Technical Field

The present invention relates, in general terms, a power management circuit. The present invention also relates to a circuit incorporating such a power management circuit. Background

Many electronic devices, such as sensors, used in Internet of Things (IoT) applications use hybrid-powering methods. These methods utilise two or more different power sources having different characteristics - e.g. different power levels. By switching between the two or more different power sources it is intended that the operational lifespan of the device will be prolonged.

One of the major hurdles of IoT devices is that they are typically always "On" - whether actively taking samples or whether in sleep mode, they continue to consume power. Moreover, there are often many such devices. This results in significant power consumption.

Reducing power consumption plays an important role in the extension of system life by reducing overall system current. The life of IoT devices is often constrained by the power consumption at the end-node - e.g. a sensor. Sensory end nodes are typically powered by batteries that last from several months to several years depending on the power consumption of the end node. Consequently, the longevity of such devices is limited by battery capacity relative to power consumption. It is possible in some cases to replace the battery towards the end of the life of the end-node. However, such replacement is not always practical or cost- effective. It would be desirable therefore to provide a power management circuit and/or a system incorporating such a circuit, that avoids or ameliorates one or more of the above-mentioned disadvantages of existing systems, or at least provides a useful alternative. Summary

Disclosed herein is a power management circuit, comprising: a power circuit for powering at least one device; a switch unit connectable to two or more power sources, the switch unit connecting the power circuit to one of the two or more power sources based on a power level of at least one said power source and an operating mode of the at least one device.

The switch unit may connect the power circuit to a first of said power sources (the first power source) when the power level of the first power source exceeds an upper predetermined threshold. When the power circuit is connected to the first power source, the switch unit may connect the power circuit to a second of said power sources (the second power source) when the power level of the first power source falls below a lower predetermined threshold. The upper and lower predetermined thresholds may be the same, or they may differ. For example, the upper predetermined threshold may be higher than the lower predetermined threshold.

Switching, by the switch unit, to the first power source may occur during an active state of the at least one device. Alternatively, or in addition, switching, by the switch unit, to the second power source may occur during an active state (i.e. while the device is performing an assigned task) of the at least one device. In each such case, the power management circuit enables uninterrupted operation of the at least one device, regardless of the state of the at least one device (active or inactive). The switch unit may determine the power level of the first power source based on a voltage level of the first power source.

The first power source may be an energy harvesting device. The switch unit may disconnect power from the power circuit when the at least one device is inactive. The switch unit may disconnect power from the power circuit once the at least one device toggles from an active mode to an inactive mode. The at least one device may be configured to execute one or more assigned tasks, and the switch unit may then disconnect power from the power circuit on receipt of a signal from the at least one device, the signal identifying when the at least one device has completed the one or more assigned tasks.

The power management circuit may further comprise a low-power timer for timing an interval between disconnection of power from the power circuit and reconnection of power to the power circuit.

Also disclosed herein is a system comprising: the power management circuit as described above; at least two of the two or more power sources (the circuit sources).

At least one of the circuit sources may be an energy harvesting device.

At least one of the circuit sources may be a battery. The system may further comprise the at least one device. The at least one device may include a light source. The at least one device may include a temperature sensor. Advantageously, the switching mechanism implemented by embodiments of the invention enables automated and seamless transition of power supply between multiple power sources. This is particularly advantageous where at least one of the power supplies is an energy harvesting source.

Advantageously, embodiments of the present invention reduce power consumption when compared with existing devices implementing power management circuits. In some cases, power consumption of the devices connected to the present power management circuit and be reduced down to nano-watt level, particularly during the standby/sleep/idle mode of the devices. Accordingly, embodiments of the invention reduce the power consumption of a device connected thereto by an order of magnitude below the internal setting levels of the sleep/deep sleep/idle/inactive mode of the device, when compared with prior art devices.

Implementing switching between power sources in the manner disclosed herein advantageously enables the use of multiple power sources, including hybrid power source options, for sensors. Such power sources include traditional power sources such as batteries and power cords, and energy harvesting sources.

Embodiments of the invention control the connection and disconnection of a device from the different energy sources without compromising operation of the device. In some embodiments, switching between power sources can take place even when the sensor or other device is performing its tasks (i.e. is in active mode), without disruption/restarting/delays.

As used herein, the term "inactive" or "inactive mode" may refer to the device in question entering a "sleep mode", "deep sleep mode", "idle mode" or any other mode where the device consumes very low power while it awaits later powering up to resume purposive operation (e.g. sensing or information gathering and transmission). The terms "assigned task", "assigned tasks", "assigned task(s)" and similar refer to tasks for which the device in question was developed. For example, a temperature sensor may be configured to periodically sense ambient temperature, and a light level sensor may be configured to periodically sense an ambient light level.

Brief description of the drawings

Embodiments of the present invention will now be described, by way of non- limiting example, with reference to the drawings in which:

Figure 1 illustrates a power management circuit and system in accordance with present teachings; and Figure 2 depicts an operating flow of the power management circuit and system of Figure 1.

Detailed description Described herein are power management circuits that provide an effective switching mechanism between multiple power sources, to ensure seamless transition between those power sources and to minimise power loss. Those same circuits can save power when compared with traditional power management circuits, to sustain device operation and save cost.

A system 100 incorporating such a power management circuit 102 is shown in Figure 1. The power management circuit 102 broadly includes a power circuit 104 and a switch unit 106. The power circuit 104 is for powering/delivering power to a device 108. For illustration purposes, embodiments herein will be described with reference to a single device 108 although it will be understood that the same teachings can be extended to two or more devices, as inferred by "N device" in Figure 1. This may involve extending the switch unit to incorporate switches for each device, or concurrently powering more than one device through the same switches. The switch unit 106 is connectable to two or more power sources, presently embodied by a first power source 110 and a second power source 112. In some embodiments there will be further power sources herein represented by N power sources 114.

The switch unit 106 connects power circuit 104 (which may include power flow line 105) to one of the power sources 110, 112 based on a power level of at least one of the power sources and an operating mode of the device 108. To that end, the switch unit 106 contains switches sufficient to affect switching between power sources. As a result, the circuit 102 and system 100 incorporating that circuit 102 can be capable of concurrently providing effective switching between multiple power sources while achieving low power consumption. Effective switching is achieved by the circuit 102 acting as an intermediary or intermediate step between the power sources 110, 112 and the end device 108, to effectively select the suitable power source 110, 112 and maintain seamless operation of the device 108. Thus, the circuit 102 is capable of auto-reconfiguring by selection of power sources based on power level of the power source and the operating mode of the device or devices.

In use, the switch unit 106 connects the power circuit 104 to a first of the power sources (e.g. the first power source 110) when the power level of the first power source 110 exceeds an upper predetermined threshold. When in this condition the power circuit 104 draws power from the first power source 110 to power the device 108. If the power circuit 104 is connected to the first power source 110, the switch unit 106 connects the power circuit 104 to a second of the power sources (e.g. the second power source 112) when the power level of the first power source 110 falls below a lower predetermined threshold. The switching signal is sent to the power sources on signal line 122, or power is simply connected to the relevant power source. In either case, on connecting a particular power source 110, 112, power then flows to the circuit 102 along respective power connector 124, 126. In view of the present teachings, the skilled person will appreciate that there may be further components on power connectors 105, 124, 126, and other components, than those explicitly shown in Figure 1. Inclusions that do not remove the functionality described herein do not step outside the scope of the present disclosure.

The switch unit 106 may determine the power level of the first power source 110 using any appropriate means, such as based on a voltage level of the first power source 110 or via a signal from the power source 110 to circuit 102. That voltage level or signal may be detected along line 120 in Figure 1. The mechanism for determining the power level of the first power source may vary depending on the nature of the first power source, such as whether it is a solar, thermal, wind, kinetic or other energy harvesting device. In general, power will be stored in a capacitor, super capacitor or battery of the first power source 110 with the voltage level or other indicator for the basis of switching to and from the first out of 110 been determined based on the manner in which power is stored. The first power source 110 may be any appropriate power source such as an energy harvesting device - for example, a solar-powered battery or kinetic power accumulator. On accumulation of charge by the energy harvesting device the power level of the first power source 110 increases. The power level increases until the upper predetermined threshold is reached. That threshold may be determined as a power level sufficient, for example, to maintain continued operation of the device 108 for a predetermined period of time - that period of time may change depending on the device in question and the application, as will be understood by the skilled person in view of present teachings. The switch unit 106 then switches power to the first power source 110 to deplete power from the first power source, until the power level of the first power source 110 reaches the lower predetermined threshold. At this time, the switch unit 106 switches back to the second power source 112. The action of switch to or from the first power source (e.g. to a second power source), can occur during an active state of the device. Therefore, the device can operate in an uninterrupted manner while the power source changes.

While the upper predetermined threshold and lower predetermined threshold can be the same, it is often desirable that those thresholds differ. In some circumstances, if they are the same, the switch unit 106 may rapidly switch back and forth between the first power source 110 and second power source 112 once the predetermined threshold power level of the first power source 110 is reached. This can disrupt device operation and thus be undesirable.

The second power source 112 is a more consistent or constant power source such as a battery, mains power or any other appropriate power source. Consequently, switching to the second power source 112 provides a more reliable source of power whereas the first power source 110, by harvesting energy, increases the total power output of all power sources over the life of the system 100. As mentioned above, some embodiments may provide three or more power sources. The switch unit may switch between each first power source - e.g. intermittent or energy harvesting device - and the second power source using any known switching scheme. For example, the switch unit may switch to the first power source that is the earliest to reach its upper predetermined threshold (the thresholds may be the same for each first power source, or each source may be provided its own upper and lower thresholds), deplete it down to its lower predetermined threshold and then switch to the first power source that was the next to reach its upper predetermined threshold. Once there are no first power sources at or above their respective upper predetermined threshold, the switch unit may switch to the second power source. Similarly, there may be two or more second power sources in some embodiments. In order to conserve power, the switch unit 106 may disconnect power from the power circuit 104 when the device 108 is inactive. The switch unit 106 may detect that the device 108 is inactive, and disconnect power from the power circuit 104, once the device 108 toggles from an active mode (e.g. for a sensor, the mode in which the sensor is sensing or measuring data) to an inactive mode. That toggling may be detected by removal of load in the power circuit 104. Alternatively, where the device 108 is configured to execute one or more assigned tasks, the switch unit 106 or circuit 102 may receive a signal from the device 108 identifying when the device 108 has completed its one or more assigned tasks. For example, if the device 108 is a temperature sensor configured to sense ambient temperature every minute, the device 108 may sense the temperature, transmit the sensed temperature measurement to a remote device (if applicable) and send a signal by signal route 116 of Figure 1 to the switch unit 106.

If the switch unit 106 disconnects power from the device 108, it needs to know when to switch back on power to the device 108 so that the device 108 can continue to perform its assigned task or tasks. To that end, the circuit 102 further comprises a low-power timer, or ultra-low power timer circuit, 118 for timing a period from disconnection of power from the power circuit 104. Once that period reaches a predetermined length of time, the low-power timer 118 causes the switch unit 106 to reconnect power to power circuit 104. To that end, the low-power timer 118 times an interval between disconnection of power from the power circuit 104 and reconnection of power to the power circuit 104. Alternatively, the low-power timer 118 may time intervals from the start of operation of the device 108.

The system 100 includes the power management circuit 102 and the power sources. In some embodiments, one of the power sources may comprise a power cord or connection to an external source of power. To that end, the term "power source" as used herein is intended to refer to a device from which power can be drawn through the switch unit 106 into power circuit 104 to power device 108.

In addition, the system 100 may also include the device or devices 108. This will be the case particularly where the system 100 is intended to be a disposable, integral unit.

This process is further described with reference to Figure 2. At the start 202, the switch unit is connected to the main source of power (e.g. second power source 112 of Figure 1) and energy harvester (e.g. first power source 110 of Figure 1). By default, the switch unit connects the main source of power (e.g. battery) to the device, while the energy harvester accumulates energy collected from the surroundings - 204. The device in the present embodiment is a sensor that starts operating (206) initially using the main source of power. If the power level in the energy harvester has not reached the predetermined upper threshold (query 208), the switch unit maintains connection between the main source of power and the power circuit - 210. If the power level in the energy harvester has reached the predetermined upper threshold (query 208), the switch unit switches to, or maintains, connection between the energy harvester and the power circuit - 212. Once the sensor finishes its assigned task or tasks (214), it sends a "DONE" signal to the switch unit (216). The switch unit then enters the system into a power saving mode (218) by disconnecting power to the device.

In the embodiment of Figure 2, as the energy stored in the harvester reaches a pre-determined level, a signal is sent (e.g. over line 120) to the switch unit to connect the energy harvester to the device. Thus, query 208 may involve determining whether that signal has been received. If the signal has not been received or the switch unit otherwise determines the upper predetermined threshold of the energy harvester is not been reached, the switch unit connects, or maintains a connection, between the main power source and device (210). If the switch unit instead determines that the upper predetermined threshold has been reached, the switch unit connects, or maintains a connection, between the energy harvester and device (212).

Once the energy harvester has been connected to the device (212), for each successive round of operation of the device the switch unit may maintain the connection between the energy harvester and the device until the lower predetermined threshold has been reached is determined at query 208. When the energy stored in the harvester is depleted to a pre-set level (i.e. the lower predetermined threshold), the switch unit disconnects the device from the energy harvesting source, switches back to the main source of power, and the energy harvester resumes accumulating power.

Query 208 may run once for each operation of the device, or may run continuously such that the power source can be switched during operation of the device (220).

The energy harvester may also continue to accumulate power as its power is being depleted and between successive operations of the sensor. As a result, the device can be powered continuously without disruption, while the lifetime of the device can be extended particularly where the main power source is a battery.

When operation of the device finishes (214), the device sends a DONE signal to the switch unit indicating that the operation has completed (216) as mentioned above. The switch unit then disconnects power to the device (218). To ensure power is reconnected to the device prior to the device needing to perform its next assigned task, a timing circuit is implemented. Thus, the time between performance of step 218 and the re- performance of step 206 (i.e. the standby duration) is determined by the timing circuit.

The timer circuit (e.g. circuit 118 of Figure 1) controls the standby duration of the device, and this can be configured based on specific application's requirements - for example, if the device is a temperature sensor that need to check a temperature every minute, the standby duration will be equal to 1 minute minus the amount of time the device takes to measure the temperature. This is referred to as the standby duration or pre-set interval. After the pre-set interval, the timer circuit sends a signal to the switch unit to wake up and provide power to the device and perform its functions (e.g. data sampling, data transmission and others). Once the device completes its assigned tasks, a DONE signal (to indicate the tasks have been completed) is sent to the timer circuit as discussed above, and the timer circuit shuts down the device. Instead of wasting energy to maintain the device in sleep/deep sleep/idle/inactive mode, which accounts for a large percentage of power consumption from the energy sources, the timer circuit is implemented to reduce the overall power consumption of the device. The power consumption during the period of time the device would normally have been in active is therefore reduced by the difference between the amount of power the device would have consumed while inactive and the amount of power consumed by the low-power timer circuit.

The present circuit 102, and a system 100 incorporating that circuit 102, may be employed for many applications such as those involving IoT sensors and devices that rely on hybrid or multiple energy sources. The skilled person will appreciate that there is no limitation intended for the device or devices 108.

Many IoT sensors and devices operate under duty-cycle operation, where they remain active for a short period of time and predominately stay in standby/sleep mode. However, devices in sleep mode still typically consume power, affecting the longevity of the sensors. In addition, the increasing demand for data requires thousands of sensors to be implemented. In such applications, the present circuit 102 and system 100 provide the effective power management necessary to ensure seamless transition between two or more power sources, while at the same time reducing the power consumption of the device. Moreover, the power management circuit can adaptively (based on power level of the harvesting source and operating mode of the device) and automatically (no manual configuration required) determine the suitable power source to connect to the end user device. This same principal can be applied across more than two power sources, such as where different first power sources 110 are connected to a switch unit 106 for managing multiple devices 108 having different energy consumption requirements.

It will be appreciated that many further modifications and permutations of various aspects of the described embodiments are possible. Accordingly, the described aspects are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.