Power switch and method for operating a power switch using a switchable current source

Abstract

This application provides a power switch comprising a switching transistor, wherein a load path of the switching transistor is coupled between an input terminal and an output terminal of the power switch, and wherein a source terminal of the switching transistor is coupled to the output terminal of the power switch. The power switch includes a control capacitor coupled between a control terminal of the switching transistor and a reference potential conductor. The power switch includes a switchable current source configured to charge the control capacitor in an on-state. A method for operating a power switch is also disclosed.

Description

Technical Field

[0001] Invention Field According to an embodiment of the present invention, the present invention relates to an electric switch.

[0002] Other embodiments of the present invention relate to a method for operating an electrical switch.

[0003] According to an embodiment of the present invention, the present invention relates to a power switch for a capacitive load for connecting a boost DC / DC converter to a power supply rail. Prior Technology

[0004] Background of the Invention In automated test equipment (ATE) systems (but also in other technical applications), many different supply voltages are typically required. Usually, several supply voltages on the test system modules are generated from a single power rail, for example, 48 V, using a DC / DC converter. For example, when the test system is powered on, these voltages may need to be switched on in a certain sequence to prevent overload or damage to, for example, some circuit components in the front end.

[0005] Different DC / DC converter technologies are associated with such applications. In many situations, boost converters are the best choice for generating higher voltages. However, it has been found that power sequencing can be complex, at least in some cases, especially when using this type of DC / DC converter. For example, even when the converter is off, its load is always connected to the input via a diode. Therefore, in some situations, an additional switch may be required before such a DC / DC converter to enable proper power sequencing.

[0006] For example, a simple MOSFET switch can be used to connect a capacitive load to the power rail. However, this has been found to be less than ideal because the current charging the load capacitor can be very large (see, for example, the simulation examples in Figures 6 and 7). It has also been recognized that slowing down the switching behavior of a MOSFET is difficult because if a certain VGS threshold (e.g., a gate-source threshold voltage) is exceeded, the transistor will turn on relatively abruptly. It has also been recognized that, under certain conditions, such charging currents can cause power failures or even damage to the test system.

[0007] For some details, see Figures 6 and 7, which show an LTSpice simulation example of a simple MOSFET switch used to connect a CAP load. Specifically, as can be seen from Figure 7, a high current spike appears.

[0008] JP 2023131302 A describes an electronic circuit. To suppress inrush current flowing in a field-effect transistor (FET) when it switches from off to on in a circuit including a capacitor disposed between the FET and a load, a circuit is provided. This electronic circuit is configured to include an N-channel MOSFET. The drain terminal of the n-channel MOSFET is connected to the positive terminal of a battery, and the source terminal is connected to the positive terminal of a load. A capacitor is connected to the source terminal of the MOSFET. A sensing element for detecting the voltages at the drain and source terminals of the MOSFET is also included. A switch is connected to the capacitor. A control element controls the operation of the switch such that when the MOSFET switches from off to on, if the voltage at the drain terminal matches the voltage at the source terminal, the current flowing in the capacitor is limited to a predetermined value or less.

[0009] The application report "Managing Inrush Current" (SLVA 670 A, August 2014, revised May 2015) published by Texas Instruments describes how, in most systems, capacitors are placed throughout the design to ensure no voltage drop on the power rails. It also describes how charging these capacitors when initially applying power to the system can result in inrush current that may exceed the nominal load current. If this problem is not addressed, it describes how this can cause voltage rail deregulation, leading to undesirable system states. It also describes how inrush current can exceed the current-carrying capacity of board connectors and PCB traces, potentially damaging them. Furthermore, it describes how these problems can be mitigated by using Texas Instruments load switches. The report discusses how the TPS229xx series load switches employ slew rate control to minimize inrush current. It should be further noted that this article explores the technical causes of inrush current, the problems caused by inrush current, and inrush current solutions that integrate load switches.

[0010] The article "Active Inrush Current Limiting Using MOSFETs," published by Motorola as Semiconductor Application Note AN1542, describes the use of MOSFETs for active inrush current limiting. Different circuits are mentioned in the article.

[0011] US 2014 / 070831 A1 describes a system and method for protecting probes using a smart current-sensing switch. It discloses an apparatus and method for protecting probes used in automated testing. The apparatus includes a probe operable to supply power from a device power supply to a device under test (DUT), wherein the probe is coupled to contact pins of the DUT and a probe protector circuit is connected in series between the device power supply and the DUT. The probe protector circuit further includes: a current-sensing module operable to monitor the current from the device power supply to the DUT to determine whether the current is below a predetermined threshold current level; and a switch for controlling the connection from the device power supply to the DUT. The switch is coupled to the current-sensing module and operable to work in conjunction with the current-sensing module to limit the current if the current exceeds the predetermined threshold current level.

[0012] US 2022 / 0107247 A1 describes a materials testing system. The materials testing system includes materials testing equipment configured to receive a power supply, wherein the materials testing equipment includes a guide member, a sample holding member configured to hold a sample, a force member configured to apply force to the sample, and a crosshead configured to support at least a portion of one or both of the sample holding member and the force member. The crosshead is movable about the guide member. The materials testing system includes a three-phase switch-mode power supply unit configured to provide power to the materials testing equipment.

[0013] CN 108693457 A describes a wafer testing method and system for eliminating power-on overshoot. The method includes the following steps: providing a DC power supply for power supply, a wafer to be tested, and a wafer test board with a wafer test socket; providing a load switch, wherein the DC power supply provides power to the wafer test socket via the load switch, wherein the input terminal of the load switch is connected to the DC power supply; connecting the enable terminal of the load switch and the ground terminal of the wafer to the wafer test socket, wherein when the wafer test socket is closed, the enable terminal of the load switch and the ground terminal of the wafer are electrically connected; connecting the enable terminal of the load switch to the DC power supply via a pull-up resistor; and inserting the wafer into the wafer test socket, tightly closing the wafer test socket, and performing testing after a time delay. The document also describes a wafer testing system for eliminating power-on overshoot. The wafer first contacts the wafer test board and is then electrified, effectively reducing the EOS (Electronic Optical Frame) failure rate during the wafer testing process.

[0014] JP 2020173197 A describes a semiconductor testing apparatus and method for testing semiconductor devices. The semiconductor testing apparatus includes a current control circuit that superimposes a second constant current corresponding to an inrush current onto a first constant current floating through a transistor channel. The duration for which the first constant current is applied through the transistor and the rate at which the current flowing through the transistor is cyclically or interrupted can be set. The semiconductor testing apparatus includes an inductive reactance circuit whose inductive reactance value can be changed or set. It is possible to set the inductive reactance value of the test circuit and apply a surge voltage suitable for the actual circuit to the transistor by controlling the inductive reactance circuit.

[0015] In light of the above, there is a need to create a power switch that strikes a good balance between the workload of implementation and the ability to avoid excessive current spikes. Summary of the Invention

[0016] Invention Summary According to embodiments of the present invention, a power switch (e.g., for a capacitive load) is created. The power switch includes a switching transistor (e.g., a switching MOSFET), wherein the load path of the switching transistor (e.g., a collector-emitter path of the switching transistor, such as in the case of a bipolar switching transistor, or a drain-source path of the switching transistor, such as in the case of a field-effect switching transistor) is coupled between the input terminal (e.g., SW_IN; for example, a conductor for applying a supply voltage, which is to be switched to the output terminal of the power switch via the switching transistor) and the output terminal (e.g., SW_OUT) of the power switch. The source terminal of the switching transistor (e.g., the emitter terminal in the case of a bipolar switching transistor or the source terminal in the case of a field-effect switching transistor) is coupled to the output terminal of the power switch. The power switch includes a control capacitor coupled between the control terminal of the switching transistor (e.g., the base terminal in the case of a bipolar switching transistor or the gate terminal in the case of a field-effect switching transistor) and a reference potential conductor (e.g., a capacitor having a capacitance greater than the internal capacitance of the transistor between the control terminal and the source terminal; for example, a capacitance greater than the gate-source capacitance of the switching transistor, or a capacitance greater than or equal to twice the gate-source capacitance of the switching transistor, or a capacitance greater than or equal to five times the gate-source capacitance of the switching transistor, or a capacitance greater than or equal to ten times the gate-source capacitance of the switching transistor). The power switch includes a switchable current source (e.g., switchable depending on a signal from a control line) configured to charge a control capacitor in the on state (e.g., charging the control capacitor in such a way that the voltage of the control capacitor increases substantially linearly over time, for example, wherein the deviation from linear evolution is less than 10% in the range of capacitor voltage from 10% of the input voltage at the input of the power switch to capacitor voltage from 90% of the input voltage of the power switch).

[0017] This embodiment is based on the idea that such an arrangement allows for good adjustment of the voltage slewing rate at the output of the power switch, which in turn allows for control of the current flowing through the power switch under capacitive load conditions. By charging the control capacitor using a switchable current source, a well-defined evolution of the voltage at the control terminal of the switching transistor can be obtained, which in turn leads to a well-defined time evolution of the voltage at the output of the power switch.

[0018] Therefore, excessive current peaks in the current flowing through the power switch (or through the switching transistor) can be avoided (for example, because in the presence of a capacitive load, the current is at least approximately proportional to the voltage slew rate).

[0019] Furthermore, it has been recognized that using a switchable current source to charge the control capacitor results in a simple implementation, where at least a substantially linear increase in voltage at the control terminal of the switching transistor leads to good control of the current through the switching transistor, the slope of which is defined primarily by the current supplied by the switchable current source and the capacitance of the control capacitor. For example, by sizing the power switch in such a way that the slewing rate of voltage at the control terminal of the switching transistor does not exceed a desired value, the current through the switching transistor caused by the known load capacitance can be limited, which in turn helps to prevent damage to the switching transistor and also helps to avoid fault conditions (e.g., excessive voltage drop at the input of the power switch).

[0020] In summary, the embodiments described above allow for relatively simple implementation and are still well-suited for limiting the current flowing through power switches and switching transistors.

[0021] In a preferred embodiment of the power switch, the switching transistor is configured to operate as a source follower (e.g., such that the voltage at the output of the power switch follows the voltage at the control terminal of the switching transistor, wherein there is a substantially constant voltage shift over a wide voltage range at the control terminal of the switching transistor).

[0022] Using this type of design (or operating mode) for power switches, the voltage slope at the output of the power switch can be clearly defined. For example, if the voltage shift between the voltage at the control terminal of the switching transistor and the voltage at the source terminal of the switching transistor remains substantially constant (e.g., where the variation does not exceed 0.5 volts or where the variation exceeds 1 volt) over at least 60% of the voltage between the input of the power switch and the reference potential conductor, then the voltage slope at the output of the power switch can be well controlled and limited to a value defined primarily by the current supplied by the switchable current source and the capacitance of the control capacitor. Therefore, the current flowing through the power switch can be limited. Furthermore, by using this design, the time evolution of the voltage at the output of the power switch can be well predicted, which can sometimes help avoid damage to the circuit system or ensure reliable operation.

[0023] Furthermore, it should be noted that with this type of design, the voltage slope at the output of the power switch is primarily determined by a quantity that can be well controlled through design. Therefore, a well-defined circuit behavior can be achieved with a moderate workload.

[0024] In a preferred embodiment of the power switch, a switchable current source is coupled between the input terminal of the power switch (e.g., a conductor for applying a supply voltage, which is to be switchably transferred to the output terminal of the power switch via a switching transistor) and the control terminal of the switching transistor (e.g., such that the switchable current source is supplied with voltage at the input terminal of the power switch). Alternatively or additionally, the switchable current source is coupled between the input terminal of the power switch (e.g., a conductor for applying a supply voltage, which is to be switchably transferred to the output terminal of the power switch via a switching transistor) and a control capacitor (e.g., such that the switchable current source is supplied with voltage at the input terminal of the power switch).

[0025] Therefore, a sufficiently high voltage can be easily achieved at the control terminals of the switching transistor. For example, the control capacitor can be charged using the relatively high supply voltage at the input of the power switch, which substantially helps to reduce the amount of implementation work.

[0026] In a preferred embodiment of the power switch, the power switch includes a floating voltage source (e.g., an optocoupler) coupled between a switchable current source and a control terminal of a switching transistor (e.g., between the current output terminal of the switchable current source and the control terminal of the switching transistor), for example, to allow a voltage shift at the control terminal of the switching transistor (e.g., shifted to a voltage higher than the input voltage at the input terminal of the power switch under a positive supply voltage condition, or shifted to a voltage lower than the input voltage at the input terminal of the power switch under a negative supply voltage condition), while maintaining a sufficient voltage drop across the switchable current source (e.g., even under a positive supply voltage condition, the voltage at the control terminal of the switching transistor is higher than the input voltage at the input terminal of the power switch, or even under a negative supply voltage condition, the voltage at the control terminal of the switching transistor is lower than the input voltage at the input terminal of the power switch).

[0027] Alternatively or additionally, a floating voltage source may be coupled between a switchable current source and a control capacitor (e.g., between the current output terminal of the switchable current source and the control capacitor) to allow a voltage shift at the control capacitor (and thus, a voltage shift at the control terminal of the switching transistor) (e.g., shifted to a voltage higher than the input voltage at the input terminal of the power switch in the case of a positive supply voltage, or shifted to a voltage lower than the input voltage at the input terminal of the power switch in the case of a negative supply voltage), while maintaining a sufficient voltage drop across the switchable current source (e.g., even in the case of a positive supply voltage, the voltage at the control terminal of the switching transistor is higher than the input voltage at the input terminal of the power switch, or even in the case of a negative supply voltage, the voltage at the control terminal of the switching transistor is lower than the input voltage at the input terminal of the power switch).

[0028] Using this concept, it is possible to charge the control capacitor to a voltage even higher than the voltage at the input of the power switch (e.g., when the input of the power switch is positive). Alternatively, it is possible to charge the control capacitor to a voltage more negative than the voltage at the input of the power switch (e.g., when there is a negative voltage at the input of the power switch).

[0029] For example, using such a floating voltage source allows for substantially higher voltages at the control terminals of the switching transistor (e.g., higher than the voltage at the input and / or output of the power switch) compared to an implementation without a floating voltage source. This allows the switching transistor to be in a low-ohmic state when the maximum output voltage is reached, resulting in low implementation effort.

[0030] Specifically, the relatively high input voltage of the power switch can be utilized, so that the floating voltage source usually only needs to provide a relatively small voltage contribution and can therefore be implemented with a moderate workload.

[0031] Furthermore, by using this concept, it can be ensured that there is a sufficient voltage drop across the switchable current source to allow it to operate properly (so that the switchable current source can provide the specified current with good accuracy).

[0032] In summary, a floating voltage source can provide a voltage that provides a sufficient voltage drop across a switchable current source and provides sufficient control voltage (e.g., gain source voltage) for the switching transistors, even when the voltage at the output of the power switch has reached its maximum value.

[0033] However, by using the relatively high input voltage at the input of the power switch and a floating voltage source (where the floating voltage source typically only needs to contribute a relatively small voltage), efficient circuit implementation is possible, which helps to reduce cost and space requirements.

[0034] In a preferred embodiment of the power switch, the power switch includes a floating voltage source coupled between the input terminal of the power switch and a switchable current source (e.g., between the input terminal of the power switch and the supply conductor of the switchable current source). (e.g., to increase the voltage at the supply conductor of the switchable current source to a level higher than the voltage at the input terminal of the power switch under a positive supply voltage condition, such that the voltage at the current output terminal of the switchable current source is higher than the voltage at the input terminal of the power switch, while maintaining a sufficient voltage drop across the switchable power source under a positive supply voltage condition; or to decrease the voltage at the supply conductor of the switchable current source to a level lower than the voltage at the input terminal of the power switch under a negative supply voltage condition, such that the voltage at the current output terminal of the switchable current source is lower than the voltage at the input terminal of the power switch, while maintaining a sufficient voltage drop across the switchable power source under a negative supply voltage condition).

[0035] This embodiment is based on considerations similar to those of the previously described embodiments. However, by coupling a floating voltage source between the input of the power switch and the switchable current source, it can be ensured that there is a sufficient voltage drop across the switchable current source and that a sufficient voltage is reached at the control terminal of the switching transistor to place the switching transistor in a low-ohm state.

[0036] Furthermore, the implementation of such circuits requires relatively little work because they utilize the typically relatively high input voltage of power switches and, due to the floating voltage source, usually only a relatively small voltage contribution is needed.

[0037] In a preferred embodiment of the power switch, the floating voltage source includes an optocoupler (e.g., an optocoupler comprising a combination of a light source such as an LED and a photovoltaic cell; e.g., an optocoupler capable of (or configured to) provide (e.g., at the output port) an output current in the range of 5 μA to 50 μA).

[0038] For example, the output port of the optocoupler is coupled (e.g., directly coupled; e.g., without any other voltage conversion circuitry) between the current output terminal of the switchable current source and the control terminal of the switching transistor. Alternatively, the output port of the optocoupler is coupled (e.g., directly coupled; e.g., without any other voltage conversion circuitry) between the current output terminal of the switchable current source and the control capacitor. Alternatively, the output port of the optocoupler is coupled (e.g., between the input terminal of the power switch and the supply conductor of the switchable current source).

[0039] Optocouplers have been found to be highly efficient components for implementing floating voltage sources and are well-suited for certain applications.

[0040] Specifically, it has been recognized that the voltage readily provided by such optocouplers is generally sufficient to ensure adequate voltage drop across the switchable current source and adequate (e.g., sufficiently high) voltage at the control terminals of the switching transistors. Furthermore, it has been recognized that the current typically provided by such optocouplers is generally sufficient in power switching.

[0041] Furthermore, optocouplers offer the following advantages: there is current blocking between the voltage at the input and output of the optocoupler (meaning the output can thus be considered as providing a floating voltage). Therefore, by using optocouplers, power switching can be implemented very efficiently with minimal space requirements. Specifically, by using optocouplers as a floating voltage source, it is unnecessary to use any transformers, which are typically relatively expensive and consume a significant amount of space.

[0042] In summary, it has been found that relying on the input voltage of the power switch and using an optocoupler to generate an additional voltage contribution provides a very efficient and reliable solution for charging the control capacitor, which takes advantage of the relatively high input voltage of the power switch.

[0043] In a preferred embodiment of the power switch, the floating voltage source includes a buffer capacitor coupled in parallel with the output port of the optocoupler. For example, the capacitance of the buffer capacitor is greater than the capacitance of the control capacitor. Alternatively, the capacitance of the buffer capacitor may be at least twice the capacitance of the control capacitor. Alternatively, the capacitance of the buffer capacitor may be at least five times the capacitance of the control capacitor. Alternatively, the capacitance of the buffer capacitor may be at least eight times the capacitance of the control capacitor.

[0044] By using this design, the circuit provides high reliability even when the current supplied by the optocoupler is relatively small. For example, this implementation can be used even when the current supplied by the optocoupler is less than the current supplied by the switchable current source. For example, when using this configuration, the snubber capacitor can be pre-charged by the output current of the optocoupler before the switchable current source is activated. Therefore, if the capacitance of the snubber capacitor is chosen to be sufficiently large, the voltage across the snubber capacitor can remain sufficiently constant (or even substantially constant) during the time the switchable current source charges the control capacitor (e.g., where the voltage drop does not exceed 20%, 30%, or 50%).

[0045] Therefore, it is possible to charge the control capacitor with a current greater than that supplied by the optocoupler at its output. In this case, the buffer capacitor helps maintain the voltage (voltage drop) at the output of the optocoupler (e.g., the voltage between the output terminals of the optocoupler) within acceptable limits, even if the current supplied by the switchable current source is greater than that supplied by the optocoupler at its output. Thus, even if the optocoupler can only provide a significantly smaller current at the desired output voltage, the control capacitor can still be charged with the current supplied by the switchable time source.

[0046] Therefore, this configuration allows the use of relatively small and inexpensive optocouplers while still maintaining the possibility of charging the control capacitor with a sufficiently large current (provided by a switchable current source) and having a sufficiently large voltage at the output of the optocoupler (where this voltage is maintained by a buffer capacitor).

[0047] In a preferred embodiment of the power switch, the power switch or the control circuitry system coupled to the power switch is configured to activate the optocoupler before the switchable current source is turned on (e.g., such that there is a predetermined minimum duration between the activation of the optocoupler and the turn-on of the switchable current source; for example, such that before the switchable current source is turned on, even in the presence of a buffer capacitor, the voltage at the output port of the optocoupler reaches a sufficiently large value, for example, at least 90% of its steady-state value).

[0048] For example, the input of the optocoupler is supplied with a supply voltage that is lower than the voltage present at the input of the power switch. For example, the input of the optocoupler is supplied with a logic supply voltage that supplies the control circuitry that controls the switching of the switchable current source.

[0049] By activating the optocoupler before the switchable current source is turned on, the buffer capacitor can be (pre-)charged to a sufficiently high voltage before the switchable current source is turned on. Therefore, reliable circuit operation can be achieved.

[0050] For example, the input of an optocoupler can be powered by a relatively low supply voltage. It should be noted that the input of an optocoupler typically includes a light source, such as one or more light-emitting diodes. Furthermore, by ensuring (e.g., through proper operating timing) that the buffer capacitor at the output of the optocoupler is charged to a sufficiently high voltage before the switchable current source is turned on, it is possible to achieve a sufficiently large charge on the buffer capacitor to fully charge the control capacitor, while still maintaining a sufficiently high voltage on the buffer capacitor to ensure a sufficient voltage drop across the switchable current source and a sufficiently high control voltage for the switching transistor when the output voltage of the power switch has reached its final value (which can be similar to the input voltage of the power switch) (e.g., fully turning on the switching transistor, for example, putting the switching transistor into a low-ohm state).

[0051] However, it should be noted that such appropriate timing for activating the input of the optocoupler before activating the switchable current source can be easily achieved using a suitable control circuit system, for example, operating with a supply voltage substantially smaller than the input voltage of the power switch. For instance, the input of the optocoupler can be activated once an available supply voltage is available in the control circuit system, or once the control circuit system is initialized.

[0052] In a preferred embodiment of the power switch, the output voltage of the floating voltage source (e.g., optocoupler) is greater than or equal to 1.5 times the threshold voltage of the switching transistor. Alternatively or additionally, the output voltage of the floating voltage source (e.g., optocoupler) is greater than or equal to 6 V, or greater than or equal to 8 V, or greater than or equal to 10 V.

[0053] By using this selection of the output voltage of the floating voltage source, it is possible to achieve a sufficiently large voltage drop across the switchable current source while still providing a sufficient control voltage (e.g., gate-source voltage) for the switching transistor. For example, it has been recognized that selecting the output voltage of the floating voltage source to be greater than or equal to 1.5 times the threshold voltage of the switching transistor allows the switching transistor to be fully turned on while still having a sufficient voltage drop across the switchable current source. Similarly, it has been found that selecting the output voltage of the floating voltage source to be greater than or equal to 6 volts, 8 volts, or 10 volts typically also allows the switching transistor to be fully turned on while having a sufficient voltage drop across the switchable current source.

[0054] Furthermore, it has been recognized that such selection of the output voltage of a floating voltage source allows for relatively inexpensive implementation, for example, using readily available inexpensive optocouplers.

[0055] In other words, it has been recognized that the aforementioned selection of the output voltage of the floating voltage source provides a good trade-off between implementation workload and circuit characteristics (e.g., having sufficient voltage drop across the switchable current source and sufficient control voltage for the switching transistor).

[0056] In a preferred embodiment of the power switch, the output current of the optocoupler is smaller than the current supplied by the switchable current source (e.g., at least 2, 10, or 20 times smaller). Alternatively, the output current of the optocoupler may be larger than the current supplied by the optocoupler.

[0057] A cheaper implementation of the optocoupler can be achieved by selecting an output current that is less than the current supplied by the switchable current source. However, sufficient voltage can still be ensured at the optocoupler's output, for example, by using a buffer capacitor, as outlined above. However, by selecting an optocoupler whose output current is greater than the current supplied by the switchable current source, the use of a buffer capacitor may be unnecessary, for example, at the cost of using a more expensive optocoupler.

[0058] In a preferred embodiment of the power switch, the switching transistor is a field-effect transistor (e.g., an N-channel MOSFET; an N-channel switching MOSFET; a P-channel MOSFET; a P-channel switching MOSFET).

[0059] It has been recognized that using a field-effect transistor (FET) as a switching transistor system is particularly advantageous because, under static or quality-static conditions, the FET does not require a control current (e.g., gate current). Therefore, the control voltage (e.g., the voltage at the gate terminal of the FET) can be well controlled by a switchable current source and a control capacitor. For example, it has been recognized that by using a FET as a switching transistor, a well-defined slope of the voltage at the gate terminal (control terminal) of the FET (which acts as a switching transistor) can be achieved, where the slope of this voltage at the gate terminal (control terminal) of the switching transistor is primarily determined by the current supplied by the switchable current source and the capacitance of the control capacitor.

[0060] Furthermore, since field-effect transistors typically require relatively small control currents (or even no control currents in static or quasi-static conditions), floating voltage sources can be easily implemented with moderate workloads. Therefore, it has been recognized that using field-effect transistors as switching transistors offers several advantages, for example, when compared to using bipolar transistors as switching transistors.

[0061] In a preferred embodiment of the power switch, the power switch includes a disconnecting circuit configured to at least partially discharge a control capacitor (e.g., selectively discharging the control capacitor (at least partially) when the switchable current source is disconnected), for example, discharging the control capacitor such that the voltage at the control terminal of the switching transistor is close to the voltage at the source terminal of the switching transistor, or such that the voltage at the control terminal of the switching transistor is close to the voltage at the output terminal of the power switch. For example, the disconnecting circuit may be coupled between the control terminal (e.g., the gate terminal) of the switching transistor and the source terminal of the switching transistor, or between the control terminal of the switching transistor and the output terminal of the power switch.

[0062] It has been recognized that the use of a disconnect circuit (also referred to herein as a discharge circuit) is advantageous because such a disconnect circuit allows for the rapid disconnection of the power switch. However, it has been found that it is advantageous for the disconnect circuit to discharge the control capacitor "automatically" (e.g., without additional control signals) in order to turn off the power switch, as this significantly reduces the control workload.

[0063] For example, a cutoff circuit can be designed such that the activation of a switchable current source causes the deactivation of a cutoff component (e.g., a cutoff transistor or a discharge transistor) that at least partially discharges the control capacitor.

[0064] Similarly, a cutoff circuit can be designed such that the deactivation of the switchable current source causes the activation of a cutoff component (e.g., a cutoff transistor or a discharge transistor) that at least partially discharges the control capacitor.

[0065] However, it should be noted that it is not necessary to fully discharge the control capacitor to deactivate the start-up (e.g., turn-off or disconnection) of the switching transistor. Specifically, in some situations, it is sufficient to discharge the control capacitor to the point that the control voltage of the switching transistor (e.g., the gate-source voltage of the switching transistor) is below the threshold voltage. However, further discharge of the control capacitor may occur when the voltage at the output of the power switch decreases (e.g., to continuously maintain the control voltage of the switching transistor below the threshold voltage).

[0066] In short, by providing a cut-off circuit (or discharge circuit) configured to at least partially discharge the control capacitor, for example when the switchable current source is cut off, good overall cut-off characteristics of the power switch can be achieved.

[0067] In a preferred embodiment of the power switch, the disconnect circuit is configured to deactivate (e.g., deactivate) the current supplied by a switchable current source that charges the control capacitor (whereby, for example, the current supplied by the switchable current source generates a bias voltage for the transistor that turns off the disconnect circuit), and if the switchable current source is turned off, the disconnect circuit is configured to be activated to at least partially discharge the control capacitor (whereby, for example, there is no current supplied by the switchable current source that causes a bias voltage for the transistor that turns on the disconnect circuit).

[0068] By using this concept, the control mechanism can be significantly simplified. For example, it can be achieved that as long as the switchable current source is on, the cut-off circuit (or discharge circuit) does not discharge the control capacitor, because the current supplied by the switchable current source can (automatically) deactivate the cut-off circuit (or discharge circuit). For example, the current supplied by the switchable current source can cause a voltage drop across circuit components (e.g., across diodes or resistors), which can have the effect of shutting off the transistor that at least partially discharges the control capacitor when on. However, the cut-off circuit can also be configured such that it automatically activates once the switchable current source is deactivated (e.g., provided the control voltage of the switching transistor is sufficiently high). Thus, a simple mechanism is created suitable for quickly shutting off power switches without requiring additional control lines.

[0069] In a preferred embodiment of the power switch, a first terminal of the control capacitor is connected to a control terminal (e.g., a gate terminal) of the switching transistor (e.g., directly connected or connected via a protective resistor). A second terminal of the control capacitor is connected to a reference potential conductor. A first output terminal of the floating voltage source (e.g., the anode output terminal of an optocoupler) is coupled to the first terminal of the control capacitor via a diode (e.g., D2). A second output terminal of the floating voltage source is coupled to the current output terminal of a switchable current source. A buffer capacitor is coupled between the first and second output terminals of the floating voltage source. The source terminal (e.g., emitter terminal or source terminal) of the discharge transistor is coupled (e.g., directly coupled) to the first terminal of the control capacitor, the sink terminal (e.g., collector terminal or drain terminal) of the discharge transistor is coupled to the output terminal of the power switch and / or to the source terminal of the switching transistor (e.g., directly coupled), and the control terminal (e.g., base terminal) of the discharge transistor is coupled to the first output terminal of the floating voltage source (and / or to the first terminal of the diode).

[0070] A resistor (e.g., R7) is coupled between the control terminal (e.g., base terminal) of the discharge transistor and the inflow terminal (e.g., collector terminal) of the discharge transistor (wherein, for example, the resistor is designed such that when the control capacitor is being charged, the current flowing through the resistor is no greater than 50% of the current supplied by the switchable current source, or where, for example, the resistor is designed such that when the control capacitor is being charged, the current flowing through the resistor is no greater than 25% of the current supplied by the switchable current source).

[0071] For example, the inlet terminal (e.g., collector terminal or drain terminal) of the current source output transistor is coupled to the second output terminal of the floating voltage source. For example, the source terminal of the switchable current source output transistor is coupled to the input terminal of a power switch (e.g., directly coupled, or with one or more circuit components therebetween; for example, a resistor therebetween), such that the switchable current source is supplied with the input voltage of the power switch. For example, one or more diodes (e.g., two diodes forming a series circuit) are coupled between the input terminal of the power switch and the control terminal of the current source transistor. For example, a series circuit is formed between the control terminal of the current source transistor and a reference potential conductor, consisting of a resistor and the load path (e.g., collector-emitter path) of the control transistor.

[0072] This implementation has been found to be particularly efficient. For example, when the switchable current source is on, the voltage drop across the diode can deactivate the discharge transistor. On the other hand, when the switchable current source is off, the discharge transistor is automatically activated by a resistor coupled between the control terminal (e.g., base terminal) and the inflow terminal (e.g., collector terminal) of the discharge transistor, causing the control capacitor to discharge rapidly to a level that deactivates (disconnects) the switching transistor.

[0073] Furthermore, the use of an optocoupler allows for a sufficiently high voltage to charge the control capacitor with moderate workload, where the typically relatively high input voltage of a power switch is also used. Additionally, the use of a buffer capacitor allows for the use of a relatively small optocoupler with an output current lower than that provided by a switchable current source.

[0074] In summary, the configuration described above can be implemented with a moderate amount of work, but provides very good functionality.

[0075] However, it should be noted that modifications can be made. For example, the order of the switchable current source and the optocoupler can be changed. Also, details regarding the disconnect circuit system can be modified. Furthermore, complementary implementations can be used.

[0076] According to an embodiment of the present invention, a method for operating a power switch is provided, the power switch comprising a switching transistor (e.g., a switching MOSFET), wherein a load path of the switching transistor (e.g., a collector-emitter path of the switching transistor (e.g., in the case of a bipolar switching transistor) or a drain-source path of the switching transistor (e.g., in the case of a field-effect switching transistor)) is coupled between an input terminal (e.g., SW_IN) of the power switch (e.g., a conductor for applying a supply voltage to be switched to an output terminal of the power switch via the switching transistor) and an output terminal (e.g., SW_OUT) of the power switch, wherein a source terminal of the switching transistor (e.g., an emitter terminal in the case of a bipolar switching transistor or a source terminal in the case of a field-effect switching transistor) is coupled to the output terminal of the power switch, and wherein the power switch comprises a control capacitor coupled between a control terminal of the switching transistor (e.g., a base terminal in the case of a bipolar switching transistor or a gate terminal in the case of a field-effect switching transistor) and a reference potential conductor.

[0077] For example, the control capacitor may have a capacitance greater than the internal capacitance of the transistor between the control terminal and the source terminal. For example, the control capacitor may have a capacitance greater than the gate-source capacitance of the switching transistor, or a capacitance greater than or equal to twice the gate-source capacitance of the switching transistor, or a capacitance greater than or equal to five times the gate-source capacitance of the switching transistor, or a capacitance greater than or equal to ten times the gate-source capacitance of the switching transistor.

[0078] The method involves charging a control capacitor using a current source (e.g., a constant current source) to obtain a voltage slope at the output of a power switch, wherein the voltage slope is substantially linear over time for a switching operation where the voltage at the output of the power switch is in the range of 10% to 90% of the maximum voltage (e.g., where the deviation from linear evolution does not exceed 10%).

[0079] This method is based on the same considerations as those discussed above regarding power switches. Furthermore, this method may be supplemented by any of the features, functionalities, and details also disclosed herein concerning power switches. Simple Explanation of the Diagram

[0080] Embodiments of the present invention will then be described with reference to the accompanying drawings, wherein... Figure 1 shows a schematic block diagram of a power switch according to an embodiment of the present invention; Figure 2 shows a schematic diagram of a power switch according to an embodiment of the present invention; Figure 3 shows a schematic diagram of a power switch according to an embodiment of the present invention; Figure 4 shows a graphical representation of the voltage and current in the power switch according to Figure 3; Figure 5 shows a flowchart of a method according to an embodiment of the present invention; Figure 6 shows a schematic diagram of a conventional power switch; and Figure 7 shows a graphical representation of voltage and current in a conventional power switch as shown in Figure 6. Implementation

[0081] Detailed Description of Preferred Embodiments 1. Based on the power switch in Figure 1 Figure 1 shows a schematic block diagram of a power switch 100 according to an embodiment of the present invention. The power switch 100 includes an input terminal 110 and an output terminal 112. Furthermore, the power switch 100 includes a switching transistor 120, wherein a load path 120a of the switching transistor (e.g., a drain-source path in the case of a field-effect transistor, or alternatively, a collector-emitter path in the case of a bipolar transistor) is coupled between the input terminal 110 and the output terminal 112 of the power switch 100. For example, the input terminal 110 of the power switch is a conductor for applying a supply voltage, which is to be switched to the output terminal 112 of the power switch via the switching transistor 120. The source terminal 120b of the switching transistor (e.g., the source terminal in the case of a field-effect transistor, or alternatively, the emitter terminal in the case of a bipolar transistor) is coupled to the output terminal 112 of the power switch (e.g., directly or via one or more circuit components therebetween). For example, the inlet terminal 120c of the switching transistor 120 (e.g., the drain terminal in the case of a field-effect transistor, or the collector terminal in the case of a bipolar transistor) may be coupled to the input terminal 110 of the power switch (e.g., directly or via one or more circuit components therebetween). Preferably, but not necessarily, the source terminal 120b of the switching transistor 120 may be coupled to the output terminal 112 of the power switch using a lower ohm connection (e.g., directly or via a shunt resistor for current measurement). Similarly, the inflow terminal 120c of the switching transistor 120 can be coupled to the input terminal 110 of the power switch via a low-ohm connection (e.g., directly or with a shunt resistor for current measurement).

[0082] Furthermore, it should be noted that the power switch 120 includes a control capacitor 130 coupled between the control terminal 120d of the switching transistor 120 (e.g., the gate terminal in the case of a field-effect transistor, or alternatively, the base terminal in the case of a bipolar transistor) and the reference potential conductor GND. For example, the reference potential conductor GND may be a ground conductor. For example, the control capacitor 130 may have a capacitance greater than the internal capacitance of the transistor between the control terminal 120d and the source terminal 120b of the switching transistor 120. For example, the control capacitor may have a capacitance greater than the gate-source capacitance of the switching transistor (e.g., in the case of a field-effect transistor), or the control capacitor may have a capacitance greater than or equal to twice the gate-source capacitance of the switching transistor, or the control capacitor may have a capacitance greater than or equal to five times the gate-source capacitance of the switching transistor, or the control capacitor may have a capacitance greater than or equal to ten times the gate-source capacitance of the switching transistor.

[0083] Furthermore, the power switch 100 includes a switchable current source 140 (e.g., switchable depending on the signal of the control line), which is configured to charge the control capacitor 130 in the on state (e.g., to charge the control capacitor in such a way that the voltage of the control capacitor increases substantially linearly over time, for example, with a deviation from linear evolution of less than 10%, for example, in the range of capacitor voltage of 10% to 90% of the input voltage of the power switch, or in the range of capacitor voltage of 20% to 80% of the input voltage of the power switch).

[0084] For example, the current output terminal of the switchable current source 140 can be directly coupled to the terminal (e.g., the first terminal) of the control capacitor 130. However, one or more circuit components may exist between the current output terminal of the switchable current source and the terminal (e.g., the first terminal) of the control capacitor 130.

[0085] Regarding the functionality of the power switch 100, it should be noted that, at least over a wide voltage range at the control terminal 120d of the switching transistor 120, the voltage at the output terminal 112 of the power switch can substantially (e.g., over a wide voltage range) follow the voltage at the control terminal 120d of the switching transistor 120. For example, the switching transistor 120 can operate as a source follower or an emitter follower, wherein, for example, the voltage at the output terminal 112 of the power switch can follow the voltage at the control terminal 120d of the switching transistor 120, where voltage shift can be determined by the threshold voltage of the switching transistor (e.g., in the case of a field-effect switching transistor). Voltage shift can also be determined by the forward voltage of the base-emitter diode, for example, in the case of a bipolar switching transistor. Therefore, the voltage at the output terminal 112 of the power switch can be well controlled by the voltage at the control terminal 120d of the switching transistor 120, and follows the voltage at the control terminal 120d of the switching transistor 120 over a wide voltage range.

[0086] Furthermore, the presence of the control capacitor 130 allows for the control and stabilization of the voltage at the control terminal 120d of the switching transistor 120. The control capacitor 130 allows the use of the switchable current source 140 to generate a well-defined voltage ramp at the control terminal 120d of the switching transistor 120, because when the switchable current source 140 is turned on, the switchable current source 140 can charge the control capacitor 130 with a substantially constant current (at least to a certain voltage).

[0087] Therefore, by switching on the switchable current source 140, a substantially linear voltage slope can be generated at the control terminal 120d of the switching transistor 120, which in turn results in a substantially linear voltage slope at the output terminal 112 of the power switch. Therefore, the voltage slope at the output terminal 112 of the power switch can be clearly defined by appropriately selecting the capacitance of the control capacitor 130 and by appropriately selecting the current supplied by the switchable current source. Therefore, it is possible to reliably adjust the voltage slope at the output terminal 112 of the power switch in such a way that the current flowing through the switching transistor does not exceed the maximum allowable current even in the presence of a capacitive load. Therefore, damage to circuit components can be avoided, and excessive load (or stress) on the power supply providing voltage at the input terminal 110 of the power switch can be avoided. Therefore, it is possible to reliably prevent excessive voltage drop at the input terminal 110 of the power switch 100.

[0088] In summary, the power switch 100 offers very advantageous characteristics, in which the voltage at the output terminal 112 of the power switch can rise in a very smooth and well-controlled manner, while avoiding excessive current peaks.

[0089] As outlined above, the switching transistor 120 can be configured to operate as a source follower (e.g., such that the voltage at the output terminal 112 of the power switch 100 follows the voltage at the control terminal 120d of the switching transistor, wherein there is a substantially constant voltage shift over a wide voltage range at the control terminal 120d of the switching transistor).

[0090] For example, the switchable current source 140 may be coupled between the input terminal 110 of the power switch 100 (e.g., a conductor for applying a supply voltage, which is to be switchably transferred to the output terminal 112 of the power switch via the switching transistor 120) and the control terminal 120d of the switching transistor 120 (e.g., such that the switchable current source 140 is supplied with the input voltage at the input terminal 110 of the power switch 100). Alternatively (or additionally), the switchable current source 140 may be coupled between the input terminal 110 of the power switch (e.g., a conductor for applying a supply voltage, which is to be switchably transferred to the output terminal 112 of the power switch via the switching transistor 120) and the control capacitor 130 (e.g., such that the switchable current source 140 is supplied with the voltage at the input terminal 110 of the power switch).

[0091] Alternatively, the power switch may include a floating voltage source (e.g., an optocoupler) not shown in FIG1, wherein the floating voltage source may be coupled, for example, between the switchable current source 140 and the control terminal 120d of the switching transistor, and / or wherein the floating voltage source may be coupled between the switchable current source 140 and the control capacitor 130. As another (optional) alternative, the power switch may include a floating voltage source, wherein the floating voltage source is coupled between the input terminal 110 of the power switch and the switchable current source 140.

[0092] In both cases, the floating voltage source helps ensure a sufficient voltage drop across the switchable current source 140, because "real-world" switchable current sources typically require a minimum voltage drop to operate as intended. Furthermore, the floating voltage source also provides the possibility of achieving a fully switched-on potential at the control terminal 120d of the switching transistor 120. For example, in some cases (e.g., when the switching transistor 120 is an N-channel MOSFET with a positive threshold voltage, such as an enhancement-mode N-channel MOSFET), a potential higher than that at the input terminal 110 of the power switch and also higher than that at the output terminal 112 of the power switch is required at the control terminal 120d of the switching transistor 120. For example, in order to fully turn on the switching transistor 120 (e.g., when the voltage at output terminal 112 has reached its maximum value), the potential at control terminal 120d should, under certain conditions, exceed the potential at source terminal 120b and the potential at inflow terminal 120c by more than the threshold voltage (so that the current path between inflow terminal 120c and source terminal 120b is in a low-ohmic state, or equivalently, to fully turn on the switching transistor 120). Therefore, the optional floating voltage source allows for efficient implementation with good characteristics.

[0093] In one example, the floating voltage may include an optocoupler. For instance, such an optocoupler can provide a voltage sufficient to ensure a sufficient voltage drop across the switchable current source and to bring the potential at control terminal 120d to the appropriate potential for fully turning on the switching transistor 120. Furthermore, the optocoupler can inherently provide sufficient current blocking so that the output voltage provided at the output of the optocoupler can be considered free-floating.

[0094] Furthermore, it has been recognized that the current capability of the optocoupler (at least when combined with a buffer capacitor) is generally sufficient to charge the control capacitor 130 at an appropriate voltage slope. Additionally, it has been recognized that optocouplers are generally smaller and more cost-effective than alternative solutions for providing floating voltage sources.

[0095] In some implementations, the floating voltage source may optionally include a buffer capacitor coupled in parallel with the output port of the optocoupler. This buffer capacitor buffers the voltage at the output of the optocoupler, thus allowing the optocoupler to be used even if the output current of the (core) optocoupler is less than the current provided by the switchable current source (and therefore less than the current used to charge the control capacitor 130). Preferably, the capacitance of the buffer capacitor may be greater than the capacitance of the control capacitor, or even at least twice as large. In some cases, the capacitance of the buffer capacitor may, for example, be at least five or at least eight times larger than the capacitance of the control capacitor 130. This allows the use of optocouplers with relatively small output current capabilities, which in turn helps to save costs.

[0096] In some embodiments, the power switch 100 or the control circuitry coupled to the power switch 100 may be configured, for example, to activate the optocoupler before the switchable current source is turned on. This may, for example, help to (pre-)charge the buffer capacitor coupled to the output of the optocoupler to a sufficient voltage before the switchable current source is activated. Thus, charging of the control capacitor 130 can be performed with good reliability even if the output current capability of the (core) optocoupler is relatively small.

[0097] In some situations, for example, the output voltage of the floating voltage source is greater than or equal to 1.5 times the threshold voltage of the switching transistor 120. Alternatively, in some situations, the output voltage of the floating voltage source may be, for example, greater than or equal to 6 volts, or the output voltage of the floating voltage source may be, for example, greater than or equal to 8 volts, or the output voltage of the floating voltage source may be, for example, greater than or equal to 10 volts. By having such an "additional" voltage contribution, a sufficient voltage drop is ensured across the switchable current source 140, which allows for reliable operation of the switchable current source and allows the switchable current source to provide the required current. Such selection of the output voltage of the floating voltage source also allows the potential at the control terminal 120d of the switching transistor 120 to reach an appropriate value so that the switching transistor 120 is fully turned on when the turn-on process is completed. Specifically, a voltage of 1.5 times the threshold voltage of the switching transistor 120, or at least 6 volts, at least 8 volts, or at least 10 volts, is generally sufficient to fully turn on the switching transistor 120 and provide a sufficient voltage drop across the switchable current source 140.

[0098] In some implementations, the output current of the optocoupler can be selected to be, for example, less than the current supplied by the switchable current source. This design can be advantageous because relatively inexpensive optocouplers can be used. However, the voltage at the output of the optocoupler can be maintained at a sufficiently high level by means of a buffer capacitor coupled in parallel with the output of the optocoupler. Therefore, this implementation offers significant advantages.

[0099] Preferably, but not necessarily, the switching transistor 120 may be a field-effect transistor (FET). Specifically, FETs have been found to be particularly suitable for this application because they exhibit substantially negligible control current (gate current) under static or quasi-static conditions and typically also have relatively low on-resistance. Therefore, using a FET (e.g., a MOSFET) as the switching transistor 120 is advantageous, but not absolutely necessary.

[0100] Furthermore, alternatively, the power switch 100 may include a disconnecting circuit (also referred to herein as a discharge circuit) configured to at least partially discharge the control capacitor 130 when the power switch 100 (or equivalently, the switching transistor 120) is disconnected as needed. However, details regarding this alternative feature will be described below.

[0101] Furthermore, it should be noted that the power switch 100 may be supplemented either individually or in combination with any of the features, functionalities and details disclosed herein. 2. According to the power switch in Figure 2

[0102] Figure 2 shows a schematic block diagram of a power switch 200 according to an embodiment of the present invention. Specifically, Figure 2 shows a block diagram of a power switch for a capacitive load.

[0103] For example, Figure 2 shows a power switch with component symbol 200 and an example of a capacitive load or mixed load with component symbol 280.

[0104] As shown in Figure 2, the input terminal 210 of the power switch 200 is coupled to a power rail, which is illustrated as a voltage source 270 in Figure 2. For example, the voltage source 270 can provide a voltage of 48 volts at the input terminal 210 of the power switch 200, and the power rail (or equivalently, the voltage source 270 modeling the power rail) can provide a charging current 272 to the input terminal 210 of the power switch 200.

[0105] However, it should be noted that different types of power supplies can be coupled to the input 210 of the power switch, where a substantially constant voltage is required (but not absolutely necessary).

[0106] Regarding load 280, it should be noted that the load 280 shown in Figure 2 should be considered as an example only, and different types of loads may be coupled to the output terminal 212 of the power switch 200.

[0107] In the example shown in Figure 2, the load 280 may include a boost converter 282, wherein the input terminal 282a of the boost converter is coupled to the output terminal 212 of the power switch. The output terminal 282b of the boost converter 282 may, for example, be coupled to one or more decoupling capacitors 284a, 284b and coupled to the load circuit system 286 (where the one or more decoupling capacitors 284a, 284b may be considered optional, and the one or more decoupling capacitors 284a, 284b may, for example, form a parallel circuit with the load circuit system 286).

[0108] However, it should be noted that, for example, a voltage source 270 providing input voltage at input terminal 210 of power switch 200 may be coupled between a reference potential (or reference potential conductor) GND and input terminal 210 of the power switch. Furthermore, the DC / DC converter (or boost converter) 282 may also be coupled to the reference potential conductor or reference potential GND. Additionally, one or more decoupling capacitors 284a, 284b and a load circuit system 286 may, for example, be coupled between the output terminal 282b of the DC / DC converter (e.g., boost converter) 282 and the reference potential conductor or reference potential GND.

[0109] In the following description, some (optional) details of a DC / DC converter will be illustrated as examples. For instance, a DC / DC converter (e.g., a boost converter) 282 may include an input capacitor 282c coupled between the input terminal 282a of the DC / DC converter 282 and a reference potential conductor or reference potential GND. Furthermore, an inductor 282d is coupled between the input terminal 282a of the DC / DC converter 282 and an internal node 282e of the DC / DC converter 282. Additionally, a switch 282f (e.g., a load path for a switching transistor) is coupled between the internal node 282e of the DC / DC converter 282 and the reference potential conductor or reference potential GND. Furthermore, a diode 282g is coupled between the internal node 282e and the output terminal 282b of the DC / DC converter. Additionally, an (optional) output capacitor is coupled between the output terminal 282b of the DC / DC converter 282 and the reference potential conductor or reference potential GND.

[0110] Regarding the DC / DC converter 282, it should be noted that the DC / DC converter 282 includes an input capacitor 282c, which is permanently coupled between the input terminal 282a of the DC / DC converter 282 and a reference potential conductor or reference potential GND. The input capacitor 282c functions to prevent excessive fluctuations in the input current of the DC / DC converter 282. The DC / DC converter 282 typically includes a control element that repeatedly (e.g., periodically; e.g., in a controlled manner) opens and closes a switch 282f, such that when the switch 282f is closed, a current is established through the inductor 282d. Once the switch 282f is opened, the current established in the inductor 282d continues to flow and through the diode 282g, thereby charging the output capacitor 282h of the DC / DC converter 282 (e.g., to a voltage higher than the voltage at the input terminal 282a of the DC / DC converter). Therefore, it is possible to achieve a situation where the output voltage at the output terminal 282b of the DC / DC converter 282 is greater than the input voltage at the input terminal 282a of the DC / DC converter 282. It should also be noted that as long as there is voltage at the input terminal 282a of the DC / DC converter, there will always be current flowing through the load circuit system 286. This is because a permanent conduction path exists from the input terminal 282a of the DC / DC converter through the inductor 282d and diode 282g to the output terminal 282b of the DC / DC converter.

[0111] However, it should be noted that the DC / DC converter 282 should be considered as an example only. It should also be noted that the power switch 200 is well-suited for use in conjunction with this (up-conversion) type of DC / DC converter because the power switch can adequately handle the presence of an input capacitor 282c, which is always active and contains a relatively large capacitance, and the fact that a current path to the load circuit system 286 is always present.

[0112] However, it should be noted that the power switch 200 can of course be used with different types of loads, and the power switch 200 does not require the presence of a capacitive load.

[0113] Turning to power switch 200, it should be noted that power switch 200 includes a metal-oxide-semiconductor field-effect transistor (MOSFET) 220 as the switching transistor. For example, MOSFET 220 is an N-channel MOSFET, but it should be noted that complementary implementations (where a P-channel MOSFET is used instead of an N-channel MOSFET, and an NPN bipolar transistor is used instead of a PNP bipolar transistor, and where the polarity of the diode and voltage source is swapped (inverted)) are of course also possible. In the example of Figure 2, the source terminal 220b of MOSFET 220 is coupled to the output terminal 212 of the power switch, and the drain terminal 220c of MOSFET 220 is coupled to the input terminal 210 of the power switch. As an example, the source terminal 220b is directly coupled to the output terminal 212 of the power switch, and the drain terminal 220c is directly coupled to the input terminal 210 of the power switch. However, low-ohmic components such as shunt resistors may be optionally coupled between individual terminals of MOSFET 220 and input 210 and / or output 212.

[0114] The power switch 200 includes a control capacitor 230, which is coupled between the control terminal (gate terminal) 220d of the MOSFET 220 and the reference potential conductor or reference potential GND.

[0115] Furthermore, the power switch 200 includes a switchable current source 240, wherein a first terminal 240a of the switchable current source 240 is coupled to the input terminal 210 of the power switch, and a second terminal 240b of the switchable current source is coupled to the second terminal 250b of the floating voltage source 250 (also specified as a floating auxiliary supply 250). The first terminal 250a of the floating voltage source (or floating auxiliary supply) 250 is coupled to the control terminal 220d of the MOSFET 220 via a bootstrap circuit (also specified as a discharge circuit or cut-off circuit) 260. Equivalently, it can be claimed that the first terminal of the floating voltage source 250 is coupled to the first terminal of the controller capacitor 230 via the bootstrap circuit system 260. However, it should be noted that the bootstrap circuit system or discharge circuit system 260 can be considered optional, such that the first terminal 250a of the floating voltage source 250 can also be directly coupled to the control terminal 220d of the MOSFET 220 or the first terminal 230a of the control capacitor 230.

[0116] Regarding the switchable current source 240, it should be noted that the switchable current source 240 can generally be considered as a current source that can be started and deactivated via a control signal or control line 242, which can be driven, for example, by a control circuit system similar to, for example, a field-programmable gate array, a microprocessor, a microcontroller, or the like. However, it should be noted that since the switchable current source 240 is a "real-world" switchable current source, it typically requires a voltage drop across its first terminal 240a and its second terminal 240b to operate correctly. Also, it should be noted that the switchable current source 240 is illustrated in Figure 2 as a series connection of a fixed current source 240c and a switch 240d, but it should be noted that different implementations of the switchable current source are of course possible. Typically, a switchable current source is implemented using one or more transistors (e.g., field-effect transistors and / or bipolar transistors), and a voltage drop of at least 1 volt or at least 2 volts may be required between the first terminal 240a and the second terminal 240b of the switchable current source 240. Furthermore, it should be noted that in some cases, the current supplied by the switchable current source may be adjustable. However, this functionality is not essential.

[0117] Referring now to the floating voltage source (or floating auxiliary supply) 250, it should be noted that the floating voltage source 250 may, for example, include polarization such that the potential at the first terminal 250a of the floating voltage source is higher than the potential at the second terminal 250b of the floating voltage source 250 (wherein it is assumed that the voltage at the input terminal 210 of the power switch is positive relative to the reference potential at the reference potential conductor GND). Therefore, the floating voltage source 250 can, for example, compensate for (or better, even over-compensate for) the normally unavoidable voltage drop between the first terminal 240a and the second terminal 240b of the switchable current source 240. Thus, the switchable voltage source 250 can achieve the effect that the potential at the first terminal 250a of the floating voltage source is higher than the potential at the input terminal 210 of the power switch, while a sufficient voltage drop still exists between the first terminal 240a and the second terminal 240b of the switchable current source 240 (sufficient to ensure the proper operation of the switchable current source).

[0118] Referring now to bootstrap circuit system or discharge circuit system or cutoff circuit system 260, it should be noted that the bootstrap circuit system or discharge circuit system or cutoff circuit system is coupled between the first terminal 250a of the floating voltage source and the control terminal 220d of the switching transistor 220 (or equivalently, the first terminal of the control capacitor 230), and the bootstrap circuit system or discharge circuit system or cutoff circuit system 260 is also coupled between the control terminal 220d of the MOSFET 220 and the source terminal 220b of the MOSFET 220.

[0119] For example, the discharge circuit system may include a diode 260a coupled between a first terminal 250a of a floating voltage source 250 and a control terminal 220d of a MOSFET 220. For example, the anode of diode 260a is coupled to the first terminal 250a of the floating voltage source 250, and the cathode of diode 260a is coupled to the control terminal 220d of the MOSFET 220. Furthermore, the discharge circuit 260 also includes a transistor (also specified as a discharge transistor) 260b, which, in the example of Figure 2, is a bipolar transistor (e.g., a PNP bipolar transistor). However, it should be noted that a field-sensing transistor may also be used (wherein the field-sensing transistor configuration, the source terminal acts as the emitter terminal, the drain terminal acts as the collector terminal, and the gate terminal acts as the base terminal). For example, the emitter terminal of the discharge transistor 260b is coupled to the cathode terminal of the diode 260a and to the control terminal 220d of the MOSFET 220 (or equivalently, to the first terminal 230a of the control capacitor 230, or equivalently, to the node between the control terminal 220d of the MOSFET 220 and the first terminal 230a of the control capacitor 230).

[0120] Furthermore, the base terminal of the discharge transistor 260b is coupled to the anode of the diode 260a (or equivalently, to the first terminal 250a of the floating voltage source 250, or equivalently, to the node between the first terminal 250a of the floating voltage source 250 and the anode of the diode 260a). The collector terminal of the discharge transistor 260b is coupled to the source terminal 220b of the MOSFET 220 (or equivalently, to the output terminal 212 of the power switch 200, or equivalently, to the node between the source terminal 220b of the MOSFET 220 and the output terminal 212 of the power switch 200). Additionally, a resistor 260c is coupled between the base terminal of the discharge transistor 260b and the collector terminal of the discharge transistor 260b.

[0121] Regarding the functionality of the discharge circuit 260, it should be noted that when charging current flows into the control capacitor 230a (via diode 260a), the discharge transistor 260b will be turned off (e.g., automatically). However, when no charging current flows into the control capacitor 230, the discharge transistor 260b will be turned on, thereby establishing a current path between the first terminal 230a of the control capacitor 230 and the source terminal 220b of the MOSFET (or the output terminal 212 of the power switch 200). For example, when (positive) current flows from the first terminal 250a of the floating voltage source 250 to the first terminal 230a of the control capacitor 230, a voltage drop will exist on diode 260a, and therefore the potential at the base terminal of the discharge transistor 260b will be more positive than the potential at the emitter terminal of the discharge transistor 260b. Therefore, in this case, the discharge transistor 260b will automatically turn off because the discharge transistor 260b is a PNP transistor. On the other hand, if there is no current flowing through diode 260a (more precisely: no forward current), resistor 260c pulls the potential at the base terminal of discharge transistor 260b toward the potential at the collector terminal of discharge transistor 260b. This will turn on discharge transistor 260b if the potential at the emitter terminal of discharge transistor 260b (which is usually equal to the potential at the first terminal of control capacitor 230) is higher than the potential at the base terminal of discharge transistor 260b (for example, the limiting condition is that the voltage difference is greater than or equal to the threshold voltage of the base-emitter diode of discharge transistor 262b). Therefore, assuming the resistor 260c is appropriately sized, if there is no (forward) current flowing through diode 260a and if the potential at the source terminal 220b of MOSFET 220 is lower than (or significantly lower than) the potential at the first terminal 230a of control capacitor 230 (or the potential at the gate terminal 220d of MOSFET 220), then discharge transistor 260b will be turned on. Therefore, if there is no (forward) current flowing through diode 260a (which is typically the case if the switchable current source is deactivated), then discharge capacitor 260b will be automatically activated if the potential at gate terminal 260d is higher than (or substantially higher than) the potential at the source terminal 220b of MOSFET 220. When the discharge transistor 260b is turned on, it allows current to flow between the gate terminal 220d and the source terminal 220b of the MOSFET 220, thereby bringing the potential at the gate terminal 220d of the MOSFET 220 closer to the potential at the source terminal 220b. As a result, the gate-source voltage of the MOSFET 220 drops to a relatively small value, which turns off the MOSFET 220.In other words, generally speaking, when there is no current flowing through diode 260a (i.e., when the switchable current source is turned off), the discharge transistor 260b will discharge the control capacitor 230, causing MOSFET 220 to turn off.

[0122] The overall functionality of the power switch 200 will be briefly outlined below. When the switchable current source 240 is turned on, the switchable current source 240 will provide a predetermined current (e.g., ICTRL), subject to a sufficient voltage drop across the switchable current source 240 (e.g., between the first terminal 240a and the second terminal 240b of the switchable current source 240).

[0123] However, a floating voltage source 250 is typically used to ensure a sufficient voltage drop across the switchable current source. This floating voltage source has the effect that the potential at the first terminal 250a of the floating voltage source is higher (generally, shifted) relative to the potential at the second terminal 250b of the floating voltage source 250. Therefore, by appropriately setting the dimensions of the floating voltage source 250, it is possible to achieve a situation where the potential at the first terminal 250a of the floating voltage source 250 is even higher than the potential at the input terminal 210 of the power switch 200, while still maintaining a sufficient voltage drop across the switchable current source 240.

[0124] Therefore, when the switchable current source 240 is turned on, current flows through diode 260a to control capacitor 230a, thereby charging control capacitor 230. Preferably, the capacitance of control capacitor 230 is significantly larger than the gate-source capacitance of MOSFET 220, so the time constant of the charging process is dominated by the capacitance of control capacitor 230 and is therefore clearly defined. The voltage slope at the first terminal 230a of control capacitor 230 is primarily determined by the current ICTRL and by the capacitance CSLP of control capacitor 230.

[0125] Therefore, starting from the initial state of discharging the control capacitor 230, once the switchable current source 240 is activated, the potential at the first terminal 230a of the control capacitor 230, and thus the potential at the gate terminal 220d of the MOSFET 220, will steadily increase (at least until saturation). However, in the absence of significant parasitic effects, the time evolution of the potential at the gate terminal 220d of the MOSFET 220 will be approximately linear over time until saturation is reached (wherein saturation can be determined, for example, by the potential at the input terminal 210 of the power switch, the voltage provided by the floating voltage source 250, and the voltage drop required by the switchable current source 240).

[0126] Therefore, since MOSFET 220 operates as a source follower, the potential at the source terminal 220b of MOSFET 220 will follow the potential at the gate terminal 220d of MOSFET 220. The potential difference between the potential at the gate terminal 220d and the potential at the source terminal 220b of MOSFET 220 will be defined by the gate-source voltage VGS of MOSFET 220 and will be approximately equal to the threshold voltage of MOSFET 220 (but typically slightly greater than the threshold voltage) (at least once the threshold voltage is reached, and until saturation). Therefore, it can be expected that once the gate-source voltage of the MOSFET reaches the threshold voltage and until saturation, the potential at the source terminal 220b of MOSFET 220 will substantially follow the potential at the gate terminal 220d of MOSFET 220. Therefore, it can be assumed that the potential at the source terminal 220b of MOSFET 220, and thus the potential at the output terminal 212 of the power switch, increases substantially linearly with time until it reaches a maximum value.

[0127] For example, when a sufficiently high gate-source voltage is eventually reached (e.g., when the voltage at gate 220d increases further and the voltage at source has reached its maximum value), the MOSFET will eventually be in a low-ohmic condition, such that in a fully on operating state, there is only a small voltage drop between the input terminal 210 and the output terminal 212 of the power switch.

[0128] Therefore, when the switchable current source 240 is activated, the voltage at the output terminal 212 of the power switch will increase in a substantially linear fashion over time.

[0129] Furthermore, as explained in detail above, when the switchable current source 240 is started, current flows through diode 260a, thereby charging control capacitor 230, which in turn causes the start (shutdown) discharge transistor 260b to be deactivated.

[0130] Therefore, the control capacitor 230 is charged over time in a substantially linear manner (e.g., with a substantially constant current) until it reaches saturation. Preferably, the MOSFET 220 is eventually fully turned on, with the gate-source voltage significantly higher than the threshold voltage of the MOSFET 220. Thus, the MOSFET 220 is eventually in a low-ohmic operating mode, resulting in only a small voltage drop between the input 210 and the output 212 of the power switch 200.

[0131] When the switchable current source 240 is deactivated, there is no longer current flowing through diode 260a and discharge transistor 260b is activated (as outlined above). In this state, resistor 260c allows the base current to flow through discharge transistor 260b. Therefore, control capacitor 230 is discharged until the potential at gate terminal 220d of MOSFET 220 is only slightly higher than the potential at source terminal 220b of MOSFET 220. Therefore, MOSFET 220 is turned off (placed in a high-ohm operating state). Consequently, the voltage at the output terminal 212 of the power switch typically decreases because there is no longer current supplied to load 280. However, discharge circuit 260 ensures that MOSFET 220 remains off. Specifically, the discharge circuit 260 ensures that, as long as there is no current flowing through the diode 260a (i.e., as long as the switchable current 240 is not turned on), the potential at the gate terminal 220d of the MOSFET 220 will not be substantially higher than the potential at the source terminal 220b of the MOSFET 220, by setting a conduction path between the gate terminal 220d and the source terminal 220b of the MOSFET 220.

[0132] However, it should be noted that the power switch 200 may be optionally supplemented by any of the features, functionalities and details disclosed herein.

[0133] Furthermore, it should be noted that complementary implementations are also possible, wherein the voltage at the input terminal 210 of the power switch 200 is negative, wherein the N-channel MOSFET 220 is replaced by a P-channel MOSFET, wherein the PNP transistor 260b is replaced by an NPN transistor, wherein the polarity of the diode 260a is reversed, and wherein the polarity of any voltage source is also reversed.

[0134] Furthermore, it should be noted that the bipolar transistor 260b can be optionally replaced by a field-effect transistor, and the MOSFET 220 can be optionally replaced by a bipolar transistor or any other type of field-effect transistor.

[0135] Furthermore, it should be noted that input terminal 210 of the power switch corresponds to input terminal 110 of power switch 100, output terminal 212 of power switch 200 corresponds to output terminal 112 of power switch 100, MOSFET 220 corresponds to switching transistor 120, control capacitor 230 corresponds to control capacitor 130, and switchable current source 240 corresponds to switchable current source 140. Any interpretation made regarding power switch 100 may also be applied. 3. According to the power switch in Figure 3

[0136] Figure 3 shows a schematic diagram of a power switch 300 according to an embodiment of the present invention. Figure 3 also shows a (simplified) schematic diagram of a load 380.

[0137] However, it should be noted that the specific types of circuit elements and their specific parameters shown in Figure 3 should be considered as examples only. It should also be noted that other types of circuit elements and other element values ​​may be used. Specifically, these details (part numbers, resistance values, capacitance values, etc.) should be considered as examples only.

[0138] As can be seen, the power switch 300 includes an input terminal 310 to which a voltage source 370 is connected. The power switch 300 also includes an output terminal 312 coupled to a load 380.

[0139] In the example of Figure 3, the load is shown as a boost converter with an input capacitor 382c and an output capacitor 382h. However, it should be noted that different types of loads may also be used, and the specific load is provided only as an example to allow for meaningful circuit simulation.

[0140] The power switch 300 includes a MOSFET 320, which corresponds to and functions as a switching transistor, and is also the switching transistor, for MOSFET 220 and MOSFET 120. MOSFET 320 is also specified as a "switching MOSFET" (even though the MOSFET primarily operates as a source follower). The source terminal 320b of the MOSFET is coupled to the output terminal 312, and the drain terminal 320c is coupled to the input terminal 310. The power switch 300 also includes a control capacitor 330, which corresponds to control capacitors 230 and 130. The first terminal 330a of the control capacitor 330 is coupled to the gate terminal 320d of the MOSFET 320.

[0141] The power switch 320 also includes a switchable current source 340, which corresponds to switchable current source 240 and switchable current source 140. A first terminal 340a of the switchable current source is coupled to an input terminal 310, and a second terminal 340b of the switchable current source 340 is coupled to a second terminal (e.g., a second output terminal) 350b of the floating voltage source 350.

[0142] The first terminal (e.g., the first output terminal) 350a of the floating voltage source 350 is coupled to the gate terminal 320d of the MOSFET 320 (or equivalently, to the first terminal 330a of the control capacitor 330) via the diode 360a of the discharge circuit 360 (which corresponds to the discharge circuit 260 and can also be considered as a cutoff circuit or bootstrap circuit). However, it should be noted that the floating voltage source 350 corresponds to the floating voltage source 250 and the discharge circuit 360 corresponds to the discharge circuit 260.

[0143] The following text will describe some details about individual components.

[0144] The switchable current source 340 includes an output transistor 340c, which is, for example, a PNP bipolar transistor. However, different transistor types may also be used. For example, the emitter terminal of the output transistor 340c is coupled to the input terminal 310 of a power switch via a resistor 340d. For example, two diodes 340e and 340f form a series circuit between the input terminal 310 of the power switch and the base terminal of the transistor 340c (e.g., to provide a relatively stable voltage across the base-to-emitter path of the output transistor 340c and across the resistor 340d). Furthermore, the switchable current source 340 includes another transistor 340g, which is, for example, an NPN bipolar transistor. For example, the collector terminal of the other transistor 340g is coupled to the base terminal of the transistor 340c via a resistor 340h. Additionally, the base terminal of the transistor 340g is coupled to a control voltage source 344 via a resistor 340i. In addition, the emitter terminal of transistor 340g is coupled to the reference potential conductor GND.

[0145] Therefore, it can be seen that the switchable current source 340 is supplied with the input voltage of the power switch 300 at the input terminal 310 of the power switch 300. When the transistor 340g is turned on by an appropriate control signal provided by the control signal source 344, an appropriate (and preferably, well-defined) bias voltage is applied to the base terminal of the transistor 340c, and a generally well-defined current flows through the collector-emitter path of the transistor 340c, subject to the constraint that there is a sufficient voltage drop on the collector-emitter path of the transistor 340c (and on the resistor 340d). Conversely, if the transistor 340g is turned off, the transistor 340c is also deactivated and there will be no current flowing through the collector-emitter path of the transistor 340c. Therefore, the switchable current source 340 can be turned on and off by a control signal provided by the control signal provider 344. Furthermore, it should be noted that for the operation of the switchable current source 340, a minimum voltage drop is required across resistor 340b and along the current emitter path of transistor 340c, which may be, for example, approximately 1 V or approximately 2 V. However, it should be noted that the switchable current source can also be implemented in different ways, such as using a current mirror circuit structure.

[0146] The floating voltage source 350 is implemented, for example, using an optocoupler 351. For example, the input side of the optocoupler may include one or more light-emitting diodes (or other types of light sources). For example, the first input terminal 351a of the optocoupler is coupled to the voltage source 354 via a resistor 353, which limits the current. The second input terminal 351b of the optocoupler is coupled, for example, to a reference potential conductor GND. However, it should be noted that how the input side of the optocoupler is powered is irrelevant to the present invention. However, it is advantageous to use a power supply that is available before the power switch is turned on.

[0147] The output side of optocoupler 351 may include, for example, one or more photodiodes or other optoelectronic elements that provide an output voltage based on illumination generated by the input voltage of optocoupler 351. For instance, the first output terminal 351c of optocoupler 351 is coupled to the first output terminal 350a of a floating voltage source, and the second output terminal 351d of optocoupler 351 is coupled to the second output terminal 350b of the floating voltage source 350. In other words, the second output terminal 351d of the optocoupler is coupled to the second terminal 340b of a switchable current source.

[0148] Furthermore, a buffer capacitor 355 is coupled between the first output terminal 351c and the second output terminal 351d of the optocoupler 351 (or equivalently, between the first output terminal 350a and the second output terminal 350b of the floating voltage source 350). For example, once a sufficient voltage is applied to the input terminals 351a, 351b of the optocoupler 351, the buffer capacitor 355 can be charged by the current supplied by the optocoupler, even before the switchable current source 340 is activated. The buffer capacitor 355 can, for example, be charged to a voltage close to the highest output voltage of the optocoupler 351. For example, the capacitor 355 can be charged before the switchable current source is turned on. For example, the output current of the optocoupler (e.g., at the desired output voltage of the optocoupler) can be less than the current supplied by the switchable current source 340.

[0149] Therefore, when the switchable current source 340 is activated, even if the (instantaneous) current supplied at the output of the optocoupler 351 is less than the current supplied by the switchable current source 340, the voltage between the first output terminal 350a and the second output terminal 350b of the floating voltage source can be maintained at least substantially constant by means of the buffer capacitor 355. Thus, the combination of the optocoupler 351 and the buffer capacitor 355 acts as a floating voltage source whose voltage remains at least substantially constant during the period when the control capacitor 330 is charged.

[0150] Therefore, the current supplied by the switchable current source 340 is transferred to charge the control capacitor 330, with only a small portion of the current being "lost" through the resistor 360c of the discharge circuit 360. Thus, once the switchable current source 340 is turned on, the control capacitor 330 is charged with a substantially constant current, for example, until it reaches the saturation region.

[0151] The explanation of the functionality of discharge circuit 360 above regarding discharge circuit 260 also applies.

[0152] Therefore, the voltage at the output terminal 312 essentially follows the voltage at the gate terminal 320d of the MOSFET 320 until saturation is reached (wherein, obviously, the voltage at the output terminal 312 cannot be higher than the voltage at the input terminal 310).

[0153] When the switchable current source 340 is turned off, there will no longer be current flowing through diode 360a of the discharge circuit. Therefore, discharge circuit 360 will start, as explained above, and MOSFET 320 will turn off.

[0154] The time evolution of the signal in circuit 300 will be described below with reference to Figure 4.

[0155] For example, in Figure 4, the horizontal axis 410 describes time. The first vertical axis 412 describes voltage, the second vertical axis 414 describes voltage, and the third vertical axis 316 describes current.

[0156] Curve 420 describes the time evolution of the control voltage used to turn the switchable current source on and off. Curve 422 describes the time evolution of the gate-source voltage of MOSFET 320. Curve 424 describes the time evolution of the voltage at input terminal 310 of power switch 300. Curve 426 describes the time evolution of the gate voltage of MOSFET 320 (between gate terminal 420d and reference potential conductor GND). Curve 428 describes the time evolution of the voltage at output terminal 312 of power switch 300. Curve 430 describes the sum of the currents in capacitors C1 (382h) and C2 (382c). Curve 432 describes the time evolution of the current flowing through resistor 390, which is a load resistor.

[0157] For example, at time t1, a control signal for the switchable current source is initiated. Therefore, the voltage at gate terminal 320d of MOSFET 320 (as shown in curve 426) begins to increase. This increase is at least substantially linear with time, exhibiting non-linearity in the initial region (e.g., between times t1 and t2) and in the saturation region (e.g., between times t3 and t4). It can also be seen that the gate-source voltage increases between times t1 and t2. However, at time t2, the gate-source voltage reaches a threshold voltage and remains substantially constant between times t2 and t3 (with only a slight increase with time). Also starting at time t2, the voltage at output terminal 312 of power switch 300 begins to rise because MOSFET 320 operates as a source follower from time t2 onwards. The substantially linear increase in output voltage at output terminal 312 with time continues until time t3. At time t3, the output voltage at the output terminal 312 of the power switch 300 reaches the input voltage at the input terminal 310 of the power switch, and therefore cannot be increased further.

[0158] However, between times t3 and t4, the gate-source voltage increases further, for example, from approximately 4 volts to approximately 8 volts. Between times t3 and t4, the increase in voltage at gate terminal 320d slows down, but the increase in voltage at gate terminal 320d continues until time t4 (and possibly even after time t4). However, the output voltage at the output terminal 312 of the power switch remains substantially constant between times t3 and t5, where the further increase in gate-source voltage between times t3 and t4 helps to reduce the on-resistance of MOSFET 320.

[0159] At time t5, the control signal for starting the switchable current source is deactivated. Therefore, due to the operation of discharge circuit 360, the gate-source voltage decreases rapidly (e.g., between times t5 and t6). Consequently, MOSFET 320 is turned off. However, the voltage decay at the output terminal 312 of the power switch is primarily caused by the load 380 (including resistor 390). In other words, after time t5, capacitors 382c and 382h are essentially discharged by resistor 390, resulting in voltage decay at the output terminal 312 of the power switch 300. However, it can be seen that the voltage at the gate terminal 320d of MOSFET 320 closely follows the voltage at the output terminal 312 of the power switch 300 after time t6, which is due to the functionality of discharge circuit 360.

[0160] Furthermore, it can be seen that the sum of the charging currents of capacitors 382c and 382h (C2 and C1) is substantially constant between times t2 and t3, with a slight decrease towards t3. This substantially constant charging current, which does not exhibit large peak values, is caused by the substantially linear increase in voltage at the output terminal 312 of the power switch over time between times t2 and t3. After time t5, the current through capacitors 382c and 382h is substantially caused by the discharge process through resistor 390.

[0161] Furthermore, the current flowing through resistor 390 is substantially proportional to the voltage at the output of boost converter 380 (or, when considering the voltage drop across the diode of the DC / DC converter, at least linearly related to that voltage).

[0162] In summary, it becomes obvious that the power switch 300 helps avoid excessive current peaks while still achieving low on-resistance and good disconnection behavior.

[0163] In addition, it should be noted that the power switch 300 can be optionally supplemented by any of its features, functions and details in both individual and combined ways. According to the method in Figure 5

[0164] Figure 5 shows a flowchart of a method for operating a power switch.

[0165] The power switch includes a switching transistor, wherein the load portion of the switching transistor is coupled between the input and output terminals of the power switch. The source terminal of the switching transistor is coupled to the output terminal of the power switch. The power switch includes a control capacitor coupled between the control terminal of the switching transistor and a reference potential conductor.

[0166] Method 500 includes charging a control capacitor (510) using a current source to obtain a voltage slope at the output of a power switch that is substantially linear over time for a switching operation where the voltage at the output of the power switch is in the range of 10% to 90% of the maximum voltage.

[0167] However, Method 500 may be supplemented either individually or in combination with any of the features, functionality and details disclosed herein regarding power switches. Conclusions and other comments

[0168] In summary, embodiments of the present invention provide a solid-state switch that can connect a capacitive load to a power supply rail while suppressing large inrush currents. For example, a typical application of such a switch is to connect a boost DC / DC converter, including its load circuitry, to a power supply rail.

[0169] It has been recognized that embodiments of the invention enable the connection of capacitive loads in a well-controlled manner. The power switch for the capacitive load generates a defined voltage ramp at its output, which allows inrush current to be limited to an allowable maximum value during switching.

[0170] The block diagram has been discussed with reference to Figure 2, which shows a block diagram of a power switch used for a capacitive load.

[0171] The following provides a brief functional description applicable to any of the embodiments disclosed herein. For example, the block diagram of Figure 2 provides an overview of the operating principle of a power switch for a capacitive load:

[0172] For example, before connecting the load circuit system (boost converter - DC / DC) (e.g., load circuit system 280) to the 48-volt power rail (e.g., power rail 270), the capacitor CSLP (e.g., control capacitor 230) in the switch (e.g., in power switch 200) and the load capacitors Cboost, input, Cboost, output (e.g., capacitors 282c, 282h) are discharged (VSLP = 0 volts, VSW, output = 0 volts).

[0173] When the control line from the FPGA (e.g., control line 242) goes high, the switchable current source (e.g., switchable current source 240) is turned on. Then, the capacitor CSLP (e.g., control capacitor 230) begins to charge. Once VGS, the threshold value, is applied to the switching MOSFET (e.g., to the gate terminal 220d of MOSFET 220), CSLP is further charged by a nearly constant current. This correspondingly creates a ramp with a constant slew rate at the MOSFET gate (e.g., at gate terminal 220d) and source (e.g., at source terminal 220b) (the switching output).

[0174] The induced voltage ramp that appears at the load capacitors (C boost, input, C boost, output...) (e.g., at load capacitors 282c, 282h, but also, for example, at decoupling capacitors 284a, 284b) results in a constant (or at least substantially constant) charging current and does not cause high current spikes.

[0175] A floating auxiliary supply (e.g., a floating voltage source 250) enables the provision of a sufficiently high VGS (e.g., the gate-source voltage between gate terminal 220d and source terminal 220b) to fully turn on the MOSFET (e.g., MOSFET 220), even if the voltage at the switch output (VSW, output) (e.g., at output terminal 212) is close to the input voltage (VSW, input) (e.g., at input terminal 210).

[0176] For example, an optocoupler (e.g., optocoupler 351) is sufficient to achieve this purpose, similar to the Toshiba TLP3914, which can provide, for example, 20 uA of current and 7 V min of voltage. The optocoupler can be supplied with, for example, a small digital supply voltage of, for example, 3.0 V, which is typically available before the actual power sequence begins (e.g., before the switchable current source is turned on).

[0177] When the switch is turned off (e.g., the control line from the FPGA goes low), the discharge of the load capacitors (e.g., load capacitors 282c, 282h) is accomplished by the load circuit system and is not a critical process that results in uncontrollable high currents. The bootstrap circuit system (e.g., the cut-off circuit or discharge circuit 260) functions to reset the switching circuit system itself to the off state: turning off the switching MOSFET (e.g., MOSFET 220) (VGS≈0) and discharging the CSLP (e.g., control capacitor 230) (VSLP≈0).

[0178] An implementation example will be described below.

[0179] For example, we will take the calculation of the switching parameters as an example.

[0180] This is an example of how a switching circuit system (e.g., a power switch disclosed herein, see Figures 1, 2 and 3) can be adjusted to obtain a charging current for a non-critical capacitive load during turn-on: ● Determine the target charging current of the load capacitor: For example, Icharging, maximum = 0.2 A ● Calculate the corresponding conversion rate (SR): ● For example, SR = I_charging, maximum / C_load = 0.2 A / 200 uF = 1 V / ms ● Determine the sufficient current for charging the CSLP during the on-time period: ● For example, ISLP=10 uA ● Calculate CSLP: ● For example, CSLP = SR / ISLP = (1 V / ms) / 10 uA = 10 nF ● Calculate ICTRL (which can be adjusted, for example, by changing the circuit system). ● Assuming, for example, IB=0, IC=0, VGS, the critical limit value ≈ 4 V: ● For example, IBS=VGS, critical limit / RBS=4 V / 2 MΩ=2 uA ● For example, ICTRL = ISLP + IBS = 10 uA + 2 uA = 12 uA

[0181] The following text will describe a simulated example of the switching sequence.

[0182] The LTSpice model shown in Figure 3 contains a complete circuit system for a power switch 300 for capacitive loads.

[0183] In other words, Figure 3 shows the LTSpice model for power switches used for capacitive loads.

[0184] Figure 4 shows the simulation results of the switch used for capacitive loads.

[0185] For example, the sequence in the simulation is as follows:

[0186] 1. V (CTRL) (e.g., controlling the voltage of switchable current source 340) changes from 0 V to 3 V → initial turn-on, (GATE, SW_OUT) (e.g., the gate-source voltage of MOSFET 320) begins to increase.

[0187] 2. V(GATE,SW_OUT) (e.g., the gate-source voltage of MOSFET 320) has exceeded VGS, the threshold value (e.g., the threshold voltage of MOSFET 320), the voltage ramp V(SW_OUT) at the switch output (e.g., at switch output 312) begins, and the charging current I(C1) + I(C2) (e.g., the charging current of capacitors 382c and 382h) is reasonably constant, for example, at 0.2 A (as calculated).

[0188] 3. When the voltage at the switch output terminal (e.g., switch output terminal 312) reaches V(SW_IN) (e.g., the voltage at switch input terminal 310), the voltage ramp ends, the charging current I(C1) + I(C2) decreases to 0, and the gate voltage V(GATE) (e.g., the voltage at gate terminal 320d) further increases.

[0189] 4. With the MOSFET (e.g., MOSFET 320) fully turned on, V(GATE) (e.g., the voltage at gate terminal 320d) is now constant.

[0190] 5. V (CTRL) (e.g., controlling the voltage of switchable current source 340) changes from 3 V to 0 V → initiating shutdown. V(GATE,SW_OUT) (e.g., the gate-source voltage of a MOSFET 320) begins to decrease. The voltage V(SW_OUT) at the switch output terminal (e.g., at switch output terminal 212) begins to decrease, and the discharge of the load capacitors (e.g., capacitors 382c, 382h) is accomplished by the resistive load current I(R1).

[0191] 6. V(GATE, SW_OUT) (e.g., the gate-source voltage of MOSFET 320) is quite stable at low voltages, and the MOSFET is turned off.

[0192] 7. The load capacitor (e.g., capacitors 382c, 382h) is almost discharged, V(SW_OUT)≈0

[0193] Some concluding comments will be provided below.

[0194] According to one embodiment of the invention, it is possible to connect capacitive loads in a well-controlled manner.

[0195] For example, a power switch for a capacitive load generates a defined voltage at its output that enables the inrush current to be limited to an allowable maximum value during the switching-on period.

[0196] According to embodiments of the present invention, it can be used in the context of active power filters for higher voltages or in combination with active power filters.

[0197] 100, 200: Power switch 110,210,282a,310,SW_IN: Input terminals 112,212,280b,312,SW_OUT: Output terminals 120: Switching transistor 120a: Load Path 120b, 220b, 320b: Source extreme sub-particles 120c: Inflow terminal 120d: Control terminal 130, 230, 330: Control capacitors 140, 240, 340: Switchable current source 220, 320: Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), switching transistor 220°C, 320°C: Absorbing extremes 220d, 320d: Control terminals, gate terminals 230a, 240a, 330a, 340a: First terminal 240B, 340B: Second terminal, current output terminal 240c: Fixed current source 240d, 282f: Switch 242: Control signal, control line 250: Floating voltage source, floating auxiliary power supply 250a, 350a, 351c: First output terminal 250b, 350b, 351d: Second output terminal 260: Bootstrap circuit, discharge circuit, cut-off circuit, bootstrap circuit system, discharge circuit system, cut-off circuit system 260a, 282g, 340e, 340f, 360a, D2: Diode 260b: Discharge transistor, PNP transistor 260c, 340d, 340h, 340i, 353, 360c, 390, R7: Resistors 270: Voltage source, power rail 272, I(C1) + I(C2): Charging current 280: Capacitive load, mixed load, load circuit system 282: Boost converter, DC / DC converter 282c: Input capacitor, load capacitor 282d: Inductor 282e: Internal Node 282h: Output capacitor, load capacitor 284a, 284b: Decoupling capacitors 286: Load Circuit System 300: Power switch, circuit 340c: Output transistor 340g: Transistor 344: Control voltage source, control signal source, control signal provider 350: Floating voltage source 351: Optical Coupler 351a: First input terminal 351b: Second Input Terminal 354, 370: Voltage source 355: Buffer capacitor 360: Discharge circuit, circuit cut-off 360b: Discharge transistor 380: Load, Boost Converter 382c: Input capacitor, capacitor C2 382h: Output capacitor, capacitor C1 410: Horizontal coordinate 412: First vertical coordinate 414: Second vertical coordinate 416: Third vertical coordinate 420: First Curve 422: Second Curve 424: Third Curve 426: Fourth Curve 428: The Fifth Curve 430: The Sixth Curve 432: The Seventh Curve 500: Methods 510: Steps C1, C2: Capacitors Boost converter (C), Input, Boost converter (C), Output: Load capacitor CSLP: Capacitor GND: Reference potential conductor, reference potential IB, IBS, IC, ISLP: Current I(R1): Current of the resistive load Icharging: Target charging current ICTRL: Preset Current RBS: Resistor t1, t2, t3, t4, t5, t6: Time V(CTRL), V(SW_IN), VSLP, VSW. Output: Voltage V(GATE): Gate voltage V(GATE,SW_OUT): Gate-Source Voltage V(SW_OUT): Voltage ramp, voltage VGS: Gate-Source Voltage

Claims

1. A power switch (100; 200; 300), wherein the power switch includes a switching transistor (120; 220; 320), wherein a load path of the switching transistor is coupled between an input terminal (110; 210; 310) and an output terminal (112; 212; 312) of the power switch, wherein a source terminal (120b; 220b; 320b) of the switching transistor is coupled to the output terminal (112; 212; 312) of the power switch, wherein the power switch includes a control capacitor (130; 230; 330), the control capacitor being coupled between a control terminal (120d; 220d; 320d) of the switching transistor (120; 220; 320) and a reference potential conductor (GND). The power switch includes a switchable current source (140; 240; 340) configured to charge the control capacitor (130; 230; 330) in an on state.

2. The power switch (100; 200; 300) of claim 1, wherein the switch transistor (120; 220; 320) is configured to operate as a source follower.

3. The power switch (100; 200; 300) of claim 1, wherein the switchable current source (140; 240; 340) is coupled between the input terminal (110; 210; 310) of the power switch and the control terminal (120d; 220d; 320d) of the switching transistor (120; 220; 320), and / or wherein the switchable current source (140; 240; 340) is coupled between the input terminal (110; 210; 310) of the power switch and the control capacitor (130; 230; 330).

4. The power switch (100; 200; 300) of claim 1, wherein the power switch includes a floating voltage source (250; 350); wherein the floating voltage source (250; 350) is coupled between the switchable current source (140; 240; 340) and the control terminal (120d; 220d; 320d) of the switching transistor (120; 220; 320), and / or wherein the floating voltage source (250; 350) is coupled between the switchable current source (140; 240; 340) and the control capacitor (130; 230; 330).

5. The power switch (100; 200; 300) of claim 1, wherein the power switch (100; 200; 300) includes a floating voltage source (250; 350); wherein the floating voltage source (250; 350) is coupled between one input terminal (110; 210; 310) of the power switch and the switchable current source (140; 240; 340).

6. The power switch (100; 200; 300) of claim 4, wherein the floating voltage source (250; 350) includes an optocoupler (352).

7. The power switch (100; 200; 300) of claim 6, wherein the floating voltage source (250; 350) includes a buffer capacitor (355) that is coupled in parallel to one output port of the optocoupler (351); wherein one capacitance of the buffer capacitor (355) is greater than one capacitance of the control capacitor (130; 230; 330), or wherein one capacitance of the buffer capacitor (355) is at least twice as large as one capacitance of the control capacitor (130; 230; 330).

8. The power switch (100; 200; 300) of claim 6, wherein the power switch or a control circuit system coupled to the power switch is configured to activate the optocoupler (351) before the switchable current source (140; 240; 340) is turned on.

9. The power switch (100; 200; 300) of claim 5, wherein the output voltage of one of the floating voltage sources (250; 350) is greater than or equal to 1.5 times the threshold voltage of one of the switching transistors (120; 220; 320); and / or wherein the output voltage of one of the floating voltage sources (250; 350) is greater than or equal to 6 V.

10. The power switch (100; 200; 300) of claim 5, wherein one of the output currents of the optocoupler (351) is less than one of the currents provided by the switchable current source (140; 240; 340).

11. The power switch (100; 200; 300) of claim 1, wherein the switch transistor (120; 220; 320) is a field-effect transistor.

12. The power switch (100; 200; 300) of claim 1, wherein the power switch includes a disconnecting circuit (260; 360) configured to at least partially discharge the control capacitor (130; 230; 330).

13. The power switch (100; 200; 300) of claim 12, wherein the disconnecting circuit (260; 360) is configured to be deactivated by a current supplied by the switchable current source (140; 240; 340) that charges the control capacitor (130; 230; 330), and wherein the disconnecting circuit (260; 360) is configured to be activated, in the event that the switchable current source (140; 240; 340) is disconnected, to at least partially discharge the control capacitor.

14. The power switch (100; 200; 300) of claim 1, wherein a first terminal (130a; 230a; 330a) of the control capacitor (130; 230; 330) is connected to a control terminal (120d; 220d; 320d) of the switching transistor (120; 220; 320), wherein a second terminal of the control capacitor (130; 230; 330) is connected to the reference potential conductor (GND), wherein a first output terminal (250a; 350a) of the floating voltage source (250; 350) is coupled to the first terminal (130a; 230a; 330a) of the control capacitor (130; 230; 330) via a diode (260a; 360a); One of the second output terminals (250b; 350b) of the floating voltage source (250; 350) is coupled to one of the current output terminals (240b; 340b) of the switchable current source (140; 240; 340); a buffer capacitor (355) is coupled between the first output terminal (250a; 350a) and the second output terminal (250b; 350b) of the floating voltage source (250; 350); and one of the source terminals of a discharge transistor (260b; 360b) is coupled to the first terminal (130a; 230a; 330a) of the control capacitor (130; 230; 330). One of the inflow terminals of the discharge transistor (260b; 360b) is coupled to the output terminal (112; 212; 312) of the power switch and / or to the source terminal (120b; 220b; 320b) of the switching transistor; one of the control terminals of the discharge transistor (260b; 360b) is coupled to the first output terminal (250a; 350a) of the floating voltage source; and a resistor (260c; 360c) is coupled between the control terminal of the discharge transistor (260b; 360b) and the inflow terminal of the discharge transistor (260b; 360b).

15. A method (500) for operating a power switch (100; 200; 300), the power switch comprising a switching transistor (120; 220; 320), wherein a load path of the switching transistor is coupled between an input terminal (110; 210; 310) and an output terminal (112; 212; 312) of the power switch, wherein a source terminal (120b; 220b; 320b) of the switching transistor (120; 220; 320) is coupled to the output terminal (112; 212; 312) of the power switch, and wherein the power switch comprises a control capacitor (130; 230; 330) coupled between a control terminal (120d; 220d; 320d) of the switching transistor and a reference potential conductor (GND). The method includes charging (510) the control capacitor (130; 230; 330) with a current source (140; 240; 340) to obtain a slope of voltage at one output terminal (112; 212; 312) of the power switch for at least one on-off operation of the voltage at that output terminal of the power switch within a range of 10% to 90% of a maximum voltage, the slope being substantially linear with time.

Images