Intelligent electronic switch

Abstract

Embodiments of the present disclosure relate to intelligent electronic switches. Described herein is a circuit that can be used in an intelligent switch. According to one embodiment, the circuit includes a monitoring circuit configured to receive a current sense signal and provide a protection signal. The monitoring circuit includes a non-linear function unit configured to receive the current sense signal and generate a power signal representative of a power of the current sense signal. The circuit also includes a first filter configured to receive the power signal and generate a first filtered signal and a second filter configured to receive an input signal dependent on the current sense signal and generate a second filtered signal. A comparison circuit is configured to receive the first filtered signal and the second filtered signal, and compare the first filtered signal to a first threshold and the second filtered signal to a second threshold. The protection signal indicates whether the first filtered signal exceeds the first threshold or the second filtered signal exceeds the second threshold.

Description

Technical Field

[0001] This invention relates to the field of intelligent semiconductor switches. Background Technology

[0002] Almost every electrical installation (e.g., in cars, homes, and electrical subsystems of large appliances) includes one or more fuses to provide overcurrent protection. A standard fuse includes a conductor that provides a low-ohmic current path when the current through the fuse is below the nominal current. However, when the current through the fuse exceeds the nominal current for a certain period of time, this conductor is designed to heat up and melt or vaporize. Once triggered, the fuse must be replaced with a new one.

[0003] Fuse are increasingly being replaced by circuit breakers. A circuit breaker is an automatically operating electrical switch designed to protect circuits from damage caused by overcurrent, overload, or short circuit. Circuit breakers may include electromechanical relays that are triggered when an overcurrent is detected (i.e., the current exceeds the nominal current) to disconnect the protected circuit from the power supply. In many applications (e.g., in automotive power supplies), circuit breakers can be implemented using electronic switches (e.g., MOS transistors, IGBTs, etc.) to disconnect the protected circuit from the power supply in the event of an overcurrent. Such electronic circuit breakers are also called electronic fuses (e-fuse or smart fuses). In addition to their function as circuit breakers, electronic fuses can also be used to periodically connect and disconnect loads. The switching state (on / off) of electronic switches (such as MOS transistors) is typically controlled using so-called driver circuits or simple drivers (gate drivers in the case of MOS transistors).

[0004] Typically, conventional and electronic fuses are designed for (hypothetically) constant electrical loads that generate a specific thermal load on the cable. That is, a constant electrical load causes a particular cable temperature to be higher than ambient temperature. The purpose of a fuse is to ensure that the thermal load on the cable remains within defined limits. Therefore, known electronic fuse circuits are designed to simulate the time-current characteristics of the cable supplying the load (it defines the length of time a specific current level can flow through the electronic fuse before the fuse triggers the disconnection of the load). However, in many applications, the load is dynamic. Given the fact that the thermal time constant of commonly used cables is in the range of several minutes (e.g., 90 seconds in some applications), the activation of an electrical load (e.g., 30 seconds) can be a highly dynamic process compared to the thermal time constant of the cable. Summary of the Invention

[0005] This document describes a circuit that can be used in a smart switch. According to one embodiment, the circuit includes a monitoring circuit configured to receive a current-sensing signal and provide a protection signal. The monitoring circuit includes a non-linear functional unit configured to receive the current-sensing signal and generate a power signal representing the power of the current-sensing signal. The circuit also includes a first filter and a second filter, the first filter being configured to receive the power signal and generate a first filtered signal, and the second filter being configured to receive an input signal dependent on the current-sensing signal and generate a second filtered signal. A comparison circuit is configured to receive the first and second filtered signals, compare the first filtered signal with a first threshold, and compare the second filtered signal with a second threshold. The protection signal indicates whether the first filtered signal exceeds the first threshold or whether the second filtered signal exceeds the second threshold.

[0006] Furthermore, a method for use with smart switches is described. According to one embodiment, the method includes providing a signal representing a load current through a power transistor, and generating a protection signal based on the current-sensing signal. Generating the protection signal includes generating a power signal representing the power of the current-sensing signal by applying a nonlinear function to the current-sensing signal; filtering the power signal to generate a first filtered signal and generating a second filtered signal based on the current-sensing signal; comparing the first filtered signal with a first threshold and comparing the second filtered signal with a second threshold. The protection signal indicates whether the first filtered signal exceeds the first threshold or whether the second filtered signal exceeds the second threshold. Attached Figure Description

[0007] The embodiments described below can be better understood by referring to the accompanying drawings and description. The components in the figures are not necessarily to scale; rather, the focus is on illustrating the principles of the invention. Furthermore, in the figures, the same reference numerals denote corresponding parts. In the figures:

[0008] Figure 1 An example of an electronic fuse circuit, including an electronic switch and control circuitry configured to drive the electronic switch, is schematically shown, along with an exemplary application of the electronic fuse circuit.

[0009] Figure 2 Showing more details Figure 1 An example of a control circuit;

[0010] Figure 3 It shows Figure 2 An example of the logic circuit used in the control circuit;

[0011] Figure 4 Explanation is shown Figure 2 The timing diagram of the control circuit shown;

[0012] Figure 5 (a) shows 0.35mm 2 A family of characteristic curves (current versus time) for cables and different maximum cable temperatures;

[0013] Figure 5 (b) is a graph showing the family of characteristic curves (current versus time) for the highest cable temperature of 25 Kelvin above ambient temperature and different cable cross-sections.

[0014] Figure 6 It shows Figure 2 An example of the monitoring circuit used in the example; the monitoring circuit includes a filter and a comparator, wherein the filter time constant and the comparator threshold determine the time-current characteristics of the monitoring circuit;

[0015] Figure 7 A first example of an electronic fuse (“smart fuse”) circuit that allows selection of conductor cross-section and maximum cable temperature is shown;

[0016] Figure 8 It is shown in Figure 6 The graph shows the effect of the filter time constant on the time-current characteristics when a first-order low-pass filter is used in the monitoring circuit.

[0017] Figure 9 It is shown in Figure 6 The graph shows the effect of the comparator threshold on the time-current characteristics when a first-order low-pass filter is used in the monitoring circuit.

[0018] Figure 10 and 11 Two alternative embodiments of the monitoring circuit are shown, both of which use multiple filters and comparators with different filter time constants and different comparator thresholds;

[0019] Figure 12 It shows that it can be used Figure 10 and 11 An example of a complex time-current characteristic implemented in an embodiment;

[0020] Figure 13 Another embodiment of the monitoring circuit is shown; and

[0021] Figure 14 Another embodiment is shown in which a portion of the monitoring circuitry is implemented in an external circuitry device such as a microcontroller. Detailed Implementation

[0022] In the following detailed description, reference is made to the accompanying drawings. The drawings form part of the specification and, for illustrative purposes, illustrate examples of how the invention can be used and implemented. It should be understood that, unless otherwise specifically indicated, features of the various embodiments described herein can be combined with each other. Furthermore, while the examples described herein relate to electronic fuse circuits, the embodiments are not limited to applications related to electronic fuses.

[0023] Figure 1 An example of an electronic circuit that can operate as an electronic fuse is shown. Therefore, the electronic circuit is also referred to as an electronic fuse circuit F. According to this example, the electronic fuse circuit includes an electronic switch 2 having a control node 21 and a load current path between a first load node 22 and a second load node 23. The electronic circuit also includes a control circuit 1 coupled to the control node 21 of the electronic switch 2 and configured to drive the electronic switch 2. The electronic fuse circuit F with the electronic switch 2 and the control circuit 1 can be monolithically integrated into a single semiconductor die (chip), or it can be integrated into two semiconductor dies arranged in an integrated circuit package. Alternatively, the gate driver and MOSFET can be integrated into separate chips. The electronic fuse circuit F is configured to drive a load Z (the wire connecting the load is such that...) Figure 1 As shown by the dashed line in the diagram, the load Z can be connected in series with the load current path of electronic switch 2. Therefore, the series circuit of the load current path of electronic switch 2 and load Z can be connected between power supply nodes, where a first power supply potential and a second power supply potential can be provided. The second power supply potential is usually referred to as ground potential GND (e.g., zero volts). In the following text, the voltage between the two power supply nodes is referred to as the power supply voltage V. B The load current i through load Z L The input signal S supplied to the control circuit 1, for example, via the microcontroller 8, can be used as a reference. IN It is switched on and off. However, depending on the application, the input signal S IN It can also be generated by any other circuit device instead of a microcontroller.

[0024] In an exemplary application, the electronic fuse circuit F can be used to drive a load Z in a vehicle. In this case, the supply voltage V... B The power source is the car battery. Typically, a "driving load" can include the load current flowing through the load by switching the electronic switch 2 on or off. The load can be any load used in the vehicle. Examples of load Z include, in particular, different types of lights, different types of motors, relays, heating systems, etc. Load Z can also represent the electrical subsystems of the vehicle's electrical system (including multiple individual electrical loads). Figure 1In the example, electronic switch 2 and load Z are connected in a high-side configuration. That is, load Z is connected between electronic switch 2 and ground node GND. However, this is just an example. Electronic switch 2 and load Z can also be connected in a low-side configuration or any other configuration. For example, in a low-side configuration, the electronic switch is connected between load Z and ground node GND.

[0025] according to Figure 1 For example, load Z can be connected to electronic switch 2 via (e.g., included in a cable) conductive wire. Depending on the location of the electronic circuit and the corresponding load Z in the vehicle's electrical system, the wire can be several tens of centimeters or even significantly longer (e.g., up to 10 meters). Modern vehicles include multiple electrical loads, thus requiring multiple wires to connect individual loads to their respective electronic switches. To save costs and resources, it may be necessary to size the individual wires so that they can withstand the nominal current of the connected load in the long term. However, if the current rises above the nominal current, the wires may be damaged or even destroyed due to overheating. According to an exemplary embodiment, control circuit 1 can therefore have a current monitoring function to monitor the load current i through electronic switch 2 (and load Z). L Current monitoring allows electronic switch 2 to be disconnected to protect the conductor (and load Z) upon detection of an "overload condition." An overload condition occurs if (within a specific time) electronic switch 2 is not disconnected to connect the conductor (and load Z) to the supplied power supply voltage V. B Disconnection of the power supply (e.g., a car battery) can lead to damage or destruction of wires or loads. This mechanism is explained in more detail below. Because the electronic fuse circuit F is configured to connect and disconnect the load Z and protect the wires, it is also referred to below as a switch protection circuit.

[0026] exist Figure 1In the example, electronic switch 2 is schematically drawn as a circuit block including a switch. Hereinafter, the term "electronic switch" includes any type of electronic switch or electronic circuit device having a control node 21 and a load current path between a first load node 22 and a second load node 23, and configured to turn on and off depending on a drive signal received at the control node 21. "On" means that electronic switch 2 operates in an on state, in which electronic switch 2 is able to conduct current between the first load node 22 and the second load node 23. "Off" means that electronic switch 2 operates in an off state, in which electronic switch 2 is able to prevent current from flowing between the first load node 22 and the second load node 23. According to one example, electronic switch 2 includes at least one transistor. The at least one transistor can be, for example, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), a JFET (Junction Field-Effect Transistor), a BJT (Bipolar Junction Transistor), or a HEMT (High Electron Mobility Transistor).

[0027] Hereinafter, an example of control circuit 1 and its function are described with reference to the accompanying drawings. In particular, the function of control circuit 1 is explained with reference to the functional blocks depicted in the drawings. Note that these functional blocks represent the function of control circuit 1, not its specific implementation. These functional blocks may be dedicated circuit blocks configured to perform the corresponding functions explained below. However, the function of individual functional blocks may also be (at least in part) performed by programmable circuitry (e.g., a processor) configured to execute software / firmware stored in memory.

[0028] Figure 2 An exemplary implementation of control circuit 1 is shown. In this example, control circuit 1 includes monitoring circuit 4, which is configured to monitor load current i. L The time-current characteristics of the load current generate the first protection signal OC. The statement "generating the first protection signal OC based on the time-current characteristics of the load current" may include monitoring circuit 4 processing the load current i. L The instantaneous current amplitude and the previous current amplitude signal are used to generate the first protection signal OC. That is, the monitoring circuit 4 evaluates the load current i within a specific time period. L This generates the first protection signal OC. In order to evaluate the load current i L Monitoring circuit 4 receives the current sensing signal CS and generates a first protection signal OC based on the current sensing signal CS. The current sensing signal CS represents the load current i. L And, according to one example, it can be related to the load current i L Proportional. In Figure 2In this example, the current sensing signal CS is available at the sensing output 24 of electronic switch 2. In this case, it is configured to measure the load current i. L Furthermore, the current measurement circuit providing the current sensing signal CS can be (at least partially) integrated into the electronic switch 2. However, this is merely an example. A current measurement circuit separate from the electronic switch 2 can also be used. Various current sensing circuits (e.g., shunt resistors, sensing FET circuits, etc.) are known and will not be explained in further detail here.

[0029] Figure 2 The control circuit 1 shown is configured based on the protection signal OC and the first input node (e.g., input pin) P of the electronic fuse circuit F. IN The input signal S received at the point IN To drive electronic switch 2. Protection signal OC and input signal S IN It is supplied to logic circuit 3, which is based on the protection signal OC and the input signal S. IN Generate drive signal S ON Drive signal S ON The control node 21 of the electronic switch 2 is supplied directly or indirectly (e.g., via driver circuit 5) to turn the electronic switch 2 on or off. According to one example, the drive signal S... ON This can be a logic signal, which has an on level indicating whether electronic switch 2 is to be turned on or an off level indicating whether electronic switch 2 is to be turned off. The driver circuit 5 (or simply the driver) is configured based on the drive signal S. ON The corresponding signal level drives the electronic switch 2. For example, the electronic switch 2 includes transistors such as MOSFETs (e.g., Figure 2 (Illustrated schematically). A MOSFET is a voltage-controlled semiconductor device that is turned on or off based on a drive voltage applied between the gate and source nodes. In this example, driver 5 is configured to operate based on the drive signal S. ON A drive voltage (gate voltage VG) is generated to turn the MOSFET on or off according to the drive signal. When using a MOSFET, driver 5 is also called a gate driver.

[0030] Figure 3 The circuit diagram illustrates an exemplary implementation of a portion of logic circuit 3. In this example, logic circuit 3 includes an inverter 33, an SR latch 31 (flip-flop), and an AND gate 32. The first input of the AND gate 32 is configured to receive an input signal S. INThe reset input R of SR latch 31 is configured to receive the inverted input signal provided by inverter 33. The set input S of SR latch 31 is configured to receive the protection signal OC. The inverted output Q' of SR latch 31 is connected to the second input of AND gate 32. Drive signal S ON It is provided at the output of AND gate 32.

[0031] exist Figure 4 The timing diagram also illustrates the function of logic circuit 3. Input signal S IN The initial low level causes the SR latch 31 to reset, which produces a high level at the inverted output Q' of the SR latch 31. Therefore, both inputs of the AND gate 32 "see" a high level, and the output of the AND gate 32 provides a drive signal S with a high level. ON When the input signal S IN When it goes low (indicating that electronic switch 2 is open, see below) Figure 4 At times t1 and t2), AND gate 32 "sees" a low level at its first input, and the output of AND gate 32 provides a drive signal S with a low level. ON (This causes power transistor 2 to turn off). In other words, assuming SR latch 31 is in its reset state, the input signal S IN The signal is fed through logic circuit 3 (i.e., drive signal S). ON Equal to the input signal S IN Once SR latch 31 is set in response to the protection signal OC going high, the inverted output Q' of SR latch 31 is set low (see [link]). Figure 4 (at time t3). Therefore, AND gate 32 sees a low level at its second input and drives signal S. ON It is set to low level. In other words, the input signal S IN The signal is blanked by AND gate 32. Drive signal S ON Stay low until input signal S IN Set to low level (indicating the opening of electronic switch 2 and the reset of SR latch 31, see below) Figure 4 (at time t4) and set to high level again (indicating the activation of electronic switch 2, see...) Figure 4 (Time t5). Again, note that... Figure 3 The exemplary implementation can also be implemented in various other ways. Furthermore, it should be noted that in other embodiments, the SR latch 31 can be triggered to reset in different ways. For example, the microcontroller 8 (see...) Figure 1 It can provide a dedicated reset signal.

[0032] As described above, the conductor connecting the load Z and the electronic fuse circuit F can be designed to withstand the nominal current of the load Z. The lifespan of the conductor (or cable) depends on the conductor temperature. Figure 5 Figures (a) and (b) in 5 are plots illustrating a family of characteristic curves (each representing the current characteristic at a specific time), where each characteristic curve is plotted against the maximum temperature difference dT (the maximum temperature above ambient temperature) and the cable cross-section (e.g., cross-sectional area in mm²). 2 Each characteristic curve can be viewed as an "isotherm" (isotherm dT) and represents the relationship between the current and the maximum permissible time period during which the conductor can carry the current without exceeding the specified temperature difference dT.

[0033] Figure 5 (a) shows different temperature differences dT and 0.35 mm. 2 The characteristic curve of a specific cross-sectional area, and Figure 5 Figure (b) shows the characteristic curves for a specific temperature difference dT at 25 K (Kelvin) and various cross-sectional areas. From Figure 5 As can be seen from (a) in 5 and (b) in 5, the cross-sectional area is 0.35 mm. 2 The conductor can carry approximately 9A (amperes) of current for a virtually unlimited period of time without exceeding a temperature difference dT of 25K above ambient temperature. From Figure 5 As can be seen from (b) in the figure, the cross-sectional area is 0.75 mm. 2 The conductor can carry a current of 10A (Amperes) for approximately 100 seconds or a current of 35A (Amperes) for approximately 1 second, then exceed a temperature difference dT of 25K above ambient temperature. Generally, the higher the current, the shorter the permissible time period for a given cross-sectional area and a given temperature difference. Note that... Figure 5 The characteristic curves shown in (a) of 5 and (b) of 5 have a linearly decreasing branch in the double logarithmic representation.

[0034] from Figure 5 As can be seen from (a) in 5 and (b) in 5, for a given current (see Figure 5 In (a), the current i x ) and specific cross-sectional area (e.g., Figure 5 0.35mm in example (a) 2 ), temperature difference dT x (For example, temperature values ​​dT1, dT2, dT3, dT4, dT5, dT6) and a given integration time t x (For example, times t1, t2, t3, t4, t5, t6) are correlated. Therefore, the load current i passing through the conductor can be correlated with time. L =i xThe generated power is integrated to determine the temperature value dT (representing the temperature above ambient temperature) for a specific conductor cross-section. The temperature value dT is determined when it reaches a defined first reference temperature difference dT. R At that time, the first protection signal OC can indicate the opening of electronic switch 2. The aforementioned integration can be efficiently implemented using a digital filter, which can be included in monitoring circuit 4 (see...). Figure 2 ). Figure 6 An exemplary implementation of the monitoring circuit is shown. In the embodiments described herein, the digital filter is a low-pass filter. In one embodiment, the low-pass filter is a first-order filter, which is sufficient when using a simple thermal model of the cable (based on Fourier's law).

[0035] basically, Figure 6 The monitoring circuit is configured to determine the first protection signal OC based on the current sensing signal CS. As described above, integration can be performed in a digital filter 42 with integration characteristics (implemented by a low-pass filter). According to the depicted example, it can be related to the load current i. L A proportional voltage current-sensing signal CS is provided to the input of filter 45 (which may be an (optional) analog low-pass filter) to eliminate transients with relatively high frequencies. The output of filter 45 can be connected to the input of analog-to-digital converter (ADC) 41, which is configured to digitize the filtered current-sensing signal CS. ADC 41 may have logarithmic characteristics to illustrate... Figure 5 The logarithmic characteristic curves are shown in (a) of 5 and (b) of 5. (e.g., logarithmically transformed) digital current sensing signal CS. DIG The temperature is then "transformed" into a temperature value dT by digital filter 42. The resulting temperature value dT (representing the temperature difference above the ambient temperature) is then provided to digital comparator 43, which can be configured to respond when the temperature value dT provided at the output of digital filter 42 exceeds a first reference temperature difference dT specified for a particular conductor cross-section. R (For example, at 25K) the first protection signal OC is set to high level.

[0036] Figure 6 The squaring unit 46 depicted may be omitted, depending on the characteristics of the ADC 41. However, if the ADC 41 has "normal" (i.e., linear) characteristics, squaring is necessary to obtain a value indicating the power. In other embodiments, if the squaring unit 46 is omitted, it should be replaced with another suitable nonlinear function. Essentially, the input signal provided to the filter 42 represents the signal generated by the load current i L The power generated.

[0037] As described above, the digital filter 42 is configured to convert (e.g., squared) load current and the associated integration time (during which the current flows through the conductor) into a temperature value dT. In this example, the filter characteristics 42 depend on parameters characterizing the conductor, such as the cross-sectional area of ​​the current-carrying conductor, and can be determined by, for example, Figure 5 The family of characteristic curves shown in figure (a) (for 0.35mm) 2 It is represented by an exemplary cross-sectional area.

[0038] Figure 7 An example of an electronic fuse circuit, also known as a smart fuse circuit 10, is shown. Figure 7 circuit and Figure 2 The circuits are basically the same, and refer to the corresponding descriptions. However, logic circuit 3 is different. Figure 2 The example is more complex, and monitoring circuit 4 is based on Figure 6 This is implemented by omitting the analog low-pass filter 45 (which is optional). However, with Figure 6 Unlike the example in the previous example, in this example, monitoring circuit 4 is configurable, allowing its characteristics to be selected based on at least one conductor parameter. This allows for, for example, selection based on a specific conductor cross-section and / or a desired reference temperature difference dT. R (Temperature threshold) is used to select characteristics. In the examples described herein, at least one conductor parameter represents the cable cross-sectional area and / or the maximum temperature value above ambient temperature. From Figure 5 As shown in the diagram, these two conductor parameters define specific characteristic curves that represent the desired behavior of an electronic fuse circuit for a particular conductor / cable. It should be understood that other parameters, such as conductor diameter or absolute temperature (e.g., in the case of measuring ambient temperature), can be used as conductor parameters. Furthermore, conductor parameters do not necessarily represent any physical quantity (such as cross-sectional area or temperature), but can simply be numerical parameters that allow for the determination (e.g., selection) of the desired characteristics used by the monitoring circuit. In one example, the conductor parameter is merely a number indicating the characteristic curve to be applied. Figure 7 As shown, the electronic fuse circuit can be an integrated circuit arranged in a single chip package, wherein the electronic switch 2 and the remaining circuit elements (driver 5, logic circuit 3, and monitoring circuit 4) can be integrated in the same semiconductor die or in two separate semiconductor dies disposed in the chip package. However, in other embodiments, the smart fuse circuit 10 can be distributed in two or more separate chip packages. Figure 7 In the example, all the circuit components depicted are integrated into a single semiconductor chip.

[0039] The load current path of electronic switch 2 can be connected between the power supply pin SUP and the output pin OUT of smart fuse circuit 10. Typically, logic circuit 3 can be configured to receive at least one wire parameter; in this example, the wire parameter includes information from a microcontroller or other control circuitry regarding the wire cross-sectional area A and the reference temperature difference dT. R Information, such as... Figure 6 As shown, logic circuit 3 can be configured to transmit signals via input pin IN (input signal S). IN See also Figure 2 ) and input pin SEL WIRE and SEL dT (Selection signal S) S1 and S S2 The signal (representing the cross-sectional area of ​​the conductor and the temperature difference) is received from the controller and a drive signal S is provided to electronic switch 2. ON Driver 5 can be configured to take signal S as a binary logic signal. ON Converted to a driving voltage or driving current suitable for turning electronic switch 2 on and off. For example, in Figure 2 In the example, monitoring circuit 4 receives a (analog) current sensing signal CS and generates a first protection signal OC based on the current sensing signal CS. This first protection signal OC can be processed, for example, by logic circuit 3, such as... Figure 3 As shown in the example.

[0040] As mentioned above, filter 42 can be implemented as a first-order low-pass filter. That is, the (continuous-time) filter transfer function H(s) can be written as follows: (1) Where τ represents the filter time constant. b This indicates the filter gain. Comparator 43 triggers the electronic switch 2 to open (by generating an overcurrent signal OC) when the following condition is met: (2) In other words, when the estimated cable temperature (represented by the filter output of filter 42) reaches or exceeds the temperature threshold. ΔT (In Equation 2, When the inverse Laplace transform is represented, the disconnection is triggered. Condition (2) above can be restated as follows: (3) in P(s) represents the Laplace transform of the filter input signal. It is clear from conditions (2) and (3) that the filter gain... b and threshold ΔT Not an independent parameter. Specific reference temperature. dTR It can be achieved through filter gain b and threshold ΔT This can be achieved through different combinations. Changing the filter gain... b With changing the temperature threshold ΔT They have similar effects. This is understandable, although... dT R It indicates temperature, but it is not measured in Kelvin (e.g., Figure 10 As shown, dT R (Physical dimensions with ampere squared).

[0041] Figure 8 and 9 This illustrates the changes in filter time constant τ and filter gain. b For the characteristic curve (see) Figure 5 The impact of ). For example Figure 8 As shown, due to the scaling of the time axis, changing the filter time constant τ will cause a vertical shift in the characteristic curve. Conversely, as... Figure 9 As shown, the filter gain changes due to the scaling of the current axis. b This will cause a horizontal shift in the characteristic curve. Note that in Figure 9 In the example, filter gain b =1 results in reference temperature dT R For ΔT / b =20 degrees Celsius. Similarly, filter gain b =0.5 results in a reference temperature dT R For ΔT / b =40 degrees Celsius, filter gain b =0.2 results in reference temperature dT R For ΔT / b =100 degrees Celsius, and filter gain b =0.1 results in a reference temperature dT R For ΔT / b =200 degrees Celsius.

[0042] To reiterate, instead of changing the filter gain... b The reference temperature can be changed. dT R To achieve the same effect. In a further description, it is assumed (without loss of generality) that the filter gain... b It is a constant and is set to b =1, and reference temperature dT R It is adjustable to match the specifications of a specific cable.

[0043] As described above, the filter output signal provided by filter 42 and supplied to the comparator input of comparator 43 can be interpreted as temperature. From Figure 8 and 9 As can be seen, the options for selecting specific time-current characteristics are very limited. Basically, the filter time constant τ and the comparator threshold... dT R The characteristic curve is determined by changing the parameters τ and dT R We can obtain the vertical and horizontal movement characteristic curves. However, it is impossible to change the shape of the time-current characteristic by changing these two parameters.

[0044] Figure 10 The modified monitoring circuit 4 is shown, which allows for flexible adaptation of the shape of the time-current characteristics and can be customized for specific applications. Figure 6 The example is the same. Figure 8 The embodiment includes an analog-to-digital converter 41 and a squaring unit 46. The analog-to-digital converter 41 receives a current sensing signal CS(t) and provides a corresponding digitized signal CS[k] (k is a time index); the squaring unit 46 provides a representation of the squared signal CS[k]. 2 The signal. The squared signal CS[k] 2 They are assigned to multiple signal paths, each of which includes a filter 42.n and a comparator 43.n (n = 1, 2, ..., N).

[0045] The output signals of filters 42.1, 42.2, ..., 42.N are represented as y1[k], y2[k], ..., y N [k]; The output signals of comparators 43.1, 43.2, ..., 43.N are represented as OC1, OC2, ..., OC... N These overcurrent signals OC1, OC2, ..., OC N It is supplied to logic circuit 47, which may be an OR gate with multiple inputs. The comparator threshold is expressed as... dT R,1 , dT R,2 ... dT R,N The output of logic circuit 47 is represented as OC[k], and when the overcurrent signals OC1, OC2, ..., OC... N An overcurrent signal indicates a fault when the corresponding comparator threshold is violated (this can trigger the disconnection of electronic switch 2). Figure 10 In the example, all filters 42.1, 42.2, ..., 42.N receive the squared current sensing signal CS[k]. 2Only the output signal y1[k] indicates the physical quantity "cable temperature".

[0046] Figure 11 The example is almost the same as Figure 10 The example is the same as the previous one, except that only the first filter 42.1 receives the squared current sensing signal CS[k]. 2 Meanwhile, the other filters 42.2, ..., 42.N receive the (non-square) current sensing signal CS[k]. As mentioned above, only the output signal y1[k] of the first filter 42.1 indicates the cable temperature, while the remaining filters 2.2, ..., 42.N and their corresponding comparator thresholds... dT R,1 , dT R,2 ... dT R,N It is only necessary to adapt the time-current characteristics in the desired way to meet the requirements of the specific application. Figure 12 An example is shown. Accordingly, the resulting time-current characteristic is a cascade of segments of characteristic curves generated by N signal paths (N=3 in the illustrated example). Due to the "OR" combination provided by logic circuit 47, the resulting time-current characteristic is determined by the minimum value among the characteristic curves of the N signal paths. That is, when one of the N signal paths signals an overcurrent trip (overcurrent signals OC1, OC2, ..., OC...), the overcurrent trip occurs. N When the signal OC is activated, the disconnection will be triggered.

[0047] Figure 13 Another embodiment is shown, which can be viewed as Figure 10 An enhancement of the example. Figure 13 circuit and Figure 10 The circuitry is essentially the same, but it has additional circuitry for determining the minimum remaining headroom before generating the overcurrent signal OC[k] (which typically triggers disconnection). Therefore, Figure 13 The circuitry includes computational circuitry (e.g., subtractors) 43.1, 43.2, ..., 43.N, which is configured to generate a representation of the difference y1[k]-dT "seen" by the comparators 43.1, 43.2, ..., 43.N. R,1 y2[k]-dT R,2 ... y N [k]-dT R,N The output signals h1[k], h2[k], ..., h N [k]. Selection circuit 49 is configured to provide signals h1[k], h2[k], ..., h N The instantaneous minimum value (min) of [k] is used as the output signal h. min [k], that is, h min[k]=min{h1[k], h2[k],……,h N [k]}. Signal h min [k] represents the available margin before signaling a fault (by setting the level of signal OC[k] to an appropriate value). Figure 13 It can be seen that this circuit can provide three types of information to be processed. One such information is the signal OC[k], which indicates overcurrent and typically triggers the opening of electronic switch 2 (see [link]). Figure 2 The tripping response to the signal OC[k] is similar to the triggering of a conventional fuse in response to an overcurrent. Other information could include the margin signal h. min [k], margin signal h min [k] indicates the proximity of the monitoring circuit to the signal OC[k] that indicates overcurrent. Third, it can also provide the cable temperature rise (temperature difference from ambient temperature) or equivalent thermal state calculated by filter 43.1.

[0048] Figure 10 , 11 The monitoring circuitry of 13 can be integrated into a single semiconductor chip package, as shown in the reference. Figure 7 The discussion. Exemplary applications in Figure 14 As shown, the integrated circuit (including electronic device switch 2, monitoring circuit 4, and logic circuit 3) is shown in the figure. Figure 2 and 7 This is called the integrated smart fuse circuit 10. In this example, the input signal S IN Provided by microcontroller 8. Furthermore, the smart fuse circuit 10 is configured to provide a current sensing signal CS(t) or any other signal representing the load current through electronic switch 2. This current sensing signal CS(t) is received and digitized by microcontroller 8.

[0049] use Figure 14 The circuit structure shown allows for the implementation of an additional filter (referred to as filter 42.N+1) within the microcontroller 8. Therefore, the microcontroller 8 digitizes the current sensing signal CS(t) and feeds the digitized signal CS[k] to the digital filter (e.g., as referenced above). Figure 10 The low-pass filter under discussion. Filtered signal y N+1 [k] and reference value dT R,N+1 Compare, if the filtered signal y N+1 [k] reaches or exceeds the reference value dT R,N+1 Then the input signal S IN 'Blank. The modified (i.e., blanked, depending on the situation) input signal is... Figure 14 The middle is represented as S IN That is to say, due to the input signal SIN Upon blanking, electronic switch 2 is opened, just as it signals an overcurrent in response to signal OC[k]. Therefore, in this example, logic circuit 3 (see...) Figure 2 and 7 The portion was transferred to the microcontroller 8.

[0050] It should be understood that, Figure 14 The additional feedback loop implemented in the microcontroller 8 in the example can also be implemented by other external circuit devices besides the microcontroller (i.e., outside of the smart fuse circuit 10).

[0051] While the invention has been described and illustrated with respect to one or more implementations, changes and / or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular, with respect to the various functions performed by the aforementioned components or structures (units, components, devices, circuits, systems, etc.), the terminology used to describe such components (including references to “means”) is intended to correspond—unless otherwise stated—to any component or structure that performs the specified function of the described component (e.g., functionally equivalent), even if structurally not equivalent to the disclosed structures shown in exemplary implementations of the invention that perform the functions described herein.

Claims

1. A circuit for a smart switch, comprising: A monitoring circuit is configured to receive a current sensing signal and provide a protection signal, wherein the monitoring circuit includes: A nonlinear functional unit is configured to receive the current sensing signal and generate a power signal representing the power of the current sensing signal; A first filter is configured to receive the power signal and generate a first filtered signal, and The second filter is configured to receive an input signal that depends on the current sensing signal and to generate a second filtered signal. A comparison circuit is configured to receive the first filtered signal and the second filtered signal, and compare the first filtered signal with a first threshold and the second filtered signal with a second threshold; the protection signal indicates whether the first filtered signal exceeds the first threshold or whether the second filtered signal exceeds the second threshold. The circuit further includes: At least a third filter is configured to receive the input signal, which depends on the current sensing signal, and to generate a third filtered signal. The comparison circuit is further configured to receive the third filtered signal and compare the third filtered signal with a third threshold; the protection signal indicates whether one of the filtered signals exceeds the corresponding threshold.

2. The circuit according to claim 1 further includes: An electronic switch is coupled between the power supply pin and the output pin; A current sensing circuit is coupled to the electronic switch and configured to generate the current sensing signal indicating the load current through the electronic switch.

3. The circuit according to claim 1 or 2, The first filter is a low-pass filter.

4. The circuit according to claim 1, The first filter is a first-order low-pass filter.

5. The circuit according to claim 1, The input signal of the second filter is the power signal.

6. The circuit according to claim 1, The input signal of the second filter is the current sensing signal.

7. The circuit according to claim 2, The current sensing circuit includes an analog-to-digital converter configured to provide the current sensing signal in digital form; and The nonlinear functional unit is implemented in the analog-to-digital converter by using nonlinear analog-to-digital conversion characteristics.

8. The circuit according to claim 1, The nonlinear functional unit is configured to perform a digital square of the current sensing signal.

9. The circuit according to claim 2, The nonlinear functional unit is configured to generate the power signal as a signal proportional to the square of the load current.

10. The circuit according to claim 2, The first filtered signal represents the temperature difference between the cable connected to the electronic switch and the ambient temperature.

11. The circuit according to claim 1, The monitoring circuit is further configured to generate a margin signal based on the difference between the filtered signal supplied to the comparison circuit and a corresponding threshold.

12. The circuit according to claim 2, further comprising: The logic circuit is configured to trigger the electronic switch to open or signal an error in response to the protection signal.

13. The circuit according to claim 12, The logic circuit is configured to receive an on command and, in response to the on command, trigger the electronic switch to be turned on.

14. The circuit according to claim 2, The current sensing circuit, the nonlinear functional unit, and the first filter are integrated into a single semiconductor chip, the semiconductor chip having output contacts configured to provide a signal representing the current sensing signal, and The second filter is implemented using an external circuit device connected to the semiconductor chip.

15. A method for a smart switch, comprising: Provides a signal representing the load current passing through the power transistor; Protection signals are generated based on current sensing signals; The generation of the protection signal includes: A power signal representing the power of the current sensing signal is generated by applying a nonlinear function to the current sensing signal. The power signal is filtered to generate a first filtered signal, and a second filtered signal is generated based on the current sensing signal; The first filtered signal is compared with a first threshold, and the second filtered signal is compared with a second threshold; the protection signal indicates whether the first filtered signal exceeds the first threshold or whether the second filtered signal exceeds the second threshold. The method further includes: A third filtered signal is generated based on the current sensing signal. The third filtered signal is compared with a third threshold; the protection signal indicates whether one of the filtered signals exceeds the corresponding threshold.

16. The method of claim 15, further comprising: Based on the protection signal, the power transistor is used to disconnect the output pin from the power supply pin.

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