Abstract:
A power supply circuit for an electrical appliance, including a turning-on stage configured for determining a transition from a turned-off state, in which the power supply circuit is off and does not supply electric power, to a turned-on state of the power supply circuit. The turning-on stage includes a transducer of the remote-control type configured for triggering the transition in response to the reception of a wireless signal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National stage patent application based on PCT Application Number PCT/EP2010/053480, filed on Mar. 17, 2010, entitled POWER SUPPLY CIRCUIT FOR REMOTELY TURNING-ON ELECTRICAL APPLIANCES, which application claims the priority benefit of Italian Patent Application Number TO2009A000214, filed on Mar. 20, 2009, entitled POWER SUPPLY CIRCUIT FOR REMOTELY TURNING-ON ELECTRICAL APPLIANCES, which applications are hereby incorporated by reference to the maximum extent allowable by law. 
     TECHNICAL FIELD 
     The present invention relates to a power supply circuit for remotely turning-on electrical appliances and more in particular to a switch-mode power supply (SMPS). 
     BACKGROUND ART 
     As is known, many electrical or electronic appliances, such as for example television sets, radios, and hi-fi systems, envisage a low-consumption mode of operation, referred to as “stand-by mode”. In this mode, the electrical appliance is inactive as regards normal operation (for example, display of images for a television set, sound reproduction for hi-fi equipment, etc.) but can be controlled in switching-on through a remote control. As is generally known, an electrical appliance in stand-by mode is in any case supplied through the electric-supply mains, such as domestic power, or battery and consumes energy. The energy consumption is due to the presence of a microcontroller and a sensor connected to the microcontroller, configured for receiving and processing possible commands issued by remote control and supplied for this purpose. Considerable efforts have been made in the last few years to limit current consumption in stand-by mode of electrical appliances, which, so far, generally have levels of consumption of a few watts. However, it is evident that, if the consumption in stand-by mode of a plurality of electrical appliances generally present in dwellings is considered, non-negligible daily consumption levels may be reached. 
       FIG. 1  shows by means of a block diagram a portion of an electrical appliance  1  (in what follows the portion being referred to as a whole as electrical appliance  1 ) comprising a power supply circuit  4  (more in particular, a switch-mode power supply circuit SMPS) designed to guarantee operation in stand-by mode of a microcontroller  5  and of a command sensor  6  connected to the microcontroller  5  of the electrical appliance  1 . The electrical appliance  1  comprises a supply port  2 , which is connected, for example, to the supply mains or to a battery (not illustrated) and receives at input a supply voltage V AL . The supply voltage V AL  is hence supplied in input to the power supply circuit  4 , which supplies the microcontroller  5  both during the normal operating mode and in stand-by mode. In particular, in stand-by mode the microcontroller  5  should be switched on and be able to process possible commands (for example, the command for switching on the electrical appliance  1 ) issued via a remote control  7  and detected by the command sensor  6 . The electrical appliance  1  moreover comprises a supply switch  8 , arranged between the supply port  2  and the power supply circuit  4 , configured so as to be operated in conduction or interdiction. The switch  8  may, for example, be a main switch of the electrical appliance  1 . If the supply switch  8  is operated in conduction (i.e., it is closed), the power supply circuit  4  and the microcontroller  5  are supplied during the stand-by mode; instead, if the supply switch  8  is operated in interdiction (i.e., it is open), the power supply circuit  4  and the microcontroller  5  are not supplied, and the stand-by mode cannot be activated. In the latter case, the electrical appliance  1  is effectively turned off and cannot be switched on via the remote control  7 . 
       FIG. 2  shows a possible embodiment, of a known type, of the power supply circuit  4 . In particular, the power supply circuit  4  is of a flyback type. 
     If the power supply circuit  4  is supplied by means of an AC supply voltage V AL , it is advisable to connect a rectifier  9 , for example a diode rectifier bridge and a filter capacitor, cascaded to the supply port  2 , in order to generate in use a DC working voltage V 1 . 
     The DC working voltage V 1  is then supplied in input to a primary winding  12  of a transformer  11 . The primary winding  12  comprises a first terminal  12 ′ connected to the rectifier  9  and a second terminal  12 ″. The second terminal  12 ″ is connected in series to a drain terminal D of a switching transistor  15 , for example a MOSFET device, which is in turn connected, through its own source terminal S, to a ground reference voltage GND. Furthermore, the second terminal  12 ″ of the primary winding  12  is connected in series to a drain terminal D of a turn-on transistor  16 , being, for instance, a MOSFET device. The turn-on transistor  16  is connected, via an own source terminal S, to a turn-on capacitor  18 , which is in turn connected to a ground reference voltage GND. 
     The switching transistor  15  and the turn-on transistor  16  are controlled in conduction and interdiction by a driving circuit  19 . The driving circuit  19  is moreover connected, through a supply port thereof, to the turn-on capacitor  18 , from which it receives the supply during its turning-on step. The supply port of the driving circuit  19  is moreover connected, via a rectifier diode  22 , to an auxiliary winding  21  of the transformer  11 , which supplies the driving circuit  19  during use, after the turning-on step. Furthermore, a turn-on resistor  23  may be present, connected between a gate terminal G of the turn-on transistor  16  and the second terminal  12 ″ of the primary winding  12 . 
     Finally, the transformer  11  comprises a secondary winding  24  for generating on an output port of the power supply circuit  4  an output voltage V OUT  that supplies the microcontroller  5 . 
     In the operating condition in which the electrical appliance is turned off (the supply switch  8  is open), the turn-on capacitor  18  is discharged and the driving circuit  19  is turned off. Closing of the supply switch  8  does not cause immediate turning-on of the driving circuit  19 , but generates a passage of current from the supply port  2  through the primary winding  12  and through the turn-on transistor  16 , which in turn charges the turn-on capacitor  18 . The turn-on transistor  16  is driven in conduction by means of the turning-on resistor  23 , which develops, after closing of the supply switch  8 , the biasing necessary for switching on (conduction state) the turn-on transistor  16 . 
     When the voltage on the turn-on capacitor  18  reaches a value V C  sufficient to supply the driving circuit  19 , the driving circuit  19  turns on and drives the turn-on transistor  16  in interdiction and the switching transistor  15  in conduction. The driving circuit  19  is hence supplied by the auxiliary winding  21 . 
     The turn-on transistor  16  and the turn-on resistor  23  form a turn-on circuit  29  of an active type, operated in order to pre-charge the turn-on capacitor  18  for turning on the driving circuit  19 . Following upon closing of the supply switch  8 , the electrical appliance  1  can switch to a normal operating mode or to a stand-by mode, awaiting a command (for instance, via the remote control  7 ) by a user. 
     Both during the normal mode of use and in the stand-by mode, the switching transistor  15  is operated by the driving circuit  19 , for example via a square-wave modulation (pulse-width modulation—PWM) signal, with a frequency usually higher than 16 kHz, and enables to transfer the supply needed for operation of the microcontroller  5  to the secondary winding  24 . Consequently, also in stand-by mode the driving circuit  19  is constantly supplied in order to drive the switching transistor  15  appropriately for supply of the microcontroller  5 . 
     Hence, it is evident that the stand-by mode generates an energy consumption that is constant and significant over time on account of the need for supply of the driving circuit  19  and the microcontroller  5 . 
     A possible solution for eliminating the energy consumption in stand-by mode consists in turning off the electrical appliance  1  via the main supply key  8  (however, not always present) or removing the supply physically from the electric-supply mains. These solutions, however, entail the loss of the convenience and practicality of having a complete control of the electrical appliance via remote control. 
     SUMMARY OF THE INVENTION 
     One aim of the present invention is to provide a power supply circuit free from the limitations described. 
     According to one embodiment of the present invention it is provided a power supply circuit for an electrical appliance, comprising a turning-on stage configured for determining a transition from a turned-off state, wherein said power supply circuit is off and does not supply electric power, to a turned-on state of said power supply circuit, characterized in that said turning-on stage comprises a transducer, of a remote-controlled type, configured for triggering said transition in response to a reception of a wireless signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of embodiments of the present invention, a preferred embodiment thereof is now described, purely by way of non-limiting example and with reference to the annexed drawings, wherein: 
         FIG. 1  shows a block diagram of a portion of an electrical appliance comprising a power supply circuit for remotely turning-on the electrical appliance; 
         FIG. 2  shows a switch-mode power supply circuit of a known type for managing remote turning-on of an electrical appliance; 
         FIG. 3  shows a power supply circuit according to an embodiment of the present circuit, for managing remote turning-on of an electrical appliance; 
         FIG. 4  shows a power supply circuit according to a further embodiment of the present circuit, for managing remote turning-on of an electrical appliance; 
         FIG. 5  shows a power supply circuit according to a further embodiment of the present circuit, for managing remote turning-on of an electrical appliance; 
         FIG. 6  shows a functional block diagram of an electrical appliance that implements the power supply circuit of any one of  FIGS. 3 to 5 . 
     
    
    
     DETAILED DESCRIPTION 
     For simplicity of description, reference will be made to a power supply circuit of a flyback type, similar to the one illustrated in  FIG. 2 ; however, other types of supply circuits can be implemented, for example, a converter of a boost type, a forward type, a resonant type, or some other type. 
       FIG. 3  shows a power supply circuit  30 , in particular a switch-mode power supply (SMPS) circuit of a flyback type. Elements of the power supply circuit  30  of  FIG. 3 , analogous to and having substantially the same function of the ones described with reference to the power supply circuit  4  of  FIG. 2 , will not be described any further herein. The power supply circuit  30  comprises a turn-on circuit  32  that can be activated remotely. 
     The turn-on circuit  32  comprises a turn-on transistor  16  similar to the one described with reference to  FIG. 2 . However, in this case the gate terminal G of the turn-on transistor  16  is not directly connected to, and controlled by, the driving circuit  19 . 
     The turn-on circuit  32 , which can be connected indifferently to the first terminal  12 ′ or to the second terminal  12 ″, further comprises a transducer  33 , which can be remote-controlled and is configured to enable, when activated, passage of a current through it. The transducer  33  is connected between the drain terminal D of the turn-on transistor  16  and the gate terminal G of the turn-on transistor  16 . 
     The transducer  33  can be a photodiode, a photomultiplier or a phototransistor, configured so as to enable passage of a current across its terminals if activated by a light beam at a particular wavelength or within a range of wavelengths. Furthermore, the transducer  33  can be formed by a plurality of photodiodes or photomultipliers or phototransistors connected in series one another. 
     Finally, the turn-on circuit  32  comprises a turn-off resistor  34 , preferably having a resistance comprised between 100 kΩ and 2 MΩ, connected between the gate terminal G of the turn-on transistor  16  and the source terminal S of the turn-on transistor  16 ; and a Zener diode  35 , connected between the gate terminal G of the turn-on transistor  16  and the source terminal S of the turn-on transistor  16 , in parallel to the turn-off resistor  34 , and having a Zener voltage V ZENER  preferably of 30 V. 
     For simplicity of description, in what follows reference will be made to a transducer  33  of an optical/electrical type, more precisely a phototransistor  36 . The phototransistor  36  is activated by means of an incident light beam, preferably not visible by the human eye and having, for example, a wavelength in the infrared (greater than 700 nm) or in the ultraviolet (less than 400 nm). The light beam may be generated by a user through a remote control (shown in) configured for generating such a light beam. 
     In use, when the phototransistor  36  is driven in conduction (by means of an incident light beam having, for example, a wavelength in the infrared), a current flows through it and a voltage develops across its terminals, biasing the gate terminal G of the turn-on transistor  16 . If the biasing voltage generated is higher than the conduction threshold of the turn-on transistor  16 , the turn-on transistor  16  turns on, connecting the supply port  2  with the turn-on capacitor  18 , through the rectifier  9  and the primary winding  12  of the transformer  11 . In this way, the turn-on capacitor  18  is charged and, when the voltage on the turn-on capacitor  18  reaches a value V C  sufficient to supply the driving circuit  19 , the driving circuit  19  turns on and drives in conduction the switching transistor  15 . Hence, the driving circuit  19  is supplied by the auxiliary winding  21 . 
     In order to guarantee turning-on of the driving circuit  19 , it is expedient for the turn-on transistor  16  to be driven in conduction by the phototransistor  36  (which, in turn, is driven in conduction by the incident light beam generated by the user) for a time sufficient to charge the turn-on capacitor  18 . When a voltage V C , sufficient to supply the driving circuit  19 , establishes on the turn-on capacitor  18 , the driving circuit  19  switches on. 
     The current that the phototransistor  36  generates, when it is activated by the incident light beam, is not very high. In particular, in the case of use of a turn-on transistor  16  having a gate capacitance of few nF (nanofarads), it is sufficient for the phototransistor  36  to generate a few tens of μA (microampere). In this case, the supply voltage V C  of the driving circuit  19  is reached in a time of the order of a few hundreds of milliseconds, practically negligible for human perception. 
     The turn-off resistor  34  has the function of draining a possible leakage current of the phototransistor  36 , for example caused by undesirable components of a light signal (e.g., natural light) accidentally incident on the phototransistor  36 . Moreover, the turn-off resistor  34  favors the switching-off (interdiction state) of the turn-on transistor  16 , draining the charge possibly accumulated on the gate terminal G of the turn-on transistor  16  during its operative state. The Zener diode  35  has the function of limiting the potential applied to the gate terminal G of the turn-on transistor  16  to a maximum value represented by the Zener voltage V ZENER , proper to the Zener diode  35 . In this way, saturation in conduction of the turn-on transistor  16  is prevented. 
     After the turning-on step, the driving circuit  19  controls in conduction the switching transistor  15 . In this way, a current flows through the primary winding  12  of the transformer  11  and supplies, via the auxiliary winding  21 , the driving circuit  19  itself. In use, the switching transistor  15  can be controlled via a square-wave modulation (pulse-width modulation˜PWM) signal with variable frequency, usually higher than 16 kHz, and enables transfer onto the secondary winding  24  of the supply for operation of the microcontroller  5 . 
     Turning-off of the power supply circuit  30  can be advantageously managed by the microcontroller  5 . For example, driving circuits  19  are known provided with a turn-off input  19   a . In this case, the microcontroller  5  is connected to said turn-off input  19   a  for turning-off the driving circuit  19  through a signal Driver_OFF, and consequently turning off the power supply circuit  30 . In fact, in the absence of an appropriate light beam incident on the active area of the phototransistor  36 , the turn-on transistor  16  is controlled in interdiction, and, after turning-off of the driving circuit  19 , also the switching transistor  15  is controlled in interdiction. Consequently, in the absence of supply, the power supply circuit  30  turns off. 
     As an alternative to the turning-off command by means of the signal Driver_OFF managed by the microcontroller  5 , there can be provided an appropriate circuit (not illustrated) for discharging of the turn-on capacitor  18  and for interrupting the supply of the driving circuit  19  managed by the microcontroller  5 . Or, yet again, the microcontroller  5  could drive in interdiction the switching transistor  15 , interrupting the flow of current through the primary winding  12  of the transformer  11 . 
     The power supply circuit  30  can be supplied by a mains supply, such as domestic power, or by a battery. In the case of battery supply, however, the power supply circuit  30  does not require the rectifier  9 . 
     Finally, a main switch of the electrical appliance in which the power supply circuit  30  is implemented (analogous to the supply switch  8  illustrated in  FIG. 2 ), connected between the supply port  2  and the transformer  11 , is not necessary. In fact, in the off state of the power supply circuit  30  (i.e., in the state in which the power supply circuit  30  does not provide electrical supply), the turn-on transistor  16 , the switching transistor  15 , and the transducer  33  are interdicted and do not conduct any current. The power supply circuit  30  performs itself the function of main switch of the electrical appliance in which it operates. 
       FIG. 4  shows a power supply circuit  30 ′ according to a further embodiment of the present disclosure. Elements of the power supply circuit  30 ′ of  FIG. 4  analogous to and having substantially the same function of elements described with reference to the power supply circuit  30  of  FIG. 3  are not further described herein. 
     In the embodiment of  FIG. 4 , the power supply circuit  30 ′ comprises a turn-on circuit  32 ′ that can be activated remotely, as already explained with reference to  FIG. 3 . The turn-on circuit  32 ′ can be connected indifferently to the first terminal  12 ′ or to the second terminal  12 ″ ( FIG. 4  shows the turn-on circuit  32 ′ connected to the second terminal  12 ″) and comprises the turn-on transistor  16 , the transducer  33  and the turn-off resistor  34 . However, unlike the embodiment of  FIG. 3 , the second terminal  12 ″ of the primary winding  12  is connected in series to a source terminal S of the turn-on transistor  16 . The turn-on transistor  16  is connected, through its own drain terminal D, to the turn-on capacitor  18 , which is in turn connected to a ground reference voltage GND. The turn-off resistor  34  is connected in parallel to the transducer  33 , i.e. one of its terminal is connected to the gate of the turn-on transistor  16  and the other terminal is connected to the source terminal S of the turn-on transistor  16  (which corresponds, in  FIG. 4 , to the second terminal  12 ″). 
     The transducer  33  is remote-controlled and is configured to enable, when activated, passage of a current through it. The transducer  33  is connected between the source terminal S of the turn-on transistor  16  and the gate terminal G of the turn-on transistor  16 . The transducer  33  according to the embodiment of  FIG. 4  is formed by a plurality of photodiodes connected in series one another. However, a single photodiode may be used, provided that, during activation, it generates across its terminals a voltage sufficiently high to control in conduction the turn-on transistor  16 . For example, in case the turn-on transistor  16  is a MOSFET device, the voltage is sufficiently high when the gate terminal G of the MOSFET device  16  is polarized above the MOSFET threshold voltage value for conduction channel formation. 
     The transducer  33  of  FIG. 4  may be activated by means of an incident light beam (generated by a user through a remote control) preferably in the infrared range. As known, a photodiode is configured to generate, when illuminated, current carriers (electrons/holes). In particular, the current carrier generation causes a direct polarization of each photodiode  40 , which develops across its terminals a voltage higher than its conduction threshold voltage, for example a voltage of about 600-700 mV. In this way, during use, the current through the photodiodes  40  is almost completely due to the incident light beam, and proportional to the incident light intensity. In absence of incident light beam, each photodiode  40  develops a voltage across its terminals which is lower than its conduction threshold voltage (and current substantially equal to zero). 
       FIG. 5  shows a power supply circuit  30 ″ according to a further embodiment of the present disclosure. Elements of the power supply circuit  30 ″ of  FIG. 5  analogous to and having substantially the same function of elements described with reference to the power supply circuit  30  of  FIG. 3  or power supply circuit  30 ′ of  FIG. 4  are not further described herein. 
     According to the embodiment of  FIG. 5 , the transducer  33  is connected in the same way as already described with reference to  FIG. 4 . However, the transducer  33  comprises an antenna  44  (e.g., a patch antenna) connected between the source S and gate G terminals of the turn-on transistor  16 . When no activation signal is provided to the antenna  44 , the source S and gate G terminals of the turn-on transistor  16  are short-circuited and thus the turn-on transistor  16  is off (i.e., it has an open circuit behavior and no current flows through it). However, when an electromagnetic signal (generated by a user through a remote control) is provided to the antenna  44  so as to induce a current flow through the antenna  44 , a voltage develops between the source S and gate G terminals of the turn-on transistor  16 . By configuring the antenna  44  (e.g., by providing a sufficient number of turns) so that the voltage developed across the antenna  44  is higher that the conduction threshold voltage of the turn-on transistor  16 , for example a voltage of about 600-700 mV, it is possible to control in an on-state the turn-on transistor  16 . 
     The advantage of the embodiments of  FIG. 4  and  FIG. 5 , with respect to the embodiment of  FIG. 3 , is that high voltage structures are not used. 
       FIG. 6  shows a block diagram of a system  50  comprising an electrical appliance  49  and a remote control  57 . By means of the remote control  57 , the electrical appliance  49  can be remotely controlled for being turned on and turned off. The electrical appliance  49  may, for example, be an audio/video system such as a television set, a hi-fi system, a video recorder, or an electrical household appliance in general, which implements the power supply circuit  30 . In particular, the remote control  57  is configured for issuing a command (i.e., an appropriate wireless signal) for remote activation of the transducer  33  of the power supply circuit  30 , in order to manage turning-on of the electrical appliance  49 . The remote activation command can be generated by pressing an appropriate key, present on the remote control  57 , which governs generation of the appropriate activation wireless signal. Such a wireless signal is, according with the described embodiment, a light beam having a wavelength and a power configured so as to control the phototransistor  36  in generation of an electrical current. 
     In some electrical devices of a known type, for example in some television sets, two supply circuits are present: a main power supply circuit, which supplies the electrical appliance as a whole during normal use (usually, for safety reasons, obtained with insulated topologies for example of a flyback type, forward type, resonant type, etc.) and an auxiliary power supply circuit, used in the step of turning-on of the electrical appliance and in stand-by mode. Separate implementation of the main power supply circuit and of the auxiliary power supply circuit guarantees a better energy efficiency, but at a higher cost. The turn-on circuit  32  according to an embodiment of the present invention can be implemented indifferently in a main power supply circuit or in an auxiliary power supply circuit. However, by implementing the turn-on circuit  32  according to an embodiment of the present invention in a main power supply circuit a high energy efficiency, a high level of integration of the components, and reduced production costs are guaranteed simultaneously. 
     The electrical appliance  49  of  FIG. 6  is supplied by means of a main power supply circuit  30  connected to the supply port  2 , which is, in turn, connected, for example, to the mains supply (e.g., household power line). The electrical appliance  49  comprises: the microcontroller  5 , which is connected to the power supply circuit  30  from which it receives the supply, and communicates with the command sensor  6 ; a sound-reproducing circuit  51 , which is connected to the power supply circuit  30  from which it receives the supply, and communicates with the microcontroller  5  and with one or more loudspeakers  55 ; optionally a memory  52 , which is connected to the power supply circuit  30  from which it receives the supply, and communicates with the microcontroller  5 , for storing possible programming information of the electronic appliance  49 ; and, optionally, a video-reproducing circuit  53 , which is connected to the power supply circuit  30  from which it receives the supply, and communicates with the microcontroller  5  and is configured for managing display of graphic information or images on a display  54 . The sound-reproducing circuit  51 , the memory  52 , the video-reproducing circuit  53 , the display  54 , and the loudspeakers  55  can be supplied by means of respective secondary windings (not illustrated) of the transformer  11  of the power supply circuit  30  of  FIG. 3 . 
     From an examination of the characteristics of the switch-mode power supply circuit provided according to the present invention the advantages that it makes possible are evident. 
     In particular, it is possible to eliminate the electric-power consumption of electrical or electronic appliances in stand-by mode, without losing the convenience of turning-on via remote control of the electrical or electronic appliance itself. 
     Furthermore, the time necessary for turning-on is of the order of a few hundreds of milliseconds, practically negligible for human perception. 
     Finally, it is clear that modifications and variations may be made to the switch-mode power supply circuit described and illustrated herein, without thereby departing from the sphere of protection of the present invention, as defined in the annexed claims. 
     For example, in order to limit the sensitivity of a transducer of an optical type (for example, a phototransistor) at a particular wavelength or within a range of wavelengths, it may prove advantageous to set an appropriate filter external to the phototransistor, configured so as to enable passage exclusively of the wavelength/wavelengths of interest. 
     Furthermore, according to the maximum voltage that the phototransistor sustains (depending upon the supply voltage V AL ), it may be expedient to connect a plurality of phototransistors  36  in series to one another. 
     In addition, the turn-on transistor  16  and the switching transistor  15  can be different from a MOSFET transistor; for example, they can be IGBT (insulated-gate bipolar transistor) devices or generic electronic switches. 
     Finally, the transducer  33  can be of a different type from what has been described. For example, it can be of an electromagnetic type, comprising an antenna and can be remotely activated by means of an electromagnetic signal. 
     Having thus described at least one illustrative embodiment of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention is limited only as defined in the following claims and the equivalents thereto.