Protection device and control circuit for a semiconductor switch and method for controlling a semiconductor switch

Abstract

The present invention relates to protecting a semiconductor switch from overvoltage. To this end, a capacitor device is provided at the input terminal of the semiconductor switch. The electric charge flowing into the capacitor device is integrated so as to trigger a protection function when a limit value is exceeded.

Description

Technical Field

[0001] The present invention relates to a protection device for a semiconductor switch and a control circuit for a semiconductor switch. The present invention further relates to a method for controlling a semiconductor switch. In particular, the present invention relates to protecting a semiconductor switch from overvoltage. Background Art

[0002] The use of semiconductor switches as switching elements is becoming increasingly important. Here, when disconnecting the switching element, especially a semiconductor switching element, due to leakage inductance, etc., overvoltage may occur at the output of the semiconductor switch. In order to avoid damage to the semiconductor switch due to such overvoltage, appropriate overvoltage protection should be provided. Such overvoltage protection is known, for example, under the term "Active Clamping".

[0003] Publication DE 10 2013 202 641 A1 discloses overvoltage protection for semiconductor switches having static components and dynamic components. For example, the dynamic component can respond in the case of an overvoltage below the steady-state value, and its response behavior is time-limited.

[0004] For a protection device for a semiconductor switch, an avalanche diode can be used, for example, to detect overvoltage. Here, as the switching speed of the semiconductor switch increases, the capacitive characteristics of such an avalanche diode must be taken into account more and more. Summary of the Invention

[0005] The present invention provides a protection device for a semiconductor switch, a control circuit for a semiconductor switch, and a method for controlling a semiconductor switch having the features of the independent patent claims. Other embodiments are the subject of the dependent patent claims.

[0006] Accordingly, it is provided that:

[0007] A protection device for a semiconductor switch, having a capacitor device, an integrator, and a comparison device. The integrator is designed to integrate the charging current flowing into the capacitor device. In this way, the charge quantity in the capacitor device can be determined from the integrated charging current. In this case, the capacitor device is arranged between the input terminal of the semiconductor switch and the integrator. The comparison device is designed to control the semiconductor switch when the determined charge quantity in the capacitor device exceeds a predefined limit value.

[0008] Furthermore, it is provided that:

[0009] A control circuit for a semiconductor switch, having a drive circuit and a protection device for a semiconductor switch according to the invention. The drive circuit is designed to receive a control signal for the semiconductor switch and to control the control terminal of the semiconductor switch using the received control signal. The drive circuit is in particular electrically coupled to the protection device. The drive circuit is furthermore designed to at least partially control the semiconductor switch when the charge quantity determined by the protection device in the capacitor device exceeds a pre-given limit value.

[0010] Finally, it is provided that:

[0011] A method for controlling a semiconductor switch, having a step of integrating a charging current in a capacitor device arranged between an input terminal of the semiconductor switch and an integrator. By integrating the charging current, the charge quantity in the capacitor device is determined. The method furthermore includes a step of comparing the determined charge quantity in the capacitor device with a pre-given limit value and controlling the semiconductor switch when the determined charge quantity in the capacitor device exceeds the pre-given limit value.

[0012] Advantages of the invention

[0013] Conventional overvoltage protection devices for semiconductor switch elements typically use clamping diodes, such as avalanche diodes or Zener diodes. As the switching speed increases, the capacitance characteristics, in particular the blocking layer capacitance of such diodes, must also be taken into account in this case. Depending on the design, the capacitance characteristics can have a negative impact on the response voltage or response behavior of the overvoltage protection device for the semiconductor switch.

[0014] Therefore, the idea of the present invention is to take this knowledge into account and to provide a protection device for a semiconductor switch, which specifically takes into account the capacitance characteristics of the device for detecting overvoltage. In this way, it is possible to reliably and quickly detect overvoltage at the semiconductor switch element, especially even at higher switching speeds. Accordingly, an occurring overvoltage can be identified early, and appropriate countermeasures can be taken to avoid the overvoltage. For example, the semiconductor switch element can be completely or partially closed in order to resist a further increase in the voltage across the terminals of the semiconductor switch element. Thereby, damage to the semiconductor switch element can be prevented or at least premature aging caused by overvoltage etc. can be prevented.

[0015] If the capacitance of the capacitor device is known, the charge quantity in the capacitor device can be determined by integrating the current flowing into the capacitor device. Accordingly, the voltage at the semiconductor switching element can be derived from the relationship between the capacitance of the capacitor device and the determined charge quantity. If the determined charge quantity in the capacitor device exceeds the charge quantity corresponding to a pre-given trigger voltage, appropriate measures can be taken in order to counteract a further voltage increase at the semiconductor switching element or to reduce the voltage across the semiconductor switching element. For example, for this purpose, the semiconductor switching element can be fully or partially actuated or closed.

[0016] In this case, especially at high switching speeds, the evaluation of the charge quantity in the capacitor device enables a rapid and effective detection of potential overvoltages at the semiconductor switching element.

[0017] According to one embodiment, the capacitor device includes a diode. In particular, the capacitor device can for example include an avalanche diode or a Zener diode. Diodes with a defined breakdown voltage, such as avalanche diodes or Zener diodes, enable the detection of overvoltages even in the case of a slow or static voltage increase. However, in addition, at higher switching speeds, capacitive properties such as the barrier capacitance of the diode must also be taken into account. The reaching of a critical overvoltage can already be detected by evaluating the charge quantity flowing into the diode before the barrier capacitance of the diode is charged and the diode is triggered. Accordingly, reliable overvoltage protection can be ensured both in the case of slow switching processes and in the case of fast switching processes.

[0018] According to one embodiment, the pre-given charge quantity can be adjusted taking into account the barrier capacitance of the diode. For example, the barrier capacitance can be determined based on the specifications in the data sheet of the respective diode. In addition, of course, any other method, especially measurement technique methods for determining the barrier capacitance of the respective diode, are also possible. By taking into account the barrier capacitance, the response of the protection device for protecting the semiconductor switch can be precisely adjusted. For example, based on the barrier capacitance and the pre-given voltage threshold for the protection device, the charge quantity can be determined, especially calculated, at which the protection device should be triggered.

[0019] According to one embodiment, the comparison device is designed to actuate the semiconductor switch when the voltage across the diode exceeds the breakdown voltage of the diode. In particular, the breakdown voltage can be the breakdown voltage of an avalanche diode or a Zener diode in the blocking direction. In this way, if the pre-given breakdown voltage of the diode in the blocking direction is exceeded, the semiconductor switch is actuated even if the charge quantity determined up to that point in time has not reached the pre-given limit value. Thereby, the reliability of the protection function can still be further improved.

[0020] According to one embodiment, the capacitor device includes a capacitor. The capacitor is a device that is simple to implement and low in cost. By using the capacitor, a cheap, simple, and reliable protection device for a semiconductor switch can be realized.

[0021] According to one embodiment, the integrator is designed to synchronize the integration of the charging current with the control signal for the semiconductor switch. For example, the integrator can be reset synchronously with the control signal for the semiconductor switch. In this way, drift of the integrator during the integration of the charging current can be avoided.

[0022] According to one embodiment, the integrator is designed to restart the integration of the charging current whenever the semiconductor switch is turned off. At the start of the integration, the value of the integrator can be reset, respectively. In this way, when the semiconductor switch is turned off, the integration of the charging current starts respectively in a defined zero-value situation and thus the voltage across the semiconductor switch increases.

[0023] According to one embodiment, the integrator can include a capacitor. In particular, the integrator can consist of one capacitor or a device having multiple capacitors. The capacitor device, in particular the capacitor, enables a particularly simple integration of the charge quantity. Here, the voltage applied across the two terminals of the capacitor can correspond to the charge quantity in the capacitor.

[0024] The above configurations and improvements can be arbitrarily combined with each other as long as they make sense. Other configurations, improvements, and implementations of the present invention also include combinations of the features of the present invention that are not explicitly mentioned previously or below in connection with the embodiments. In particular, those skilled in the art will also add individual aspects here as improvements or supplements to the corresponding basic forms of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following describes other features and advantages of the present invention with reference to the drawings. Here:

[0026] Figure 1 A schematic diagram showing a circuit schematic of a control circuit for a semiconductor switch having a protection device according to one embodiment;

[0027] Figure 2 A schematic diagram showing a circuit schematic of a control circuit for a semiconductor switch according to another embodiment;

[0028] Figure 3 A schematic diagram showing a circuit schematic of a control circuit for a semiconductor switch according to yet another embodiment; and

[0029] Figure 4 A schematic diagram showing a flowchart based on a method for controlling a semiconductor switch according to one embodiment. DETAILED DESCRIPTION

[0030] Figure 1 Schematic diagram showing the circuit schematic of the control circuit 2 for the semiconductor switch 3. The control circuit 2 includes a drive circuit 20 for driving the control terminal 32 of the semiconductor switch 3. For this purpose, the drive circuit 20 receives a control signal D, amplifies the control signal D and controls the control terminal 32 of the semiconductor switch 3 in accordance with the control signal D. In this way, the electrical connection between the input terminal 31 and the output terminal 33 of the semiconductor switch 3 can be interrupted or closed. For example, the semiconductor switch 3 can be a MOSFET or a bipolar transistor with an insulated gate terminal (IGBT). Of course, in principle any other semiconductor switch is possible. For example, the semiconductor switch 3 can be the semiconductor switch of a power stage (such as a rectifier, etc.). If the electrical connection between the input terminal 31 and the output terminal 33 of the semiconductor switch 3 is interrupted, a voltage increase between the input terminal 31 and the output terminal 32 can occur, for example due to leakage inductance. If the voltage increase between the input terminal 31 and the output terminal 32 exceeds the permitted level, the semiconductor switch 3 can thereby be damaged or even destroyed if necessary. To prevent such overvoltage, for example, a protection device 1 can be provided.

[0031] The protection device 1 includes a capacitor device 11, an integrator 12 and a comparison device 13. In addition, the protection device 1 can also include, for example, a logic gate 14 and, if necessary, other components. The capacitor device 11 is arranged between the input terminal 31 of the semiconductor switch and the input terminal of the integrator 12. If the voltage at the input terminal 31 of the semiconductor switch 3 increases, the capacitor device 11 is charged via the integrator 12. Here, the integrator 12 integrates the charging current flowing into the capacitor device. By this integration, the integrator 12 can determine the amount of charge flowing into the capacitor device 12. With the capacitance C of the capacitor device 11 being constant, the amount of charge in the capacitor device 11 is thus proportional to the voltage across the capacitor device 11.

[0032] The integrator 12 outputs an output signal proportional to the determined charge quantity Q in the capacitor device 11. This can be an analog or digital output signal in this case. In this way, the determined charge quantity Q is supplied to the comparator 13. The comparator 13 compares the determined charge quantity Q with a pre-given limit value S. For example, the comparator 13 can be a subtractor that forms the difference between the determined charge quantity Q and the pre-given rated value S. If the determined charge quantity Q exceeds the pre-given rated value S, then, for example, the control input 32 of the semiconductor switch 3 can then be controlled. In this way, the semiconductor switch 3 can be fully or at least partially turned on between the input terminal 31 and the output terminal 33. Thereby, the voltage between the input terminal 31 and the output terminal 32 is reduced. For example, the control terminal 32 of the semiconductor switch 3 can also be controlled by the drive circuit 20.

[0033] Furthermore, after detecting that the determined charge quantity exceeds the rated value S, the control of the semiconductor switch 3 can additionally be associated with the control signal D. For this purpose, the result of the comparator 13 and the control signal D can be fed to the logic gate 14. The logic gate 14 correlates the result of the comparator 13 with the control signal D with each other. For example, the semiconductor switch 3 can only be controlled if, according to the control signal D, the semiconductor switch should not be controlled, but the comparator 13 determines that the charge quantity Q exceeds the rated value S. And as long as the control signal D pre-gives the active control of the semiconductor switch 3, no further influence is exerted by the protection device 1.

[0034] The integrator 12 can be any analog or digital integrator. The integrator 12 can be implemented, for example, by means of any known or novel integrator circuit.

[0035] Furthermore, the integration of the integrator 12 can be synchronized with the control signal D. For example, if the semiconductor switch 12 should be turned off according to the control signal D, the integration of the integrator 12 can be reset and restarted respectively. In this way, for example, drift of the integrator can be avoided. Furthermore, of course, any other synchronization of the integrator 12 is also possible, especially in the case of using the control signal D.

[0036] Figure 2 A schematic diagram showing a circuit schematic of the control circuit 2 for the semiconductor switch 3 according to another embodiment. The control circuit 2 and especially the protection device 1 correspond to the above embodiment to the greatest extent. According to Figure 2The embodiment is different from the above-described embodiment especially in that the capacitor device 11 is a diode 11a. For example, the diode 11a can be an avalanche diode or a Zener diode. Such a diode 11a can have a defined breakdown voltage at which the diode 11a becomes conductive even in the blocking direction. However, before the diode turns into the conductive state, the diode 11a also has capacitive characteristics. Before the diode 11a breaks down, the blocking layer capacitance of the diode 11a is charged here. The integrator 12 integrates the charging current flowing into the diode 11a and accordingly transfers the determined charge quantity Q to the comparator 13. If it is detected that the charge quantity Q exceeds a pre-given nominal value S, the semiconductor switch 3 can be controlled as already described previously. In addition, when the diode 11a turns into the conductive state after exceeding the breakdown voltage, the semiconductor switch 3 can also be controlled. For this purpose, the terminal of the diode 11a connected to the integrator 12 is additionally also connected to another driver stage 15 which outputs an output signal for controlling the semiconductor switch 3 after the diode 11a breaks down. In addition, the output of the comparator 13 is also connected to this other driver stage 15 via the above-described logic gate 14 if necessary. In this way, in the case of a fast dynamic process, overvoltage protection can be achieved by evaluating the charge quantity in the diode 11a. In addition, even in the case of a slow, possibly static overvoltage, triggering of the protection device can be achieved by triggering (igniting) the diode 11a.

[0037] Figure 3 Shows another embodiment of the control circuit 2 for the semiconductor switch. In this embodiment, the capacitor device 11 includes a capacitor 11b. Accordingly, overvoltage protection can be achieved by integrating the charging current flowing into the capacitor 11b and comparing the charge quantity from the integrated charging current with the nominal value S. If necessary, the integrator 12 can be implemented as a capacitor 12b, for example, in a simple embodiment. Such a circuit arrangement having two capacitors 11b and 12b as the capacitor device and the integrator enables a particularly simple and thus cost-effective overvoltage protection for the semiconductor switch 3.

[0038] Figure 4 Shows a schematic view of a flow chart on which a method for controlling the semiconductor switch 3 is based according to an embodiment. The method can in principle include any suitable method steps of the types already described previously in connection with the protection device 1 and the control circuit 2. In addition, the protection device 1 and the control circuit 2 can also include any suitable components to implement the method steps described subsequently.

[0039] The method includes step S1 for integrating the charging current flowing into capacitor device 11. The capacitor device may be arranged between the input terminal 31 of semiconductor switch 3 and integrator 12. In this way, the electric charge quantity Q in capacitor device 11 can be determined from the integrated charging current. The method further includes step S2 for comparing the determined electric charge quantity Q in the capacitor device with a pre-given limit value S. Finally, the method includes step S3 for controlling semiconductor switch 3 when the determined electric charge quantity Q in capacitor device 11 exceeds the pre-given limit value S.

[0040] In particular, the integration of the charging current can be synchronized with the control signal D for semiconductor switch 3. For example, when semiconductor switch 3 is closed, the integration of the charging current can be reset and started.

[0041] In summary, the present invention relates to protecting a semiconductor switch from overvoltage. For this purpose, a capacitor device is provided at the input terminal of the semiconductor switch. The electric charge quantity flowing into the capacitor device is integrated so as to trigger a protection function when a limit value is exceeded.

Claims

1. A protection device (1) for a semiconductor switch (3), comprising: Capacitor elements (11, 11a, 11b); Integrators (12, 12b) designed to integrate the charging current flowing into the capacitor elements (11, 11a, 11b) in order to determine the charge quantity (Q) in the capacitor elements (11, 11a, 11b) from the integrated charging current; Comparison means (13) designed to control the semiconductor switch (3) when the determined charge quantity (Q) in the capacitor elements (11, 11a, 11b) exceeds a pre-given limit value (S); wherein the capacitor elements (11, 11a, 11b) are arranged between the input terminal (31) of the semiconductor switch (3) and the integrators (12, 12b).

2. The protection device (1) according to claim 1, wherein the capacitor elements (11, 11a, 11b) comprise a diode (11a).

3. The protection device (1) according to claim 2, wherein the diode (11a) is an avalanche diode.

4. The protection device (1) according to claim 2, wherein the pre-given limit value (S) can be adjusted using the blocking layer capacitance of the diode (11a).

5. The protection device (1) according to any one of claims 2 to 4, wherein the comparison means (13) is designed to control the semiconductor switch (3) when the voltage across the diode (11a) exceeds the breakdown voltage of the diode (11a).

6. The protection device (1) according to claim 1, wherein the capacitor elements (11, 11a, 11b) comprise a capacitor (11b).

7. The protection device (1) according to any one of claims 1 to 4, wherein the integrators (12, 12b) are designed to synchronize the integration of the charging current with a control signal (D) for the semiconductor switch (3).

8. The protection device (1) according to claim 7, wherein the integrators (12, 12b) are designed to start the integration of the charging current when the semiconductor switch (13) is turned off.

9. The protection device (1) according to any one of claims 1 to 4, wherein the integrator (12b) comprises a capacitor.

10. A control circuit (2) for a semiconductor switch (3), comprising: A drive circuit (20) designed to receive a control signal (D) for the semiconductor switch (3) and to control the control terminal (32) of the semiconductor switch (3) using the received control signal (D); and The protection device (1) according to any one of claims 1 to 9, wherein the drive circuit (20) is electrically coupled to the protection device (1), and the drive circuit (20) is designed to at least partially control the semiconductor switch (3) when the charge quantity (Q) determined by the protection device (1) in the capacitor elements (11, 11a, 11b) exceeds the pre-given limit value (S).

11. A method for controlling a semiconductor switch (3), having the following steps: Integrating (S1) a charging current flowing into capacitor elements (11, 11a, 11b) in order to determine the charge quantity (Q) in the capacitor elements (11, 11a, 11b) from the integrated charging current, the capacitor elements being arranged between an input terminal (31) of the semiconductor switch (3) and an integrator (12, 12b); Comparing (S2) the determined charge quantity (Q) in the capacitor elements (11, 11a, 11b) with a pre-given limit value (S); and Controlling (S3) the semiconductor switch (3) when the determined charge quantity (Q) in the capacitor elements (11, 11a, 11b) exceeds the pre-given limit value (S).

12. The method according to claim 11, wherein the integration (S1) of the charging current is started when the semiconductor switch (3) is opened.

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