WO2013108187A2

WO2013108187A2 - Ultra low standby power system for electronic devices

Info

Publication number: WO2013108187A2
Application number: PCT/IB2013/050394
Authority: WO
Inventors: Lennart Yseboodt; Pieter Gerrit Blanken; Johan-Paul Marie Gerard LINNARTZ
Original assignee: Koninklijke Philips N.V.
Priority date: 2012-01-18
Filing date: 2013-01-16
Publication date: 2013-07-25
Also published as: WO2013108187A3

Abstract

The present invention relates to a hardware/software solution that allows electronic devices to be self-powered from an external source without additional cabling. This is achieved through energy scavenging or harvesting, which is robust and short-circuit proof. A software protocol extension allows greater amounts of power to be transferred. Together with a zero power mains switch the system removes the need for separate power supplies in the control circuit and achieves zero power standby properties.

Description

ULTRA LOW STANDBY POWER SYSTEM FOR ELECTRONIC DEVICES

FIELD OF THE INVENTION

The present invention relates to a method and device for controlling energy supply to an electronic device.

BACKGROUND OF THE INVENTION

Reduction of standby power is an important aspect of making electronic devices "green", i.e., more ecologically friendly. Standby power is a well known issue in consumer electronic devices, such as television sets, set top boxes, internet routers.

Increasingly, lamps and lighting installations also provide a standby mode, thereby dissipating power. Particularly the transition from incandescent and fluorescent lighting to light emitting diode (LED) lighting accelerates this, firstly because many LED lamps are no longer switched on or off by switching the mains to enable more elaborate control including dimming, color point setting, beam steering, or responsiveness to sensor signals, secondly because of the trends towards more distributed illumination that consists of multiple LEDs modules, each of which needs to be controlled.

In the past, the above standby problem was solved by using a very-low- power controller circuit in combination with an energy storage element and a bi-stable or latching relay. Major disadvantages of the relay are the audible switching noise, the limited lifetime, the large physical size, limited reliability under mechanical shocks, and eventually high cost. Audible noise and mechanical wear during switching mandates avoiding frequent recharging of the energy storage and thus demand for a substantial capacity of the storage element, leading to higher cost. Return of the mains voltage after a blackout leads to synchronous inrush current of all connected devices which may trip circuit breakers and thus may lead to another blackout.

Conventional receivers for remote control also consume power as they need to listen for incoming commands during standby. This is the case for remotely controlled lighting systems, e.g. by means of Digital Addressable Lighting Interface (DALI), ZigBee, DMX or other lighting or building control solutions, as well as consumer lifestyle appliances, such as television (TV) sets, set- top-boxes, household appliances, or consumer lighting solutions. Currently, standby powers for devices that only need to be able to respond to a control command or to a sensor input by waking up other electronic circuits range from 100 mW to 1W.

A number of solutions are known to reduce the power consumption of communication receivers or of sensors. One example is a wake-up radio that consumes only 51 μ\¥ and has been described by Xiongchuan Huang et al.: "A 2.4GHz/915MHz 51· W Wake-Up Receiver with Offset and Noise Suppression", Digest of Technical Papers 2010 IEEE International Solid-State Circuits Conference ISSCC2010, Febr. 7-11, 2010, pp. 222-223. This power is small enough to ensure that it can be scavenged from the environment, e.g. by a miniature photovoltaic cell. The radio has been designed to wake up other circuitry, thus to reduce standby power. Such a receiver can deliver a (binary) control signal but the power that its gets from the scavenger is insufficient to drive a mechanical relay.

Another wake-up radio has been described by Bas van der Doom et al.: "A prototype low-cost wakeup radio for the 868 MHz band", Int. J. Sensor Networks, Vol. 5, No. 1, 2009. In this paper it has been recognized that battery-powered nodes must operate for years, which necessitate the need for advanced power management of the radio. The contribution is a second, ultra low-power radio that can be used to trigger a remote interrupt, so that a receiver can fire up its primary radio to engage in efficient high-speed communication with the sender. The proposed wakeup radio avoids the complex bookkeeping associated with energy-efficient Media Access Control (MAC) protocols, but at the price of additional hardware.

In 2001, the PicoRadio project was the first to advocate the advantages of wakeup radio and boldly estimated that a specialized radio interface could consume as little energy as 1 · W. The PicoRadio project was described by da Silva Jr. et al.: 'Design methodology for PicoRadio networks', Design Automation and Test in Europe (DATE), Munich, Germany, 2001, pp.314-325. In follow-up work, the term "reactive radio" was introduced and the design target moved to a more realistic power consumption level of around 50 · W which is sufficiently low to derive the energy from a scavenger. L. Gu et al.: "Radio-Triggered Wake-Up Capability for Sensor Networks", Real-Time Systems Journal, special issue of best papers from RTAS, Vol. 29, No. 2-3, March 2005 proposed a fully passive design for an ultimate low-power wakeup receiver consuming no energy at all. In such case the radio extracts all its energy from the radio waves. This principle is known from radio frequency identification (RF ID) tags. However, a key problem is that receivers cannot deliver enough power to switch mains (230 Volts) safely.

A solution is needed to overcome or mitigate issues with standby power in DMX control networks or other control or communication networks.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and device for reducing standby power in DMX control networks or other control or communication networks.

This object is achieved by a device as claimed in claim 1, by a method as claimed in claim 12, by a computer program product as claimed in claim 13, by a receiver circuit as claimed in claim 14, and by a communication signal as claimed in claim 15.

Accordingly, the proposed solution combines the use of a semiconductor switch combined with a self powering control circuit, e.g. DMX receiver. It is based on the insight that the creation of a semiconductor mains power switch with reliable blackout behaviour and low control power shifts the paradigm and enables new solutions.

More specifically, an electronic device (e.g. a lighting device) is connected to a power supply (e.g. an AC or DC power grid) via a semiconductor switch circuit, in which the semiconductor switch contains power transistors to connect/disconnect the device from the mains power supply, and in which the switch is controlled from a receiver circuit which extracts (at least part of) its power from a scavenging principle. The scavenging principle may be based on extracting power from the control data or on extracting power from the environment such as a photovoltaic cell. The control principle may be a wired line communication system, such as DMX, or Ethernet or a radio communication system or an infrared (IR) remote control system. A galvanic isolation may be provided between the DMX receiver and the power transistors.

In an exemplary DMX environment, a DMX receiver is provided, in which a power extracting circuit is connected to the two differential DMX data lines and delivers power to the DMX decoding circuit. A DMX energy scavenger works by scavenging small amounts of power from the differential DMX data signals (e.g. called RS485-A and RS485-B). The power extracting circuit may contain a capacitive voltage doubler, tripler, quadrupler, etc. Here, the proposed power scavenging is advantageous in that the value of the capacitors is one of the factors that determine the amount of energy that can be extracted from the lines per line transition. This yields a very well defined behavior with regard to the line drivers. Moreover, the circuit only contains simple and cheap devices and is very robust. Additionally, a short circuit at the output does not necessarily jam the communication channel, it may continue to run with slightly reduced voltage levels.

The scavenged supply may, but does not necessarily, share ground with the driver of the differential signal wire pair. Although there is no galvanic isolation the conduction path is capacitive only.

As another advantage, the proposed circuit is also resistant against external grounds loops. If the 'ground' of the scavenged supply is connected to the ground of the line drivers the circuit will still work. Nevertheless, galvanic isolation (e.g. by means of a 1: 1 transformer) of the RS485 lines is still possible, the scavenger will continue to work.

The amount of power that the scavenger can extract from the lines is limited. This power is used to power the DMX decoder. The DMX decoder can operate a power switch to connect or disconnect a load from or to a power supply such as the mains supply. The power consumption of the DMX decoder determines how many of these decoders can be connected to the DMX network before too much power is extracted from the DMX coder and the system fails.

Furthermore, the proposed solution leads to an increase of the amount of power that can be transferred. A special DMX transmitter may anticipate on power extracting receivers.

The proposed control scheme may be implemented as a computer program product stored on a computer-readable medium or downloadable from a network, which comprises code means for producing the steps of method claim 6 when run on a computing device.

Further advantageous embodiments are defined below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, based on embodiments with reference to the accompanying drawings, wherein:

Fig. 1 shows a schematic block diagram of a lighting device according to a first embodiment;

Fig. 2 shows a schematic circuit diagram of a power control circuit to

which the present invention can be applied;

Fig. 3 shows a schematic circuit diagram of a scavenging system according to a second embodiment;

Fig. 4 shows a schematic representation of a DMX packet;

Fig. 5 shows a circuit diagram of a capacitive voltage tripler; and

Fig. 6 shows a schematic block diagram of multiple scavenging receivers according to a third embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

Various embodiments of the present invention will now be described based on a DMX power supply system for lighting systems.

DMX is a popular communication standard to control lighting installations in entertainment applications. DMX was developed by the Engineering Commission of United States Institute for Theatre Technology (USITT), the standard was created in 1986, with subsequent revisions in 1990 leading to USITT DMX512/1990. The DMX512(-A) standard describes the physical implementation (connectors, cables), the electrical workings of the communication medium (EIA485) and the packet format. A DMX environment consists of a DMX master (which transmits only) and a limited number of slaves (which only listen). DMX is increasingly being used for applications beyond the entertainment business. However, particularly in permanent installations such as illumination in offices and homes or in city beautification lighting, the power consumption in standby mode (when the lights are off) makes it less attractive.

One way to overcome this can be to switch the mains power for the main device functions off during periods of long inactivity. However the DMX receiver needs to remain powered to function. It needs to wake up the main application device (for instance a lamp) as soon as messages are transmitted over the DMX cables requiring an action from the device.

Fig. 4 shows an example of a most common packet according to the DMX- 512 protocol with start code (S) of "0x00". The DMX packet format is of a variable size and very simple. Only one-way communication is possible, from one master to a limited number of slaves. The (software defined) maximum is 512 listening slaves. The standard provides up to 512 data bytes (D) to be transmitted in one packet, each byte in the packet corresponds to an address. The address is determined by the location of the data byte in the packet. The first data byte is for address 0 (ADDR:0), the second data byte is for address 1 (ADDR:1) and so on. Slave devices are configured to listen to certain addresses. A device which is configured for address 1 (ADDR:1) would use the second data byte (D) after the start code (S). The meaning of the data is determined by the device that receives it.

The DMX-512(-A) standard specifies EIA-485 as the electrical standard for the data communication. It is also known as RS485, the differential version of the ubiquitous RS232 standard. RS485 is defined as a differential voltage communication medium with speeds ranging from lOOkbit/s to 10 Mbit/s. For DMX a speed of 250kbit/s is used. The maximum differential voltage is +5V. The cable is terminated with a 120Ω resistor to avoid reflections.

However, the standard does not provide for power transport via the DMX cables (e.g. a low voltage DC auxiliary supply). Hence, many manufacturers of DMX compatible products use one of the wire pairs in the cable to provide low voltage direct current (DC) supply to the slaves. This power is used in the slave devices to power the DMX receiver/decoder, but causes incompatibilities and risk of damage to the equipment.

A DMX slave is a remote controlled device. The device can be in an active state (e.g. lamp on) or in an inactive state (e.g. lamp off). In the inactive state there is still power consumption, the so called standby power. Even though the load is not active, a small amount of power is needed to listen to the remote interface.

This power can be derived from the mains, by means of a galvanically isolated power supply. The isolation is required due to the fact that a direct electrical connection between mains and the DMX interface is not suitable. Such a power supply is relatively expensive and will in most cases also exhibit a larger amount of standby power itself.

As another option, the power can be derived from the DC voltage that may be provided via an extra wire pair in the DMX cable. However, this option is not standard compliant, violates the DMX-512 standard, and has the potential to create troublesome ground loops.

Fig. 1 shows a block diagram of a lighting device 100 with DMX interface according to a first embodiment. A power stealing circuit 10 is used to derive the supply power for a DMX receiver 20 from the DMX control lines. The DMX receiver 20 controls semiconductor switching device 50 via a galvanic isolation element 60. The switching device 50 switches an AC mains power line (e.g. 230V) to a main power supply 30 which supplies power to the main application 40 (e.g. lighting device(s)). The main application 40 may also be controlled by the DMX receiver 20. The link between the DMX receiver 20 and the main application 40 is not essential but likely to be needed in many applications. If the DMX receiver 20 and the main application 40 are linked, then the main power supply 30 must provide galvanic isolation from the mains.

The power stealing circuit 10 can also be a scavenger circuit, such as photovoltaic cell which derives power from light energy. In general, any energy or power harvesting circuit can be used, by which energy is derived from external sources (e.g., solar power, thermal energy, wind energy, salinity gradients, and kinetic energy). Thus, the power stealing circuit 10 provides a very small amount of power for low-energy electronics, which is available as ambient background and is free.

Fig. 2 shows a schematic circuit diagram of a zero power mains switch which can be used as the switching device 50 of Fig. 1 for controlling power supply to a load LD. A bidirectional semiconductor switch comprising metal oxide semiconductor field effect transistors (MOSFETs) Ml, M2 with extremely low control power consumption and a bootstrap circuit which allows reliable start of operation of the switch and the hosting device after unlimited duration of mains interruptions. A capacitive power supply circuit 54 with a diode D, a Zener diode ZD, a storage capacitor C_stor and two capacitors CI, C2 generates a DC voltage supplied to a watchdog circuit 51 which supplies an input signal to a latch 52 (e.g. S/R flip flop circuit). A set/reset input of the latch 52 is controlled by a pulse shaping circuit 53 which receives a control input (e.g. short set and reset pulses) via a transformer 60 from a galvanically separated control circuit (not shown) which may be a DMX or DALI control circuit.

Fig. 3 shows a schematic circuit diagram of a power supply control system according to a second embodiment. A DMX master 70 supplies DMX control signals via a transmission (TX) driver 80, which may be an RS485 line driver, and a line receiver (RX) 82 to a DMX decoder 72, i.e. a DMX slave. It is noted that ground potential GND_TX of the TX driver 80 differs from ground potential GND_RX of the reception side. An energy or power scavenger 90 derives from the DMX control signaling a small amount of power for operating the line receiver 82 and the DMX decoder 72 which is galvanically separated from the controlled load side by a galvanic isolation device 60, e.g., a transformer which transfers electrical energy from the DMX decoder side to the load control side through inductively coupled conductors— the transformer's coils. On the load side, supply of an AC voltage between line potential L and the neutral potential N to a load LD is switched by two power semiconductor switches Ml and M2 (e.g. MOSFETs) which are controlled by a supply and control circuit 22 in response to the output signal of the DMX decoder 72. At the load LD a switched potential L' is obtained. The power scavenger 90 is combined with the line receiver 82 and the DMX decoder 72, e.g. a microcontroller. The DMX decoder 72 can then control the mains switches Ml, M2, such as a zero power mains switch as shown in Fig. 2.

The power consumption of an implementation of the circuit of Fig. 3 was measured to be less than 3mW on the mains side, while the DMX receiver side extracted less than 2mW from the RS485 data lines. The signal integrity on the data lines was not affected by the power scavenger 90. Multiple of these scavengers can be connected to the DMX bus. IEC 62301 Clause 4.5 classifies power usage of less than 5 mW as "zero". Fig. 5 shows an exemplary circuit diagram of the power scavenger 90. This circuit is a voltage tripler, while it is noted that doublers, quadruplers etc. are also possible. Also linear voltage regulators can be added to stabilize the output voltage at the cost of some power dissipation. The voltage tripler is a three-stage voltage multiplier connected between the DMX wires, which may be RS485-A and RS485-B lines, for example. It converts AC electrical power transferred on the DMX lines from a lower voltage to a higher DC voltage by means of a network of capacitors and diodes. The output voltage of the tripler is in practice below three times the peak input voltage due to their high impedance, caused in part by the fact that as each capacitor in the chain supplies power to the next, it partially discharges, losing voltage doing so. Of course, other circuit options and types of voltage multipliers may be used as the power scavenger 90.

The power scavenger 90 can take energy when there is a data line transition. The amount of power than can be taken depends on the value of the capacitors and on the number of transitions per unit of time. The DMX master 70 can optimize for maximum power transfer by sending out e.g. as many bytes as possible containing either hexadecimal "0x55" or "OxAA". These values are optimal because they have the largest number of bit transitions per byte. In binary they are represented as "ObOlOlOlOl" and "OblOlOlOlO", respectively. Depending on the start bit (preceding the data byte) and the stop bit (trailing the data byte), one of these will have the highest possible energy transfer. Of course, other suitable bit patterns could be used as well.

These bytes can be transmitted in the normal data stream (e.g. with start code 0) at the locations of unused addresses. It will have no influence on the operation of any device in the network other than to enable maximum power transfer to the scavenging receivers. As an alternative, the DMX master 70 could send a packet with an alternate start code (e.g. a comment packet, Session Initiation Protocol (SIP) packet) that contains a large number of bit transitions (e.g. payload contains only "0x55" or "OxAA").

Thus, the communication signal transmitted by the DMX master 70 is enhanced by a packet or preamble structure adapted to be used by the power scavenger 90 for generating a power supply voltage for the line receiver 82 and the DMX decoder 72.

Optionally, the DMX slave, i.e. DMX decoder 72, can be adapted to enter a standby mode if it detects that the DMX master 70 device is capable of sending a DMX control signal which can be used by the power scavenger 90 to generate the supply voltage or power. Otherwise, the DMX decoder 72 may not be allowed to enter the standby mode.

Fig. 6 shows a schematic block diagram of a multiple scavenging DMX receiver system according to a third embodiment, which can be connected to a DMX network with DMX master 300 and differential twisted wire pair 320 and freely mixed with non-scavenging DMX slaves. Several DMX slaves 100-1, 100-2, 100-3 are connected to the wire pair 320 via respective power scavengers 12 which are adapted to supply energy to respective DMX receivers 20 controlling respective power switches 50 so as to control power supply from respective AC mains 200-1, 200-2, 200-3 to respective loads LD1, LD2, LD3.

In combination with a zero power mains switch as shown for example in Fig. 2, a zero power standby (which means e.g. less than 5mW according IEC 62301 Clause 4.5) DMX-512(-A) compatible system can be obtained. In addition, a software solution to increase the amount of transitions may be added to allow a greater amount of power to be transferred.

The proposed solution can be applied in all DMX slaves, so that a mains powered galvanically isolated supply in the DMX receivers 20 can be replaced by a low cost and robust scavenging power supply that does not pose ground loop problems.

In summary, a hardware/software solution has been described, that allows electronic devices to be self-powered from an external source without additional cabling. This is achieved through energy scavenging or harvesting, which is robust and short-circuit proof. A software protocol extension allows greater amounts of power to be transferred. Together with a zero power mains switch the system removes the need for separate power supplies in the control circuit and achieves zero power standby properties.

While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed DMX based lighting control embodiments. The proposed control scheme can be used for home lighting, office lighting, outdoor lighting, professional lighting (e.g. retail, city beautification etc.), emergency lighting, and all kinds of consumer devices. Moreover, the above embodiments are focused on a DMX communication receiver. However, a similar system can be built without a communication receiver, but that responds to a sensor input. The sensor can be power from a scavenger. As an example, a light sensor or a passive infrared (PIR) motion sensor can be used, that is powered by a photovoltaic cell, and that controls a semiconductor switch.

Furthermore, a self-powered or self -powering DMX receiver may be provided in an electronic device controlled by a DMX communication system without controlling any electronic power or mains switch of the electronic device.

In general, the proposed scavenging or harvesting approach is identifiable at the output communication wire by a special packet or preamble structure that allows the receiver to build (i.e. scavenge or harvest) a power supply voltage.

The control system could as well be light wave remote control system including but not limited to infrared (IR), optical fiber or visual light communication. In fact, cheap plastic optical fiber can in future be attractive because it does not require galvanic isolation. As an alternative option, the wired communication receiver for DMX lighting control signals can be operated as a scavenging receiver which can scavenge power from the data lines. Such circuit would neither need an external power supply, nor a battery.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art and which may be used instead of or in addition to features already described herein.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality of elements or steps. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

CLAIMS:

1. An electronic device comprising:

a. a semiconductor switch circuit (50) for connecting said electronic device (100) to a power supply (200-1 to 200-3); and

b. a control circuit (20; 72) for controlling said switch circuit (50) to connect or disconnect said electronic device (50) from said power supply (200-1 to 200-3);

c. wherein said control circuit (20; 72) is adapted to derive its power supply based on a scavenging or harvesting principle from an external source which differs from said power supply (200-1 to 200-3).

2. The device according to claim 1, further comprising a scavenging circuit (10, 90) for supplying power to said control circuit (20; 82; 72).

3. The device according to claim 1, wherein said external source is a control data signal supplied to said control circuit (20; 82; 72).

4. The device according to claim 1, wherein said control circuit (20) is a slave device adapted to enter a standby mode if it detects that its master device is capable of sending said control data signal.

5. The device according to claim 3 or 4, wherein said control circuit (20; 82; 72) is adapted to receive said control data signal via a radio communication system.

6. The device according to claim 1, wherein said external source is a photovoltaic cell.

7. The device according to claim 1, wherein said control circuit (20; 82; 72) is controlled by a light wave remote control system.

8. The device according to claim 1, further comprising a galvanic isolation element (60) adapted to isolate said control circuit (20; 82; 72) from said switch circuit (50).

9. The device according to claim 1, wherein said control circuit (20; 82; 72) is a DMX receiver (20).

10. The device according to claim 1, wherein said power supply (200-1 to 200-3) is a power grid.

11. The device according to claim 1, wherein said electronic device (100) is a lighting device.

12. A method of controlling power supply to an electronic device (100), said method comprising:

a. controlling a switch circuit (50) to connect or disconnect said electronic device (50) from a power supply (200-1 to 200-3) by using a control circuit (20; 82; 72); and

b. deriving a power supply for said control circuit (20;

82; 72) based on a scavenging or harvesting principle from an external source which differs from said power supply (200-1 to 200-3).

13. A computer program product comprising code means for producing the steps of method claim 12 when run on a computing device.

14. A self-powered receiver circuit for an electronic device (100), said receiver circuit (20) being adapted to derive its power supply based on a scavenging or harvesting principle from an external source which differs from the power supply of said electronic device (100).

15. A communication signal comprising a packet or preamble structure adapted to be used for generating a power supply voltage at a receiver device (100) based on a scavenging or harvesting principle.