Overvoltage protection for variable output voltage sMPS

Abstract

A method of detecting an overvoltage of an output of a variable output (SMPS) during a transition from a first target output voltage to a higher second target output voltage, and a corresponding apparatus and controller, comprising: determining a signal representative of an output voltage, where the output voltage is the output voltage of the SMPS; determining a time-varying signal representative of a maximum allowable output voltage; comparing the signal representative of the output voltage with an instantaneous value of the signal representative of a maximum allowable output voltage; and indicating an overvoltage in response to the signal representative of the output voltage being greater than an instantaneous value of the signal representative of a maximum allowable output voltage. A corresponding SMPS comprising such a method controller or device is also disclosed.

Description

Technical Field

[0001] The present disclosure relates to overvoltage protection for a variable output voltage switched mode power supply (SMPS). In particular, but not exclusively, the present disclosure relates to providing overvoltage protection during a transition from a first target output voltage to a second, higher target output voltage. Background Art

[0002] Switched mode power supplies (SMPS) are widely used to convert a high voltage, such as the mains voltage, to a lower voltage for a specific application. Typical example applications include voltage adapters for computers, laptops, tablets, phones, etc. Since applications have different power requirements and usually operate at different voltage levels, conventional SMPSs are specific to one application or one type of application.

[0003] SMPSs compatible with different applications have been developed, however, the interface to the application (tablet computer, mobile phone, etc.) is still usually specific to the type of application. Recently, a universal interface compatible with applications with different supply voltage power requirements has been proposed and developed. One such universal interface is the "Universal Serial Bus" (USB), for which international standards have been established. A recent development in the USB standard is to implement and standardize power delivery at a voltage that can be determined (that is, requested or set) by the application rather than the power supply. This has been implemented under the USB-PD version of the standard. The USB-PD standard has been extended to address power levels greater than 240W as the extended power range (EPR) part of the standard.

[0004] An important aspect of power supply and power delivery is protection against overvoltage. The introduction of supply voltages set by the application brings challenges regarding the implementation of overvoltage protection (OVP), especially since the threshold or trigger voltage of the OVP should be related to the voltage requested by the application (in normal operation, without failure modes). Summary of the invention

[0005] According to a first aspect of the present disclosure, a method for detecting an overvoltage on the output of a variable output voltage SMPS is provided, the method comprising: determining a signal representing an output voltage, wherein the output voltage is the output voltage of the SMPS; determining a time-varying signal representing a maximum allowable output voltage; comparing the signal representing the output voltage with an instantaneous value of the signal representing the maximum allowable output voltage; and indicating an overvoltage in response to the signal representing the output voltage being greater than the instantaneous value of the signal representing the maximum allowable output voltage. By using the time-varying signal representing the maximum allowable output voltage, during a transition from a first lower voltage to a second higher voltage, the method according to the present disclosure can set a trigger or threshold voltage for an overvoltage event to vary over time, thereby avoiding the trigger or threshold voltage from transiently changing to a trigger or threshold voltage for a higher target voltage in a steady state. The margin between the maximum expected voltage in any case and the trigger threshold voltage of the overvoltage event at the moment can be controlled, for example, to obtain a constant or near-constant margin between the expected instantaneous voltage during the transition and the threshold. Exposure of the load to overvoltage can thereby be reduced or eliminated. The threshold or trigger voltage is an indication of an overvoltage event and can trigger a response (e.g., shutting down the SMPS).

[0006] In one or more embodiments, the method is implemented during a transition from a first target output voltage to a higher second target output voltage. Conventional single-step switching from a first lower voltage OVP trigger or threshold to a second higher voltage OVP trigger or threshold is particularly prone to failure because during the transition of the output voltage, the margin between the expected voltage and the trigger level may greatly exceed the margin during normal (i.e., steady-state voltage) operation.

[0007] In one or more embodiments, the signal representing the output voltage is a digital signal. Processing in the digital domain may be more convenient than processing in the analog domain.

[0008] In one or more embodiments, the instantaneous value of the signal representing the maximum allowed output voltage is determined from the first target output voltage by adding the time integral of the maximum slew rate to the first target voltage and adding an offset voltage. Thus, a time-varying signal representing the maximum allowed output voltage can be calculated, for example, as a linearly increasing value during transitions.

[0009] In one or more embodiments, the instantaneous value of the signal representing the maximum allowed output voltage is predetermined and stored in a lookup table. Each instantaneous value may be predetermined by a previous calculation and stored in a memory such as a lookup table. Predetermining the instantaneous value may reduce the processing required during operation and thereby reduce the power consumption or efficiency of the controller.

[0010] In one or more other embodiments, the time varying signal representing the maximum allowed output voltage is determined from the signal representing the output voltage. Determining the time varying signal from the signal representing the output voltage itself may be particularly convenient as this may require a relatively small amount of memory space.

[0011] In one or more such embodiments, the time-varying signal representing the maximum allowed output voltage is determined from the signal representing the output voltage by applying a slew rate limiting filter to the signal representing the output voltage and adding a voltage offset. Using a slew rate limiting filter can be a convenient way to determine the maximum expected value of the voltage, and adding a voltage offset can help avoid spurious overvoltage events or unintentional overvoltage events. Without limitation, the offset can be an absolute offset, i.e., a fixed value, or a relative offset, i.e., a fixed percentage, or a combination of the two.

[0012] In one or more such embodiments, the time varying signal representative of a maximum allowed output voltage is determined from the signal representative of the output voltage by applying a slew rate limiting filter to the signal representative of the output voltage and adding a voltage offset.

[0013] According to a second aspect of the present disclosure, an overvoltage protection (OVP) device for a variable output voltage switch mode power supply (SMPS) is provided, the OVP device comprising: a voltage sensor for sensing a signal representing an instantaneous output voltage of the SMPS; a calculation unit configured to determine a maximum allowable instantaneous output voltage; and a comparator configured to compare the signal representing the instantaneous output voltage with the maximum allowable instantaneous output voltage, and provide an overvoltage indicator in response to the instantaneous output voltage exceeding the maximum allowable instantaneous output voltage.

[0014] In one or more embodiments, the OVP device further comprises a lookup table configured to store the maximum allowed instantaneous output voltage.

[0015] In one or more embodiments, the OVP device further includes a calculation unit configured to determine the maximum allowed instantaneous output voltage according to the first target voltage by adding an offset voltage to a maximum instantaneous expected voltage.

[0016] In one or more such embodiments, the OVP device additionally includes a slew rate limiting filter configured to determine a maximum instantaneous expected voltage based on an integration of the signal representing the instantaneous output voltage.

[0017] According to a third aspect of the present disclosure, there is provided a controller for an SMPS, comprising the OVP device as described above.

[0018] According to a fourth aspect of the present disclosure, there is provided an SMPS comprising a controller as described above and a transformer having an auxiliary winding on the primary side, wherein the signal representing the instantaneous output voltage is a scaled version of the voltage across the auxiliary winding. The signal representing the instantaneous output voltage may be derived from the voltage across the auxiliary winding by means of, for example, a voltage divider. Furthermore, the voltage across the auxiliary winding will itself be a scaled version of the output voltage.

[0019] A computer program may be provided which, when run on a computer, causes the computer to configure any apparatus including the circuits, controllers, sensors, filters or devices disclosed herein or to perform any method disclosed herein. The computer program may be a software implementation and the computer may be considered to be any suitable hardware including a digital signal processor, a microcontroller and implementations in a read-only memory (ROM), an erasable programmable read-only memory (EPROM) or an electrically erasable programmable read-only memory (EEPROM) as non-limiting examples. The software implementation may be an assembler.

[0020] The computer program may be provided on a computer readable medium, which may be a physical computer readable medium such as a disk or a memory device, or may be embodied as another non-transitory signal.

[0021] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Embodiments will be described, by way of example only, with reference to the accompanying drawings in which

[0023] Figure 1 schematically illustrates portions of a system using USB-PD;

[0024] Figure 2 In more detail, Figure 1 The system corresponding to the system;

[0025] Figure 3 shows the target voltage and trigger voltage of OVP for variable output voltage SMPS;

[0026] Figure 4 schematically illustrates the actual output voltage of the SMPS during a transition from a target output voltage to a higher target output;

[0027] Figure 5a schematically illustrates a time-varying threshold trigger voltage for an OVP event during a transition from a first target voltage to a second, higher target voltage according to one or more embodiments;

[0028] Figure 5b schematically illustrates a time-varying threshold trigger voltage for an OVP event during a transition from a first target voltage to a second, higher target voltage according to one or more other embodiments;

[0029] Figure 6a Schematically showing the voltage V SNSOUT An embodiment representing an output voltage;

[0030] Figure 6b An embodiment is shown in which the instantaneous OVP trigger value or threshold is derived directly from the measured output voltage;

[0031] Figure 7 illustrates detection of an overvoltage event; and

[0032] Figure 8 An SMPS and an SMPS control IC according to an embodiment of the present disclosure are shown.

[0033] It should be noted that the figures are diagrammatic and not drawn to scale. For clarity and convenience in the drawings, the relative sizes and proportions of the parts of these figures have been shown by being enlarged or reduced in size. The same reference numerals are generally used to refer to corresponding or similar features in modified and different embodiments. DETAILED DESCRIPTION

[0034] Figure 1Schematically illustrated is a portion of a USB-PD system 100, which is included in the application field of the present disclosure. The system 100 includes a switch mode power supply SMPS 110, which has a controller 120 associated therewith. The controller 120 may be embodied in an integrated circuit (IC) and may be an integral part of the SMPS 110 as shown, or may be external to the SMPS 110. The SMPS 110 has an input 112 at an input voltage 112. It outputs an output voltage Vout_smps at an output 114. The system further includes a USB-PD controller 130. The controller 130 may be embodied in an integrated circuit. The integrated circuit for the USB-PD controller 130 may be part of the same IC that embodies the SMPS controller 120, or may be a separate IC. The USB-PD controller 130 may control a switch 140 and / or other circuit systems, and provide an output 132 Vout, which is supplied to a load 150. The load 150 communicates with the USB-PD controller 130, as shown by control signals 152 and 154. The communication may include an indication of the voltage required by the load 150. The USB-PD controller 130 communicates with the SMPS controller 120, as shown by signal 134. Typically, the SMPS controller 120 is arranged on the primary side or high voltage side of the SMPS. Therefore, the system may include an optocoupler 160 or other means to galvanically isolate the USB-PD IC 130 from the SMPS controller 120.

[0035] Figure 2 In more detail, Figure 1 200. Specifically, the figure shows the details of the SMPS. As shown, the SMPS can be a half-bridge converter, including a low-side switch S1 210 and a high-side switch S2 215. The gates of the low-side switch S1 210 and the high-side switch S2 215 are connected to the pins GATELS and GATEHS of the SMPS controller 120, respectively.

[0036] The low side switch S1 210 is connected to the primary side ground, and the high side switch S2 215 is connected to the input voltage Vin 112. The input voltage Vin 112 can be connected to the primary side ground through a capacitor 225. The half bridge node 220 between the low side switch 210 and the high side switch 215 is optionally connected to the primary side winding Lp of the transformer 235 through a series inductor Ls 230 as shown. The primary side winding Lp is connected to the primary side winding Lp through a resonant capacitor C R240 is connected to the primary side ground. The resonant capacitor 240 provides resonant behavior together with the series inductor Ls230. One end of the secondary side winding is connected to the secondary ground 245, and the other end is connected to the output Vout_smps 114 of the SMPS via a diode 250. A capacitor 255 connecting the output Vout_smps 114 to the secondary ground may be included. The switch 140 may be implemented as a transistor S3, typically a MOSFET. The optocoupler 160 is shown by an LED 160a on the secondary side and a photodiode 160b on the primary side. The photodiode 160b is connected to the feedback sense pin SNSFB of the SMPS controller 120.

[0037] A signal representing the output voltage Vout_smps at the output 114 of the SMPS is connected to the pin SNSOUT of the SMPS controller 120. To provide said signal, the transformer is provided with an auxiliary winding 260 on the primary side of the transformer. The voltage Vaux across the auxiliary winding is related to the output voltage by the turns ratio between the secondary winding and the auxiliary winding. The voltage Vaux can be scaled by means of a voltage divider comprising two resistors Rsnsout1 265 and Rsnsout2 270. If the secondary side winding of the transformer 235 has ns turns and the auxiliary winding 260 has na turns, the voltage at the pin SNSOUT represents the output voltage of the SMPS by the following formula:

[0038]

[0039] Now turn to Figure 3 , this figure shows the target voltage and trigger voltage of OVP for a variable output voltage SMPS. As shown at 310. The SMPS may have a first target output voltage of, for example, 5V. The corresponding trigger or threshold voltage of OVP may be 6V as shown at 320. A second target output voltage is also shown at 330, which is 48V in this case, and a corresponding trigger or threshold voltage of OVP corresponding to the target voltage is shown, which may be 55V as shown at 340. In the case of a multi-output voltage SMPS, the target output voltage may be initially set to a first voltage, in this case 5V. However, if the application requires a target voltage of 48V, the application may communicate with the SMPS (e.g., using the USB-PD protocol), and the target output voltage of the SMPS may be switched to 48V. This is Figure 3 350. Figure 3 As shown in , the output voltage Vout increases from 5V to 48V. However, in practice, the change cannot be instantaneous as shown in the figure, but requires a finite time. This is Figure 4 Shown in.

[0040] Figure 4 The actual output voltage of the SMPS is schematically shown during a transition from a first, lower target output voltage, in this case 5V, to a second, higher target output voltage, in this case 48V. The target voltage changes at time t0 350. (In some cases, the load may also increase in response to an increase in current drawn from the output, and so initially the voltage may drop, as shown at 410. However, this is not necessarily the case.) Thereafter, the power available from the SMPS increases, causing the output voltage to rise at a finite slew rate, as shown at 420. Due to the finite slew rate, a finite amount of time is required to reach the target voltage, which may be on the order of 100ms, or up to 285ms for a rise to 20V, or up to 700ms for a rise to 48V, depending on different parts of the USB-PD standard. As shown at 430, there may even be an overshoot beyond the target voltage, in this case 48V, before the output settles at the target voltage, or within a predetermined range R1 of the target voltage, as shown at 440. During the transition, the standard may provide for an extended range, such as Figure 4 Indicated by R2.

[0041] The inventors of the present disclosure have realized that since the expected change in voltage from the first target value to the second target value does not occur instantaneously, but occurs within a finite time at the maximum limit of the slew rate, it may be useful to similarly change the triggering threshold voltage of the OVP event within a finite time rather than instantaneously. Figure 5a-5b Shown in.

[0042] Figure 5a The time-varying threshold trigger voltage of an OVP event during a transition from a first target voltage to a second, higher target voltage is schematically illustrated. Figure 5a The transition of the actual output voltage outputted from a first target value of 5V in this case to a second target value of 48V in this case is shown at 520. The transition takes a finite time, primarily because the increase in voltage 520 occurs at a finite slew rate dV / dt. There may be an overshoot period 530 as shown. Those skilled in the art will appreciate that the actual slew rate dV / dt will depend on the design of the overall system, in particular the design of the secondary USB-PD controller present therein, and the values ​​of its components. However, in general, the voltage transition will not be instantaneous. And for any particular design of the system, there is a maximum slew rate that can be expected. Therefore, Figure 5a Curve 520 shown in may also correspond to a maximum expected rate of change of voltage.

[0043] Then, as shown, the time-varying threshold trigger voltage for an OVP event can be defined as a voltage that is always higher than the maximum expected voltage 520, but is time-varying in the sense that the voltage does not immediately transition from its initial value 552 to its final value 554. It can be equivalently described as a non-instantaneous transition or a gradual transition. In the example shown, the initial value is at 6V and the final value is at 55V, both of which are about 20% higher than the regulation level. The threshold trigger voltage 550 is a level ΔV higher than the maximum expected output voltage. ΔV can be a fixed value, or it can be a slowly varying value that changes from the difference between the OVP threshold or trigger for a first lower target voltage (in this case 1V, which is the difference between 6V and 5V) to the difference between the OVP threshold trigger for a second higher target voltage (in the case shown, 7V, which is the difference between 55V and 48V). Typically, the OPV trigger or threshold is about 20% higher than the expected or measured output voltage, or can be fixed at an absolute value, or can be a combination of the two.

[0044] Steering Figure 5b , which schematically illustrates a time-varying threshold trigger voltage for an OVP event during a transition from a first target voltage to a second, higher target voltage according to one or more other embodiments of the present disclosure. In this example, the OVP trigger turn-off threshold voltage changes in a series of steps from an initial value of 6V (which is the OVP trigger or threshold for the lower target output voltage) to a final value of 55V (which is the OVP trigger threshold for the higher target output voltage), rather than Figure 5a . For embodiments where the value at any time is stored in memory as a series of values, it may be particularly convenient to provide the trigger or threshold voltage as a series of steps. As an example, if the maximum expected slew rate of the output voltage produces a transition period of 100ms, the OVP trigger or threshold may be increased in a series of 100 steps - that is, once every 1ms.

[0045] The instantaneous OVP trigger or threshold may be stored in a memory such as a look-up table, which is useful for example Figure 5b The embodiment shown in may be convenient. Figure 6a Schematically showing the voltage V SNSOUT Such an embodiment represents the output voltage. Figure 6a In the embodiment of the embodiment shown in , the voltage on the pin SNSOUT 610 of the SMPS control IC is processed in the digital domain and the signal is therefore digitized by means of an analog-to-digital converter 620. This signal, which represents the output voltage of the SMPS and varies with time, is compared with a time-varying signal representing the maximum allowed output voltage Vtr(t). In e.g. Figure 6aIn the embodiment shown in the embodiment, the time-varying signal representing the maximum allowed output voltage is predetermined. For example, the time-varying signal may be stored in a memory (e.g., 640 shown) as a series of values ​​at specific times after the transition begins. In other embodiments, the time-varying signal may be calculated during operation as a series of values ​​that increase over time starting from an initial overvoltage trigger or threshold. One non-limiting type of function is a linear increasing function that increases over time at a preset rate, which may generally correspond to the maximum predicted conversion rate for a particular SMPS design. At time t i The maximum allowable output voltage Vtr(t i ) value and represents the time t i The output voltage V SNSOUT The digital instantaneous signal is compared with the Figure 6a is shown at comparator 650. If the signal V SNSOUT The digital version is greater than Vtr(t i ), then it is possible that an OVP event has occurred. The skilled person will appreciate that there may be noise in the system, so optionally, as shown at 665, and also optionally, as shown at 660, before the comparator, further filtering is applied (for example, applying a low pass filter to filter out individual aberrations in the digitization). The result of the (optionally filtered) comparator is the OVP detection signal (OVP_det).

[0046] In other embodiments, the instantaneous OVP trigger value or threshold value may be calculated instead of being retrieved from memory. For example, in the case of a maximum expected conversion rate M and an initial target voltage V0, the instantaneous OVP trigger value or threshold value Vtr at time t after the start of the transition may be calculated according to the following formula:

[0047] 1. Vtr(t)=(V0+Voffset)+Mt

[0048] According to one or more other embodiments, the instantaneous OVP trigger value or threshold may be derived directly from the measured output voltage. Figure 6b As described above, the voltage V SNSOUT represents the output voltage. This voltage on pin SNSOUT 610 of the SMPS control IC can be processed in the analog domain or in the digital domain. Processing in the digital domain is usually preferred, and in order to process this voltage in the digital domain, the signal is first digitized with the aid of an analog-to-digital converter 620. This Figure 6b, as it is optional. The signal then passes through a slew rate limiter 635. The function of this limiter will be familiar to the skilled person and will be described in more detail below. As the next processing stage, at 645, an offset is added to the slew rate limited signal, which in this case is an offset ΔV that increases from 1V to 7V over time. The result is a slew rate limited signal with an offset ΔV, and this signal can be used as a time-varying OVP threshold or trigger value Vtr(t).

[0049] A convenient numerical implementation of this would be, at time n:

[0050] Vtr(t(n))=min(Vtr(t(n-1))+M*(t(n)-t(n-1)), Voffset_rel*Vsnsout+Voffset_abs),

[0051] Where Vtr(t(n)) is the new OVP level and Vtr(t(n-1)) is the previously defined OVP level at time (t(n-1)), and Vtr(t(n)) is defined as the minimum value of the OVP level based on the measured SNSOUT or limited by the slew rate based on the previously defined OVP level.

[0052] To determine whether an OVP event has occurred, Vtr(t) is compared with the signal V SNSOUT This is done by Figure 6b The comparator 650 is shown in FIG. SNSOUT If the digitized version of is greater than Vtr(t), then it is likely that an OVP event has occurred. Optional filtering may be included, as shown at 665 after the comparator and / or at 660 before the comparator, and the result of the (optionally filtered) comparator is the OVP detection signal (OVP_det).

[0053] As the skilled person will appreciate, a slew rate limiter is a filter that prevents a signal from changing rapidly. Typically, a slew rate filter prevents a very rapid increase or a very rapid decrease in a signal. For the present disclosure, only the positive slew rate needs to be limited. If the input signal rises greater than the maximum allowed slew rate Msl, the filter acts to limit the increase in the output to this maximum slew rate Msl, such that:

[0054]

[0055] For signals that change only slowly, the slew rate limiter has essentially no effect.

[0056] Now turn to Figure 7, this figure shows the detection of an overvoltage event. In this example, the voltage output by the SMPS increases rapidly, as shown at 720. This may occur, for example, in the event of a secondary controller failure, such that, for example, for a high power device operating at a high voltage, the USB-PD control IC requests a transition from a first target voltage to a second higher target voltage, but there is a fault in the second controller, such as the USB-PD control IC, such that the output voltage is effectively unconstrained. For example, if the secondary USB-PD controller fails, the SMPS power supply assumes that it must increase its output voltage. Due to the failed USB-PD controller, the switch 140 ( Figure 1 ) may close, and the output voltage (Vout) may increase to a voltage higher than the load allows. This may be unsafe or damage the load. Or there may even be no secondary switch 140 (e.g. Figure 1 The application of the secondary switch shown in FIG. 1 ) is shown in FIG. 1 , where for example, an optocoupler (in Figure 1 160 in FIG. 1 ) has failed.

[0057] At 722, a slew rate limited version of the output voltage of 720 is shown. It can be seen that this curve is similar to 720, except that the gradient of the voltage increase is constrained to be no greater than Msl. 724 shows a curve corresponding to 722, except that the voltage offset ΔV has been added to the slew rate limited value. As shown at 730, there is a moment when the actual output voltage 720 crosses the slew rate limited version with the voltage offset. By comparing these two signals, as shown in FIG. Figure 6a-6b As described in , it can be concluded that an OVP event has occurred.

[0058] Will be from Figure 7 It can be appreciated that overvoltage detection occurs at 730 much faster than would be the case in a conventional OVP arrangement where an overvoltage would only be detected at a slightly later time as shown at 730. Specifically, overvoltage detection occurs at a much lower voltage - in the example shown, overvoltage detection at 730 occurs at around 7V, rather than around 55V as would be the case with conventional overvoltage detection at 732. This can be beneficial because in the event of a component failure or optocoupler short circuit in a USB-PD system, for example, the load device is only exposed to a much lower voltage than in a conventional system. By applying appropriate protection in the event of overvoltage detection, the load device is exposed to a high voltage (e.g., 55V), which can cause damage to the device, particularly for low voltage devices designed to operate at lower voltage levels (e.g., 5V shown).

[0059] Reference now Figure 8, this figure shows an SMPS 800 and an SMPS control IC 810 according to an embodiment of the present disclosure. Most SMPSs are similar to conventional SMPSs except for the control IC 810 including OVP. As shown, the voltage on the pin SNSOUT representing the output voltage Vout_smps of the SMPS is captured by a sample and hold unit 820 and converted to a digital value by an ADC 830. A time-varying signal representing the maximum allowed output voltage is then generated from this analog value. First, the signal is filtered in a slew rate limiter. As shown, the slew rate limiter can be implemented as a low-pass filter 840, but such filters introduce delays. Then, a voltage offset (“offset”) is added to the slew rate limited signal at an adder 850. A comparator 860 is used to compare the digitized signal (“A”) with the slew rate limited signal (“B”) including the offset. In the case where the comparator determines that the actual signal digitized is greater than the slew rate limited signal including the offset, an overvoltage detection indicator (OVP_det) is generated. Appropriate response actions can then be taken, such as shutting down the SMPS or disconnecting the load.

[0060] Other changes and modifications will be apparent to those skilled in the art from reading this disclosure. Such changes and modifications may involve equivalent and other features that are already known in the field of overvoltage protection and may be used as a replacement or supplement to the features already described herein.

[0061] Although the attached claims are directed to specific feature combinations, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel feature combination or any generalized form of the novel feature disclosed explicitly or implicitly herein, regardless of whether the novel feature relates to the same invention as the present invention currently claimed in any claim or whether the novel feature alleviates the same technical problem as any or all of the technical problems alleviated by the present invention.

[0062] It should be noted that one or more of the embodiments above have been described with reference to different subject matters. Specifically, some embodiments may have been described with reference to method claims, while other embodiments may have been described with reference to apparatus claims. However, those skilled in the art will appreciate from the foregoing that, unless otherwise stated, any combination of features relating to different subject matters, in addition to any combination of features belonging to one type of subject matter, in particular a combination of features of a method claim with features of an apparatus claim, is also deemed to be disclosed with this document.

[0063] Features described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable sub-combination.

[0064] For the sake of completeness, it is also provided that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude that a plurality, a single processor or other unit can perform the functions of several components recited in the claims [which may be deleted if not relevant], and the reference numerals in the claims should not be interpreted as limiting the scope of the claims. In addition, the word "may" is used in a permissive sense (i.e., meaning likely) rather than a mandatory sense (i.e., meaning must). Similarly, the words "include", "including" and "includes" mean including but not limited to.

Claims

1. A method of detecting an overvoltage on the output of a variable output voltage SMPS during a transition from a first target output voltage to a higher second target output voltage, characterized in that The method comprises: determining a signal representative of an output voltage, wherein the output voltage is an output voltage of the SMPS; determining a time varying signal representing a maximum allowable output voltage; comparing the signal representative of the output voltage with an instantaneous value of the signal representative of a maximum allowed output voltage; and In response to the instantaneous value of the signal representing the output voltage being greater than the signal representing a maximum allowable output voltage, an overvoltage is indicated.

2. The method according to claim 1, characterized in that The signal representing the output voltage is a digital signal.

3. The method according to claim 1 or 2, characterized in that: The instantaneous value of the signal representing a maximum allowed output voltage is determined from the first target output voltage by adding a time integral of a maximum slew rate to the first target voltage and adding an offset voltage.

4. The method according to claim 1 or 2, characterized in that: Said instantaneous value of said signal representing the maximum allowed output voltage is predetermined.

5. The method according to claim 4, characterized in that The instantaneous value of the signal representing the maximum allowed output voltage is stored in a look-up table.

6. The method according to claim 1 or 2, characterized in that: The time varying signal indicative of a maximum allowed output voltage is determined based on the signal indicative of the output voltage.

7. The method according to claim 6, characterized in that The time varying signal representing a maximum allowed output voltage is determined from the signal representing the output voltage by applying a slew rate limiting filter to the signal representing the output voltage and adding a voltage offset.

8. An overvoltage protection OVP device for a variable output voltage switch mode power supply SMPS, characterized in that: The OVP device comprises: a voltage sensor for sensing a signal representing an instantaneous output voltage of the SMPS; a calculation unit configured to determine a maximum allowed instantaneous output voltage; and A comparator is configured to compare the signal representing the instantaneous output voltage to the maximum allowed instantaneous output voltage and to provide an overvoltage indicator in response to the instantaneous output voltage exceeding the maximum allowed instantaneous output voltage.

9. A controller for SMPS, characterized in that: Comprising an OVP device according to claim 8.

10. A SMPS, characterized in that: comprising a controller according to claim 9 and a transformer having an auxiliary winding on the primary side, wherein the signal representing the instantaneous output voltage is a scaled version of the voltage across the auxiliary winding.

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