S. Kang et al.: Zero Standby Power Remote Control System using Light Power Transmission 1623appliance, but this solution is cumbersome and not veryeffective due to human laziness. To overcome this problemand achieve absolute zero standby power, we have designedand herein present a new light-powered remote control system.The main idea of this proposed system is conceptually shownin Figure 1.Fig. 1. Block diagram of the zero standby power remote control system.The home appliance is initially disconnected from the ACpower line by the latch relay to consume absolute zero power.Whenever a laser beam impinges upon the PV array to turnon the appliance, the PV array converts the photon energy toelectric power and accumulates it in a storage capacitor. Inorder to prevent energy leakage during this energyaccumulation stage, the latch relay is separated from thestorage capacitor by the ACC until sufficient energy isaccumulated in the storage capacitor. When the amount ofaccumulated energy is sufficient to drive the latch relay, theACC autonomously connects the storage capacitor to thecontrol port of the latch relay, and the relay connects thehome appliance to the AC power line. The operatingappliance can be turned off using a commercial remotecontroller as conventional way, but in our system, thereceiver unit latches off the relay to physically disconnectthe appliance from the AC power line and return it tostandby mode consuming absolute zero power. As explainedabove, a dead receiver receives the light energy, revives fromdeath and connects the appliance to AC power.The remote control system shown in Fig. 1 can be directlyapplied to low-power (a few tens of watts) home appliancessuch as small TVs, computer monitors, and audio equipment.However the high-capacity power relays mounted on higherpower appliances require too much power to be activated bylight power transmission. Furthermore, the system shown inFig. 1 is susceptible to light noises such as sunlight,lightning, fluorescent light, and other infrared (IR)commanding lights of adjacent appliances. Thus, anadvanced system that can be applied to high-power homeappliances that has an identification (ID) function isproposed here.The architecture of the advanced system is shown inFigure 2. Unlike the system in Fig. 1, a small capacityauxiliary latch relay and a small capacity AC/DC converterare utilized to supply power for an ID check unit. As with thesystem shown in Fig. 1, the home appliance is disconnectedfrom the AC power line by a main latch relay, making itconsume absolute zero power.Fig. 2. Block diagram of the zero standby power remote control systemfor high power application with the function of identification.When ON button is pressed on the remote controller, a 15mW, 830 nm laser diode (LD) mounted on the remote controllercontinuously transmits a laser beam for 1 s followed by thecoded ID and ON command signals as shown in Fig. 2. Thecoded ID and ON command signals are transmitted from the IRlight-emitting diode (LED) of the remote controller. Using laserbeam energy, the ACC sets the auxiliary relay and then theauxiliary AC/DC converter supplies power to the ID check unit,which checks whether the received ID and command signalmatch the appliance’s ID and command. If they match, themicrocontroller unit (MCU) in the ID check unit sends a pulseto set the main relay, the main AC/DC converter is activated,and the appliance turns on. After that, the auxiliary AC/DCconverter and ID check unit remain live and wait for anothercommand from the conventional remote controller. If coded IDand ON command signal do not match, the MCU sends a pulseto reset the auxiliary latch relay as shown in Fig. 2. In thissituation, the main latch relay stays in a cut-off state in which itconsumes absolute zero standby power.In our experiment, the ID check unit that is embedded in theappliance is taken out from the appliance and modified toinclude the latch relay controller. The nominal operatingpower of the main relay is about 10 times higher than that ofthe auxiliary relay.When the OFF command is received by the ID check unitwhile the appliance is working, the receiver unit sends twopulses, one to reset the main relay to cut off the appliance andthe other to reset the auxiliary relay to cut off the receiveritself returning to an absolute zero power standby mode.By the way, since the LD works for 1 s, usually a few timesa day only if the ON button is pressed, the decline in thebattery life time of the remote controller is consideredinsignificant.The ACC and the optical system, the most important partsof this system, are described in following sections.III. SYSTEM DESIGNA. ACC DesignTo accumulate incoming energy in a storage device and useit at once without any external intervention, an elaboratedevice is required that can monitor energy level, make a
1624 IEEE Transactions on Consumer Electronics, Vol. 57, No. 4, November 2011decision and connect the load. It is natural that power isrequired to perform these functions. However, in our system,the only available power source is the accumulated energy inthe storage capacitor. Furthermore, the extracted electricalenergy from the light of the LD is very low, in the order ofmicrowatts and the voltage across the storage capacitor is notconstant, since it increases from 0 volts. Therefore, aswitching circuit that can monitor the energy level withextremely low power leakage and autonomously connect theload when the accumulated energy is sufficiently high to drivethe load is needed.Figure 3 is a schematic of the ACC connected to the auxiliarylatch relay as a load. The ACC is adapted from a similar circuitdesigned for energy harvesting - and has been revisedto reflect the very low impedance of the latch relay.Fig. 3. Schematic of the autonomous connection circuit.This circuit works as follows. Q1, Q2, and Q3 are initiallyoff, meaning that the ground is floating due to the off state ofQ2 and Q3, and the latch relay is unpowered. Since there is nodischarge path for the storage capacitor Cs, charges generatedby the photovoltaic array are accumulated on the storagecapacitor Cs. The leakage in this accumulation stage consistsof an emitter-collector leakage current of Q1 and a leakagecurrent of the zener diode D1. As the storage capacitor voltageincreases to values comparable to the zener voltage, theleakage currents also increase and induce low voltage on theQ2 gate. This low gate voltage and a large resistance R3 forceon Q2 operate in the sub-threshold region. Since the sub-threshold current in the order of pA is much smaller than thephoto-generated current, the storage capacitor voltage keepsincreasing. When the storage capacitor voltage increases toVACC (i.e., the zener voltage plus the base-emitter voltage dropof Q1), Q1 turns on and the emitter-collector current abruptlystarts to increase. The current increase subsequently increasesthe gate voltage of Q2, resulting in its activation. Voltageacross R3 then increases, and Q3 gate voltage increases andactivates Q3. This connects the ground line to the completedischarge loop of the storage capacitor through the latch relaycoil, and a large current then flows through the relay coil tolatch the relay. As soon as the large discharge current flowsthrough the relay coil, the Cs voltage drops sharply below thethreshold gate voltages of Q2 and Q3, deactivating them andfloating the ground. If the relay was directly connected to Q2without Q3, the storage capacitor voltage would never reach tothe VACC since the relatively large discharge current flowsthrough the low impedance of the relay coil. Finally, R4 andD2 were included to protect FETs from counter-electromotiveforces in the relay coil and further incoming laser beam willincrease the storage capacitor voltage.Figure 4 shows the voltage (upper trace) of 10 μF Cs and theoutput voltage (lower trace) of the auxiliary AC/DC convertershown in Fig. 2. When the laser beam illuminates the PV arrayin a dark room, the capacitor voltage is raised from zero (Fig.4(a)). After 620 ms, when the voltage of the storage capacitorreaches to 5.6 V, the storage capacitor starts discharge and thelatch relay is set. As mentioned above, since the laser turn-ontime is set to 1 s, the voltage of the storage capacitor increasesagain after discharging.(a) (b)Fig. 4. The waveform of the voltage on the storage capacitor (upper trace)and the supply auxiliary AC/DC converter output (lower trace); (a) in thedark, and (b) at 300 lx indoor illumination.Fig. 4(b) shows the waveforms when the laser beamilluminates the PV array in a bright room with 300 lxillumination. Although the room light is not sufficient tooperate the ACC, the capacitor voltage is raised from 1.4 Vdue to the ambient light. It is found that the ACC turns ontwice in 1 s of laser illumination but that there is no change inthe auxiliary AC/DC converter output. Since the indoor homeor office illumination is generally about 300 lx, the actualsituation is closer to that in Fig. 4(b) than that in Fig. 4(a).B. Optical System DesignThe optical system has a major effect on our system’s delaytime. The amount of time, T, required to turn on the ACC withthe light power can be expressed as follows:S ACCph dC VQTi i i (1)where Cs is the capacitance of the storage capacitor, VACC isthe threshold operation voltage of the ACC, iph and id are thephotocurrent and the diffusion current, respectively, of the PVcell. The photocurrent iph can be expressed as follows:opphP Aeih (2)where η is the external quantum efficiency (EQE) of the PVcell, Pop is the optical power density [W/ cm2], A is thephotovoltaic cell area [cm2], e is the electronic charge, h is the
S. Kang et al.: Zero Standby Power Remote Control System using Light Power Transmission 1625Planck’s constant and ν is the light frequency. Using (2), (1)can be rewritten as:S ACCopdC VTP Aeih(3)In our system, Cs is 10 uF, VACC is 5.6 V, and Pop isdetermined by the light source characteristic. η, A and id aredetermined by the PV cell characteristics. The goals of opticaldesign are to maximize the operation distance and minimizethe laser on time. The design parameters are determined asdescribed below.An LD with a 15 mW total output light power and an 830nm wavelength was used for light power transmitter. The totaloutput light power of an LED mounted to a commercialremote controller is 50 mW. Although the total output lightpower of the LD is much lower than that of the LED, the LDintensity is much higher. Therefore, the LD was chosen tomaximize the energy transfer efficiency and working distanceof our remote control system. Since the LD beam size was toosmall to cover the PV array area, a lens was inserted to expandthe beam size. The half divergence angles were measuredhorizontally at 4.5 mrad and vertically at 7.5 mrad at 50 %beam truncation. Assuming uniform illumination within thedivergence angle, the average intensity Pop at the distance of dcan be estimated as follows:20.5 154.5 7.5opmWPd mrad mrad (4)where the denominator is the area of the truncated ellipticalbeam.(a) (b)Fig. 5. Photographs of the GaAs PV devices: (a) PV cell with and withouta concentrator and (b) a PV array.A GaAs-based PV cell was used for the laser powerreceiver since it has higher EQE at 830 nm than a silicon-based PV cell -. The GaAs PV cell generally has anopen circuit voltage of 0.9-1.0 V at AM 1.5 (= 0.1 W/cm2);however, since the light intensity in our application is muchlower than this value, the open circuit voltage is very low. Toachieve the ACC threshold operation voltage, VACC, thenumber of cells in the series should be increased and the lightintensity impinging on the cells should be increased.Furthermore, the size of the optical power receiver should beminimized and have a wide acceptance angle. Consideringthese requirements, the optical power receiver is composed ofthe GaAs PV cells with a plastic concentrator lens as shown inFigure 5(a). The area A in (3), the area of a single cell, is 0.28cm2(Figure 5(a)). The measured EQE, including the reflectioneffect, is about 0.3.A total of 7 GaAs PV cells are used and ellipticallypositioned (Figure 5(b)) to match the beam shape. The 7 cellsare connected in a series to obtain higher output voltage thanthe VACC which is 5.6 V. The area of the PV array, 2 cm 2.5cm, is small enough to be attached to home appliances.The diffusion current of the PV cell id is given by:20 ( 1)PVeVkTdi I e (5)where VPV is the output voltage of the PV cell, k is theBoltzmann constant, T is temperature in Kelvin and I0 is thereverse saturation current. I0 is measured to be 8.8 pA. It canbe seen that id is zero at 0 V of VPV and that is exponentiallyincreases as VPV increases until it is equal to iph.Using the parameters obtained as above, it was possible toobtain the T of the designed optical system. In Figure 6, thedesigned T and measured T at the various distances are shown.Despite the rough approximation, the measured values fit wellwith the designed values.Fig.6. Designed and measured T with respect to the distance between theLD and the PV array.The ACC does not work when the distance is longer than 3m since the beam size is much larger than that of PV arrayarea and, therefore, the effective light energy decreases.There are several ways to increase the working distance, e.g.,increasing the light source’s optical power, using a higherEQE PV cell, or using more PV cells in the series.IV. EXPERIMENT RESULTSThe proposed system was constructed and implemented ona 190 W commercial LCD TV that has standby power of 9.7W. The receiver unit including the PV array was attached tothe front side of the TV, which is 3 m away from remotecontroller. AC power consumption was measured using adigital power meter with 1 mW resolution.Figure 7 shows the PCB (9 cm 9.5 cm) of the constructedreceiver unit, which includes a PV array, an IR detector, aMCU, an auxiliary AC/DC converter, an ACC and two relays.
1626 IEEE Transactions on Consumer Electronics, Vol. 57, No. 4, November 2011Fig. 7. Constructed receiver unit.Figure 8 shows, from top to bottom, the waveforms of thestorage capacitor voltage, the IR detector output, the MCUoutput pulse for the relay control, and AC input voltage of theappliance. The standby power consumption is initially absolutezero since the appliance and the receiver unit are physicallydisconnected from the AC power line by the two latch relays.Fig. 8. The voltage waveforms observed when the appliance performs theturn-on process.When the LD is turned on, as described in section III, thestorage capacitor voltage starts to increase (top trace). TheACC then operates and the ID check unit is activated insequence. Since the IR coded ID and command were designedto follow the laser light, the incoming coded IR signal wasidentified. When a valid appliance ID with a correct on signalis received (second trace), the MCU generates a 30 ms pulse(third trace) to set the main relay and the AC power line isthen connected to supply AC voltage (bottom trace) to theappliance. If the ID is not correct or is not entered within 3 s,the MCU will reset the auxiliary relay to return to the initialstandby mode as programmed, which makes the systeminsensitive to the surrounding light noise or other IR signalsfor adjacent appliances.Figure 9 shows the waveforms while the TV is performingthe turn-off process. Contrary to the turn-on process, the TV isturned off by the LED signal of the commercial remotecontroller. Therefore, there is no change in the storagecapacitor voltage, which is not shown here.Fig. 9. The voltage waveforms when the appliance is performing the turn-off process.When a turn-off signal is received (top trace), the MCUgenerates a 30 ms pulse (second trace) to reset the main relayand a 5 ms pulse (third trace) to reset the auxiliary relay. Inthis manner, both the appliance and the receiver unit aredisconnected from the AC power line (bottom trace). Thebottom trace shows that AC voltage applied to the appliancebecomes zero. The top trace shows a typical voltage decay ofRC circuit when the circuit is switched off. Finally, the wholesystem goes back into the initial standby mode, consumingabsolute zero power.Without the proposed system, the TV consumes 9.7 W instandby mode, most of which is conversion loss of the mainAC/DC converter at a very low load. Figure 10 shows powerconsumption measurement results in the time domain usingour system in a dark room.Fig. 10. Power consumption of the TV with the zero standby powerremote control system.When the TV is in the off state, the power consumption is 0W. ID check unit is activated 620 ms after the LD is turned on.For next 680 ms, the ID check unit waits for signals andoperates to confirm that the ID and command are correct,consuming 220 mW. When they are correct, the TV turns onand it consumes normal operation power, 190 W.
S. Kang et al.: Zero Standby Power Remote Control System using Light Power Transmission 1627V. CONCLUSIONThe home appliances have become more efficient, causing agradual decrease in standby power consumption in recentyears. However, total standby power is probably growing inthe future as the number of home appliances increases. In thiswork, we proposed, implemented, and tested a new remotecontrol system that decreases the standby power to absolutezero. One idea is to mount an LD on a remote controller totransmit the light energy to the remote receiver unit, whileanother involves using an elaborate ACC. Using incominglight power alone, the ACC can accumulate the energy,monitor the energy level, and autonomously connect the loadonce the accumulated energy level is sufficient to drive theload. Implementing these two ideas in a commercial appliance,a zero standby power system was constructed. It was foundthat, using a 15 mW laser diode, 620 ms laser illumination isenough to turn on the appliance at a 2 m distance in acompletely dark room. As PV cell efficiency is improvingthese days, the laser aiming time and operation distance willbe further improved. It is expected that this proposed systemwill be applied to all remotely controllable appliances in thefuture to conserve energy and save the environment.REFERENCES IEA, “Fact Sheet: Standby Power Use and the IEA “1 Watt Plan”,” Apr.2007. A. Meier, “A worldwide review of standby power use in homes,”Proceedings of the International Symposium on Highly Efficient Use ofEnergy and Reduction of its Environmental Impact, pp. 123-126, Dec.2001. H. P. Siderius, B. Harrison, M. Jakel and J. Viegand, “Standby: TheNext Generation,” Proc. EEDAL, London, Jun. 2006. S. Zhou and B. Liu, “Design of 80 W two-stage adapter with highefficiency and low no load input power,” Proc. APEC, pp. 728-732, Mar.2002. B. T. Huang, K. Y. Lee, and Y. S. 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Electron Devices, vol. 56, no. 2, pp.170-175, 2009.BIOGRAPHIESSungmuk Kang was born in Pohang, Korea, in 1984.He received B.S. and M.S. degrees in electronic andelectrical engineering from Chung-Ang University,Korea, in 2007 and 2009, respectively. Currently, he ispursuing a Ph.D. degree in electronic and electricalengineering at Chung-Ang University. His researchinterests include energy-harvesting circuit design,wireless sensor networks, and power managementsystems.Kyungjin Park was born in Busan, Korea, in 1981. Hereceived B.S. and M.S. degree in electronic andelectrical engineering from Chung-Ang University,Korea, in 2008 and 2010, respectively. Currently, he ispursuing a Ph.D. degree in electronic and electricalengineering at Chung-Ang University. His researchinterests include MEMS, energy harvesting, wirelesssensor networks, and power management systems.Seunghwan Shin was born in Busan, Korea in 1983.He received a B.S. degree in electronic and electricalengineering from Chung-Ang University, Korea, in2010. Currently, he is pursuing an M.S. degree inelectronic and electrical engineering at Chung-AngUniversity. His research interests include energyharvesting, wireless sensor networks, and powermanagement systems.Keunsu Chang was born in Seocheon, Korea in 1983.He received a B.S. degree in electronic and electricalengineering from Chung-Ang University, Korea, in2010. Currently, he is pursuing an M.S. degree inelectronic and electrical engineering at Chung-AngUniversity. His research interests include energyharvesting, wireless sensor networks, and powermanagement systems.Hoseong Kim was born in Seoul, Korea, in 1957. Hereceived a B.S. degree in electrical engineering fromSeoul National University in 1980. He received M.S.and Ph.D. degrees in electrical and computerengineering from State University of New York atBuffalo in 1988 and 1992, respectively. He joinedChung-Ang University in 1993 and is currently aprofessor in the School of Electrical and ElectronicsEngineering. He is currently the head of the CircuitDesign and Light Applications Laboratory. His currentresearch interests include energy harvesting, wireless sensor networks, opticalsensors and metrology, and circuit design.