CONTROL SYSTEM FOR CONTROLLING A TRANSISTOR, ELECTRIC VEHICLE COMPRISING A CONTROL SYSTEM, AND METHOD FOR CONTROLLING A TRANSISTOR - Patent application

Abstract

1. A control system for controlling a transistor having a gate, the control system comprising a control unit adapted to: connect a voltage source to the gate via a first electrical path to enable the voltage source to supply a first voltage to the transistor when the transistor is in a first state; control the voltage source to apply the first voltage to the transistor via the first electrical path to switch the transistor from the first state to a second state; disconnect the voltage source and the gate from each other; and connect the voltage source to the gate to enable the voltage source to supply a second voltage to the transistor via a second electrical path when the transistor is in the second state; and control the voltage source to apply the second voltage to the gate, the second electrical path being adapted to conduct current from the voltage source to the transistor based on a leakage current of the transistor.

Description

[Technical field]

[0001] The present invention relates to a control system for controlling a transistor comprising a gate, a source and a drain.The present invention further relates to an electric vehicle comprising the control system.Furthermore, the present invention relates to a method for controlling a transistor. [Background technology]

[0002] A transistor is a semiconductor device used to amplify or switch electrical signals and power. Transistors are one of the fundamental building blocks of modern electronics. The most widely used type of transistor is the metal-oxide-semiconductor field-effect transistor (MOSFET). However, there are several types of transistors, e.g., bipolar transistors, HEMT (high electron mobility transistor) devices. HEMT devices, such as GaN HEMTs, are characterized by their relatively high electron mobility. The high electron mobility of HEMTs helps achieve larger gains, making them useful as amplifiers. HEMTs also provide high switching speeds. Hence, HEMTs are becoming popular for integration into the electrical systems of electric vehicles, such as electric cars.

[0003] However, HEMT devices suffer from the drawback that the leakage current flowing between the gate and source of a HEMT device is temperature dependent. For temperatures up to 80°C, the leakage current becomes small due to impact ionization caused by deep acceptors. When the temperature is increased, the leakage current starts to grow slowly again and increases exponentially near 150°C due to tunneling of electrons through to the gate, at which point the device experiences a short circuit. Under normal operating conditions, these types of temperatures are not uncommon.

[0004] Transistors, and especially HEMT devices, have the drawback of being sensitive to currents that significantly exceed those under normal operating conditions. Due to high temperatures, short circuits of the transistors can occur. For example, GaN devices can only withstand short circuits for a few hundred nanoseconds. If a short circuit occurs in a transistor during this very short period of time, the transistor becomes damaged and even non-functional. Furthermore, it is difficult to detect a short circuit. Due to these drawbacks, timely prediction before any damage related to the transistor occurs due to a short circuit is difficult to achieve. Summary of the Invention [Problem to be solved by the invention]

[0005] It is an object of the present invention to provide a control system for controlling transistors, or at least to provide an alternative control system, which is not significantly affected by the above mentioned drawbacks. [Means for solving the problem]

[0006] The object of the present invention is achieved by a control system for controlling a transistor having a gate, a source and a drain, the control system comprising: a gate connector connectable to a gate of a transistor; - a voltage connector connectable to a voltage source; - a first electrical path extending from the voltage connector to the gate connector; - a second electrical path extending from the voltage connector to the gate connector, the second electrical path comprising a first resistive element, the first electrical path and the second electrical path being at least partially in parallel with each other; The control system further comprises a control unit, the control unit comprising: connecting a voltage source to the gate via a first electrical path to enable the voltage source to supply a first voltage to the gate connector via the first electrical path when the transistor is in a first state; - controlling a voltage source to apply a first voltage to the gate connector via a first electrical path to switch the transistor from a first state to a second state; - disconnecting the voltage source and the gate from each other via a first electrical path when the transistor is in a second state; connecting a voltage source to the gate via a second electrical path to enable the voltage source to supply a second voltage to the gate connector via the second electrical path when the transistor is in a second state; - controlling a voltage source to apply a second voltage to the gate connector via a second electrical path, the second electrical path conducting a current from the voltage connector to the gate connector through the first resistive element based on a leakage current of the transistor; The present invention is adapted to

[0007] The invention thus concerns a control system for controlling a transistor with a gate, a source and a drain. The transistor is, for example, a GaN HEMT. HEMT devices are typically powered when the voltage between the gate and the source exceeds a threshold voltage. The threshold voltage of GaN HEMTs is at about 2V. This behavior is called enhancement mode (e-mode devices or eHEMTs). When the voltage between the gate and the source is less than the threshold voltage, such a transistor is turned off. This type of mode is called depletion mode (d-mode devices or dHEMTs).

[0008] The control system comprises a gate connector connectable to the gate of the transistor. For example, the gate connector is connected to the gate of the transistor through a switch. For example, the gate connector is connected to the gate of the transistor by soldering the gate connector to the gate. The source or drain can be connected to a load. The load can be either inductive, for example a power boost converter or a motor, or resistive, for example a heater.

[0009] The control system further comprises a voltage connector connectable to a voltage source. The voltage connector is, for example, a switch. The voltage connector is, for example, a plug or a switch plug. The voltage source is, for example, a DC voltage source derived from a mains supply by an AC / DC converter. The voltage source comprises, for example, a battery. The voltage source applies, for example, a voltage of 5V to the voltage connector.

[0010] The control system further comprises a first electrical path extending from the voltage connector to the gate connector. The first electrical path is, for example, an electrical wire capable of transmitting a voltage or a current from the voltage connector to the gate connector. The voltage source is configured to provide a first voltage to the gate of the transistor via the first electrical path by connecting the voltage source to the voltage connector and the gate connector to the gate.

[0011] The control system further comprises a second electrical path extending from the voltage connector to the gate connector. The second electrical path is, for example, an electrical wire capable of transmitting a voltage or a current from the voltage connector to the gate connector. The voltage source is configured to supply a second voltage to the gate of the transistor via the second electrical path by connecting the voltage source to the voltage connector and the gate connector to the gate. The second electrical path comprises a first resistive element, for example, a resistor. The first electrical path and the second electrical path are at least partially in parallel with each other. In one example, the first electrical path and the second electrical path are in parallel with each other between the voltage connector and the gate connector.

[0012] The control system further comprises a control unit. The control unit is adapted to connect a voltage source to the gate via a first electrical path to enable the voltage source to supply a first voltage to the gate connector via the first electrical path when the transistor is in a first state. The first state is, for example, a situation in which the transistor is "off", meaning that no current flows between the drain and the source. The control unit controls the voltage source to apply the first voltage to the gate connector via the first electrical path. When the voltage source supplies the first voltage to the transistor, the voltage at the gate is equal to the first voltage. This may happen, for example, almost instantly. The first voltage is, for example, 5V. By having the first voltage at the gate, the transistor is switched from the first state to a second state. The transistor is turned on in the second state, for example, where a current flows between the drain and the source. The current flowing between the drain and the source is also called a forward current.

[0013] When the transistor is in the second state, the transistor is, for example, "on", and the control unit is adapted to disconnect the voltage source and the gate from each other via the first electrical path. Furthermore, the control unit is adapted to connect the voltage source to the gate via the second electrical path to enable the voltage source to supply a second voltage to the gate connector via the second electrical path when the transistor is in the second state. The second voltage is, for example, 5V. The second voltage is high enough to keep the transistor in the second state and to prevent the transistor from returning to the first state. For example, the control unit is adapted to provide the second voltage to the gate when disconnecting the voltage source and the gate from each other via the first electrical path to keep the transistor in the second state.

[0014] The control unit is adapted to control the voltage source to apply a second voltage to the gate connector via a second electrical path. The second electrical path is adapted to carry a current from the voltage connector to the gate connector via the first resistive element based on a leakage current of the transistor. By applying the second voltage to the gate connector, the transistor is held in a second state. In the second state, a forward current flows between the source and the drain. The forward current induces heat in the transistor, increasing the temperature of the transistor. As a result of the increase in temperature, a leakage current begins to flow between the gate and the source. The leakage current increases as a function of temperature. As the second electrical path is connected to the gate connector, the leakage current flows not only between the gate and the drain, but also from the voltage source to the gate via the second electrical path. The first resistive element is arranged to cause a voltage drop based on the leakage current. The voltage drop across the first resistive element increases with the increasing leakage current. For example, at 150° C., the leakage current may be 1 mA. The voltage drop across the first resistive element, for example a resistor with a resistance of 1 kilohm, is then 1 V. As a result of the voltage drop across the first resistive element, the voltage at the gate is reduced. By reducing the voltage at the gate, the leakage current is reduced. In this way, large leakage currents are prevented, which prevents damage to the transistor.

[0015] In one embodiment, the first resistive element is arranged to, in response to the current, reduce the gate voltage at the gate connector to a value lower than the first voltage to switch the transistor from the second state to the first state. For example, the voltage at the gate is reduced by 1V. As a result, the gate voltage is reduced, making the voltage at the gate insufficient to power the transistor, thereby switching the transistor from the second state to the first state. Since the transistor is off in the first state, no forward current flows in the first state. As a result, the temperature of the transistor decreases, further reducing the leakage current.

[0016] In one embodiment, the control system further comprises a discharge switch. The discharge switch is arranged between the first electrical path and / or the second electrical path and the ground to connect the first electrical path to the ground and / or to connect the second electrical path to the ground. The discharge switch is, for example, a bipolar transistor. When the voltage source supplies a first voltage via the first electrical path or a second voltage via the second electrical path to the gate of the transistor, the discharge switch is open. When the discharge switch is open, no current is drained from the first electrical path or the second electrical path to the ground through the discharge switch. At the moment when the transistor is switched from the second state to the first state due to a voltage drop, the discharge switch is closed. In the closed state of the discharge switch, the discharge switch discharges the gate of the transistor. The control unit is, for example, configured to control the switching of the discharge switch.

[0017] When the transistor switches back to the first state due to a voltage drop, there may still be a residual voltage applied to the gate. The residual voltage is lower than the first voltage. The residual voltage may cause leakage current to continue. By discharging the gate with a discharge switch, the residual voltage is removed from the gate, stopping the leakage current. In this way, the control system provides a safer way of controlling the transistor.

[0018] In one embodiment, the control system further comprises a first switch disposed in the first electrical path to connect a voltage source to the gate via the first electrical path. According to this embodiment, the first switch is configured to make a connection between the voltage source and the gate to enable the voltage source to apply a first voltage to the gate. The first switch is, for example, a bipolar transistor. For example, the control unit is configured to control the first switch by closing the first switch between the voltage source and the gate.

[0019] In one embodiment, the control system comprises a pull-up driver, and the first switch is controlled by the pull-up driver adapted to generate a pulse for switching the first switch. For example, applying a high pulse closes the first switch and applying a low pulse opens the first switch. The pulse is, for example, generated by a first-order high-pass filter. The pulse is, for example, generated digitally. The pull-up driver is, for example, integrated in the control unit. The pull-up driver is associated with a relatively large drive current. This allows the pull-up driver to drive a transistor, for example a HEMT device, at high speed.

[0020] In one embodiment, the first electrical path comprises a second resistive element. The second resistive element is, for example, a resistor. When a voltage source is connected to the gate via the first electrical path, the first electrical path is adapted to carry a current from the voltage connector to the gate connector via the second resistive element. The second resistive element allows the transistor to be powered gradually until the gate voltage is equal to the first voltage. This prevents abrupt changes in the gate voltage.

[0021] In one embodiment, the second resistive element has a lower resistance than the first resistive element. Because the second resistive element has a lower resistance, the voltage source creates a large current on the first electrical path when applying the first voltage. As a result of the large current, the voltage at the gate increases to the first voltage quickly. This allows for rapid switching of the transistor. In comparison, if the second resistive element were to have a high resistance, the transistor would take longer to switch. Because the first resistive element has a higher resistance, even a small leakage current would cause a relatively large voltage drop. This helps to create a sufficient voltage drop at the gate to reduce leakage current even for small leakage currents. The voltage drop may be sufficient to switch the transistor from the second state back to the first state. This helps to protect transistors that are sensitive to small leakage currents. For example, the resistance of the second resistive element is between 1 and 10 ohms, preferably between 1 and 5 ohms. For example, the resistance value of the first resistive element is between 100 and 2000 ohms, preferably between 500 and 1500 ohms.

[0022] In one embodiment, the first electrical path and the second electrical path are arranged in a series connection to the gate of the transistor. The first electrical path and the second electrical path may overlap each other. By arranging the first electrical path and the second electrical path in a series connection to the gate, the gate only needs a single connection to connect to both the first electrical path and the second electrical path. This allows for a simple connection between the control system and the transistor.

[0023] In one embodiment, the control system further comprises a second switch disposed in the second electrical path to connect the voltage source to the gate via the second electrical path. According to this embodiment, the second switch is configured to make a connection between the voltage source and the gate to enable the voltage source to apply a second voltage to the gate. The second switch is, for example, a bipolar transistor. For example, the control unit is configured to control the second switch by closing the second switch between the voltage source and the gate.

[0024] For example, when the transistor is in the second state, the transistor is "on" and the control unit is adapted to disconnect the voltage source and the gate from each other via a first electrical path, for example, by controlling the first switch to switch the first switch open. Further, the control unit is adapted to connect the voltage source to the gate by closing a second switch between the voltage source and the gate. In this way, a voltage is allowed to supply a second voltage to the gate connector via the second electrical path when the transistor is in the second state. The second voltage is, for example, 5V.

[0025] In one embodiment, the control system further comprises a leakage current detection system configured to determine a leakage current of the transistor based on a voltage across the first resistive element. Because the first resistive element causes a voltage drop as a result of leakage current, the voltage across the first resistive element provides an easy-to-measure quantity representative of the leakage current. The leakage current can be accurately determined by detecting the voltage across the first resistive element, especially when the first resistive element has a high resistance value. The leakage current detection system, for example, measures the voltage drop across the first resistive element.

[0026] The leakage current detection system is configured, for example, to compare the measured voltage drop across the first resistive element with a predetermined reference voltage. The predetermined reference voltage is, for example, selected to represent a leakage current that may cause damage to the transistor. The predetermined reference voltage is, for example, set to 1V.

[0027] In a further embodiment, the leakage current detection system is configured to provide a signal to the control unit representative of the leakage current of the transistor. The control unit is configured to switch the transistor from the second state to the first state in response to the signal. For example, when the leakage current of the transistor reaches a level that may be harmful to the transistor, the leakage current detection system is configured to provide the signal to the control unit. In response to the signal, the control unit turns off the transistor, for example, by disconnecting a voltage source from the gate. For example, the control unit controls the second switch to disconnect the voltage source from the gate connector in response to the signal. The signal from the leakage current detection system serves as a feedback signal. For example, the leakage current detection system continuously monitors the voltage drop across the first resistive element. In this way, the control system is adapted to anticipate large leakage currents more quickly.

[0028] For example, the control unit is adapted to control a discharge switch. In response to the signal, the control unit controls the discharge switch, for example, to connect a gate of a transistor to ground. In response to the signal, the control unit controls the discharge switch, for example, to connect a first electrical path to ground and / or to connect a second electrical path to ground.

[0029] In a further embodiment, the signal representative of the transistor's leakage current is representative of a short circuit of the transistor. As previously mentioned, transistors, and in particular HEMT devices, can only tolerate a short circuit for a short period of time. As soon as the leakage current reaches a level representative of a short circuit of the transistor, the leakage current detection system provides, for example, a signal to a control unit. In response to the received signal, the control unit switches the transistor from the second state to the first state.

[0030] In one embodiment, the transistor is a HEMT, preferably a GaN HEMT. According to this embodiment, a control system is adapted to control the HEMT transistor. The HEMT transistor can switch at a high frequency and can carry a large forward current. However, upon reaching some temperature, the leakage current of the HEMT transistor becomes large quickly. The large leakage current can damage the HEMT transistor in a very short amount of time. Typical safety mechanisms cannot respond within this short amount of time to prevent damage to the HEMT transistor. By providing a control system, the leakage current is automatically reduced or eliminated due to the voltage drop across the first resistive element. In this way, the protection of the HEMT transistor is improved.

[0031] In one embodiment, there is provided an electric vehicle comprising a control system according to any of the embodiments disclosed above. By using the control system in the electric vehicle, the risk of damage to transistors in the electric vehicle is reduced or eliminated, so that the electric vehicle may be operated more safely.

[0032] In one embodiment, an electric vehicle includes an inverter or power converter and at least one of a drive train and a solar panel. The inverter or power converter includes a transistor. The drive train is for providing power for driving the electric vehicle. The solar panel is for generating electrical energy based on solar energy. The inverter or power converter is adapted to exchange electrical energy with at least one of the drive train and the solar panel.

[0033] According to this embodiment, the transistor is involved in transferring electrical energy using a drive train or a solar panel. Usually, in the case of an electric vehicle, this transfer of electrical energy involves a large current. The large current causes the risk of increasing the temperature of the transistor, resulting in a large leakage current. By providing a control system, damage to the transistor due to an unacceptably large leakage current is reduced or prevented.

[0034] In a further aspect of the invention, there is provided a method for controlling a transistor comprising a gate, a source and a drain, the method comprising: providing a first voltage to the gate via a first electrical path when the transistor is in a first state; switching the transistor from a first state to a second state in response to a first voltage; ceasing to provide the first voltage to the gate via the first electrical path when the transistor is in the second state; providing a second voltage to the gate via a second electrical path when the transistor is in a second state, the second electrical path comprising a first resistive element, the first electrical path and the second electrical path being at least partially in parallel with each other; conducting a current through the first resistive element to the gate based on a leakage current of the transistor; Equipped with.

[0035] According to a further aspect of the invention, the first electrical path can transmit a first voltage to the gate of the transistor when the transistor is in a first state. The first voltage is provided, for example, by a voltage source. In the first state, the transistor is turned off, for example. Due to the applied first voltage at the gate, the transistor switches from the first state to a second state. In the second state, the transistor is turned on, for example. When the transistor is in the second state, providing the first voltage to the gate via the first electrical path is discontinued, and a second voltage is provided to the gate via the second electrical path. The second electrical path comprises a first resistive element, for example a resistor. A current flows to the gate via the first resistive element based on a leakage current of the transistor. If a leakage current flows between the first resistive element and the gate, the leakage current induces a voltage drop across the first resistive element. If the temperature increases due to a forward current, the leakage current becomes larger. As the leakage current becomes larger, the voltage drop across the first resistive element becomes larger. As a result, the voltage at the gate decreases, which helps to reduce the leakage current. If the leakage current reaches a level that is dangerous for the transistor, the associated voltage drop across the first resistive element causes the transistor to switch from the second state to the first state. The present invention improves the safety and lifetime associated with the transistor, since the transistor is automatically switched off if the leakage current becomes too large.

[0036] In one embodiment, the method comprises: The method further includes determining a leakage current of the transistor based on the voltage across the first resistive element.

[0037] According to this embodiment, the leakage current flowing between the gate and the source is determined, which provides feedback on the value of the leakage current.

[0038] According to a further embodiment, the step of determining the leakage current of the transistor based on the voltage across the first resistive element comprises comparing the voltage across the first resistive element to a reference voltage representative of a short circuit of the transistor. If the voltage across the first resistive element exceeds the reference voltage, the leakage current flowing through the transistor causes a short circuit of the transistor. In this way, it is ensured that the transistor is instantly switched from the second state to the first state upon the occurrence of a short circuit.

[0039] In one embodiment, the method comprises: After determining the leakage current, the method further comprises reducing the gate voltage at the gate to a value lower than the second voltage to switch the transistor from the second state to the first state.

[0040] In one embodiment, the method comprises: Further comprising producing a voltage drop across the first resistive element in response to the current to reduce the gate voltage.

[0041] The invention will be described below with reference to the drawings, which serve as examples for illustrating the invention and are not to be construed as limiting the scope of the claims, in which similar features are indicated by similar reference numbers. [Brief description of the drawings]

[0042] [Figure 1] FIG. 1 shows a schematic diagram of a first embodiment of a control system according to the invention; [Diagram 2] FIG. 2 shows a schematic diagram of a second embodiment of a control system according to the invention; [Diagram 3] FIG. 4 shows a schematic diagram of a third embodiment of a control system according to the invention. [Figure 4] FIG. 2 illustrates a schematic diagram of an embodiment of the switching behavior as a function of time associated with a first switch, a second switch and a discharge switch of a control system according to the present invention. [Diagram 5]FIG. 2 shows a schematic representation of an embodiment of a flow diagram of a method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] 1 shows a first embodiment of a control system 1 for controlling a transistor 2. The transistor 2 comprises a gate G, a source S and a drain D. The transistor 2 is, for example, a GaN HEMT. The control system 1 comprises a gate connector 3 connectable to the gate G of the transistor 2. For example, the gate connector 3 is connected to the gate G of the transistor 2 by soldering the gate connector 3 to the gate G. The drain D is connected to a load 4. The load 4 is, for example, an inductive load, for example a power boost converter or a motor. Alternatively, the load 4 is resistive, for example a heater.

[0044] The control system 1 further comprises a voltage connector 5 connectable to a voltage source 6. The voltage connector 5 is, for example, a plug or a switched plug. In Fig. 1, the voltage source 6 is a DC voltage source. In one embodiment, the voltage source 6 comprises, for example, a battery. The voltage source 6 applies a voltage of, for example, 5V to the voltage connector 5.

[0045] The control system 1 further comprises a first electrical path 7 extending from the voltage connector 5 to the gate connector 3. The first electrical path 7 comprises an electrical wire capable of transmitting a voltage or a current from the voltage connector 5 to the gate connector 3. The voltage source 6 is configured to supply a first voltage, for example 5V, to the gate G of the transistor 2 via the first electrical path 7. The control system 1 further comprises a first switch 8 disposed in the first electrical path 7 to connect the voltage source 6 to the gate G via the first electrical path 7. The first switch 8 is configured to make a connection between the voltage source 6 and the gate G to enable the voltage source 6 to apply a first voltage to the gate G. In FIG. 1 , the first switch 8 is an NPN bipolar transistor. The first switch 8 is controlled by a pull-up driver 9 adapted to generate a pulse for switching the first switch 8. For example, by applying a high pulse the first switch 8 is closed and by applying a low pulse the first switch 8 is open. The pull-up driver 9 is integrated in the control unit 10. When the first switch 8 is closed, the first switch 8 allows current to flow through the first switch 8 along the first electrical path 7. When the first switch 8 is open, the first switch 8 interrupts the first electrical path 7.

[0046] The control system 1 further comprises a second electrical path 11 extending from the voltage connector 5 to the gate connector 3. The second electrical path 11 comprises an electrical wire capable of transmitting a voltage or a current from the voltage connector 5 to the gate connector 3. The voltage source 6 is configured to supply a second voltage, for example, 5V, to the gate G of the transistor 1 via the second electrical path 11. The second electrical path 11 comprises a first resistive element 12. In FIG. 1, the first resistive element 12 is a resistor. The first electrical path 7 and the second electrical path 11 are at least partially in parallel with each other between the voltage connector 5 and the gate connector 3. A second switch 13 is disposed in the second electrical path 11 to connect the voltage source 6 to the gate G via the second electrical path 11. The second switch 13 is configured to make a connection between the voltage source 6 and the gate G to enable the voltage source 6 to apply the second voltage to the gate G. In FIG. 1, the second switch 13 is an NPN bipolar transistor. The switching of the second switch 13 is controlled via a PWM (Pulse Width Modulation) controller 14. The PWM controller 14 is integrated in the control unit 10.

[0047] The control system 1 further comprises a control unit 10. The control unit 10 controls the first switch 8 by closing the first switch 8 to connect the voltage source 6 to the gate G via the first electrical path 7 to enable the voltage source 6 to supply a first voltage to the gate connector 3 via the first electrical path 7 when the transistor 2 is in a first state. The first state is for example a situation in which the transistor 2 is "off", meaning that no current flows between the drain D and the source S. The control unit 10 controls the voltage source 6 to apply the first voltage to the gate connector 3 via the first electrical path 7. When the voltage source 6 supplies the first voltage to the transistor 2, the voltage at the gate G becomes equal to the first voltage. This may happen for example almost instantly. By having the first voltage at the gate G, the transistor 2 is switched from the first state to the second state. The transistor 2 is turned on in the second state, for example, in which a forward current flows between the drain D and the source S.

[0048] When the transistor 2 is in the second state, it is, for example, "on", and the control unit 10 disconnects the voltage source 6 and the gate G from each other via the first electrical path 7 by opening the first switch 8. Almost simultaneously, the control unit 10 controls the second switch 13 by closing the second switch 13 to connect the voltage source 6 to the gate G via the second electrical path 11, in order to allow the voltage source 6 to supply a second voltage to the gate connector 3 via the second electrical path 11, when the transistor 2 is in the second state. By providing the second voltage to the gate G when disconnecting the voltage source 6 and the gate G from each other via the first electrical path 7, the transistor 2 is kept in the second state. The second voltage is, for example, 5V. The second voltage is high enough to keep the transistor 2 in the second state and to prevent the transistor 2 from returning to the first state.

[0049] By providing a second voltage to the gate G, the second electrical path 11 carries a current from the voltage connector 5 to the gate connector 3 through the first resistive element 12 based on the leakage current of the transistor 2. By applying a second voltage to the gate connector 3, the transistor 2 is held in a second state. In the second state, a forward current flows between the source S and the drain D. The forward current induces heat in the transistor 2, increasing the temperature of the transistor 2. As a result of the increase in temperature, a leakage current starts to flow between the gate G and the source S. The leakage current increases as a function of temperature. As the second electrical path 11 is connected to the gate connector 3, the leakage current flows not only between the gate G and the drain D, but also from the voltage source 6 to the gate G through the second electrical path 11. The first resistive element 12 causes a voltage drop based on the leakage current. The voltage drop across the first resistive element 12 increases with the increasing leakage current. For example, at 150° C. the leakage current may be 1 mA. The voltage drop across the first resistive element 12, which has a resistance value of, for example, 1 kilohm, is then 1 V. As a result of the voltage drop across the first resistive element 12, the voltage at the gate G is reduced. By reducing the voltage at the gate G, the leakage current is reduced. In this way, large leakage currents are prevented, which prevents damage to the transistor 2.

[0050] The first resistive element 12, in response to the leakage current, reduces the gate voltage at the gate connector 3 to a value lower than the first voltage to switch the transistor 2 from the second state to the first state. For example, the voltage at the gate G is reduced by 1V. As a result, the gate voltage is reduced, making the voltage at the gate G insufficient to power the transistor 2, thereby switching the transistor 2 from the second state to the first state. Since the transistor 2 is off in the first state, no forward current flows in the first state. As a result, the temperature of the transistor 2 drops, further reducing the leakage current.

[0051] The control system 1 further comprises a discharge switch 15. The discharge switch 15 is arranged for connecting the first electrical path 7 to ground and / or for connecting the second electrical path 11 to ground. The discharge switch 15 can connect the first electrical path 7 to ground. The discharge switch 15 can connect the second electrical path 11 to ground. The discharge switch 15 is a PNP bipolar transistor. When the voltage source 6 supplies a first voltage via the first electrical path 7 or a second voltage via the second electrical path 11 to the gate G of the transistor 2, the discharge switch 15 is open. When the discharge switch 15 is open, no current is discharged from the first electrical path 7 or the second electrical path 11 to ground via the discharge switch 15. At the moment when the transistor 2 is switched from the second state to the first state due to a voltage drop, the discharge switch 15 is closed. Additionally, the control unit 10 is configured to open the second switch 13 to disconnect the voltage source 6 from the gate G of the transistor 2. In the closed state of the discharge switch 15, the discharge switch 15 discharges the gate G of the transistor 2. The control unit 10 controls the switching of the discharge switch 15 via the same PWM signal provided to the second switch 13, whereby both switches are operated simultaneously. When the second switch 13 is closed, the discharge switch 15 is opened to prevent current from being drained to ground. When the second switch 13 is switched open, the discharge switch 15 is closed to discharge the gate.

[0052] When the transistor 2 switches back to the first state due to a voltage drop, there may still be a residual voltage applied to the gate G. The residual voltage is lower than the first voltage. The residual voltage may cause leakage current to continue. By discharging the gate G with the discharge switch 15, the residual voltage is removed from the gate G, stopping the leakage current. In this way, the control system 1 provides a safer way of controlling the transistor 2.

[0053] Figure 2 shows a second embodiment of a control system 21 for controlling a transistor. Features of the control system 21 which correspond to features of the control system 1 shown in Figure 1 are indicated in Figure 2 with the same reference numbers.

[0054] In Fig. 2, the first electrical path 7 comprises a second resistive element 22. The second resistive element 22 is a resistor. When a voltage source 6 is connected to the gate G via the first electrical path 7, the first electrical path 7 is adapted to carry a current from the voltage connector 5 to the gate connector 3 via the second resistive element 22. The second resistive element 22 allows to gradually power the transistor 2 until the gate voltage is equal to the first voltage. This prevents abrupt changes in the gate voltage.

[0055] The second resistive element 22 has a lower resistance value than the first resistive element 12. Because the second resistive element 22 has a lower resistance value, the voltage source 6 generates a large current on the first electrical path 7 when applying the first voltage. As a result of the large current, the voltage at the gate G increases to the first voltage quickly. This allows for rapid switching of the transistor 2. In comparison, if the second resistive element 22 were to have a high resistance value, the switching of the transistor 2 would take longer. Because the first resistive element 12 has a higher resistance value, even a small leakage current would cause a relatively large voltage drop. This helps to create a sufficient voltage drop at the gate G to reduce the leakage current even for small leakage currents. The voltage drop may be sufficient to switch the transistor 2 from the second state back to the first state. This helps to protect transistors that are sensitive to small leakage currents. For example, the resistance value of the second resistive element 22 is between 1 and 10 ohms, preferably between 1 and 5 ohms. For example, the resistance value of the first resistive element 12 is between 100 and 2000 ohms, preferably between 500 and 1500 ohms.

[0056] Figure 3 shows a third embodiment of a control system 31 for controlling a transistor. Features of the control system which correspond to features of the control system shown in Figures 1-2 are indicated in Figure 3 with the same reference numbers.

[0057] In Fig. 3, the control system 31 includes a leakage current detection system 32. The leakage current detection system 32 is configured to determine the leakage current of the transistor 2 based on the voltage across the first resistive element 12. Because the first resistive element 12 causes a voltage drop as a result of the leakage current, the voltage across the first resistive element 12 provides an easy-to-measure quantity representative of the leakage current. The leakage current can be accurately determined by detecting the voltage across the first resistive element 12, especially when the first resistive element 12 has a high resistance value. The leakage current detection system 32 measures the voltage drop across the first resistive element 12.

[0058] In Fig. 3, the leakage current detection system 32 comprises a first operational amplifier (opamp) 33 and a second operational amplifier (opamp) 34 connected in a series connection. The first operational amplifier 33 outputs the voltage across the first resistive element to the second operational amplifier 34. The second operational amplifier 34 corresponds to an opamp voltage comparator. The second operational amplifier 34 compares a voltage representative of the measured voltage drop across the first resistive element 12 with a predetermined reference voltage 35. The predetermined reference voltage 35 is selected, for example, to represent a leakage current that may cause damage to the transistor 2. The predetermined reference voltage 35 is set, for example, to 1V.

[0059] Additionally, the leakage current detection system 32 is configured to provide the control unit 10 with a signal 36 representative of the leakage current of the transistor. The second operational amplifier 34 outputs a digital signal 36, for example, indicating which of the voltages to be compared, i.e. the voltage across the first resistive element 12 and a predefined reference voltage 35, is greater. If the voltage across the first resistive element 12 is lower than the reference voltage 35, the second operational amplifier 34 outputs a digital "low". This represents a situation in which the value of the leakage current is acceptable. If the measured voltage is higher than the reference voltage 35, the second operational amplifier 34 outputs a digital "high". This represents a situation in which the value of the leakage current is unacceptable. The control unit 10 is configured to switch the transistor 2 from the second state to the first state in response to the signal 36. For example, when the leakage current of the transistor 2 reaches a level that may be harmful to the transistor 2, the leakage current detection system 32 provides the "high" signal 36 to the control unit 10. In response to the signal 36, the control unit 10 turns off the transistor 2, for example by disconnecting the voltage source 6 from the gate G. For example, the control unit 10 controls the second switch 13 to disconnect the voltage source 6 from the gate connector 3 in response to the signal 36. The signal 36 from the leakage current detection system 32 serves as a feedback signal. For example, the leakage current detection system 32 continuously monitors the voltage drop across the first resistive element 12. In this way, the control system 31 is adapted to anticipate large leakage currents more quickly.

[0060] Additionally, in response to the signal 36, the control unit 10 controls the discharge switch 15 to connect the gate G of the transistor 2 to ground. In response to the signal 36, the control unit 10 controls the discharge switch 15, for example, to connect the first electrical path 7 to ground and / or to connect the second electrical path 11 to ground.

[0061] In a further embodiment, the signal 36 representative of the leakage current of the transistor 2 is representative of a short circuit of the transistor 2. As soon as the leakage current reaches a level representative of a short circuit of the transistor 2, the leakage current detection system 32 provides the signal 36 to the control unit 10. In response to the received signal, the control unit 10 switches the transistor 2 from the second state to the first state.

[0062] 4 shows a schematic representation of an embodiment of the switching behavior as a function of time associated with the first switch 8, the second switch 13 and the discharge switch 15 of a control system according to the invention. The control system is for example the control system 31 shown in FIG.

[0063] In Fig. 4, a logic signal 41 associated with the first switch, a logic signal 42 associated with the second switch, and a logic signal 43 associated with the discharge switch are disclosed. These logic signals 41, 42, 43 are expressed as on / off signals. When the signal is high, i.e., the signal represents a digital "1", the respective switch is switched on (i.e., the switch is closed). When the signal is low, i.e., the signal represents a digital "0", the respective switch is switched off (i.e., the switch is open). The logic signal 41 associated with the first switch is generated, for example, by a pull-up driver. The logic signal 42 associated with the second switch and the logic signal 43 associated with the discharge switch, respectively, are generated, for example, by a PWM controller.

[0064] As explained in the previous figures, due to the switching behavior of the respective switches, leakage current can flow through the first resistive element 12, causing a voltage drop. This voltage drop is illustrated in FIG. 4 by the solid line 44. The dotted line 45 represents a predetermined reference voltage that represents a short circuit of the transistor 2. If the voltage across the first resistive element 12, as illustrated by the solid line 44, exceeds the reference voltage 45, the leakage current flowing through the transistor 2 will cause a short circuit of the transistor.

[0065] During the period between t0 and t1, the first switch 8 and the second switch 13 are closed as their respective signals are high, as shown with lines 41 and 42. Through the first switch 8, a current can flow through the first electrical path 7 to the gate G of the transistor 2. Similarly, through the second switch 13, a current can flow through the second electrical path 11 to the gate G of the transistor 2. As a result, a relatively small leakage current flows through the first resistive element 12. At time t1, the first switch 8 is switched off. Thus, the leakage current flowing through the first resistive element 12 becomes large, and therefore the voltage drop across the first resistive element also becomes large at time t1. This is shown by the increase illustrated by the line 44 at t1. At time t2, the second switch 13 is switched off and the discharge switch 15 is switched on. Switching the second switch 13 off switches the transistor 2 to another state, for example, the transistor 2 is switched off. At the same moment, the discharge switch 15 is closed. In the closed state of the discharge switch 15, the discharge switch 15 discharges the gate G of the transistor 2. By discharging the gate G with the discharge switch 15, any residual voltage is removed from the gate G, stopping the leakage current. Since the residual voltage is removed from the gate G, the voltage drop across the first resistive element 12 is reduced as shown by the line 44 at the time t2. In this way, the control system provides a safer way of controlling the transistor 2.

[0066] At time t3, the first switch 8, the second switch 13 and the discharge switch 15 are switched on again. Thus, leakage current can again flow through the transistor 2, causing a voltage drop across the first resistive element 12. The process during the period t0-t3 is repeated during the time window t3-t6.

[0067] During the time period between t6 and t7, leakage current flowing through the transistor 2 may cause a short circuit. Since the first switch 8 is switched on, it is not detectable whether the transistor 2 encounters a short circuit. This is due to the resistance value of the second resistive element 22 being somewhat lower compared to the first resistive element 12. When the first switch 8 is opened at time t7, it is shown that the voltage across the first resistive element 12 suddenly increases rapidly, as shown by the line 44. The voltage across the first resistive element 12 exceeds the reference voltage 45. The leakage current detection system 32 as described in FIG. 3 can detect such an eventuality, so that the control system is adapted to anticipate a large leakage current more quickly.

[0068] FIG. 5 illustrates generally one embodiment of a flow diagram of a method for controlling a transistor 2 comprising a gate G, a source S and a drain D.

[0069] The method according to the invention comprises a first step 50 of supplying a first voltage to the gate G via a first electrical path 7 when the transistor 2 is in a first state. The first electrical path 7 is capable of transmitting a first voltage to the gate G of the transistor 2 when the transistor 2 is in the first state. The first voltage is for example supplied by a voltage source 6. In the first state the transistor 2 is for example turned off.

[0070] A next step 51 of the method according to the invention comprises switching the transistor 2 from a first state to a second state in response to a first voltage. Due to the applied first voltage at the gate G, the transistor 2 switches from the first state to the second state. In the second state the transistor 2 is for example turned on.

[0071] When the transistor 2 is in the second state, the first voltage is no longer provided to the gate via the first electrical path 7 (step 52).

[0072] In a further step 53 of the method according to the invention, when the transistor 2 is in the second state, a second voltage is supplied to the gate G via the second electrical path 11. The second electrical path comprises a first resistive element 12, e.g. a resistor. Furthermore, the first electrical path 7 and the second electrical path 11 are at least partially parallel to each other. Preferably, steps 52 and 53 are performed almost simultaneously.

[0073] In step 54 of the method, a current is conducted to the gate G via the second electrical path 11 based on the leakage current of the transistor 2. If a leakage current flows between the first resistive element 12 and the gate G, the leakage current induces a voltage drop across the first resistive element 12. If the temperature rises due to a forward current, the leakage current becomes larger. As the leakage current becomes larger, the voltage drop across the first resistive element 12 becomes larger. As a result, the voltage at the gate G decreases, which helps to reduce the leakage current. If the leakage current reaches a level that is dangerous for the transistor 2, the associated voltage drop across the first resistive element 12 causes the transistor 2 to switch from the second state to the first state. The present invention improves the safety and lifetime associated with the transistor, since the transistor 2 is automatically switched off if the leakage current becomes too large. [Explanation of symbols]

[0074] 1. Control System 2. Transistor 3 Gate Connector 4. Load 5 Voltage Connector 6. Voltage Sources 7 First Electrical Path 8. First Switch 9 Pull-up driver 10. Control Unit 11 Second Electrical Path 12 First resistive element 13 Second Switch 14 PWM (Pulse Width Modulation) Controller 15 Discharge switch 21 Control System 22 Second resistive element 31 Control System 32 Leakage Current Detection System 33 First operational amplifier 34 Second operational amplifier 35 Reference Voltage 36 signal 41 Logic signal associated with the first switch 42 Logic signal associated with the second switch 43 Logic signals related to the discharge switch 45 Reference Voltage

Claims

1. 1. A control system for controlling a transistor having a gate, a source, and a drain, comprising: a gate connector connectable to the gate of the transistor; a voltage connector connectable to a voltage source; a first electrical path extending from the voltage connector to the gate connector; a second electrical path extending from the voltage connector to the gate connector, the second electrical path comprising a first resistive element, the first electrical path and the second electrical path being at least partially in parallel with each other; The control system further comprises a control unit, the control unit comprising: connecting the voltage source to the gate via the first electrical path to enable the voltage source to provide a first voltage to the gate connector via the first electrical path when the transistor is in a first state; controlling the voltage source to apply the first voltage to the gate connector via the first electrical path to switch the transistor from the first state to a second state; disconnecting the voltage source and the gate from each other via the first electrical path when the transistor is in the second state; connecting the voltage source to the gate via the second electrical path to enable the voltage source to provide a second voltage to the gate connector via the second electrical path when the transistor is in the second state; controlling the voltage source to apply the second voltage to the gate connector via the second electrical path, the second electrical path adapted to conduct a current from the voltage connector to the gate connector through the first resistive element based on a leakage current of the transistor; a control system adapted to:

2. 2. The control system of claim 1, wherein the first resistive element is arranged to, in response to the current, reduce a gate voltage at the gate connector to a value lower than the first voltage to switch the transistor from the second state to the first state.

3. 3. The control system of claim 1 or 2, further comprising a first switch disposed in the first electrical path to connect the voltage source to the gate via the first electrical path.

4. 4. The control system of claim 3, comprising a pull-up driver, the first switch being controlled by the pull-up driver adapted to generate pulses for switching the first switch.

5. 5. The control system of claim 1, wherein the first electrical path comprises a second resistive element.

6. The control system of claim 5 , wherein the second resistive element has a lower resistance value than the first resistive element.

7. A control system according to claim 5 or 6, wherein the resistance value of the second resistive element is between 1 and 10 Ohms, preferably between 1 and 5 Ohms.

8. A control system according to any one of the preceding claims, wherein the resistance value of the first resistive element is between 100 and 2000 Ohms, preferably between 500 and 1500 Ohms.

9. 9. The control system of claim 1, wherein the first electrical path and the second electrical path are arranged in a series connection to the gate of the transistor.

10. 10. The control system of claim 1, further comprising a second switch disposed in the second electrical path to connect the voltage source to the gate via the second electrical path.

11. 11. The control system of claim 1, further comprising a leakage current detection system configured to determine the leakage current of the transistor based on a voltage across the first resistive element.

12. 12. The control system of claim 11, wherein the leakage current detection system is configured to provide a signal representative of the leakage current of the transistor to the control unit, and the control unit is configured to switch the transistor from the second state to the first state in response to the signal.

13. 13. The control system of claim 12, wherein the signal representative of the leakage current of the transistor is representative of a short circuit of the transistor.

14. 14. A control system according to any one of claims 1 to 13, wherein the transistor is a HEMT, preferably a GaN HEMT.

15. 15. The control system of claim 1, further comprising a discharge switch disposed between the first electrical path and / or the second electrical path and the ground to connect the first electrical path to ground and / or to connect the second electrical path to the ground.

16. An electric vehicle comprising a control system according to any one of claims 1 to 15.

17. an inverter or power converter and at least one of a drive train and a solar panel; the inverter or the power converter comprises the transistor, the drive train is for providing power to drive the electric vehicle; The solar panel is for generating electrical energy based on solar energy, the inverter or the power converter is adapted to exchange electrical energy with at least one of the drive train and the solar panel; 17. The electric vehicle of claim 16.

18. 1. A method for controlling a transistor having a gate, a source, and a drain, comprising: providing a first voltage to the gate via a first electrical path when the transistor is in a first state; switching the transistor from the first state to a second state in response to the first voltage; ceasing to provide the first voltage to the gate via the first electrical path when the transistor is in the second state; providing a second voltage to the gate via a second electrical path when the transistor is in the second state, the second electrical path comprising a first resistive element, the first electrical path and the second electrical path being at least partially in parallel with each other; conducting a current through the first resistive element to the gate based on a leakage current of the transistor; A method comprising:

19. determining the leakage current of the transistor based on a voltage across the first resistive element; 20. The method of claim 18, further comprising:

20. 20. The method of claim 19, wherein the step of determining the leakage current of the transistor based on the voltage across the first resistive element comprises comparing the voltage across the first resistive element to a reference voltage representative of a short circuit of the transistor.

21. After determining the leakage current, reducing a gate voltage at the gate to a value less than the second voltage to switch the transistor from the second state to the first state. The method of claim 20, further comprising:

22. generating a voltage drop across the first resistive element in response to the current to reduce the gate voltage.

22. The method of claim 21, further comprising:

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