Current detection device and method for detecting an electric current

Abstract

Current detection device (10) for detecting an electric current (I Sense ) in a measuring path that leads to an electrical current (l E ) in a power path corresponding electrical current, with: a current measuring device (11) arranged in the measuring path and configured to provide an output signal corresponding to an electrical current flowing through the current measuring device (11); and a current limiting device (12) which is designed to limit the electrical current through the current measuring device (11) to a predetermined maximum limit value when the electrical current (l E ) in the power path exceeds a specified threshold.

Description

[0001] The present invention relates to a current detection device and a method for detecting an electric current. In particular, the present invention relates to a current detection device and a method for detecting an electric current in a measurement path that carries an electric current corresponding to an electric current in a power path.

[0002] Although the present invention is described in connection with IGBTs having a sense terminal, the present invention can also be used for any other applications in which a current in another current path is to be evaluated, which current corresponds to the current in a power path.

[0003] US Pat. No. 5,877,617 A discloses a circuit arrangement in which a load is supplied with a current in a current path. Furthermore, the circuit arrangement comprises a further transistor that provides a current corresponding to this current to the load. The current provided via the further transistor is used to monitor and evaluate the current flow to the load.

[0004] US 5 061 863 A discloses a transistor with a current detection function. The magnitude of a main current is detected based on a voltage drop caused by an internal resistor.

[0005] For measuring and evaluating a current through a semiconductor switch, insulated-gate bipolar transistors (IGBTs) are also known. These transistors provide a current at an additional sense terminal that is proportional to the main current through the semiconductor switch. The current from the sense terminal is smaller than the main current in the emitter path of the IGBT by an approximately constant factor.

[0006] The circuitry for evaluating the current in the sense path of such an IGBT must be dimensioned for the maximum duty cycle of the IGBT and also for the maximum currents that occur. Relatively large currents can also occur in the sense path, especially in the event of a fault.

[0007] There is therefore a need for an improved evaluation circuit for a circuit arrangement in which current evaluation is performed via a separate measurement path. In particular, there is a need for a current evaluation circuit that is not overloaded even when large currents occur in the measurement path. Disclosure of the invention

[0008] This is achieved by the features of the independent patent claims. Advantages of the invention

[0009] The present invention is based on the idea of ​​limiting the electrical current to be evaluated to a maximum electrical current when evaluating an electrical current in a measuring path. If, however, the electrical current in the measuring path falls below this maximum limit, the electrical current in the measuring path is not affected. By limiting the electrical current in the measuring path to a maximum limit, the individual components for evaluating the electrical current in this path can be designed for this predetermined maximum limit. Since a further increase in the electrical current is not to be expected due to the limitation, the individual components can therefore be dimensioned significantly smaller. On the one hand, this enables a more cost-effective design of the evaluation circuit for the electrical current.Furthermore, such components also require a smaller size for a lower maximum electrical current, so that the evaluation circuit also requires a smaller installation volume than would be the case with an evaluation circuit without the inventive limitation of the electrical current to be evaluated. Furthermore, by limiting the maximum electrical current, the associated maximum power loss and thus the amount of heat to be dissipated can be reduced. This reduced heating of the evaluation circuit for the electrical current to be monitored has a positive effect on the service life of the evaluation circuit.

[0010] The current measuring device of the current evaluation circuit according to the invention can be any device through which an electrical current can flow between two terminals. The current measuring device provides an output signal that depends on the electrical current flowing through the current measuring device. For example, the output signal can be a voltage signal that corresponds to the electrical current through the current measuring device. Such a voltage signal can be generated, for example, by means of a shunt resistor through which the electrical current flows. This makes it easy to generate a voltage signal that is proportional to the electrical current through the shunt resistor. Other options for generating an output signal that depends on the electrical current through the current measuring device are also possible.

[0011] Especially when converting an electrical current into an electrical voltage using a resistor, power loss occurs at the electrical resistor, which depends on the electrical current through the resistor. As the electrical current increases, so do the losses at the current measuring device. To avoid large losses, the electrical current through the current measuring device is limited to a maximum threshold. By limiting the maximum current through the current measuring device, losses and the resulting thermal heating are simultaneously limited. This can prevent, for example, excessive heating.

[0012] To determine the current through the current evaluation device, the output signal of the current measuring device can be used, for example. If the output signal provided by the current evaluation circuit determines that the electrical current through the current evaluation circuit exceeds a predetermined limit, the current limiting device can then be activated, which in turn limits the maximum current through the current evaluation device, in particular through the current measuring device. In this way, a simple limitation of the maximum current through the current measuring device can be achieved.

[0013] According to one embodiment, the current measuring device is designed to provide a voltage signal that is proportional to the electrical current flowing through the current measuring device. By providing a voltage signal at the output of the current measuring device, the magnitude of the electrical current through the current measuring device can be determined particularly advantageously.

[0014] According to one embodiment, the current measuring device comprises an analog-to-digital converter. The analog-to-digital converter is designed to convert the output signal provided by the current measuring device into a digital signal. Preferably, the analog-to-digital converter has a high impedance. This allows the current measuring device to further process the electrical current value digitally without placing a significant electrical load on the current evaluation circuit.

[0015] According to one embodiment, the current-limiting device comprises a reference voltage source. The reference voltage source is designed to provide a predetermined reference voltage. Furthermore, the current-limiting device is designed to compare a voltage signal with the reference voltage provided by the reference voltage source. The current-limiting device adjusts the electrical current through the current-measuring device based on this comparison. By providing a reference voltage source and comparing a voltage signal with the reference voltage, it is particularly easy to determine whether the electrical current through the current-measuring device has been exceeded. Accordingly, based on this comparison, if the electrical current is exceeded, this electrical current can be automatically limited.

[0016] According to one embodiment, the current-limiting device comprises a transistor with a control terminal. The current-limiting device is designed to provide a control signal at the control terminal of the transistor, which control signal depends on the comparison between the provided reference voltage and a voltage signal. In this way, the current through the current measuring device can be limited, preventing the electrical current through the current measuring device from being exceeded.

[0017] The present invention further relates to a circuit arrangement for providing an electrical current, comprising a current control device configured to provide an electrical current in a power path and to provide an electrical measuring current (ISense) corresponding to the provided electrical current in a measuring path; and a current detection device according to the invention.

[0018] According to one embodiment, the current control device comprises an insulated-gate bipolar transistor (IGBT). Preferably, the insulated-gate bipolar transistor has a measurement terminal that provides a measurement current corresponding to the current at the power output.

[0019] According to one embodiment, the method for detecting an electric current further comprises the steps of providing a predetermined reference voltage and comparing the provided reference voltage with a voltage value. The step of limiting the electric current adjusts the electric current depending on the comparison of the provided reference voltage with the voltage value.

[0020] Further embodiments and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. Short description of the drawings

[0021] Showing: Fig. 1: a schematic representation of an example circuit for a circuit arrangement with a current detection device according to an embodiment; Fig. 2: a schematic representation of a current-voltage characteristic curve as it forms the basis of a current detection device according to an embodiment; and Fig. 3: a schematic representation of a flow chart for a method as it forms the basis of a further embodiment. Description of implementation examples

[0022] Fig. 1 shows a schematic example circuit of a circuit arrangement for controlling an electric current in a power path. The circuit arrangement 1 comprises a current control device 20. The current control device 20 can, for example, be an installed-gate bipolar transistor (IGBT). The IGBT comprises an input terminal C, an output terminal E, and a control terminal G. By applying a control signal to the control terminal G, the current between the input terminal C and the output terminal E can be controlled. In addition, the IGBT further comprises a sense terminal S. At this sense terminal S, a measuring current I Sense This measuring current I Sense corresponds to the current I E in the power path of the circuit shown. For a known IGBT, the measuring current I Sense of the sense path on the electric current IE of the power path. The measuring current I Sense of the sense path is usually smaller than the current I by a known transmission factor E , which is provided at the output E of the IGBT. Since the relationship between electrical current and voltage drop in the power or measurement path is not linear, the constant relationship between I E and I Sense only if the voltage between the input terminal C and the sense terminal S is identical to the voltage between the input terminal C and the output terminal E. In order to set these identical voltage ratios, a compensation circuit 30 is connected to the sense terminal S and the output terminal E, which sets the same voltage ratios at the sense terminal S and the output terminal E. In the embodiment shown here, the compensation circuit comprises, for example, the two voltage sources UB,1 and U B,2 , as well as the power source I 0 . Furthermore, the compensation circuit 30 comprises the four transistors T 1 , T 2 , T 3 and T 4 . This circuit arrangement controls the transistor T 5 controlled.

[0023] The circuit arrangement 1 further comprises a current evaluation circuit 10, by means of which the measuring current I Sense can be detected by the current control device 20 and converted into an evaluation signal suitable for further processing. For this purpose, the measuring current I Sense via the transistor T 5 and the current measuring device 11. The current measuring device 11 can, for example, be represented by a shunt resistor R S can be realized. Across the shunt resistor R S one to the measuring current I Sense proportional voltage signal U S With increasing measuring current I Sensethus the voltage signal U also increases S .

[0024] The transistor T 5 by the compensation circuit 30 in such a way that the same potential is established at the measuring terminal S of the IGBT as at the power terminal E of the IGBT. In this way, it is achieved that between the current I E in the power path of circuit 1 and the current I Sense in the measuring path a constant transmission ratio is set and thus reliably from the measuring current I Sense on the current in power path I E can be closed.

[0025] With increasing current I E In the power path of circuit arrangement 1, the measuring current I also initially increases Sense in the measuring path of circuit 1. To measure the current I Sense However, in order not to allow the current to rise arbitrarily in the measuring path of the circuit arrangement 1, the current I Sensein the measuring path to a predetermined limit value. This can be achieved, for example, by controlling the transistor T 5 a limitation of the current I Sense in the measuring path. The control signal for the control terminal of the transistor T 5 to limit the measuring current I Sense can be generated, for example, by a suitable circuit which converts the output signal of the current measuring device 11, for example in the voltage drop U S across the shunt resistance R S For example, the voltage drop U S across the shunt resistance R S with a voltage of a reference voltage source U Ref For this purpose, for example, the voltage signal of the reference voltage source U Ref and the voltage drop U S across the shunt resistance R San operational amplifier OP. The operational amplifier OP compares the two voltage signals and outputs a control signal based on this comparison. This control signal can, if necessary after suitable amplification by the transistor T 6 the control terminal of the transistor T 5 For this purpose, the output of the operational amplifier OP can be connected to the control terminal of the transistor T 6 Of course, other alternative ways of limiting the measuring current I Sense possible.

[0026] The output signal of the current measuring device 11, for example the voltage drop U SThe signal across the shunt resistor can be converted into a digital signal for further processing by an analog-to-digital converter (not shown here). This is preferably an analog-to-digital converter with a high impedance, so that the output signal of the current measuring device 11 is not, or not significantly, influenced by the corresponding converter. In this way, further digital processing of the output signal of the current detection device 10 according to the invention is also possible.

[0027] Fig. Figure 2 shows a schematic representation of a voltage-current characteristic curve, as it forms the basis of an embodiment of the present invention. In a first section I, the current detection device 10 according to the invention first generates an output signal U S , which leads to the current I Ein the power path. As shown here, there is preferably a linear relationship between the output voltage U S and current in power path I E If the current exceeds I E in the power path exceeds a predetermined threshold, the corresponding current I Sense in the measuring path will also continue to increase. Due to the inventive limitation of the current I Sense in the measuring path to a maximum specified limit, this further increase can be limited in section II, so that the output voltage U S , which leads to the current I Sense in the measuring path, is limited to a specified maximum value.

[0028] Fig. 3 shows a schematic representation of a flow chart as it is used in a method 100 for detecting an electrical current I Senseaccording to one embodiment. In step 110, a current measuring device 11 is first provided. This current measuring device 11 provides an output signal U in step 120 S at the current measuring device 11, which corresponds to the electric current I Sense by the current measuring device 11. Preferably, there is a linear relationship between the output signal U S the current measuring device 11 and the current I Sense by the current measuring device.

[0029] In step 130, the electric current I Sense limited by the current measuring device 11 to a predetermined maximum limit value.

[0030] To limit the maximum electrical current through the current measuring device 11, a predetermined reference voltage U Ref provided which are connected to the output signal U provided in step 120 SIn this case, the electric current limiting step 130 adjusts this current I Sense depending on the comparison of the output signal U S with the provided reference voltage U Ref to.

[0031] Although the present invention has been described above preferably with reference to an insulated gate bipolar transistor (IGBT), in which the IGBT has an additional sense terminal, the present invention can also be applied to any other circuit arrangements in which a current in a power path is determined based on a measurement current corresponding to this current. Furthermore, the limitation of the current in the measurement path is not limited to a comparison of a reference voltage with an output voltage corresponding to the measurement current. Other possibilities for limiting the current in the measurement path are also possible. Alternatively, the output of a voltage signal corresponding to the measurement current I Sense any other output signal can be provided by means of which the measuring current I Sense and thus the current in the power path can be determined.

[0032] In summary, the present invention relates to an evaluation of the magnitude of an electrical current in a power path by evaluating another electrical current in a measurement path. To avoid excessively large electrical currents in this measurement path, the current in this measurement path is limited to a predetermined maximum limit.

Claims

[1] Current detection device (10) for detecting an electric current (I Sense ) in a measuring path that leads to an electrical current (l E ) in a power path corresponding electric current, with: a current measuring device (11) arranged in the measuring path and configured to provide an output signal corresponding to an electrical current flowing through the current measuring device (11); and a current limiting device (12) which is designed to limit the electrical current through the current measuring device (11) to a predetermined maximum limit value when the electrical current (l E ) in the power path exceeds a specified threshold. [2] Current detection device (10) according to claim 1, wherein the current measuring device (11) is designed to provide a voltage signal that is proportional to the electric current flowing through the current measuring device (11). [3] Current detection device (10) according to claim 1 or 2, wherein the current measuring device (11) comprises an analog / digital converter (13) which is designed to convert the output signal dependent on the electrical current through the current measuring device (11) into a digital signal. [4] Current detection device (10) according to one of claims 1 to 3, wherein the current limiting device (12) comprises a reference voltage source (U Ref ) which is designed to provide a predetermined reference voltage and the current limiting device (12) is designed to generate a further voltage signal with the reference voltage source (U Ref) provided reference voltage and adjust the electric current through the current measuring device (11) based on the comparison. [5] Current detection device (10) according to claim 4, wherein the current limiting device (12) comprises a transistor (T5) with a control terminal, and the current limiting device (12) is designed to provide a control signal at the control terminal of the transistor (T5) based on the comparison between the provided reference voltage and the further voltage signal. [6] Circuit arrangement (1) for providing an electric current (l E ) , with: a current control device (20) designed to control an electric current (l E ) in a power path, and in a measuring path a voltage corresponding to the provided electrical current (l E ) corresponding electrical measuring current (I Sense ) provide; and a current detection device (10) according to one of claims 1 to 5. [7] Circuit arrangement (1) according to claim 6, wherein the current control device (20) comprises an insulated gate bipolar transistor, IGBT. [8] Method (100) for detecting an electric current (I Sense ) in a measuring path that leads to an electrical current (l E ) in a power path corresponding electrical current, with the steps: Providing (110) a current measuring device (11); Detecting (120) an electric current by the provided current measuring device (11); Outputting (130) an output signal at the current measuring device (11) as a function of the detected electrical current; and Limiting (140) the electric current through the current measuring device (11) to a predetermined maximum limit value when the electric current (l E) in a power path exceeds a specified threshold. [9] The method (100) of claim 8, further comprising the steps of: Providing a predetermined reference voltage; Comparing the output signal with the provided reference voltage; wherein the step (140) of limiting the electrical current adjusts the current in dependence on the comparison of the provided reference voltage with a voltage value.

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