Power management system for energy harvesting applications and operating method

Abstract

According to the invention, there is provided a power management system for energy harvesting applications, comprising: - a DC-DC converter configured to transfer energy from an energy source to a storage device, - a protection system configured to prevent voltage surges at an output of the DC-DC converter, - a monitoring circuit configured to monitor a voltage at the output of the DC-DC converter and to compare it to a predetermined reference voltage that is higher than the regulation voltage of the DC-DC converter. According to the invention, the monitoring circuit is enabled only during periods of active energy harvesting. Further, the protection system remains active until the voltage at the output of the DC-DC converter falls down below the predetermined reference voltage, or until the power management system deactivates it. Thereby, the system minimizes quiescent current consumption when energy harvesting is not occurring to reduce the impact on the storage device and ensure efficient energy management. In other words, the monitoring circuit is only turned on when necessary and is turned off when the risk of voltage surge at the output of the DC-DC converter is no longer present.

Description

Power management system for energy harvesting applications and operating method

[0001] Description

[0002] The present patent application relates to the technical field of energy harvesting. In particular, the invention relates to a power management system for energy harvesting applications, to a semiconductor device comprising such a power management system and to a method for operating the same.

[0003] Prior art

[0004] With the proliferation of loT devices deployed in environments where reliable and stable power sources are not guaranteed, energy harvesting, the process of collecting energy from an object's environment (such as solar, thermal, electromagnetic or kinetic energy), has become an increasingly popular approach in powering small, low-power electronic devices. The need for dedicated power management solutions for energy harvesting applications has led to the development of Power Management Integrated Circuits (PMICs). These PMICs are designed to efficiently manage the energy flow from an external source to a storage device, which could be a rechargeable battery, a large capacitor, or a supercapacitor.

[0005] At the heart of this system is a DC-DC converter, a critical component that regulates the energy transfer from the energy harvester to the storage device. The storage device acts as a large reservoir, controlling the voltage levels at the output of the PMIC and ensuring a steady voltage increase. This stability is key to the proper functioning of energy harvesting systems in varied environmental and operational conditions.

[0006] While energy harvesting systems have become more efficient, they face significant challenges, particularly during unexpected disconnections of the storage device. Such disconnections can occur under several scenarios: during the assembly of the system when the storage device is not yet connected, during testing, after mechanical shocks or vibrations in the final product, due to accidental user interactions or when the energy harvester is reactivated after a period of sleep. These events expose the PMIC to potential risks, especially when the DC-DC converter remains active.

[0007] When a disconnection happens, and the converter is still running, the absence of a storage device can lead to a rapid and significant increase in the output voltage. This sudden voltage spike can exceed the rated voltage capacity of the electronic components such as the PMIC, potentially causing permanent damage to the integrated circuit. As the DC-DC converter continuously tries to feed energy into a disconnected circuit, the lack of a moderating storage device causes the output voltage to surge uncontrollably.

[0008] One potential solution could involve the use of a monitoring circuit that continuously checks the connection status of the storage device. However, keeping such a circuit active at all times is not ideal. Energy harvesting systems often generate low energy levels, and any unnecessary power consumption, like having an always-on monitoring system, could depletethe storage device. This would result in a net negative energy flow, where the power consumed by the PMIC exceeds the energy being harvested.

[0009] A power management system is already known from an integrated energy management subsystem sold by the applicant under the name AEM 10940 that extracts DC power from photovoltaic cells or thermoelectric generator to simultaneously store energy in a rechargeable element and supply the system with two independent regulated voltages. In this subsystem, the monitoring of the connection status of the storage device is continuous.

[0010] Summary of the invention

[0011] According to a first aspect of the invention, there is provided a power management system for energy harvesting applications, comprising:- a DC-DC converter configured to transfer energy from an energy source to an energy storage device,- a protection system configured to prevent voltage surges at an output of the DC-DC converter,- a monitoring circuit configured to monitor a voltage at the output of the DC-DC converter and to compare it to a first predetermined reference voltage that is higher than the regulation voltage at the output of the DC-DC converter and to activate the protection mechanism when the voltage at the output of the DC-DC converter exceeds the first predetermined reference voltage. According to the invention, the DC-DC converter is configured to regulate the voltage on the energy source connected to said energy source input and to transfer energy to the energy storage device connected to said energy source output until the voltage on the energy storage device connected to said energy source output reaches the regulation voltage. Also, according to the invention, the monitoring circuit is enabled only during periods where the DC- DC converter actively transfers energy from the energy source towards the energy storage device. Further, the protection system remains active until the voltage at the output of the DC- DC converter falls down below a second predetermined reference voltage that is equal or smaller than the first predetermined reference voltage, or until the power management system deactivates it.

[0012] Thereby, the system minimizes quiescent current consumption when energy transfer is not occurring to reduce the impact on the storage device and ensure efficient energy management. In other words, the monitoring circuit is only turned on when necessary and is turned off when the risk of voltage surge at the output of the DC-DC converter is no longer present.

[0013] The term "regulation voltage" designates the predetermined voltage threshold used by the DC-DC converter to control its energy-transfer operation. When the voltage at the output of the converter reaches this threshold, the converter ceases initiating new charge-discharge cycles of the inductor regardless of energy availability on the DC-DC converter input, so as to prevent the output voltage from rising above the desired level.

[0014] When, the DC-DC converter operates in discontinuous conduction mode (DCM), energy is transferred from the energy source to the storage device in the form of successive charge and discharge cycles of the inductor, separated by intervals during which the inductor current is equal to zero. These intervals correspond to so-called idle periods, during which the converter performs no energy transfer. In case of energy harvesting applications, those idle periods can be long, for instance because the energy harvester does not produce any energy. An illustration would be a photovoltaic cell which is not illuminated at night. As classically illustrated by DCM waveforms, the inductor current increases when the main switch is turned on, then decreases until it reaches exactly zero after the switch is opened. The period during which the current is non-zero constitutes an active transfer period within the meaning of the present invention.

[0015] According to the invention, the monitoring circuit is enabled only during these active transfer periods, i.e. only when the inductor current is non-zero and the converter is effectively transferring energy to the storage device. Conversely, the monitoring circuit remains disabled during periods in which the inductor current is zero and no energy transfer takes place.

[0016] Operationally, a comparator monitoring the voltage of the energy source may inhibit the initiation of a new conversion cycle if the source voltage falls below a predefined regulation value. The converter thus remains in an inactive period as long as the input voltage has not risen back above this value. The duration of this inactive period directly depends on the instantaneous amount of energy provided by the source, a more energetic source enabling a faster return to the regulation voltage.

[0017] When, the DC-DC converter operates in continuous conduction mode (CCM) operation, if the input voltage drops below the regulation threshold, the converter is controlled so as to allow the inductor current to decay to zero before enforcing an inactive period, after which the transfer operation is resumed once the input voltage has recovered to the desired level.

[0018] Accordingly, activating the monitoring circuit only during periods of actual energy transfer significantly reduces the overall power consumption of the system, while avoiding the detection of overvoltage conditions or anomalies during phases in which no energy flows through the converter.

[0019] Thanks to the invention, the protection mechanism is activated as soon as overvoltage conditions or anomalies are detected, that is, typically only in a few microseconds when the voltage at the output of the DC-DC converter exceeds the first predetermined reference voltage.

[0020] In a variant of the system, the monitoring circuit is also enabled as long as the protection system is active. This variant avoids relying on another monitoring circuit within the device, that could be slower, to activate or deactivate the monitoring circuit and protection mechanism.

[0021] In an embodiment, the monitoring circuit is a comparator having the following inputs:- a predetermined voltage reference and- the voltage monitored at the output of the DC-DC.

[0022] A comparator does not consume a lot of silicon area and can thus easily be integrated to the same integrated circuit as the DC-DC converter. Further, it can be designed to react fast to such events and allow a quick reaction in case of a failure consisting of an unexpected disconnection of the storage device.

[0023] If the monitored voltage exceeds the first predetermined voltage reference, the protection system is enabled and stops the voltage surge. In an embodiment, the first predetermined voltage reference is defined as the maximum operating voltage that the PMIC can afford without risk of failure; thereby, the power management system protects the PMIC. This first predetermined voltage reference is a characteristic of the PMIC and is generally provided by the manufacturer or can be determined easily by routine experiments. It is desirable that the triggering of the protection mechanism by the monitoring means does not prevent the storage device from reaching its maximum allowable voltage as it would result in a loss of a portion of its capacity. If the maximum operating voltage of the PMIC without risk of failure due to an overvoltage is higher than the end of charge of the energy storage device, this maximum operating voltage can be used to trigger the protection mechanism without impacting the end of charge of the storage device.

[0024] In a variant, the predetermined voltage reference is defined as the maximum programmed voltage of the storage element which is defined as the end-of-charge voltage during the charging process for the cell or module in a battery management system. This voltage is set based on the specific characteristics of the battery to prevent overcharging, overheating, or damage to the battery, which could reduce its lifespan or even cause safety incidents. This maximum programmed voltage takes also into account any circuit connected to the storage element. If other circuits are connected to the same power rail as the storage device, reusing the end of-charge voltage of the storage device as the first predetermined reference voltage for the monitoring circuit allows protecting those other circuits against a failure consisting of a voltage increase following an unexpected disconnection of the storage device. Indeed, those circuits must have a safe operating voltage of at least the end of charge voltage of the storage device since they are connected to the same power rail as the storage device.

[0025] In an embodiment, the protection system is configured to disable the DC-DC converter when activated. If the DC-DC converter charging the energy storage device is deactivated, the voltage on the energy storage device cannot increase further. This is a convenient way to implement the protection mechanism while not relying on other circuitry such as a power switch connected in series between the output of the DC-DC converter and the storage device,as it would require an additional component, increasing the cost of the system and reducing its efficiency because of the thermal losses occurring in this additional switch. Thereby, it is certain that the output voltage of the storage element will not rise higher if the DC / DC stops harvesting energy from the source. It is not necessary to make a more complex adjustment to implement, as we are trying to protect against malfunctions in the event of an untimely disconnection of the storage element.

[0026] In another embodiment of the invention, the DC-DC converter has multiples outputs that are monitored by the monitoring circuit and that are protected by the protection circuit.

[0027] Indeed, if the PMIC manages several storage elements, all of these outputs are protected. Typically, this could happen in systems that include a small capacity storage element and another larger capacity storage element or supercapacitor. With this mechanism, the system including the PMIC is able to boot up faster on the small capacity storage element while recharging the large capacity storage element once the system is in operation.

[0028] When a Power Management Integrated Circuit (PMIC) manages multiple storage elements across different outputs, it ensures protection for all these outputs. This typically occurs in systems incorporating both a small capacity storage element and a larger capacity storage element or supercapacitor. With this configuration, the PMIC system can initiate more quickly and start delivering energy to an application load using the small capacity storage element, while simultaneously recharging the larger capacity storage element once the system is operational.

[0029] In another embodiment, the monitoring circuit includes a startup mechanism. Indeed, the monitoring circuit should start quickly to detect failures caused by an unexpected disconnection of the storage device, which leads to a rise in its output voltage. In such cases, the output voltage of the DC-DC converter rises rapidly when it is actively transferring energy to its output, which can cause overvoltage stress and potentially damage to the circuitry.

[0030] In yet another embodiment of the power management system of the invention, the monitoring circuit includes a masking mechanism that masks its output until the power monitoring circuit's output is valid after its activation. A masking mechanism in general is quite conventional in this field of technology and refers to a system designed to selectively enable or disable specific functions, signals, or components based on predefined conditions. Its primary purpose is to enhance operational reliability. According to this embodiment, the masking mechanism prevents false detection by the monitoring circuit when such false detection results from an invalid output during its wake-up process.

[0031] If we consider that the DC-DC converter receives a setpoint (a voltage value that is typically calculated by an MPPT module or is directly set by the user) to regulate its input voltage, a module within the DC-DC converter will check whether the input voltage exceeds this setpoint. If the setpoint is not exceeded, the output is deemed valid.

[0032] In yet another embodiment, the storage device comprises a rechargeable battery, large capacitor, or supercapacitor.

[0033] A capacitor or large capacitor as a storage device is cost-effective, fits within a minimal volume, and has low leakage. A supercapacitor, on the other hand, offers high energy density and compatibility with a wide operating temperature range. It also has a long operational life. A rechargeable battery provides even higher energy density and maintains an operating voltage within a narrow range.

[0034] Another aspect of the invention is directed to a semiconductor device comprising a power management system for energy harvesting applications as described above.

[0035] A third aspect of the invention relates to a method of operating such a semiconductor device. According to a first embodiment, the method comprises the following steps:(i) (a) enabling a DC-DC converter to an IDLE state wherein the controller of the DC-DC converter monitors a source connected to its power input; and(b) keeping a monitoring circuit disabled;(ii) when the DC-DC converter detects that energy can be extracted from the source connected to its input(a) activating the DC-DC converter to an ON state wherein the DC-DC converter actively extracts energy from its input and transfers it to its output;(b) enabling the monitoring circuit so as to monitor that the voltage on the converter output does not rise above a first predetermined reference voltage;(c) if the DC-DC converter detects that no further energy can be extracted from its input, returning to step (i);(iii) when the monitoring circuit detects that the voltage on the converter output has risen above the first predetermined reference voltage;(a) disabling the DC-DC converter to an OFF state;(b) monitoring that the DC-DC converter output has fallen below the second predetermined reference voltage;(iv) when the monitoring circuit or the DC-DC converter detects that the voltage on the converter output has fallen below the second predetermined reference voltage, returning to step (ii) or disabling the monitoring circuit and going back to step (i).

[0036] In order to detect that energy can be extracted from the source, for example, it is possible to detect with a comparator that the input voltage of the DC-DC converter exceeds the regulation setpoint. This regulator can be included in the control circuitry of the DC-DC converter.

[0037] In another a variant of this aspect of the invention, the operating method, comprises the following steps:(i) (a) enabling a DC-DC converter to an IDLE state wherein the controller of the DC-DCconverter monitors a source connected to its power input; and(b) keeping a monitoring circuit disabled;(ii) when the DC-DC converter detects that energy can be extracted from the source connected to its input;(a) activating the DC-DC converter to an ON state wherein the DC-DC converter actively extracts energy from its input and transfers it to its output as long as the DC-DC converter detects that energy can be extracted from the source connected to its input and deactivating the DC-DC converter to the IDLE state as long as the DC-DC converter detects that energy cannot be extracted from the source connected to its input;(b) enabling the monitoring circuit so as to monitor that the voltage on the converter output does not rise above a first predetermined reference voltage;(c) enabling a masking mechanism that masks the output of the monitoring circuit until its output is valid;(iii) when the output of the monitoring is valid,(a) disabling the masking mechanism and read at least once the output of the power monitoring circuit;(b) returning to step (i) if the DC-DC converter detects that no further energy can be extracted from its input;(iv) when the masking mechanism is disabled and when the monitoring circuit detects that the voltage on the converter output has risen above the first predetermined reference voltage;(a) disabling the DC-DC converter to an OFF state;(b) monitoring that the DC-DC converter output has fallen below the second predetermined reference voltage;(v) when the monitoring circuit or the DC-DC converter detects that the voltage on the converter output has fallen below the second predetermined reference voltage, returning to step (iii) or disabling the monitoring circuit and going back to step (i). In this embodiment, once energy transfer by the DC-DC converter has commenced, the monitoring circuit is activated. Although it takes some time to do so, once the activation process has begun, it must be completed to read the output of the monitoring circuit at least once. This means that during the period required to wake-up the monitoring circuit, the DC-DC converter deactivate / reactivate depending on the source availability. The mandatory reading ensures event detection is not missed in cases where the source's sporadic availability causes each energy transfer duration by the DC-DC converter to be shorter than the time required to activate the monitoring circuit.

[0038] In a preferred embodiment compatible with the two variants of the operating method, the energy transfer to activate the monitoring circuit can occur on any DC-DC converter within the device operating towards the protected output. If multiple converters share a commonoutput, a single monitoring circuit can monitor the outputs of the multiple DC-DC converters. This eliminates the need to duplicate the monitoring circuit for each DC-DC converter.

[0039] Advantageously, the protection system deactivates all the DC-DC converters within the device operating towards the protected output. If multiple converters share a common output, a single monitoring circuit can control the protection mechanism for all the DC-DC converters simultaneously. This ensures synchronized control and eliminates the need for communication between multiple monitoring circuits and protection systems.

[0040] In an advantageous embodiment, the DC-DC converter can be disabled by other means at any time, resetting the system to a state where the DC-DC converter, the monitoring circuit and the protection system are OFF. Typically, a battery management system embedded into a power management integrated circuit dedicated to energy harvesting cannot deactivate the DC-DC converter quickly enough if a storage device is disconnected. In this scenario, the monitoring circuit functions as a failure detection mechanism that operates alongside the battery management system.

[0041] Brief description of the figures

[0042] An embodiment of the invention will now be presented with reference to the appended figures. Said embodiment and figures have no other purpose than illustrating an embodiment of the invention and have no limiting function.

[0043] Fig. 1 represents schematically a semiconductor device according to the invention.

[0044] Fig. 2 depicts another semiconductor device of the invention.

[0045] Fig. 3 to 5 are schematic representations of methods of the invention.

[0046] Fig. 6 and 7 depict chronographs demonstrating the operations of the system according to the invention.

[0047] Detailed description of the invention

[0048] Fig. 1 is a representation of a semiconductor device according to the invention comprising an energy harvester, a DC-DC converter, a storage element, and a monitoring circuit. The DC-DC converter regulates the voltage on the energy harvester connected to its input so as to maximize the amount of energy being extracted from the energy harvester. The DC-DC converter output is unregulated, meaning that the DC-DC converter does not regulate its output voltage to a fixed value. The protection system is indicated by the disabling arrow from the monitoring circuit to the DC-DC converter. The monitoring circuit is enabled only when its EN input is active, indicating the DC-DC converter is actively transferring energy from its input to its output. The monitoring circuit is designed to disable the DC-DC converter in the event of a system failure. A system failure being defined as a situation where the regular storage device becomes disconnected. In such an event, the output voltage of the DC-DC converter would rapidly increase, potentially causing an electrical failure of the system because of overvoltage.

[0049] The DC-DC converter typically functions as a switching converter to boost the voltage from a low-voltage input to a higher-voltage output. Examples of low-voltage inputs include energy sources made of a solar cel I, thermoelectric generator (TEG), or an RF antenna. Alternatively, it might be a down converter reducing the voltage from a high-voltage input to a lower-voltage output. Examples of high-voltage inputs include energy sources from piezoelectric harvesters or solar cells with several cells connected in series. The converter can be any type of switching converter, such as an inductive switching converter or a capacitive converter.

[0050] The storage device can be any means of storing electric energy, such as a capacitor, supercapacitor, rechargeable battery, or a hybrid lithium-ion supercapacitor. The monitoring means can consist of a comparator that compares an image of the output voltage of the DC-DC converter with a reference voltage. The image of the output voltage can be obtained, for instance, through a resistive divider.

[0051] Fig. 2 is a representation of a variant of the electronic device of Fig. 1 wherein the monitoring circuit further comprises a startup mechanism. The startup mechanism allows a fast start of the monitoring circuit so that its output is quickly available when the DC-DC converter starts to actively transfer energy from its input to its output. The startup mechanism can for instance be made of capacitive coupling with signal of the monitoring circuit, or a sleeping branch of bias current of the monitoring circuit allowing a faster wake-up of the monitoring circuit. In the figure, the output of the monitoring circuit is masked as long as the wake-up of the monitoring circuit is not completed in order to prevent a false detection of failure. The masking circuit can be made of a timer whose duration is longer than the time required for the startup mechanism to wake up the monitoring circuit. In this case, the timer is started when the monitoring circuit is enabled, and its output is used with combinatory circuitry to mask the output of the means used to monitor the output of the DC-DC converter (in this figure a comparator) as long as the timer duration has not elapsed.

[0052] Fig. 3 shows schematically a method wherein the DC-DC converter is initially disabled. When the DC-DC converter is enabled, it starts monitoring energy availability on its input (the IDLE state). Such enabling can occur for instance when the power management circuit including the DC-DC converter has started following the connection of an energy source to its input. In the IDLE state, the DC-DC converter monitors its input, typically to determine when the source voltage rises above a reference value that maximizes the energy provided by an environmental harvester connected to the DC-DC input. While no energy is being transferred (in other words, when the voltage on the harvester is below the reference voltage), the monitoring circuit remains off to save power consumption. When the DC-DC detects that energy must be transferred from its regulated input, it changes to the ON state where energy is actively being transferred to the DC-DC converter output, the monitoring circuit is thenenabled until the DC-DC converter stops transferring energy to the storage device because of lack of energy on the harvester. While the monitoring circuit is active, if the output voltage of the DC-DC converter rises above a first predetermined reference voltage, the monitoring circuit sends a command to the DC-DC converter to set it to the OFF state in order to prevent further increases in the output voltage. This disabling lasts until the voltage at the output of the DC-DC converter has fallen below a second predetermined reference voltage which is equal or lower than the first predetermined reference voltage. The monitoring system is not used to regulate the output of the voltage converter, as it does not trigger a charge transfer by the DC-DC converter when its output voltage falls below a target.

[0053] Fig. 4 shows schematically an alternative method where the DC-DC converter can be disabled to an OFF state by other means in addition to the monitoring system. Other means can for instance be a battery management system. In this method, the DC-DC converter is initially disabled. When the DC-DC converter is enabled, it starts monitoring energy availability on its input (the IDLE state). In the IDLE state, the DC-DC converter monitors its input, typically to determine when the source voltage rises above a regulation value that maximizes the energy provided by an environmental harvester connected to the DC-DC input. While no energy is being transferred (in other words, when the voltage on the harvester is below the regulated voltage), the monitoring circuit remains off to save power consumption. When the DC-DC detects that energy must be transferred from its regulated input, it changes to the ON state where energy is actively being transferred to the DC-DC converter output, the monitoring circuit is then enabled until the DC-DC converter stops transferring energy to the storage device because of lack of energy on the harvester. While the monitoring circuit is active, if the output voltage of the DC-DC converter rises above a first predetermined reference voltage, the monitoring circuit sends a command to the DC-DC converter to set it to the OFF state in order to prevent further increases in the output voltage. This disabling lasts until the voltage at the output of the DC-DC converter has fallen below a second predetermined reference voltage which is equal or lower than the first predetermined reference voltage. At any step, the other means (the battery management system in our example) can terminate the operation of the DC-DC converter and set it to the OFF state upon detecting that the storage device has reached its maximum charge voltage.

[0054] Fig. 5 illustrates an alternative method in which the monitoring system utilizes a masking mechanism and a start-up circuitry and where the DC-DC converter can be disabled by other means in addition to the monitoring system. In this method, the DC-DC converter is initially disabled. When the DC-DC converter is enabled, it starts monitoring energy availability on its input (the IDLE state). In the IDLE state, the DC-DC converter monitors its input, typically to determine when the source voltage rises above a regulation value that maximizes the energy provided by an environmental harvester connected to the DC-DC input. While noenergy is being transferred (in other words, when the voltage on the harvester is below the regulated voltage), the monitoring circuit remains off to save power consumption. When the DC-DC detects that energy must be transferred from its regulated input, it changes to the ON state where energy is actively being transferred to the DC-DC converter output. The masking mechanism is activated, and the startup mechanism helps the monitoring circuit to wake up as fast as possible. The monitoring system cannot be deactivated until the startup is considered as completed. As long as the startup of the monitoring system is not considered complete, the monitoring system cannot disable the DC-DC converter. During this period the DC-DC converter is either ON or IDLE depending on the availability of energy on the source. Once the startup of the monitoring system is considered as complete, the masking mechanism is disabled. Then, while the monitoring circuit remains active, if the output voltage of the DC-DC converter rises above a first predetermined reference voltage, the monitoring circuit sends a command to the DC-DC converter to set it to the OFF state in order to prevent further increases in the output voltage. The monitoring circuit remains enabled until the DC-DC converter stops transferring energy to the storage device because of lack of energy on the harvester. At any step, the other means (the battery management system in our example) can terminate the operation of the DC-DC converter upon detecting that the storage device has reached its maximum charge voltage.

[0055] Fig. 6 depicts a chronograph demonstrating the operation of a system featuring the object of this invention. A solar energy harvester is connected at the input of the DC-DC converter and a storage device such as a rechargeable battery is connected to its output. At the start of this chronograph, the DC-DC converter remains idle due to the voltage on the energy harvester being below the target regulated voltage, which could be the result of no energy production by the harvester. The monitoring circuit is disabled as there is no energy transfer from the regulated energy harvester to the energy storage device connected to the output of the DC-DC converter. When the voltage on the energy harvester increases as it starts producing energy, the DC-DC converter begins transferring energy from the harvester to the energy storage device connected to its outputs. During this phase, it regulates the voltage on the harvester, and the monitoring circuit is activated only when energy transfer occurs. In the graphs, the monitoring circuits thus alternates between the ON and OFF states. Meanwhile, the voltage on the storage device increases slowly. After some time, energy production ceases, causing the DC-DC converter to remain idle and the monitoring circuit to turn off. When energy becomes available again, the DC-DC converter reactivates, and the monitoring circuit turns on. The voltage at the converter output increases slowly again as energy transfers to the storage device. However, the storage device is disconnected at some point, and the output voltage of the DC-DC converter rises sharply, potentially damaging the converter circuitry. This may occur for instance due to a user error while testing the electronic device embedding the DC-DCconverter or because of a replacement of the battery while the device is harvesting energy. The monitoring circuit detects this situation and disables the DC-DC converter. The voltage on the energy harvester reaches its open-circuit voltage as it becomes unregulated. As there is no more storage device connected to the converter output, its voltage reduces because of the converter leakage and because of the consumption of the circuitry connected to it such as sensors, a microcontroller or wireless communication means. The DC-DC converter remains disabled while the output voltage exceeds the second predetermined reference voltage. When this event occurs, there is no more energy available from the harvester.

[0056] Fig. 7 depicts another chronograph demonstrating the operation of a system featuring the object of this invention. A solar energy harvester is connected at the input of the DC-DC converter and a storage mean such as a rechargeable battery is connected to its output. This system includes other means, such as a battery monitoring system, to deactivate the DC-DC converter. At the start of this chronograph, the DC-DC converter remains idle due to the voltage on the energy harvester being below the target regulated voltage, which could be the result of no energy production by the harvester. The monitoring circuit is disabled as there is no energy transfer from the regulated energy harvester to the energy storage device connected to the output of the DC-DC converter. When the voltage on the energy harvester increases as it starts producing energy, the DC-DC converter begins transferring energy from the harvester to the energy storage device connected to its outputs. During this phase, it regulates the voltage on the harvester, and the monitoring circuit is activated only when energy transfer occurs. In the graphs, the monitoring circuits thus alternates between the ON and OFF states. Meanwhile, the voltage on the storage device increases slowly. After some time, energy production ceases, causing the DC-DC converter to remain idle and the monitoring circuit to turn off. When energy becomes available again, the DC-DC converter reactivates, and the monitoring circuit turns on. The voltage at the converter output increases slowly again as energy transfers to the storage device. When the voltage at the output of the DC-DC converter finally reaches its end-of- charge voltage, the other means to deactivate the DC-DC converter triggers and prevents further charges from being transferred to the storage device. The voltage on the energy harvester reaches its open-circuit voltage as it becomes unregulated. In this example, the monitoring circuits did not trigger as the voltage on the output of the DC-DC converter never increased above the first predetermined reference voltage since no unexpected disconnection of the storage device occurred.

Claims

Claims1. A power management system for energy harvesting applications, comprising:- a DC-DC converter configured to transfer energy from an energy source to an energy storage device,- a protection system configured to prevent voltage surges at an output of the DC-DC converter,- a monitoring circuit configured to monitor a voltage at the output of the DC-DC converter and to compare it to a first predetermined reference voltage that is higher than the regulation voltage at the output of the DC-DC converter and to activate the protection mechanism when the voltage at the output of the DC-DC converter exceeds the first predetermined reference voltage, characterized in that the DC-DC converter is configured to regulate the voltage on the energy source connected to said energy source input and to transfer energy to the energy storage device connected to said energy source output until the voltage on the energy storage device connected to said energy source output reaches the regulation voltage, in that the monitoring circuit is enabled only during periods where the DC-DC converter actively transfers energy from the energy source towards the energy storage device and in that the protection system remains active until the voltage at the output of the DC-DC converter falls down below a second predetermined reference voltage that is equal or smaller than the first predetermined reference voltage, or until the power management system deactivates it.

2. A power management system for energy harvesting applications according to claim 1, wherein the monitoring circuit is also enabled as long as the protection system is active.

3. A power management system for energy harvesting applications according to claim 1 or2, wherein the monitoring circuit is a comparator having the following inputs:- a predetermined voltage reference and- the voltage monitored at the output of the DC-DC.

4. A power management system for energy harvesting applications according to any one of claims 1 to 3, wherein the first predetermined voltage reference is defined as the maximum operating voltage that the PMIC can afford without risk of failure.

5. A power management system for energy harvesting applications according to any one of claims 1 to 3, wherein the first predetermined voltage reference is defined as the maximum programmed voltage of the storage element.

6. A power management system for energy harvesting applications according to any one of claims 1 to 5, wherein the protection system is configured to disable the DC-DC converter when activated.

7. A power management system according to any one of claims 1 to 6 wherein the DC-DC converter has multiples outputs that are monitored by the monitoring circuit and that are protected by the protection circuit.

8. A power management system according to any one of the claims 1 to 7 wherein the monitoring circuit includes a startup mechanism.

9. A power management system as described in any one of the claims 1 to 8, wherein the monitoring circuit includes a masking mechanism that masks its output until the power monitoring circuit's output is valid after its activation.

10. A power management system for energy harvesting applications according to any one of the preceding claims, wherein the storage device comprises a rechargeable battery, large capacitor, or supercapacitor.

11. Semiconductor device comprising a power management system for energy harvesting applications according to any one of the claims 1 to 10.

12. A Method for operating a semiconductor device according to claim 11, comprising the steps of(i) (a) enabling a DC-DC converter to an IDLE state wherein the controller of the DC-DC converter monitors a source connected to the power input of the DC-DC converter; and (b) keeping a monitoring circuit disabled;(ii) when the DC-DC converter detects that energy must be extracted from the source connected to its input(a) activating the DC-DC converter to an ON state wherein the DC-DC converter actively converts energy from its input and transfers it to its output;(b) enabling the monitoring circuit so as to monitor that the voltage on the converter output does not rise above a first predetermined reference voltage;(c) if the DC-DC converter detects that no further energy can be extracted from its input, then returning to step (i);(iii) if the monitoring circuit detects that the voltage on the converter output has risen above the first predetermined reference voltage then;(a) disabling the DC-DC converter to an OFF state;(b) monitoring that the DC-DC converter output has fallen below the second15 predetermined reference voltage;(iv) when the monitoring circuit or the DC-DC converter detects that the voltage on the converter output has fallen below the second predetermined reference voltage, returning to step (ii) or disabling the monitoring circuit and going back to step (i).

13. A method for operating a semiconductor device according to claim 11, comprising the steps of(i) (a) enabling a DC-DC converter to an IDLE state wherein the DC-DC converter monitors a source connected to its power input; and(b) and keeping a monitoring circuit disabled;(ii) when the DC-DC converter detects that energy must be extracted from the source connected to its input;(a) activating the DC-DC converter to an ON state wherein the DC-DC converter actively converts energy from its input and transfers it to its output as long as the DC-DC converter detects that energy must be extracted from the source connected to its input and deactivating the DC-DC converter to the IDLE state as long as the DC-DC converter detects that no energy must be extracted from the source connected to its input;(b) enabling the monitoring circuit so as to monitor that the voltage on the converter output does not rise above a first predetermined reference voltage;(c) enabling a masking mechanism that masks the output of the monitoring circuit until its output is valid;(iii) when the output of the monitoring is valid,(a) disabling the masking mechanism and read at least once the output of the power monitoring circuit;(b) returning to step (i) if the DC-DC converter detects that no further energy must be extracted from its input;(iv) when the masking mechanism is disabled and if the monitoring circuit detects that the voltage on the converter output has risen above the first predetermined reference voltage then;(a) disabling the DC-DC converter to an OFF state;(b) monitoring that the DC-DC converter output has fallen below the second predetermined reference voltage;(v) when the monitoring circuit or the DC-DC converter detects that the voltage on the converter output has fallen below the second predetermined reference voltage, returning to step (iii) or disabling the monitoring circuit and going back to step (i).

14. The method of claim 12 or 13, wherein the energy transfer to activate the monitoring circuit occurs on any DC-DC converter within the device operating towards the protected output.

15. The method according to any one of the claims 12 to 14, wherein the protection system deactivates all the DC-DC converters within the device operating towards the protected output.

16. The method according to any one of the claims 12 to 15, wherein the DC-DC converter can be disabled by other means at any time, resetting the system to a state where the DC-DC converter, the monitoring circuit and the protection system are OFF.

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