Short-circuit protection for a circuit breaker

Abstract

A power supply circuit (100, 120, 300) configured to provide a current at an output voltage (321) for a load (106) at an output of the power supply circuit (100, 120, 300), the power supply circuit (100, 120, 300) comprising: -a power transistor (201, 301, 451) designed to draw the current from a supply voltage (322), wherein a resistance of the power transistor (201, 301, 451) is controlled by means of a control voltage (325) applied to a control terminal of the power transistor (201, 301, 451); and - a short-circuit protection circuit (400) designed to couple the control terminal of the power transistor (201, 301, 451) to a first terminal of the power transistor (201, 301, 451) in order to put the power transistor (201, 301, 451) into an off state when the output voltage (321) drops; wherein the short-circuit protection circuit (400) comprises a short-circuit control transistor (403) having a first terminal and a second terminal configured to couple the control terminal and the first terminal of the power transistor (301); wherein a state of the short-circuit control transistor (403) is controlled via a control terminal of the short-circuit control transistor (403); wherein a voltage level at the control terminal of the short-circuit control transistor (403) depends on the output voltage (321); wherein the short-circuit protection circuit (400) further comprises: - a control terminal amplifier (421) designed to amplify a voltage derived from the output voltage (321) before being applied to the control terminal of the short-circuit control transistor (403) and thus increase the response speed of the short-circuit protection circuit (400); and - a filter current source (432) coupled between the control terminal and the first terminal of the short-circuit control transistor (403) and configured to provide a predetermined current intensity.

Description

Technical area

[0001] This document relates to the protection of a circuit breaker, for example the pass-through device of a voltage regulator, in the event of a short circuit at an output terminal of the circuit breaker. background

[0002] An electronic circuit that supplies electrical power to a load, for example, a voltage regulator such as a low minimum voltage difference (LDO) regulator, may include a bypass switch to provide a direct connection to the supply voltage VDD of the electronic circuit. Such a direct connection may be advantageous for increasing the response speed of the electronic circuit during a load transient. The bypass switch may be in a situation where, due to external conditions or due to non-linear conditions such as a bypass mode, a regulating device of the electronic circuit (e.g., an intermediate gain stage) is fully opened to attempt to regulate the output voltage of the electronic circuit.Therefore, the bypass switch can be in a state of maximum current carrying capacity, also known as the state of least resistance, regardless of the actual load situation of the electronic circuit.

[0003] If an external event causes a "short circuit," which represents a low-resistance, low-inductance connection to another node, while the bypass switch is in a state of least resistance, a situation may arise in which a significant current is drawn directly from the electronic circuit's supply voltage VDD. It is desirable to limit or interrupt such a short-circuit current through the bypass switch, as the bypass switch and / or a power supply providing the supply voltage can be damaged by significant short-circuit currents.

[0004] US 6 781 502 B1 describes electronics and in particular methods for manufacturing semiconductor components and structures.

[0005] US 5 537 064 A describes protection circuits for power transistors and in particular protection circuits for deactivating a transistor having an inductive component in the event of a short circuit at the output of the transistor.

[0006] US 7 158 359 B2 describes a circuit arrangement with a semiconductor switch and a protective circuit, in particular a protective circuit for protecting the semiconductor switch in the event of a short circuit on the load side.

[0007] This document addresses the technical problem of providing efficient and reliable means for reducing the current through a power switch or power transistor in a short-circuit situation. Summary

[0008] According to one aspect, a power supply circuit is described that is configured to supply a current at an output voltage to a load at an output of the power supply circuit. The power supply circuit may be or include a bypass circuit, for example, a bypass circuit for a voltage regulator. Alternatively or additionally, the power supply circuit may include or be a voltage regulator (e.g., an LDO regulator).

[0009] The power supply circuit comprises a power transistor (which may also be referred to as a power switch, bypass transistor, or bypass switch) configured to source the current for the load from a supply voltage. The power transistor may comprise a bipolar junction transistor (BJT), an insulated-gate bipolar transistor (IGBT), and / or a metal-oxide-semiconductor transistor (MOS transistor). In general, the power transistor may comprise any type of electrically controllable switch. A resistor (e.g., a drain-source resistor in the case of a MOS transistor) of the power transistor is controlled by a control voltage (e.g., a gate voltage in the case of a MOS transistor) applied to a control terminal (e.g., a gate in the case of a MOS transistor) of the power transistor.By varying the resistance, the current through the power transistor can be controlled, i.e. the current through the power transistor, which is obtained from the supply voltage, can be controlled via the control voltage.

[0010] The power transistor may comprise a p-type metal-oxide-semiconductor (PMOS) transistor. The source of the power transistor may be (directly) coupled to the supply voltage, and the drain of the power transistor may be (directly) coupled to the output of the power delivery circuit. More generally, the source may be referred to as a first terminal and the drain as a second terminal. Thus, the first terminal of the power transistor may be (directly) coupled to the supply voltage, and the second terminal of the power transistor may be (directly) coupled to the output of the power delivery circuit. Therefore, the current through the power transistor may be derived directly from the supply voltage and delivered directly to the load.

[0011] The power supply circuit further comprises a short-circuit protection circuit configured to couple the control terminal of the power transistor to the first terminal of the power transistor in order to put the power transistor into an off state when the output voltage drops. The short-circuit protection circuit comprises a short-circuit control transistor having a second terminal (e.g., a drain) and a first terminal (e.g., a source) configured to couple the control terminal (e.g., the gate) and the first terminal (e.g., the source) of the power transistor to one another. In particular, the short-circuit control transistor may be configured to provide a direct connection between the control terminal and the first terminal of the power transistor via a conduction channel (e.g.,via the drain-source channel) of the short-circuit control transistor (without any further intermediate components). A state and / or the resistance (in particular the drain-source resistance) of the short-circuit control transistor can be controlled via the control terminal (e.g., the gate) of the short-circuit control transistor, and a voltage level at the control terminal (e.g., the gate) of the short-circuit control transistor can depend (e.g., only) on the output voltage. In particular, the voltage level at the control terminal (e.g., the gate) of the short-circuit control transistor can be independent of a current limit of the current-limiting control circuit of the power supply circuit and / or of a reference voltage, which can be used to determine a level of the output voltage of the power supply circuit.

[0012] Similar to the power transistor, the short-circuit control transistor may comprise or be a p-type metal-oxide-semiconductor transistor. The drain of the short-circuit control transistor may be (directly) coupled to the gate of the power transistor, and the source of the short-circuit control transistor may be (directly) coupled to the source of the power transistor. More generally, the second terminal of the short-circuit control transistor may be (directly) coupled to the control terminal of the power transistor, and the first terminal of the short-circuit control transistor may be (directly) coupled to the first gate of the power transistor.

[0013] By utilizing the short-circuit protection circuit, which is designed to provide a short circuit between the control terminal and the first terminal of the power transistor directly in response to a drop in the output voltage, the current through the power transistor can be quickly interrupted in response to a "short-circuit" condition at the output of the power supply circuit. Therefore, efficient, reliable, and fast means for reducing the current through a power transistor in a short-circuit situation are provided.

[0014] The short-circuit protection circuit (in particular, the short-circuit control transistor) can be designed to couple the control terminal of the power transistor to the first terminal of the power transistor only when a "short-circuit" condition is met. Otherwise, the short-circuit protection circuit (in particular, the short-circuit control transistor) cannot couple the control terminal to the first terminal of the power transistor. Therefore, the short-circuit protection circuit can be inactive during normal operation of the power supply circuit and can only be used when a "short-circuit" condition is met. In this way, the short-circuit protection circuit can be added to the power supply circuit without affecting the other components of the power supply circuit (e.g.,a control loop of the current limiting circuit and / or a control loop of a voltage regulator) during normal operation of the power supply circuit.

[0015] The "short-circuit" condition can be met when a slope of a drop in the output voltage exceeds a predetermined slope threshold and / or when a height of the drop in the output voltage exceeds a predetermined height threshold. The short-circuit protection circuit (in particular the short-circuit control transistor) can be designed in accordance with the slope threshold and / or the height threshold. In particular, a threshold voltage of the short-circuit control transistor can be selected depending on the slope threshold and / or the height threshold. Alternatively or additionally, a drive circuit of the short-circuit control transistor (which is designed to derive the voltage level at the gate of the short-circuit control transistor based on the output voltage) can be dependent on the slope threshold and / or the height threshold.In this way, it can be ensured that the short-circuit control transistor is only activated when the "short-circuit" condition is met and that the short-circuit control transistor remains open when the "short-circuit" condition is not met (e.g. because the slope and / or the height of the drop of the output voltage is not sufficiently high).

[0016] The short-circuit protection circuit (in particular, the drive circuit for the short-circuit control transistor) may comprise high-pass filter means configured to derive the voltage level at the control terminal (e.g., the gate) of the short-circuit control transistor by high-pass filtering the output voltage. The high-pass filter means may be configured to depend on the slope threshold. In particular, the high-pass filter means may be configured to modify the voltage level at the control terminal (e.g., the gate) of the short-circuit control transistor such that the short-circuit control transistor only transitions from an off state to an on state when the "short-circuit" condition is met.In other words, the high-pass filter means can be configured to provide a voltage level at the control terminal of the short-circuit control transistor such that the threshold voltage of the short-circuit control transistor is exceeded when the short-circuit condition is met. Furthermore, the high-pass filter means can be configured to otherwise provide a voltage level at the control terminal of the short-circuit control transistor such that the threshold voltage of the short-circuit control transistor is not exceeded (to ensure that the short-circuit control transistor remains open when the "short-circuit" condition is not met).

[0017] The short-circuit protection circuit (in particular the drive circuit of the short-circuit control transistor and even more specifically the high-pass filter means) may comprise a filter resistor that is (directly) coupled between the control terminal and the first terminal of the short-circuit control transistor. Furthermore, the short-circuit protection circuit (in particular the drive circuit of the short-circuit control transistor and even more specifically the high-pass filter means) may comprise a filter capacitor that is (directly) coupled to the control terminal of the short-circuit control transistor on one side and to the output of the power supply circuit on another side of the filter capacitor. The filter resistor and the filter capacitor may form an RC circuit with a time constant. The time constant may depend on the slope threshold and / or the height threshold.Such an RC circuit provides efficient means for controlling the short-circuit control transistor so that the short-circuit control transistor is only activated when the "short-circuit" condition is met.

[0018] The short-circuit protection circuit (in particular, the drive circuit of the short-circuit control transistor and more particularly, the high-pass filter means) may comprise an amplifier and / or an attenuation element configured to amplify and / or attenuate a voltage derived from the output voltage, i.e., a voltage at the output of the high-pass filter means, prior to applying the attenuated / amplified voltage to the gate of the short-circuit control transistor. In particular, the voltage at a midpoint between the filter resistor and the filter capacitor may be amplified by the amplifier or attenuated by the attenuation element, respectively. The output of the amplifier or attenuation element may be (directly) coupled to the control terminal of the short-circuit control transistor. The gain of the amplifier or attenuation element may depend on the threshold voltage of the short-circuit control transistor and / or the amplitude threshold.Therefore, the amplifier or attenuator used to tune the short-circuit protection circuit can only be activated when the "short circuit" condition is met.

[0019] The power supply circuit may further comprise a current limiting circuit configured to limit the current through the power transistor in accordance with a predetermined current limit. The current limiting circuit may comprise sensing means configured to provide an indication of the current through the power transistor. Furthermore, the current limiting circuit may comprise comparison means configured to provide a feedback voltage by comparing the indication of the load current with the predetermined current limit. In addition, the current limiting circuit may comprise feedback means configured to set the control voltage (e.g., the gate voltage) at the control terminal of the power transistor depending on the feedback voltage.

[0020] Therefore, the current-limiting circuit can be used to limit the current through the power transistor, thereby protecting the power transistor and the supply voltage (during normal operation of the power supply circuit). However, the short-circuit protection circuit can be configured to couple the control terminal to the first terminal of the power transistor during a first response period upon a drop in the output voltage, and the current-limiting circuit can be configured to limit the current through the power transistor during a second response period upon a drop in the output voltage in accordance with the predetermined current limit. The first response period can be shorter than the second response period.The relatively short response time of the short-circuit protection circuit can be achieved by directly coupling the control terminal and the first terminal of the power transistor via the short-circuit control transistor. On the other hand, the current limiting circuit typically includes a feedback loop that allows the current limit to be set and / or regulated. Such a feedback loop can be relatively slow compared to the direct coupling of the control terminal and the first terminal of the power transistor, which is achieved by the short-circuit control transistor.

[0021] Therefore, the power supply circuit may comprise a combination of a relatively slow and precise current limiting circuit (for setting a current limit during "normal" operation of the power supply circuit, i.e., in cases where the "short-circuit" condition is not met) and a short-circuit protection circuit (for interrupting the current through the power transistor in short-circuit situations, i.e., in cases where the "short-circuit" condition is met).

[0022] The detection means of the current limiting circuit may comprise a sensing transistor having a control terminal (e.g., a gate) coupled (directly) to the control terminal of the power transistor, a first terminal (e.g., a source) coupled (directly) to the first terminal of the power transistor, and a second terminal (e.g., a drain) coupled to the second terminal (e.g., the drain) of the power transistor via a current mirror. Furthermore, the feedback means may comprise a feedback transistor having a control terminal (e.g., a gate) to which the feedback voltage is applied, wherein the control voltage depends on a resistance (e.g., a drain-source resistance) of the feedback transistor. Furthermore, the comparison means may comprise a current mirror configured to compare a current intensity through the sensing transistor to the control terminal (e.g.,the gate) of the feedback transistor, and a current source configured to supply a current to the control terminal (e.g., the gate) of the feedback transistor that is in accordance with the current limit.

[0023] As stated above, the power supply circuit may include or be a voltage regulator configured to regulate the output voltage in accordance with a reference voltage. The voltage regulator may include voltage sensing means configured to provide an indication of the output voltage and a differential gain stage configured to provide an input voltage based on the reference voltage and based on the indication of the output voltage at the output node. The control voltage applied to the control terminal of the power transistor may depend on the input voltage (for example, via an intermediate stage or the second gain stage of the voltage regulator).

[0024] In principle, the control of the power transistor can be embedded in the regulation of a voltage regulator. Within the scope of such regulation, the power transistor may be set to a relatively low resistance, in particular a drain-source resistance (e.g., in the case of a transient load at the output of the power supply circuit). The short-circuit protection circuit described in this document is particularly advantageous for protecting the power transistor and / or the supply voltage if a short-circuit situation occurs when the power supply circuit is operated in such a situation.

[0025] The voltage regulator may include a pass device configured to supply a current to the load. The pass device may be arranged in parallel with the power transistor between the supply voltage and the output of the power supply circuit. Therefore, the power transistor may assist the pass device in providing additional current to the output of the power supply circuit during load transients.

[0026] According to a further aspect, a method for protecting a power transistor in the event of a short-circuit situation is described. The method comprises drawing current for a load from a supply voltage via a power transistor, wherein a resistance (e.g., a drain-source resistance) of the power transistor is controlled by a control voltage (e.g., a gate voltage) applied to a control terminal (e.g., a gate) of the power transistor, and wherein the current is delivered to the load at an output voltage. Furthermore, upon a drop in the output voltage, the method comprises coupling the control terminal of the power transistor to a first terminal (e.g., a source) of the power transistor to place the power transistor in an off state.

[0027] It should be noted that the methods and systems, including their preferred embodiments, as described in this document can be used alone or in combination with other methods and systems disclosed in this document. Furthermore, the features presented in connection with a system can also be applied to a corresponding method. Furthermore, all aspects of the methods and systems presented in this document can be combined in any desired manner. In particular, the features of the patent claims can be combined with one another in any desired manner.

[0028] In this document, the term "couple" or "coupled" refers to elements that are in electrical connection with each other, whether connected directly, for example by wires, or by other means. Short description of the drawings

[0029] The invention is explained below by way of example with reference to the accompanying drawings, in which Fig. 1a illustrates an exemplary block diagram of an LDO regulator; Fig. 1b illustrates the exemplary block diagram of an LDO regulator in more detail; Fig. 2 shows a circuit diagram of an exemplary bypass switch with a current limiting circuit; Fig. 3a, Fig. 3b and Fig. 3c shows circuit diagrams of an exemplary short-circuit protection circuit; Fig. 4a and Fig. 4b shows circuit diagrams of an exemplary short-circuit protection circuit for a bipolar transistor; and Fig. 5 shows a flowchart of an exemplary method for protecting a circuit breaker during a short circuit. Detailed description

[0030] As stated above, electronic power supply circuits such as voltage regulators may include one or more bypass switches designed to couple an output of the power supply circuit directly to a supply voltage of the power supply circuit. This may be advantageous for increasing the response speed of the power supply circuit, which is subject to load transients at the output of the power supply circuit. An example of a power supply circuit is an LDO regulator. A typical LDO regulator 100 is shown in Fig. 1a. The LDO regulator 100 comprises an output amplifier stage 103, for example, a field-effect transistor (FET), at the output and a differential amplifier stage or differential amplifier 101 (also referred to as an error amplifier) ​​at the input. A first input (fb) 107 of the differential amplifier 101 receives a fraction of the output voltage Vout , which is determined by the voltage divider 104, which includes the resistors R0 and R1. At the second input (ref) to the differential amplifier 101, a stable reference voltage V ref 108 (also called the bandgap reference). When the output voltage V out with respect to the reference voltage V ref changes, the drive voltage at the output amplifier stage, e.g., the power FET, changes through a feedback mechanism called the main feedback loop to maintain a constant output voltage V out to maintain.

[0031] The LDO regulator 100 from Fig. 1a further includes an additional intermediate amplification stage 102 configured to amplify the output voltage of the differential amplification stage 101. As such, an intermediate amplification stage 102 can be used to provide additional gain in the amplification path. Furthermore, the intermediate amplification stage 102 can provide phase inversion.

[0032] In addition, the LDO regulator 100 can have an output capacitance C out (also referred to as output capacitor or stabilizing capacitor or bypass capacitor) 105, which is connected in parallel with the load 106. The output capacitor 105 is used to stabilize the output voltage V out , which is subject to a change in the load 106 and in particular to a change in the load current I load It should be noted that the output current I out at the output of the output amplification stage 103 of the load current Iload through the load 106 of the regulator 100 (apart from typically smaller currents through the voltage divider 104 and the output capacitance 105). Consequently, the terms output current I out and load current I load used synonymously unless otherwise stated.

[0033] Typically, it is desirable to have a stable output voltage V out even when (positive or negative) load transitions 106 occur. For example, the regulator 100 can be used to provide a stable output voltage V out to the processor of an electronic device (such as a smartphone). The load current I load can vary significantly between a sleep and an active state of the processor, causing the load 106 of the regulator 100 to vary. To ensure reliable operation of the processor, the output voltage V outremain stable even in response to such load transitions. In particular, overvoltage and / or undervoltage situations for the output voltage V out to avoid.

[0034] At the same time, the LDO regulator 100 should be able to respond quickly to load transients, ie the LDO regulator 100 should be able to quickly supply the requested load current I load to deliver a voltage that is subject to load transients. This means that the LDO regulator 100 should have a high bandwidth.

[0035] Fig. Figure 1b shows the block diagram of an LDO regulator 120, with the output gain stage A3 (reference numeral 103) shown in more detail. In particular, the pass transistor or pass device 201 and the drive stage 110 of the output gain stage 103 are shown. Typical parameters of an LDO regulator are a supply voltage of 3 V, an output voltage of 2 V, and an output current or load current of 1 mA to 100 or 200 mA. Other configurations are possible. The present invention is described with respect to a linear regulator. However, it should be noted that the present invention is applicable to power supply circuits in general.

[0036] As indicated above, a bypass circuit may be provided in conjunction with a voltage regulator 100, 120 to increase the response speed of the voltage regulator 100, 120 subject to a load transient. An exemplary bypass circuit 300 is shown in Fig. 2. The bypass circuit can be considered as an example of a generic power supply circuit. The bypass circuit 300 includes a power transistor 301 (also referred to herein as a bypass transistor) which is used to couple the output voltage V out 321 with the supply voltage VDD 322 (in Fig. 1b also referred to as Vin). As such, the power transistor 301 can be arranged in parallel with the pass device 201 of the voltage regulator 100, 120. In another exemplary arrangement, the power transistor 301 corresponds (e.g., is equal to) the pass device 201 of the voltage regulator 100, 120. In the example shown in Fig. 2, the power transistor 301 is a PMOS transistor.

[0037] The power transistor 301 can be controlled by the gate voltage 325 applied to the gate of the power transistor 301. The gate voltage 325 is set using the input control transistor 311, wherein a state of the input control transistor 311 depends on the activation voltage 323 applied to the gate of the input control transistor 311. The activation voltage 323 can be the output voltage of the second amplification stage 102 (i.e., out_s2) of the voltage regulator 100, 120 included in Fig. 1a, Fig. 1b. In the example shown, the input control transistor 311 is an NMOS transistor.

[0038] When the input control transistor 311 is activated by the activation voltage 323, the gate voltage 325 is pulled low, activating the power transistor 301. A level of the gate voltage 325 can be adjusted by a resistance value of the gate resistor 312. As such, the power transistor 301 can be opened depending on the level of the activation voltage 323, supplying a current to the output node of the bypass circuit 300 and thereby stabilizing the output voltage 321.

[0039] The bypass circuit 300 of Fig. 2 further includes a current-limiting circuit configured to limit the current through power transistor 301. The current-limiting circuit includes a sensing transistor 304 configured to detect a state of power transistor 301. Sense transistor 304 may be similar to power transistor 301, but with reduced dimensions. In particular, sensing transistor 304 may be configured to provide an indication of the current through the power switch. In other words, the current through sensing transistor 304 may be similar (e.g., equal) to the current through power transistor 301 up to a predetermined scaling factor, where the scaling factor depends on the dimensions of sensing transistor 304 relative to the dimensions of power transistor 301.

[0040] The current limiting circuit may further include a first current mirror comprising transistors 302, 305. The current mirror is coupled to the drain of power transistor 301 (which corresponds to the output node of bypass circuit 300) and to the drain of sense transistor 304. In this way, the output voltage 321 can be "copied" from the drain of power transistor 301 to the drain of sense transistor 304, thereby setting sense transistor 304 to the same operating point as power transistor 301. The current through sense transistor 304 (also referred to as sense current) indicates the current through power transistor 301 (e.g., is proportional to the current through power transistor 301).

[0041] The sensor current may be compared with a predetermined current limit set by a first current source 308. For this purpose, a second current mirror comprising transistors 306, 307 may be used, as shown in Fig. 2. The second current mirror "copies" the sense current from transistor 306 to transistor 307 (possibly in an amplifying or attenuating manner). A drain of transistor 307 is coupled to the first current source 308 so that the sense current is compared to the current limit. The drain of transistor 307 is coupled to the gate of a feedback transistor 310, which in the illustrated example is implemented as an NMOS transistor. If the current limit is higher than the (amplified / attenuated) sense current, then the gate of feedback transistor 310 is pulled high, thereby opening feedback transistor 310 and allowing power transistor 301 to be controlled by enable voltage 323.On the other hand, if the current limit is less than the (amplified / attenuated) sense current, the gate of feedback transistor 310 is pulled low, closing feedback transistor 310 and interrupting the current flowing through enable transistor 311 (regardless of the level of enable voltage 323). As a result, gate voltage 325 is pulled high, closing power transistor 301 and reducing the current through power transistor 301.

[0042] As such, the current limiting circuit provides a control loop to ensure that the current through the power transistor 301 does not exceed a level set using the current limit provided by the first current source 308.

[0043] The current limiting circuit may further include a gate capacitor 309 that couples the gate of feedback transistor 310 to ground 324. Such a gate capacitor 309 may be used to ensure safe shutdown of the current limit in the event of a situation where the current through power transistor 301 does not exceed the current limit. Furthermore, a second current source 303 may be used to balance the drain-source voltage across transistor 306 to ensure precise alignment of the operating points of power transistor 301 and sense transistor 304.

[0044] Due to the design of the current-limiting circuit, and in order to keep power consumption relatively low, the activation time of the current-limiting circuit can be relatively long before the current through power transistor 301 is limited. This can lead to a situation, particularly in the case of a short circuit, in which the current through power transistor 301 becomes very high, thereby overloading supply voltage 322. Due to the low-impedance nature of a short circuit, the propagation and speed of the peak current through power transistor 301 undergoing a short circuit can be highly variable.

[0045] Fig. 3a illustrates an exemplary short-circuit protection circuit 400 that can be used to protect the supply voltage 322 and the power transistor 301 from a short-circuit situation. The short-circuit protection circuit 400 is preferably used in conjunction with a current limiting circuit (such as the one shown in Fig. 2). The short-circuit protection circuit includes a short-circuit control transistor 403 configured to couple the gate of power transistor 301 to supply voltage 322 to close power transistor 301. In the example shown, short-circuit control transistor 403 is implemented as a PMOS transistor.

[0046] The short-circuit control transistor 403 is controlled based on the output voltage 321. As a result of a short circuit (simulated by switch 410), the output voltage 321 typically exhibits a significant drop, resulting in a drop in the voltage at the gate of the short-circuit control transistor 403, thereby opening the short-circuit control transistor 403 and coupling the gate of the power transistor 301 to the supply voltage 322. This causes the power transistor 301 to close, thereby reducing the current drawn from the supply voltage 322.

[0047] The short-circuit protection circuit may further comprise means for filtering the output voltage 321 (also referred to herein as high-pass filter means). In particular, the filtering means may be designed as a high-pass filter, so that only relatively fast fluctuations (such as a drop caused by a short circuit) are passed through to the gate of the short-circuit control transistor 403, and so that relatively slow fluctuations of the output voltage 321 are not passed through to the gate of the short-circuit control transistor 403. As a result, the gate of the short-circuit control transistor 403 may be floating (in the absence of a significant drop in the output voltage 321), so that the short-circuit control transistor 403 remains open, whereby the gate of the power transistor 301 is not coupled from the drain of the power transistor 301.

[0048] The means for filtering the output voltage 321 may comprise an RC circuit 401, 402 as shown in Fig. 3a, wherein the RC circuit 401, 402 comprises a filter resistor 402 and a filter capacitor 401. The filter resistor 402 is arranged between the gate and source of the short-circuit control transistor 403, and the filter capacitor 401 is used to couple the gate of the short-circuit control transistor 403 to the output voltage 321. As a result, a fast transition of the output voltage 321 is directly coupled to the gate of the short-circuit control transistor 403. In particular, a drop in the output voltage 321 directly affects the voltage at the gate of the short-circuit control transistor 403, thereby closing the short-circuit control transistor 403. On the other hand, relatively slow changes in the output voltage 321 are filtered by the filter capacitor 401 and the filter resistor 402, so that the state of the short-circuit control transistor 403 remains unaffected (i.e., open) by such slow fluctuations.

[0049] The RC circuit 401, 402 has the additional effect that the voltage at the gate of the short-circuit control transistor 403 increases again with an increasing time period from the drop in the output voltage 321. In particular, the gate of the short-circuit control transistor 403 returns to a potential-free state, thereby reopening the short-circuit control transistor 403, which in turn reopens the power transistor 301. The length of the time period between the closing of the short-circuit control transistor 403 and the reopening of the short-circuit control transistor 403 depends on the time constant τ = RC of the RC circuit 401, 402, where R is the resistance of the filter resistor 402 and C is the capacitance of the filter capacitor 401. The time constant τ can be chosen sufficiently large to allow the current-limiting circuit to react to the short-circuit situation.In other words, the short-circuit protection circuit 400 may be configured to automatically deactivate after a predetermined period of time from a short circuit, thereby bridging a reaction time of the current limiting circuit of the power supply circuit 300.

[0050] Therefore, instead of waiting for the current limiting control of the current limiting circuit to become active, this process is abbreviated by switching power transistor 301 from a conduction mode to an off mode. As a result, the current drawn from supply voltage 322 is stopped.

[0051] To enable stable current control of the current-limiting circuit, the frequency response of the current-limiting circuit typically must be limited, which creates a delay in the current-limiting circuit's response to a short circuit. Furthermore, due to the low-power nature of the current-limiting circuit, the current-limiting circuit's limiting response may require a certain amount of time until the power transistor 301 is turned off. During this time, a significant current flows through the power transistor 301, with the current limited only by a very small on-resistance (i.e., drain-source resistance) of the power transistor 301.

[0052] The short-circuit protection circuit 400 is configured to monitor the output voltage 321. When a rapid drop in the output voltage 321 is detected (with a relatively large slope with a magnitude greater than a slope threshold), the short-circuit control transistor 403 is activated to quickly discharge the gate of the power transistor 301, stopping any current through the power transistor 301.

[0053] The current limiting circuit then reactivates the power transistor 301, originating from an off state of the power transistor 301 (and not from an overdriven on state of the power transistor 301). This ensures stable activation of the current limiting circuit's control mode.

[0054] As already mentioned above, the current limiting circuit of Fig. 2 a certain period of time before limiting the current through the power transistor 301. As a result, a relatively high current can be drawn from the voltage supply 322 before the current limit is activated. This leads to a situation in which a compromise must be found between a low switching resistance of the power transistor 301, a limited short-circuit current, and a low internal power consumption of the current limiting circuit.

[0055] To address this technical problem, an RC element 401, 402 connected to the output voltage 321 can be used to detect a rapid drop in the output voltage 312, indicating a "short circuit" condition. Such a "short circuit" condition can be distinguished from a "load transient" condition by the magnitude of the drop in the output voltage 321. Typically, the magnitude of the voltage drop in the case of a "short circuit" condition is higher than the magnitude of the voltage drop in the case of a "load transient" condition.

[0056] The magnitude of the voltage drop of a "short circuit" condition may correspond to the threshold voltage of the short circuit control transistor 403. As such, the threshold voltage of the short circuit control transistor 403 may be set such that the short circuit control transistor 403 is closed only when the magnitude of the voltage drop is sufficiently high to indicate a "short circuit" condition (as opposed to a "load transition" condition). As in Fig. As shown in Figure 3b, an amplifier 421 can be used to adjust the appropriate voltage drop to the threshold voltage of the short-circuit control transistor 403. Alternatively or additionally, a differential input stage can be used to activate the short-circuit control transistor 403 when the voltage drop of the output voltage 321 is lower than the threshold voltage of the short-circuit control transistor 403. However, this may increase the power consumption required to ensure fast operation of the short-circuit protection circuit 400.

[0057] Fig. Figure 3b shows an exemplary short-circuit protection circuit 400 that includes a gate voltage amplifier 421. The gate voltage amplifier 421 can be used to adjust the response speed of the short-circuit protection circuit 400 by amplifying the voltage at the midpoint between the filter capacitor 401 and the filter resistor 402 and applying the amplified voltage to the gate of the short-circuit control transistor 403. As such, an amplifier 421 can be used to maximally short-circuit the gate of the power transistor 301. Stopping the current flow from the voltage supply 322 typically increases the slope of the discharge. This forms a positive feedback loop until the output is discharged and the slope becomes zero.

[0058] While the short-circuit protection circuit 400 is activated, in particular while the short-circuit control transistor 403 couples the gate to the source of the power transistor 301, other circuits (e.g., current limiters) of the power delivery circuit 300 may be temporarily turned off to avoid adverse effects of the gate short-circuit either through function and / or capacitive coupling effects.

[0059] The short-circuit protection circuit 400 uses only the drop in the output voltage 321 as an indication of a "short circuit" condition. The drop in the output voltage 321 typically requires some current flow through the power transistor 301. The level of current through the power transistor 301 typically depends on the resistance of the power transistor 301. Therefore, the resistance of the power transistor 301 can influence the distinction between a "short circuit" condition and a "load transient" condition.

[0060] Typically, the peak current through the power transistor 301 increases with the delay in detecting the "short circuit" condition and in activating the short circuit protection circuit 400.

[0061] Fig. 3c shows an exemplary short-circuit protection circuit 400 that includes a current source 432, referred to herein as the filter current source 432. In the illustrated example, the filter current source 432 replaces the filter resistor 402. The filter current source 432 can be used to detect the slope of a drop in the output voltage 321. In particular, the filter current source 432 can be configured to provide a predetermined current level, wherein the predetermined current level allows the short-circuit protection circuit 400 to be adjusted such that the short-circuit control transistor 403 is closed when the slope of a drop in the output voltage 321 indicates a "short circuit" condition, and that the short-circuit control transistor 403 is left open when the slope of a drop in the output voltage 321 indicates a "load transient" condition.Therefore, the predetermined current provided by the filter current source 432 may depend on the slope threshold.

[0062] It can be demonstrated experimentally how the load current at the output of the current supply circuit 300 increases in response to a short circuit. As a result, the output voltage 321 drops. The drop in the output voltage 321 causes the short-circuit control transistor 403 to turn off the power transistor 301. This is achieved by pulling up the gate voltage 325 at the gate of the power transistor 301. After a period of time (which depends on the time constant of the RC circuit 401, 402), the short-circuit control transistor 403 is opened again, thus releasing the gate of the power transistor 301. As a result, the relatively slower current regulation starts and regulates the output current of the power transistor 301 to the setpoint specified by the current limit set by the first current source 308 (if such regulation is possible due to external conditions).A return to normal operation is possible as soon as the short circuit condition has been eliminated.

[0063] Therefore, it can be observed that the current increase through the power transistor 301 subject to a short circuit can be limited by the short-circuit protection circuit 400 described in this document. A change in the slope of the output voltage 321 can be observed during the activation of the short-circuit protection circuit 400. Such a change in the slope indicates that the current increase from the supply voltage 322 has been stopped within the transition of the slope of the output voltage 321.

[0064] It should be noted that the short-circuit protection circuit 400 can also be applied to a bipolar junction transistor (BJT) and / or an insulated-gate bipolar transistor (IGBT). Furthermore, one or more of the transistors of the short-circuit protection circuit 400 can comprise or be implemented as bipolar junction transistors (BJT) and / or insulated-gate bipolar transistors (IGBT). Fig. 4a and Fig. 4b shows a short-circuit protection circuit 400 in conjunction with a bipolar junction transistor 451. The bipolar transistor 451 is coupled to the short-circuit protection circuit 400 in a manner analogous to the power transistor (MOSFET) 301, wherein the gate of the power transistor 301 corresponds to the base of the BJT 451, the source of the power transistor 301 corresponds to the emitter of the BJT 451, and the drain of the power transistor 301 corresponds to the collector of the BJT 451. In this description, the MOS transistor 301 and the BJT 451 are referred to as power transistors. Furthermore, the gate or base is referred to as a control terminal, the source or emitter is referred to as a first terminal, and the drain or collector is referred to as a second terminal. Furthermore, the resistance of a power transistor 301, 451 corresponds to the drain-source resistance of a MOS transistor 301 or the collector-emitter resistance of a BJT 451.

[0065] Fig.5 shows a flowchart of an exemplary method 500 for protecting a power transistor 301 in the event of a short-circuit situation at an output of a power supply circuit 300. The method 500 includes obtaining 501 a current for a load 106 from a supply voltage 322 via a power transistor 301 of the power supply circuit 300. A drain-source resistance of the power transistor 201, 301 is controlled by a gate voltage 325 applied to a gate of the power transistor 201, 301. The current is supplied to the load 106 at an output voltage 321. Furthermore, subject to a drop in the output voltage 321, the method 500 includes coupling 502 the gate of the power transistor 201, 301 to a source of the power transistor 201, 301 to place the power transistor 201, 301 in an off state.The coupling 502 can be performed directly by means of a short-circuit control transistor 403, thereby bypassing other circuits (e.g., a current limiting circuit) of the power supply circuit 300.

[0066] As such, the short-circuit protection circuit 400 has been described, which enables efficient and reliable protection of a power supply circuit 300 subject to a “short-circuit” condition, particularly in combination with a regulated current limiting circuit.

[0067] It should be noted that the description and drawings merely illustrate the principles of the proposed methods and systems. Those skilled in the art will be able to implement various arrangements that, while not explicitly described or shown, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and embodiments set forth herein are expressly intended for illustrative purposes only to assist the reader in understanding the principles of the proposed methods and systems. Furthermore, all statements made herein that provide principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to include their equivalents.

Claims

[1] Power supply circuit (100, 120, 300) configured to provide a current at an output voltage (321) for a load (106) at an output of the power supply circuit (100, 120, 300), the power supply circuit (100, 120, 300) comprising: -a power transistor (201, 301, 451) designed to draw the current from a supply voltage (322), wherein a resistance of the power transistor (201, 301, 451) is controlled by means of a control voltage (325) applied to a control terminal of the power transistor (201, 301, 451); and - a short-circuit protection circuit (400) designed to couple the control terminal of the power transistor (201, 301, 451) to a first terminal of the power transistor (201, 301, 451) in order to put the power transistor (201, 301, 451) into an off state when the output voltage (321) drops; wherein the short-circuit protection circuit (400) comprises a short-circuit control transistor (403) having a first terminal and a second terminal configured to couple the control terminal and the first terminal of the power transistor (301); wherein a state of the short-circuit control transistor (403) is controlled via a control terminal of the short-circuit control transistor (403); wherein a voltage level at the control terminal of the short-circuit control transistor (403) depends on the output voltage (321); wherein the short-circuit protection circuit (400) further comprises: - a control terminal amplifier (421) designed to amplify a voltage derived from the output voltage (321) before being applied to the control terminal of the short-circuit control transistor (403) and thus increase the response speed of the short-circuit protection circuit (400); and - a filter current source (432) coupled between the control terminal and the first terminal of the short-circuit control transistor (403) and configured to provide a predetermined current intensity. [2] The power supply circuit (100, 120, 300) of claim 1, wherein the short-circuit protection circuit (400) is configured to couple the control terminal of the power transistor (201, 301, 451) to a first terminal of the power transistor (201, 301, 451) when a slope of the drop in the output voltage (321) exceeds a predetermined slope threshold. [3] Power supply circuit (100, 120, 300) according to one of the preceding claims, wherein the short-circuit protection circuit (400) comprises: -a filter capacitor (401) coupled to the control terminal of the short-circuit control transistor (403) on one side and to the output of the power supply circuit (100, 120, 300) on another side of the filter capacitor (401). [4] Power supply circuit (100, 120, 300) according to one of the preceding claims, wherein -the power supply circuit (100, 120, 300) further comprises a current limiting circuit (304, 302, 305, 306, 307, 308, 309, 310) designed to limit the current through the power transistor (301) according to a predetermined current limit; -the short-circuit protection circuit (400) is designed to couple the control terminal to the first terminal of the power transistor (201, 301, 451) when the output voltage (321) drops in a first reaction time period; -the current limiting circuit (304, 302, 305, 306, 307, 308, 309, 310) is designed to limit the current through the power transistor (301) upon a drop in the output voltage (321) in a second response period according to the predetermined current limit; and -the first reaction time is shorter than the second reaction time. [5] The power supply circuit (100, 120, 300) of claim 4, wherein the current limiting circuit (304, 302, 305, 306, 307, 308, 309, 310) comprises: -detection means (304, 302, 305) adapted to provide an indication of the current through the power transistor (301); -comparison means (306, 307, 308) adapted to provide a feedback voltage by comparing the indication of the load current with the predetermined current limit; and -Feedback means (309, 310) designed to set the control voltage (325) at the control terminal of the power transistor (301) as a function of the feedback voltage. [6] Power supply circuit (100, 120, 300) according to claim 5, wherein -the detection means (304, 302, 305) comprise a sensing transistor (304) having a control terminal coupled to the control terminal of the power transistor (301), a first terminal coupled to the first terminal of the power transistor (301), and a second terminal coupled to a second terminal of the power transistor (301) via a current mirror (302, 305); and / or -the feedback means (309, 310) comprise a feedback transistor (310) having a control terminal to which the feedback voltage is applied, wherein the control voltage (325) is dependent on a resistance of the feedback transistor (310); and / or -the comparison means (306, 307, 308) comprise a current mirror (306, 307) designed to map a current through the sensing transistor (304) to the control terminal of the feedback transistor (310), and a current source (308) designed to supply a current to the control terminal of the feedback transistor (310) that is in accordance with the current limit. [7] Power supply circuit (100, 120, 300) according to one of the preceding claims, wherein the power supply circuit (100, 120, 300) comprises a voltage regulator (100, 120) configured to regulate (321) the output voltage in accordance with a reference voltage (108). [8] Power supply circuit (100, 120, 300) according to claim 7, wherein -the voltage regulator (100, 120) comprises voltage sensing means (104) designed to provide an indication (107) of the output voltage (321), and a differential amplification stage (101) designed to provide an input voltage (323) based on the reference voltage (108) and based on the indication (107) of the output voltage at the output node (301); and -the control voltage (325) depends on the input voltage (323). [9] Power supply circuit (100, 120, 300) according to one of claims 7 to 8, wherein -the voltage regulator (100, 120) comprises a pass-through device (201) designed to supply a current to the load (106); and -the pass device (201) is arranged in parallel with the power transistor (301) between the supply voltage (322) and the output of the power supply circuit (100, 120, 300). [10] Power supply circuit (100, 120, 300) according to one of the preceding claims, wherein -the power transistor (301) is a p-type metal oxide semiconductor transistor; -the first terminal comprises a source of the power transistor (301); -the first terminal of the power transistor (301) is coupled to the supply voltage (322); -the second terminal comprises a drain of the power transistor (301); and -the second terminal of the power transistor (301) is coupled to the output of the power supply circuit (100, 120, 300). [11] A method (500) for protecting a power transistor (301) in the event of a short-circuit situation, the method (500) comprising: -drawing (501) a current for a load (106) from a supply voltage (322) via a power transistor (301), wherein a resistance of the power transistor (201, 301, 451) is controlled by means of a control voltage (325) applied to a control terminal of the power transistor (201, 301, 451), wherein the current is supplied to the load (106) at an output voltage (321); and -when the output voltage (321) drops, coupling (502) the control terminal of the power transistor (201, 301, 451) to a first terminal of the power transistor (201, 301, 451) by means of a short-circuit control transistor (403) comprising a first terminal and a second terminal configured to couple the control terminal and the first terminal of the power transistor (201, 301, 451) to place the power transistor (201, 301, 451) in an off state; - amplifying a voltage derived from the output voltage (321) before applying it to a control terminal of the short-circuit control transistor (403); and - Providing a predetermined current intensity by means of a filter current source (432) coupled between the control terminal and the first terminal of the short-circuit control transistor (403).

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