Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
  • H02J1/04—Constant-current supply systems
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
  • G06F1/26—Power supply means, e.g. regulation thereof
  • G06F1/266—Arrangements to supply power to external peripherals either directly from the computer or under computer control, e.g. supply of power through the communication port, computer controlled power-strips
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
  • H02J1/06—Two-wire systems
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
  • H02J13/00002—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by monitoring
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
  • H02J13/00032—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for
  • H02J13/0005—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for the elements or equipment being or involving power plugs or sockets
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L12/00—Data switching networks
  • H04L12/02—Details
  • H04L12/10—Current supply arrangements
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L12/00—Data switching networks
  • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
  • H04L12/40—Bus networks
  • H04L12/40006—Architecture of a communication node
  • H04L12/40045—Details regarding the feeding of energy to the node from the bus
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
  • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
  • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
  • Y04S10/30—State monitoring, e.g. fault, temperature monitoring, insulator monitoring, corona discharge

Definitions

• the present invention relates to power consumption of a slave device on a current controlled communication bus.
• Wired communication links based on current control providing both communication infrastructure and power to slave devices, such as for example industry standard 4-20mA current loops and M-Bus protocols for metering applications, may have significantly fluctuating voltage due to the current control, the possibly significant wire lengths, and other electrical parameters. Further the communication protocol, for example in an M-Bus environment, may provide for a master device to communicate by voltage drops, while the slave devices communicate by alternating between different constant currents.
• a slave device In practice, in a bus system based on a current controlled communication bus, a slave device is in control of the current drawn from the bus, which is known already at design time, but must expect and be able to handle bus unknown voltage levels and fluctuations, including significant voltage drops during indefinite periods. This means, that the slave device cannot expect to be able to draw more power at any given time than provided by a minimum bus voltage multiplied by the known, constant current.
• the power supplies of slave devices are typically designed to be able to perform their functionality with only this minimum power available.
• the slave device functionality may not be able to consume the higher power resulting from the same, constant current combined with the higher voltage, as it is designed to maintain its function with only the minimum power.
• slave device power supplies have typically been provided with an overflow circuit to allow a part of the constant current to bypass the slave device functionalities to absorb the excess power during periods with higher than minimum bus voltage.
• a typical prior-art solution as illustrated in Fig. 3, provides a Zener diode to maintain a constant voltage of the power supply output Vfunc. Combined with the constant current, this prior-art solution provides a well-defined and reliable voltage, and thereby power, to the slave device functionality.
• the Zener diode is typically chosen with a Zener breakdown voltage a few volts below the absolute minimum bus voltage to ensure a constant voltage level at the output.
• the inventors have identified the above-mentioned problems and challenges related to power supplies of slave device of current controlled communication busses, and subsequently made the below-described invention which may increase the efficiency of slave devices by providing for utilizing a higher amount of the delivered power.
• the invention relates to a slave device power supply for a two-wire current controlled communication bus, the current controlled communication bus providing a variable bus voltage to a slave device, the slave device being arranged to draw a constant slave current from said current controlled communication bus and provide slave device functions, the slave device comprising a slave device power supply comprising: an energy storage arranged to power said slave device functions; a charger for charging said energy storage from said constant slave current, thereby affecting a charge voltage; said charger comprising an overflow circuit arranged to draw excess charge from said constant slave current; wherein said overflow circuit is arranged to draw said excess charge when a relationship between said charge voltage and said variable bus voltage fulfils a predetermined overflow criterion.
• the present invention provides an advantageous power supply solution to be used in aslave device of current controlled communication busses to power the slave device from the bus, by providing for improved power efficiency.
• the present invention allows the slave devices to utilize a higher bus voltage during periods where it is available, thereby providing a more efficient use of the bus power.
• a slave device power supply of the present invention may be able to provide the improved functionality by utilizing higher bus voltages when available, thereby enabling a lower constant slave current.
• the present invention may be particularly advantageous for improved slave device functionality which would conventionally require the slave device to settle on a constant slave current outside the recommend range of the communication bus protocol, arrange for alternative power supply outside the bus, or jeopardizing the capability of the master device to power the entire bus.
• a slave device with improved slave device functionality with higher power consumption than normal slave devices may be used in a conventional current controlled communication bus without exceeding the regulations, without abusing the master device and without alternative external power supply arrangements.
• the bus voltage of an M-Bus may for example have an average bus voltage of 15V, varying between 8V and 20V when a master device is communicating on the bus.
• a prior art slave device with demanding slave device functionality for example a gateway, may require a current supply corresponding to 7 M-Bus unit loads, i.e. 10.5mA, which even requires special system considerations because the current draw is outside the standardized range.
• the embodiment may for example set a constant operational current at a modest 3 M-Bus unit loads, i.e. 4.5mA, which is within the standardized range.
• a constant operational current at a modest 3 M-Bus unit loads, i.e. 4.5mA, which is within the standardized range.
• 12V energy storage voltage from the example average 15V bus voltage
• the present invention while dissipating only 43% (67.6mW/l57.5mW) of the prior art power, anyway delivers 43% (54mW/37.8mW) higher power to the slave device functionality.
• the present invention embodiment example has an efficiency of 80% (54mW/67.5mW), i.e. more than 3 times higher than the prior art, and achieved with an embodiment that does not require exemptions from the standard and special considerations to install.
• a further achievement of the present invention in continuation of the above example, is that the delivered power of the present invention will even increase with increased bus voltage, maintaining about the same efficiency, whereas the prior art example will become even poorer with respect to power efficiency with higher bus voltages, and provide the same power regardless of bus voltage.
• the criterion for invoking the overflow circuit is not based on the voltage exceeding a minimal bus voltage as in prior-art solutions, but is instead based on a relationship between the but voltage and the charging voltage. Thereby the present invention takes advantage of periods with higher than minimum bus voltage, contrary to the prior art.
• the present invention does not change any requirements of the slave device with respect to the current controlled communication bus, and embodiments may thus fully comply with various bus standards and regulations, for example the M-Bus or 4-20mA current loops.
• a slave device power supply of the present invention may be retrofitted into existing slave devices, and slave devices incorporating the power supply of the present invention may be used in existing bus systems, e.g. by adding or replacing slave devices of any existing M-Bus system in order to add more power demanding functionality.
• the slave devices of the present invention may likewise be used in new installations of, for example, M-Bus systems, thereby taking advantage of less requirements to the master device power supply.
• a communication bus in the context of the present invention is a wired connection comprising at least two devices which are in practice parallel-coupled from an electrical point of view.
• the wired connection may have a significant length, for example several meters, such as more than 2m or more than lOm or even more than lOOm in some embodiments.
• the devices may for example be a master device and one or more slave devices.
• the communication bus enables one or more of data, status and control communication from the slave devices to one or more of the other devices, for example to the master device.
• the communication bus also enables communication, in particular control communication, from the master device to the slave devices.
• current controlled communication bus is referred to a communication bus where the bus current is regulated according to predetermined rules, for example because the current level may be used for signalling.
• each device is required to draw a constant, although adjustable, current from the bus.
• Current controlled communication busses may for example comprise the M-Bus standard EN 13757-2, or so-called current loops, for example according to the 4-20mA industrial standard, with or without an overlaid HART communication protocol.
• Advantages of a current controlled communication bus, as compared to a voltage controlled bus is among others, a robustness to voltage drops over long wires and high noise immunity. Further, a current controlled communication bus allows powering of the slave devices from the bus current as long as the slave devices do not require more power than defined by the constant current together with the available fluctuating bus voltage.
• the current controlled communication bus further provides a variable bus voltage to the slave device, which comprises a slave device power supply to power the functionality of the slave device.
• the slave device provided the available bus power is sufficient, do not require external power to be provided, thereby increasing the flexibility and simplicity in location, installation, maintenance and troubleshooting.
• the current controlled communication bus according to the present invention is a two-wire bus, for example established by conventional electricity cables or, preferably, by twisted pair cables.
• the two-wire restriction further provides that both the powering of slave devices and the communication from and to slave devices takes place over the same two wires. This further increases flexibility and simplicity, as well as reduces costs.
• a constant current in accordance with the present invention may be adjustable between two or more quantized current level, or over a continuous range, but is substantially independent from the supply voltage.
• the constant slave current is in an embodiment substantially independent from the variable bus voltage.
• the constant slave current is for example adjusted between a constant operational current during normal operation and modulated between the constant operational current and a constant transmission current during communication.
• the slave device preferably comprises a slave device current generator for drawing the constant slave current from said current controlled communication bus.
• the slave device current generator may in an embodiment be a controllable current generator CCG adjustable between generating a constant operational current as slave current, and an increased slave current established increasing the constant operational current by a constant transmission current, together defining the constant slave current.
• the slave device current generator may in an embodiment comprise an operational current generator generating the constant operational current and a transmission current generator alternatingly turning a constant transmission current on and off depending on communication requirements, together forming the constant slave current alternating between the operational current and the increased current consisting of the operational current and the transmission current.
• an operational current generator generates a constant operational current corresponding to an integer number of M-Bus unit loads according to the M-Bus standard EN 13757-2, for example l.5mA, 3.0mA or 4.5mA.
• Slave device functions may be provided by a slave device functionality circuit, e.g. implemented by an analog or digital circuit, a microprocessor or signal processor, a complete system-on-chip or system-on-module, an embedded computer controller, a single-board computer, etc., as long as it can be powered by the constant bus current and available fluctuating bus voltage.
• the slave device functionalities may for example involve measuring or controlling external parameters, e.g. temperature, flow, pressure, valves, switches, alarms, etc., providing a user interface for output and/or input, providing gateway or data conversion functionality, e.g. for receiving or transmitting data over a different communication channel, e.g. a wireless channel, etc.
• the voltage of the current controlled communication bus is variable or non constant due to the current control, the possibly significant wire lengths, and other electrical parameters.
• the communication protocol of the current controlled communication bus provides for the master device to communicate by voltage drops, while the slave devices communicate by alternating between different constant currents.
• a slave device is in control of the current drawn from the bus, but must expect and be able to handle bus voltage fluctuations, including significant voltage drops during indefinite periods. This in turn means, that the slave device must also be able to handle a fluctuating power, and when necessary in order to maintain a constant current, be able to discard excess power through an overflow circuit.
• an energy storage In order to accommodate the fluctuating bus voltage, an energy storage is provided.
• Main components of the energy storage preferably comprise one or more capacitors or other components suitable for storing electric energy.
• the energy storage may comprise additional components, e.g. various safety and monitoring circuits, e.g. for avoiding unintended discharge, e.g. through the charger, avoiding extreme discharge current, etc.
• the energy storage may power said slave device functions directly, or through a power converter or regulator, e.g. a DC-to-DC converter.
• the energy storage is charged from the constant slave current by a charger.
• the voltage level required to add charge into to energy storage is herein referred to as a charge voltage.
• the charger may direct the full amount of the constant slave current, or in other embodiments the constant operational current, into the energy storage, thereby increasing the charge voltage and an energy storage voltage.
• the slave device functionality may consume power from the energy storage.
• the charger is not able to direct further current into the energy storage, and an overflow circuit is provided to dissipate the excess current I vent required to maintain the constant slave device current required by the constant current communication bus protocol.
• the overflow circuit is arranged to step in when a relationship between the charge voltage V C hr g and the variable bus voltage Vbus fulfils a predetermined overflow criterion.
• the relationship between the charge voltage V C hr g and the variable bus voltage Vbus may in an embodiment correspond a voltage difference between the bus voltage and the charge voltage. In an embodiment this voltage difference corresponds to a voltage drop over the slave device current generator or a part of it, for example a controllable current generator or an operational current generator, generating the constant slave current.
• the relationship between the bus voltage and the charge voltage may in various embodiments be expressed in terms of voltage, e.g. an absolute voltage difference, or expressed in percent or ratio, e.g. a charge voltage to bus voltage ratio or voltage difference in percent of the bus voltage or the charge voltage.
• the predetermined overflow criterion applies to the relationship between the charge voltage and bus voltage to determine when the overflow circuit should be activated.
• the overflow criterion may involve a threshold for the voltage difference or ratio, e.g. by defining the overflow circuit to activate when the voltage difference gets below a certain threshold or when the charge voltage increases above a certain percentage of the bus voltage, and defining the overflow circuit to deactivate when the voltage difference gets above the threshold or above a certain percentage of the bus voltage.
• the overflow criterion may comprise difference thresholds for activation and deactivation, thereby implementing a hysteresis function, and/or may comprise an activation or deactivation range over which the overflow circuit gradually activates or deactivates.
• the overflow criterion is predetermined, meaning that the parameters compared by the criterion and the threshold or range for activating and deactivating the overflow circuit are predetermined in accordance with the design of the current generators, energy storage and overflow circuit, and preferably also in accordance with the intended application, for example expected levels of minimum and maximum bus voltage, etc.
• An advantageous embodiment is obtained when said overflow criterion is fulfilled when a difference between said charge voltage and said variable bus voltage gets below a predetermined voltage difference.
• the difference between the bus voltage and the charge voltage is compared with a voltage reference, or the voltage reference is subtracted from the bus voltage or added to the charge voltage, respectively, and compared with the charge voltage or the bus voltage, respectively.
• the skilled person is aware of numerous circuits and algorithms to compare values, and which can readily be implemented in the present invention for determining when the overflow criterion is fulfilled. Examples of suitable embodiments of comparison circuits are provided below.
• the predetermined voltage difference V ref may be a reference voltage generated in any suitable way well-known to the skilled person, e.g. by drawing a constant current through a constant resistance, or by application of a diode, a Zener diode or a voltage regulator.
• a key principle advantageously applied by the present invention involves keeping the slave device current generator transferring charge to the energy storage regardless of the charge voltage as long as it is able to maintain the constant slave current this way. This is in contrast to prior art, where charging is stopped at a predetermined charge voltage, typically defined by a Zener breakdown voltage.
• the energy storage voltage is in embodiments of the present invention most of the time increased significantly above the minimum voltage which is precautionary chosen in prior art solutions, whereby the present invention enables more efficient use of the energy stored in the energy storage, e.g. by power conversion requiring a certain voltage level before it gets efficient.
• the charging of the energy storage is only stopped when sufficient charge can no longer be moved because the charge voltage approaches the bus voltage or the bus voltage decreases to or below the charge voltage.
• a preferred overflow criterion is therefore based on this principle, so that the overflow criterion is determined to engage the overflow circuit only when it becomes impossible to transfer the necessary charge required to maintain the constant slave current to the energy storage.
• slave device comprises a slave device current generator arranged to generate said constant slave current.
• the slave device current generator according to the present invention may be implemented by one or more current generators arranged to establish and maintain the constant slave current required by a current controlled communication bus.
• the current generator may be implemented by discrete analog components, by dedicated current generator integrated circuits, or any other suitable means.
• said slave device current generator comprises a controllable current generator adjustable between generating a constant operational current and an increased current being the constant operational current increased by a constant transmission current, said constant operational current and said increased current defining the constant slave current.
• a controllable current generator may be advantageous as it may be arranged to provide the correct constant slave current during normal operation, also herein referred to as a constant operational current, as well as for providing the correct constant slave current during transmission of communication, for slave devices on a communication bus where slave devices communicate by means of changing the constant slave current.
• Both the lower, constant operational current and the higher current formed by the constant operational current and the constant transmission current may be used to charge the energy storage, and be led through the overflow circuit when the energy storage is not able to absorb the provided current.
• said slave device current generator comprises an operational current generator generating a constant operational current and a transmission current generator generating a constant transmission current, said constant operational current and said constant transmission current defining the constant slave current.
• two current generators are provided, for generating the constant operational current and the constant transmission current, respectively.
• the operational current generator is generating current, which is used for charging the energy storage or bypassed through the overflow circuit.
• both current generators are invoked, thereby together generating the increased slave current consisting of the constant operational current and the constant transmission current.
• the transmission current generator may provide the constant transmission current to the energy storage and/or overflow circuit, or may be provided with another power dissipation circuit, e.g. a resistor connected to ground.
• said charger comprises a voltage controlled switch arranged to test said relationship between said charge voltage and said variable bus voltage.
• the overflow circuit is controlled in accordance with an overflow criterion related to a relationship between the charge voltage and the bus voltage. Determining when this overflow criterion is fulfilled may in an embodiment be done by a voltage controlled switch, e.g. letting the switch be controlled by a voltage difference between the charge voltage and the bus voltage being above or below a reference voltage.
• the voltage controlled switch is an electronic switch, e.g. transistor based, arranged to activate or deactivate the overflow circuit in dependency of the relationship between the charge voltage and the bus voltage.
• said voltage controlled switch comprises one or more transistors.
• the voltage controlled switch is preferably implemented as an electronic switch based on transistors, such as for example bipolar junction transistors, field-effect transistors, etc.
• said voltage controlled switch comprises a Darlington transistor circuit.
• An embodiment with a Darlington transistor circuit as voltage controlled switch may provide a stable, reliable and high-current capable switch.
• An advantageous embodiment is obtained when a representation of said charge voltage is applied to an emitter terminal or source terminal of a transistor based circuit, and a representation of said variable bus voltage minus a predetermined voltage difference is applied to a base terminal or gate terminal of said transistor based circuit. [0054] Thereby a comparison of the voltage difference between the charge voltage and the bus voltage with a predetermined voltage difference may be implemented.
• said overflow circuit comprises one or more transistors.
• the transistors may be any kind of transistor technology, preferably capable of transferring relatively high currents, in case that the complete constant slave current needs to bypass the energy storage through the overflow circuit.
• said overflow circuit comprises a Darlington transistor circuit for drawing said excess charge.
• Darlington transistor circuits have an advantageous high-current capability, but other circuits may be implemented to achieve the same or different advantages.
• An advantageous embodiment is obtained when said overflow circuit comprises a Darlington transistor circuit arranged to both determine when said overflow criterion is fulfilled and to draw said excess charge when said overflow criterion is fulfilled.
• the energy storage comprises one or more capacitors.
• Capacitors are typically able to charge and discharge very fast, making them excellent for temporary energy storage.
• the capacitors may be any kind of capacitors.
• the capacitor has a capacitance in the range of lpF - lOOOpF, for example lOpF.
• the capacitor should preferably be dimensioned with respect to the maximum and minimum bus voltages expected, and with a capacity sufficient to accommodate energy for powering the slave device during periods where the bus voltage may drop due to communication.
• the energy storage comprises a diode arranged to avoid the energy storage to discharge through the overflow circuit.
• a diode is provided in the charging connection.
• Other rectification means or active switches may be used to prevent discharging, while still allowing charging.
• An advantageous embodiment is obtained when the charge voltage is above
• An advantageous feature of an embodiment of the present invention is that the charge voltage is considerably higher most of the time, than in prior art solutions. This is because the present invention is able to utilize the higher bus voltage present most of the time, while still being able to handle the voltage drops occurring during communication.
• the slave device power supply comprises a power converter to convert an energy storage voltage to a device functions voltage.
• the energy storage voltage of the present invention is considerably higher than in prior art solutions, and considerably higher than usually required by the slave device functions, which may for example require 3.6V DC, it may be sufficiently high to make a power conversion beneficial, thereby being able to transfer power very efficiently to the slave device functionality.
• the power converter is a DC- to-DC converter, preferably a switching DC-to-DC converter.
• Examples of advantageous power converters are for example DC-to-DC converters, in particular high-efficient switching DC-to-DC converters.
• the slave device power supply is arranged to provide a functions current to said slave device functions, the functions current being greater than said constant operational current.
• the slave device functions may be provided with a higher current than the constant slave current, thereby overcoming the usual constraint in the prior art where the constant slave current must be high enough to power all functions of the slave device because the voltage, and thereby power, is precautionary clipped at a minimum voltage.
• the slave device may draw a constant operational current of 3 M-Bus unit loads corresponding to 4.5mA, but due to the power- conserving solution of the present invention where the higher bus voltage is used when available, the current provided to the slave device functionality by the slave device power supply may be for example l5mA at the lower voltage of for example 3.6V.
• said slave device comprises a gateway, for example a wireless transceiver.
• the improved power efficiency of the present invention enables powering a communication gateway or a wireless transceiver, e.g. a gateway for converting between the wired communication bus and wireless communication.
• slave device functions comprises utility metering, utility consumption monitoring or automated metering system concentrator functions.
• present invention is particularly advantageous for use in utility metering systems as power supply for an M-Bus-connected concentrator or gateway unit, or an M-Bus-connected meter, e.g. an ultrasonic flow meter.
• an advantageous embodiment is obtained when said constant operational current is in the range of approx. l.5mA to approx. 6mA, for example in the range of approx. 3mA to approx. 4.5mA or in the range of approx. 4.5mA to approx. 6mA, such as approx. 4.5mA.
• the constant operational current is relatively low, e.g. in the range of 1.5mA to 6mA, as prescribed by current controlled communication busses such as for example M-Bus.
• a slave device with constant operational current in this range may be readily accepted by the system designer and conventional master devices, without exemptions or tweaks.
• An advantageous embodiment is obtained when said constant operational current is an integer multiple of approx. l.5mA.
• An embodiment is particularly useful when designed specifically for the M- Bus standard.
• variable bus voltage is in the range of 6V to 75V, for example in the range of 12V to 42V, such as in the range of 24V to 36V.
• the present invention is particularly advantageous in low voltage systems, where safety requirements are easily satisfied, but where the available power is therefore also low, considering operational currents in for example the range of 1.5m A to 6mA, as the present invention achieves to more efficiently utilize the available power. Further, where a variable bus voltage also often challenges prior art systems or requires them to precautionarily stick to a minimum voltage, the present invention allows to utilize the higher voltages within the low voltage range when available. [0089] An advantageous embodiment is obtained when said current controlled communication bus is an M-Bus, for example in accordance with European standard EN 13757-2.
• the M-Bus standard appreciates low current slave devices robust to significant voltage variations.
• the present invention is highly advantageous over prior art solutions in such scenarios.
• said constant operational current is an integer multiple of M-Bus unit loads, for example in the range of 1 to 6 unit loads, such as 2 to 4 unit loads, e.g. 3 unit loads.
• the constant operational current is chosen at an M-Bus level, preferably within the recommend range.
• the relatively low current e.g. in the range of 1.5mA to 6mA, corresponding to a few M-Bus unit loads, e.g. 1 - 4 unit loads, may further be readily accepted by the system designer and conventional master devices, without exemptions or tweaks.
• Twisted pair cables are highly flexible, easy to install, available in numerous variants at reasonable costs, and are very robust to electric noise.
• said current controlled communication bus is at least 25m long, for example at least 50m long, such as more than lOOm or more than 200m long.
• the current controlled communication bus may be relatively long, thereby causing a high voltage drop along the wires, and thereby different bus voltages along the bus wire.
• the present invention is particularly advantageous in scenarios with long cables, as is provides a better efficiency by utilizing higher bus voltages, while at the same time being very robust to voltage variations and drops.
• An advantageous embodiment is obtained when at least 5 slave devices, for example at least 10 or 20 slave devices, such as more than 50 or 100 slave devices are connected to said current controlled communication bus.
• said current controlled communication bus comprises a master device supplying power to said current controlled communication bus and thereby to said slave device.
• the master device may be an integration of a bus power supply providing the bus voltage and the relevant level of bus current to the current controlled communication bus.
• An advantageous embodiment is obtained when said current controlled communication bus provides for the slave device to transmit communication by increasing said slave device current from said constant operational current by said constant transmission current to indicate a symbol on said current controlled communication bus.
• An advantageous embodiment is obtained when a master device of the current controlled communication bus provides communication to the slave device by affecting a voltage drop of the variable bus voltage of at least 5.5 V or at least 8.2V, such as a voltage drop of 12V, to indicate a symbol.
• variable bus voltage varies with the length of the current controlled communication bus and with communication sent to slave devices from a master device.
• the invention relates to a slave device comprising a slave device power supply according to any of the above.
• the slave device may advantageously be arranged for connection to a current controlled communication bus as described above, for example an M-Bus or a 4-20mA current loop, and with the slave device power supply of the present invention being more power efficient and/or less current demanding than prior art slave devices.
• the slave device is a gateway for a wired M-Bus system, the gateway comprising a wireless transceiver arranged to communicate with wireless devices.
• a wireless gateway for connecting wireless devices, e.g. wireless flow meters or the like, to a wired M-Bus requires more power than most M-Bus devices. It has therefore conventionally required a local power supply in addition to the power drawn from the bus, or has required drawing an excessive number of M-Bus unit loads, for example 7 unit loads, i.e. 10.5mA.
• figs. 1-3 illustrate prior art embodiments
• figs. 4 illustrates an embodiment of the invention
• figs. 5-7b illustrate various current generator embodiments of the invention
• figs. 8-10 illustrate various overflow circuit embodiments of the invention
• fig. 11-12 illustrate various energy storage embodiments of the invention
• fig. 13 illustrates a combined view of an embodiment of the invention
• fig. 14 is an overview according to the invention
• fig. 15 is a plot showing a characteristic difference between the voltage development in a prior art solution and the present solution.
• Fig. 1 illustrates a prior art two-wire current controlled communication bus CB.
• the bus CB may for example be an M-Bus, primarily used for metering systems with wired remote reading functionality.
• the bus CB is a current loop industrial communication bus, for example a 4-20mA or HART bus, for example used to propagate data from sensors or control signals to actuators.
• the master device MD typically provides power and control information to the slave devices SD, who return data and status information.
• the current controlled communication bus CB may be considerably long, for example tens or hundreds of meters in larger buildings or factory facilities, and may preferably be established using twisted pair cables.
• Fig. 2 illustrates a simplified prior art slave device SD coupled to a current controlled communication bus CB such as for example an M-Bus.
• the slave device is required by the M-Bus standard to draw a constant operational current I op during normal operation, and modulate this by a transmission modulator when transmitting data, by adding a constant transmission current I tx to indicate communication symbols on the communication bus CB.
• the constant operational current I op sometimes modulated by the constant transmission current I tx , is referred to as the constant slave device current I s iave.
• V bus The supply voltage of the current controlled communication bus CB is denoted V bus and is associated with one of the two bus wires. The other wire is associated with ground GND.
• the bus voltage V bus as supplied by the master device may typically be in the range 12V - 40V, but will of course decrease with the distance between the master device and a slave device, depending on the type of cable.
• the master device In order for the master device to indicate communication symbols on the bus, it decreases the bus voltage V bus by 12V, whereby the bus voltage drops to, for example, 0V - 32V.
• a receiver RX is provided in the slave device SD to recognize the bus voltage drops and interpret them as communication from the master device MD.
• the slave device SD further comprises slave device functions, i.e. the purpose of the slave device.
• the functions FUNC may for example be metering or concentration of meter readings.
• the slave device SD is powered from the current controlled communication bus CB via a slave device power supply PS, primarily for powering the slave device functions by a functions voltage V fUnc and functions current I fUnc .
• the power supply PS must be designed so that it consumes all the current that is expected from the communication bus, as the constant operational current CS must be maintained at all times.
• FIG. 3 illustrates a prior art slave device power supply.
• a current generator is provided in order to ensure the provision of a constant slave current I siave .
• the constant slave current I siave is used to charge a capacitor C, which may be discharged by the slave device functions via a low-dropout voltage regulator LDO, for example a 3.6V regulator to provide a functions voltage V fUnc of 3.6V.
• LDO low-dropout voltage regulator
• the conventional M-Bus slave device power supply of Fig. 3 is, however, not very efficient. Because of the precautionary constantly low capacitor voltage, a large voltage drop, and thereby power, must be handled by the current generator, during all the periods with higher bus voltage, for example 20-40V. Besides the higher demands on current generator components to handle this power dissipation, it is also a big disadvantage that a huge amount of energy is lost. Actually, most of the operational time, more power is lost than utilized in the slave device, as the voltage drop over the current generator will typically most of the time be much more than the utilized 6V.
• slave devices with more complex functions than, for example, simple metering must be designed with a relatively high constant slave current I siav e in order to receive sufficient power.
• I siav e constant slave current of more than 3 or 4 M-Bus unit loads of l.5mA each, i.e. 4.5 - 6mA
• wireless gateway slave devices have been produced, which requires a constant slave current of, for example, 7 M-Bus unit loads, i.e. 10.5mA, which is approaching twice the acceptable amount.
• a voltage regulator is required to provide, for example, 3.6V supply voltage to the slave device functions.
• a low-dropout voltage regulator LDO or other voltage regulator is typically used, thereby clipping the voltage instead of converting the power.
• LDO low-dropout voltage regulator
• Fig. 4 illustrates a block diagram of an embodiment of the invention of a power supply PS of a slave device SD of a current controlled communication bus CB.
• the slave device SD comprises slave device functions FUNC, which may be similar to the functions described above with regard to prior art. Additionally, the slave device functions FUNC may be more complex and power demanding than conventionally imagined, because of the much better power efficiency of the present invention.
• the slave device SD is parallel coupled to the current controlled communication bus CB as in the conventional systems, and the current controlled communication bus CB, a master device MD (not shown) and other slave devices SD (not shown), may be the same as in prior art systems, for example conventional M- Bus or 4-20mA busses.
• the present invention does not require changes of the master device or bus specifications.
• a huge advantage of the present invention is that it may provide the improved power efficiency even with complete compatibility with existing installations and conventional bus products such as master devices, relays, other slave devices, etc.
• Embodiments of the power supply of the present invention may even be retrofitted into conventional slave devices to achieve the improved efficiency.
• the slave device SD is arranged to draw a constant slave current I s iave from the current controlled communication bus CB .
• the constant slave current I siav e is used by a charger CH to charge an energy storage ES of the power supply PS at a charge voltage V C hrg.
• the charger CH comprises an overflow circuit OC to allow excess charge I ve nt to bypass the energy storage ES and slave device functions FUNC if the entire, mandatory constant slave current I s iave cannot be completely consumed by the energy storage ES and slave device functions FUNC.
• the overflow circuit OC is arranged to activate the bypass of excess charge
• the present embodiment of Fig. 4 does not limit the charge voltage V C hr g to a precautionary, constant minimum Zener breakdown voltage of e.g. 6V.
• the charge voltage V C hr g is in the embodiment allowed to increase during the charging, as long as it stays below the bus voltage V bus by a predetermined threshold as defined by the overflow criterion, to allow the constant slave current I slave to continue flowing.
• Fig. 5 is a block diagram of an embodiment of the present invention.
• the power supply PS of Fig. 4 has been simplified to a box, and Fig. 5 illustrates that the slave device SD comprises a slave device current generator SDCG to generate the constant slave current I sia% e-
• the slave device current generator SDCG may in various embodiments be a single, dedicated current generator, a combination of several current generators, or a combination of other circuit elements in practice performing a constant current generation.
• the power supply PS comprises the overflow circuit OC to bypass any excess current I ve nt, possibly directly to ground GND.
• Fig. 6 is a block diagram of an embodiment of the present invention, exemplifying one possible embodiment of the slave device current generator SDCG introduced above with reference to Fig. 5.
• the slave device current generator SDCG is a controllable current generator CCG, which can be adjusted between different constant currents.
• the controllable current generator CCG may preferably be operable at two different, constant currents.
• the controllable current generator CCG is controlled to generate a constant operational current I op corresponding to the predetermined M- Bus unit loads that the slave device should consume, for example 3 M-Bus unit loads at l .5mA each, totaling a constant operational current I op of 4.5mA.
• the constant operational current I op corresponds to the constant slave current Isiave described above.
• the controllable current generator CCG is controlled to increase the constant operational current I op with a constant transmission current I tx , which may for example be 11 -20mA according to the M-Bus specification, resulting in a total constant slave current I siav e of selected in the range of 15.5-24.5mA during the transmission of zeroes.
• Fig. 7a is a block diagram of an embodiment of the present invention, exemplifying one possible embodiment of the slave device current generator SDCG introduced above with reference to Fig. 5.
• the slave device current generator SDCG comprises an operation current generator OCG and a transmission current generator TCG.
• the operational current generator OCG generates a constant operational current I op to constitute the constant slave current Isiave, for example, in an M-Bus system, during non-communicating periods, or when the slave device is communicating digital‘ G as described above.
• the transmission current generator TCG generates a constant transmission current I tx which when added to the constant operation current I op signals a digital‘O’ in an M-Bus system, as described above.
• the transmission current generator TCG is operable between on and off states, or a controllable switch is provided to be able to activate and deactivate the constant transmission current I tx .
• the constant transmission current I tx is bypassing the power supply PS, and is therefore not used for anything else than signaling.
• Fig. 7b is a block diagram of an embodiment of the present invention, exemplifying one possible embodiment of the slave device current generator SDCG introduced above with reference to Fig. 5.
• the current embodiment comprises for slave device current generator SDCG an operation current generator OCG and a transmission current generator TCG.
• the transmission current generator TCG in Fig. 7b is also provided with an on/off function or a switch as illustrated in Fig. 7a.
• the embodiment of Fig. 7b resembles the embodiment of Fig. 7a, with the difference, that also the constant transmission current I tx is lead through the power supply PS and thereby utilizable. If the combination of constant operational current I op and constant transmission current I tx is more than the energy storage ES and functions FUNC can consume, the power supply PS still provides the overflow circuit to bypass excess charge Ivent ⁇
• Fig. 8 is a block diagram of an embodiment of the present invention, illustrating a principle embodiment of the power supply PS.
• a slave device current generator SDCG is drawing a constant slave current I siave through the power supply PS, in order to charge the energy storage ES at a charge voltage V chrg , as described above with reference to Figs. 4 and 5.
• the embodiment of Fig. 8 further comprises a voltage controlled switch VCS receiving as control inputs the charge voltage V Chrg and the bus voltage V bus .
• the voltage controlled switch VCS is thereby able to control the overflow circuit OC in dependency of a relationship between the charge voltage V Chrg and the bus voltage V bus .
• the voltage controlled switch VCS may be arranged to close the switch and allow excess charge I ve m to bypass directly to GND when the relationship between the charge and bus voltage fulfils a predetermined overflow criterion, for example that the charge voltage V Chrg comes within a threshold limit of the bus voltage V bus , or becomes a certain ratio, e.g. 80% or 90%, of the bus voltage V bus .
• the voltage controlled switch VCS or the connection between the switch and ground GND may preferably comprise a resistor or other component suitable to dissipate the excess charge Ivent ⁇
• Fig. 9 is a block diagram of an embodiment of the present invention, illustrating a principle embodiment of the power supply PS.
• a slave device current generator SDCG is drawing a constant slave current I siave through the power supply PS, in order to charge the energy storage ES at a charge voltage V chrg , as described above with reference to Figs. 4 and 5.
• the embodiment of Fig. 9 further comprises an implementation with a voltage controlled switch VCS different from the embodiment of Fig. 8.
• the voltage controlled switch VCS receives as control signals the charge voltage V Chrg and the bus voltage V bus reduced by a predetermined voltage difference V ref .
• the voltage controlled switch VCS should close and allow excess charge I ve nt to flow to ground GND, preferably through a power dissipating component such as a resistor.
• the overflow circuit OC is in practice arranged to compare the difference between the bus voltage V bus and the charge voltage V Chrg with the predetermined voltage difference V ref , and control the overflow circuit on that basis.
• the predetermined voltage difference V ref may in an embodiment for example be in the range of 1 - 4V, for example 2 - 3 V, and may for example be established by a Zener diode breakdown voltage, a standard diode forward voltage drop, or by drawing a small constant current through an impedance, etc.
• Fig. 10 illustrates a block diagram of a more detailed example implementation of the voltage controlled switch VCS of the embodiment of Fig. 9.
• the voltage controlled switch VCS is implemented by a Darlington transistor circuit DTC consisting of two PNP transistors. Further, a resistor R is provided for dissipating the power of the excess charge I ve nt when the Darlington circuit starts to conduct current from the slave device current generator SDCG.
• the predetermined voltage difference V ref is applied between the bus voltage V bus and the base terminal of the Darlington transistor circuit DTC, thereby making the based terminal biased at Vbus - Vref, for example a few volts lower than the bus voltage, for example 3 V lower than the bus voltage.
• V C hr g coupled to the emitter terminal of the Darlington transistor circuit DTC is lower than the Vbus - Vref, the Darlington transistors does not conduct current.
• the resistor may for example be a 3kQ resistor.
• the Darlington transistor circuit may comprise two discrete transistors, for example general purpose BC557C PNP transistors, or a dedicated Darlington package, or be included in an integrated circuit. Other embodiments comprise alternative transistor-based circuits, or uses NPN-based transistors, FET transistors, etc.
• the Darlington transistor circuit DTC is advantageous for being able to accommodate a much higher excess charge font than a single transistor would.
• Any of the overflow circuit embodiments of Figs. 8, 9 and 10, or other overflow circuit embodiments may be implemented with any of the current generator embodiments described above with reference to Figs. 5, 6, 7a and 7b, or any other current generator implementations.
• Fig. 11 is a block diagram illustrating an energy storage ES of a power supply PS of an embodiment of the present invention.
• a slave device current generator SDCG generates a constant slave current I siav e and conducts it to a charger CH.
• the energy storage ES is charged at a charge voltage V C hr g by the charger CH.
• the charger CH is able to bypass excess charge I ve nt to ground GND by an overflow circuit, for example as described above.
• the slave device functions FUNC are powered by a functions voltage Vf nc and functions current If U nct from the energy storage ES.
• the energy storage comprises a capacitor C for temporarily storing energy during bus voltage drops and for smoothing variations of the bus voltage.
• One or more capacitors of the same or different types, or in combination with other circuit components, may form the capacitor C.
• the capacitor C may for example have a capacity of 1 - lOOOpF, for example lOpF, and may for example be an electrolytic capacitor.
• the skilled person would know how to select a suitable type and value of the capacitor C for a particular application.
• the voltage rating of the capacitor needs to be increased as compared to prior art slave device power supplies, as the charge voltage V C hr g of the present invention increases with increasing bus voltage Vbus, where prior art capacitors can simply be voltage rated according to the Zener diode regulation applied.
• the energy storage ES may in an embodiment comprise a diode D arranged so as to allow current conducting from the charger CH to the energy storage ES, but preventing the energy storage ES, in this example the capacitor C, from discharging through the charger CH and overflow circuit.
• the diode D may for example be a standard silicon diode with a forward voltage drop of about 0.7V or more preferably, for example a Schottky diode with a forward voltage drop of about 0.2V.
• the current and power rating of the diode should be selected to accommodate the full constant slave current I siave at almost the maximum expected bus voltage V bus .
• Two or more diodes may be coupled in parallel to improve their collective current and power rating.
• the energy storage voltage V es is a little lower than the charge voltage V C hr g . This point should be considered when selecting a predetermined voltage difference V ref by which the charge voltage cannot get closer to the bus voltage V bus to ensure continuous maintenance of the constant slave current Ei ave .
• the energy storage voltage V es is used directly as functions voltage Vr U nc.
• the diode ensures that current does not start to flow from the energy storage ES to the charger during periods where the bus voltage V bus suddenly drops below the charge voltage V chrg , which may for example happen when a master device MD starts to communicate, for example by 12V drops in an M-Bus system. Thereby the stored energy may be maintained or slave device functions continuously provided until depletion of the energy storage, even during periods with bus voltage drops.
• Fig. 12 illustrates an alternative, preferred embodiment of a power supply PS of a slave device SD according to the invention.
• the embodiment of Fig. 12 differs from the embodiment described above with reference to Fig. 11 by the addition of a power converter PC, arranged between the energy storage ES output and the slave device functions FUNC.
• the power converter PC is arranged to convert the energy storage voltage V es to a suitable functions voltage V fUnc , while maintaining to the highest degree possible the available power. As the energy storage voltage V es may vary with the bus voltage V bus , the power converter may also be advantageous for regulating the functions voltage Vi unc at a more stable and predetermined level.
• the power converter PC is a DC-to-DC converter, for example a switching converter, thereby achieving a high power conversion efficiency.
• the power converter PC is a buck converter stepping the energy storage voltage V es , for example 12 - 40V, down to a lower, stable functions voltage V fUnc , for example 2.5V, 3.6V or 5V.
• the power converter may for example be based on a Texas Instruments TPS54062 Synchronous Step-Down Converter.
• a power converter With the significantly higher gap between the energy storage voltage and the functions voltage in the present invention, a power converter becomes highly beneficial, and, besides a small loss in the converter, achieves a conversion of power where current increases at the rate of voltage decrease, instead of the prior art method of clipping the voltage without gaining a current increase.
• Any of the energy storage embodiments of Figs. 11 and 12, or other energy storage embodiments may be implemented with any of the overflow circuit embodiments of Figs. 8, 9 and 10, or any other overflow circuit embodiments, and/or any of the current generator embodiments described above with reference to Figs. 5, 6, 7a and 7b, or any other current generator implementations.
• Fig. 13 illustrates a preferred embodiment of the present invention, combining the overflow circuit OC embodiment of Fig. 10 with the energy storage ES and power converter PC embodiment of Fig. 12, incorporating the above description referring to these two drawings.
• Table 1 compares simulations of the power dissipation and efficiencies of the conventional M-Bus slave device power supply described above with reference to Fig. 3, with an embodiment of the present invention as described above with reference to Fig. 13.
• the embodiment of the present invention is able to provide at least the same current If U nc to the slave device functions, while drawing only about 43% of the bus current, i.e. 3 unit loads vs. 7 unit loads, thereby also dissipating only about 43% of the bus power compared to the conventional solution. Moreover, during periods with higher bus voltages, the embodiment of the present invention even improves the efficiency and available power to the slave device functions, thereby enabling even higher demanding functions if suitably controlled in accordance with the available bus voltage, or if sufficient energy is stored in the energy storage during high voltage periods.
• Fig. 14 is a principle diagram illustrating an M-Bus, i.e. a current controlled communication bus according to the present invention. Attached to the M-Bus is a number of slave devices SD of different types, and master device MD providing power to the slave devices. Some of the slave devices are utility meters, and one of the slave devices in this example is a gateway G.
• the M-Bus may have a length of several tens or hundreds of meters, and simply comprises a two-wire cable, or two wires of a multi- wire cable, e.g. a twisted pair.
• the slave devices SD, G is connected to the M-Bus in the way describe with the previous drawings.
• the gateway G implements a transceiver and software for a wireless technology to communicate with wireless devices WD.
• Such a gateway has complex and demanding slave device functions requiring more power than, for example, utility meters, etc..
• Fig. 15 comprises 3 curves illustrating a difference between the prior art solution and an embodiment of the present invention.
• the horizontal axis represents the bus voltage V bus between 0V and 40V.
• the vertical axis represents voltage values.
• the bus voltage curve V bus marked by a dash-dot line, is of course tied to the horizontal V bus axis, so that the V bus curve follows the 1 : 1 line as illustrated.
• the charge voltage V Chrg of the new embodiment according to the invention increases with the variable bus voltage, although being behind by a small offset substantially corresponding to the predetermined voltage difference V ref .
• Vftinc device functions voltage

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