. Figure 7 shown.

[0059] Figure 8 The circuit is shown in a start-up test configuration, wherein the first switch 11 is operated to connect the first capacitor 15 to the first terminal 12 via the resistor 17, and the second switch 14 is operated to connect the second capacitor 16 to the second terminal 13. This establishes a current flow from the first capacitor 15 to the second capacitor 16. If the overcurrent protector 4 is functioning properly, it should react within the maximum specified reaction time t react.DUT.spec.max The flow of current is interrupted.

[0060] In t react.DUT.spec.maxLong predetermined test duration t test.dur After that, the self-test controller 18 switches the circuit to Figure 9 The disconnect configuration shown is used and the voltage of the second capacitor 16 is evaluated using an evaluation circuit (not shown). If the voltage of the second capacitor 16 exceeds the threshold value, this indicates that the overcurrent protector 4 is disconnected at t react.DUT.spec.max If the current flow is not interrupted within the threshold, a fault is identified. Conversely, if the voltage of the second capacitor 16 is below the threshold, the current flow is successfully interrupted and the overcurrent protector 4 has passed the self-test. In other embodiments, the self-test controller 18 may alternatively evaluate the held voltage of the first capacitor 15, where a voltage drop below the threshold indicates an overcurrent protector fault, while a voltage drop within the threshold indicates a pass.

[0061] If the self-test passes, the self-test controller 18 may operate the first switch 11 and the second switch 14 to connect the terminals 12 , 13 to the battery 1 as well as the PMIC 7 and the safety controller 9 .

[0062] Figure 11 A third embodiment is shown in which existing capacitors within the application circuit are reused for the self-test circuit. In this example, the overcurrent protector 4 includes an associated input circuit comprising existing capacitors 15e and 16e. The existing capacitors 15e and 16e can be switched by pre-charge switches 20, 22 to connect them to the input circuit (e.g. Figure 11 The capacitors 19 and 21 are disconnected to first precharge them using the precharge power supplies 19 and 21, and then left unconnected to run the self-test in accordance with the previous embodiment. In this way, existing capacitors can be temporarily reused for the self-test, saving component cost and space.

[0063] The above structure allows the overcurrent protector to be tested without shorting the device to ground. This allows the self-test circuit to be used with a wider range of overcurrent protection devices. Furthermore, since the maximum voltage and current are predefined by the component selection, even in the event of a fault, higher voltages and currents will not occur. This improves safety and reliability. Furthermore, since the self-test circuit does not require a shunt resistor or active current monitoring, the structure saves space and reduces losses and costs. Furthermore, since current is not actively monitored, the control and test evaluation steps can be performed relatively slowly, increasing the simplicity of the self-test controller and further reducing costs.

[0064] It will be understood that the embodiments illustrated above are only used for illustrative purposes. In practice, the embodiments may be applied to many different configurations, the details of which are readily apparent to those skilled in the art.

[0065] For example, although in the exemplary embodiments described above the test circuit has been described as a separate device, it will be appreciated that the circuit may be incorporated into the overcurrent protector unit.

Claims

1. A test device for testing an overcurrent protector, the overcurrent protector having a first terminal and a second terminal and configured to interrupt the current when the current between the first terminal and the second terminal exceeds an overcurrent threshold, the test device comprising: a first switch switchable to a test position to connect the first terminal to a first capacitor; a second switch switchable to a test position to connect the second terminal to a second capacitor; a pre-charging circuit configured to charge the first capacitor to a first voltage and the second capacitor to a second voltage, wherein the second voltage is lower than the first voltage; and a controller that switches the first switch and the second switch to their test positions to establish a current path from the first capacitor through the overcurrent protector to the second capacitor, wherein the first voltage and the second voltage are configured to generate a peak current in the current path that is greater than the overcurrent threshold. 2 . The test device according to claim 1 , further comprising a first capacitor for connecting to the first terminal and a second capacitor for connecting to the second terminal.

3. The testing device according to claim 2, wherein: At least one of the first capacitor and the second capacitor is grounded. 4 . The test device of claim 1 , further comprising a resistor connected along the current path to limit current.

5. The testing device according to claim 4, wherein: The resistor is connected between the first capacitor and the first switch. The testing device according to claim 1 , wherein: The first switch and the second switch are switchable to an operating position, in which the first switch and the second switch connect the first terminal and the second terminal to a power source and a load, respectively.

7. The testing device according to claim 1, wherein: The precharge circuit includes one or more precharge switches that connect the first capacitor and the second capacitor to a precharge power supply to charge to the first voltage and the second voltage, respectively.

8. The testing device according to claim 1, wherein: The controller switches the first switch and the second switch to their test positions for a predetermined test duration, wherein the predetermined test duration is longer than a specified maximum reaction time of the overcurrent protector. 9 . The testing device of claim 8 , further comprising an evaluation module that identifies a fault in the overcurrent protector based on a voltage of one of the first capacitor and the second capacitor after the predetermined test duration. 10 . An overcurrent protector, comprising the testing device according to claim 1 .

11. A method for testing an overcurrent protector, the overcurrent protector having a first terminal and a second terminal and configured to interrupt current when a current between the first terminal and the second terminal exceeds an overcurrent threshold, the method comprising the following steps: precharging the first capacitor to a first voltage and precharging the second capacitor to a second voltage using a precharging circuit, wherein the second voltage is lower than the first voltage; and Using a controller, controlling the first switch and the second switch to switch to a test position to connect the first terminal to the first capacitor and the second terminal to the second capacitor to establish a current path from the first capacitor through the overcurrent protector to the second capacitor, The first voltage and the second voltage are configured to generate a peak current in the current path that is greater than the overcurrent threshold.

12. The method according to claim 11, wherein The step of controlling the first switch and the second switch includes switching the first switch and the second switch from a working position to the test position, in which the first switch and the second switch connect the first terminal and the second terminal to a power source and a load, respectively.

13. The method according to claim 11 or 12, wherein: The precharging step includes switching one or more precharging switches to connect the first capacitor and the second capacitor to a precharging power supply to charge to the first voltage and the second voltage, respectively.

14. The method according to claim 11 or 12, wherein: The step of controlling the first switch and the second switch includes switching the first switch and the second switch to their test positions for a predetermined test duration, wherein the predetermined test duration is longer than a specified maximum reaction time of the overcurrent protector.

15. The method according to claim 14, wherein Controlling the first switch and the second switch includes identifying, using an evaluation module, a fault in the overcurrent protector based on a voltage of one of the first capacitor and the second capacitor after the predetermined test duration.

Images