Patent Publication Number: US-9906026-B2

Title: Device for reducing standby-mode energy consumption of an electric household appliance

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to a device for reducing standby-mode energy consumption of an electric household appliance. 
     As is known, some last-generation electric household appliances are designed to switch to a standby or rest mode pending command to restart the operating cycle. 
     Though less than in operating mode, energy consumption of the electric loads and the main electronic control unit of the appliance in standby mode is still relatively high. 
     Accordingly, systems for reducing standby-mode energy consumption have been devised, in which the main electronic control unit selectively opens one or more switches, e.g. monostable relays, to disconnect the electric loads of the appliance from the power mains. 
     Systems of this sort have the drawback of having to keep the main electronic control unit powered with a low voltage, so that, albeit reduced, energy consumption fails to comply with last-generation electric household appliance energy consumption standards, which call for less than 1 watt standby energy consumption of the appliance. 
     To reduce energy consumption further, electric household appliances have been designed with systems which, in standby mode, set the power unit to low voltage to power the main electronic control unit in an idle state. 
     German Patent Application DE-102006054539B3, for example, relates to a system for generating low voltage to power a washing machine electronic control unit, wherein a low-voltage main power unit is designed to go from an active state, in which it supplies the electronic control unit with low voltage, to an idle state, in which it cuts off low-voltage supply to the electronic control unit, but still remains partly active so it can be reactivated by a control signal. 
     More specifically, in the above system, the low-voltage main power unit receives the control signal via a control input, and switches state alongside a change in state of the control signal. 
     Though effective, the above system fails to actually zero energy consumption of the low-voltage main power unit, on account of this still being partly powered in the idle state, so as to detect the change in state of the control signal and reactivate quickly. 
     In other words, in the above system, the main power unit has to maintain power to its own internal electronic circuits responsible for detecting the change in state of the control signal and reactivating low voltage supply to the electronic control unit. 
     SUMMARY OF SELECTED INVENTIVE ASPECTS 
     It is therefore an object of the present invention to provide a device for further reducing standby-mode energy consumption of an electric household appliance, as compared with known systems. 
     According to the present invention, there is provided an electric household appliance featuring a device for reducing standby-mode energy consumption, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  shows a schematic of an electric household appliance featuring an electronic device for reducing standby-mode energy consumption and in accordance with the teachings of the present invention; 
         FIG. 2  shows an electric diagram of the electronic device for reducing standby-mode energy consumption of the  FIG. 1  electric household appliance; 
         FIG. 3  shows an electric diagram of the electronic device for reducing standby-mode energy consumption of the  FIG. 1  electric household appliance in accordance with a variation of the present invention; 
         FIG. 4  shows a schematic of an oven featuring an electronic device for reducing standby-mode energy consumption of a display and in accordance with the teachings of the present invention; 
         FIG. 5  shows a schematic of an oven featuring a device for powering a display with low voltage and in accordance with a variation of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Number  1  in  FIGS. 1, 2 and 3  indicates as a whole an electric household appliance (shown schematically) connected to an electrical power network  3  comprising a neutral line N at a reference potential V REF  corresponding to a neutral potential, and a phase line F at a phase potential V 1 . 
     In the example shown, potentials V REF  and V 1  of neutral line N and phase line F are set to obtain an alternating main supply voltage V A  of roughly 220-230 V. 
     Appliance  1  comprises an electronic device (preferably a control unit)  5 ; and a low-voltage power unit  6  having an input connected to electrical power network  3  to receive main supply voltage V A , and an output connected to electronic device  5  to supply it with a low supply voltage V B , e.g. of about 4-12 volts. 
     Appliance  1  also comprises a device  7  for reducing the standby energy consumption of appliance  1 , and in turn comprising switching means  8 , which are located along at least one of the power lines  9  connecting low-voltage power unit  6  to phase line F and neutral line N of electrical power network  3 , and operate between a closed state—in which they close power line  9  to connect low-voltage power unit  6  to electrical power network  3  and so turn on low-voltage power unit  6  and electronic device  5 —and an open state—in which they open power line  9  to disconnect low-voltage power unit  6  from electrical power network  3  and so turn low-voltage power unit  6  and electronic device  5  off completely. 
     Preferably, switching means  8  are switched from the open to the closed state by a low-voltage enabling signal S 2 , or from the closed to the open state by a disabling signal S 3 . 
     Device  7  also comprises, preferably, a low-voltage capacitive power unit  10  input-connected to electrical power network  3  to receive main supply voltage V A , and designed to generate low-voltage enabling signal S 2  at the output. 
     In the  FIG. 1  example, appliance  1  may be a washing machine, dishwasher, washer-dryer or drier, and comprises a number of known electric devices—hereinafter referred to simply as electric loads  2 —for performing the known washing/drying functions appliance  1  is designed for. 
     Being known electric/electronic devices, electric loads  2  are not described, except to state that each has at least one power input connected to an electrical power network  3  by a switch  4  opened/closed by a control signal S 1  to receive a main supply voltage V A  from electrical power network  3 . 
     In the  FIGS. 1 and 2  example, electronic device  5  is a main electronic control unit  5  (for example a microprocessor) designed to control operation of each electric load  2  of appliance  1 , and, operable to generate control signal S 1  to selectively disconnect each electric load  2  from electrical power network  3  when the washing/drying cycle is concluded and/or when the appliance  1  switches to a standby mode. 
     Device  7  also comprises a hand-operated control device  11 , e.g. a tactile switch or any other similar control device, connected between low-voltage capacitive power unit  10  and switching means  8  to supply switching means  8  with low-voltage enabling signal S 2 . 
     Switching means  8  are designed to switch from the closed to the open state on receiving disabling signal S 3  generated by main electronic control unit  5  when appliance  1  switches to standby mode, and to switch from the open to the closed state on receiving low-voltage enabling signal S 2  generated by user operation of control device  11 . 
     In the  FIGS. 1 and 2  example, switching means  8  comprise two input terminals  12 ,  13  connected respectively to phase line F and neutral line N of electrical power network  3 ; and two output terminals  14 ,  15  supplying supply voltage V A  to corresponding power terminals  16 ,  17  of low-voltage power unit  6 . 
     Switching means  8  also comprise a first control input  18  connected to an output  19  of main electronic control unit  5  to receive disabling signal S 3 ; and a second control input  20  connected to the output terminal of control device  11  to receive enabling signal S 2 . 
     Preferably, switching means  8  comprise a bistable relay  21 , which has an electric contact  22  movable between a first position associated with said open state and in which it opens power line  9  connecting low-voltage power unit  6  to electrical power network  3 , and a second position associated with said closed state and in which it closes power line  9  to connect low-voltage power unit  6  to electrical power network  3 . 
     Bistable relay  21  also comprises an electromagnetic device comprising, for example, two coils for moving movable electric contact  22  from the first to the second position on the basis of low-voltage enabling signal S 2 , or from the second to the first position on the basis of disabling signal S 3 . 
     In the  FIGS. 1 and 2  example, electric contact  22  is interposed between input terminal  12  and output terminal  14 , so as to open/close them on command. Electromagnetic device  23 , preferably, comprises a terminal connected to second control input  20  to receive low-voltage enabling signal S 2 ; a terminal connected to first control input  18  to receive disabling signal S 3 ; and a terminal connected to input terminal  13 . 
     Low-voltage capacitive power unit  10 , preferably, has a terminal  24  connected to phase line F; a terminal  25  connected to neutral line N; a terminal  26  connected by control device  11  to second control input  20  of switching means  8 ; and a terminal  27  at a predetermined reference potential V REF  preferably, though not necessarily, corresponding to the neutral potential. 
     Low-voltage capacitive power unit  10  preferably comprises a capacitive dividing circuit  28 ; and preferably a current-limiting circuit  29  interposed between capacitive dividing circuit  28  and switching means  8 . 
     In the  FIG. 2  circuit example, capacitive dividing circuit comprises two input terminals  30 ,  31  connected respectively to terminals  24 ,  25  to receive main supply voltage V A ; and two output terminals  32 ,  33  at a potential V C3  and reference potential V REF  respectively. 
     Current-limiting circuit  29 , when envisaged, comprises, preferably, an input terminal  34  connected by control device  11  to output terminal  32  of capacitive dividing circuit  28 ; and an output terminal  35  connected to second control input  20  of switching means  8 . 
     Preferably, capacitive dividing circuit  28  comprises a capacitive divider  36  connected between input terminals  30  and  31  and comprising a first capacitor  37  and a second capacitor  38  connected in series between input terminals  30  and  31  via a common node  39 . 
     Capacitive dividing circuit  28  also preferably comprises a Zener diode  40  with the anode terminal connected to input terminal  31 , and the cathode terminal connected to node  39 ; a third, preferably electrolytic, capacitor  41  connected between output terminals  32  and  33 ; and a diode  42  with the anode terminal connected to node  39 , and the cathode terminal connected to output terminal  32 . 
     In use, when capacitive dividing circuit  28  is powered by the negative half-wave of supply voltage V A , Zener diode  40  conducts to only circulate a current I 1  through first capacitor  37 , thus excluding second capacitor  38  and third capacitor  41 , which is therefore not charged at this stage. 
     It should be pointed out that, in the  FIG. 2  example, the capacity C 1  of first capacitor  37  and the capacity C 2  of second capacitor  38  of capacitive divider  36  are advantageously such that, during the positive half-wave of supply voltage V A  to terminals  30  and  31 , the voltage V C2  at the terminals of second capacitor  38  is lower than the Zener voltage VZ of Zener diode  40 , which is therefore never reverse-biased. 
     Preferably, when capacitive dividing circuit  28  is powered by the positive half-wave of supply voltage V A , capacitive divider  36  divides supply voltage V A  to generate, at the terminals of second capacitor  38 , voltage V C2 , which is lower than Zener voltage VZ of Zener diode  40 , so that, at this stage, Zener diode  40  remains off, and third capacitor  41  is charged with voltage V C3 . 
     It should be pointed out that first capacitor  37 , second capacitor  38 , and third capacitor  41  together define, preferably, a reactive circuit, which is supplied as a whole with a current I 1  having a predominantly capacitive component, which advantageously uses mainly reactive power. 
     Preferably, keeping Zener diode  40  off during the positive half-wave of main supply voltage V A , a current I 1  with a highly capacitive component is circulated, so that the power dissipated by capacitive dividing circuit  28  is predominantly characterized by a reactive power component, and advantageously by a negligible active power component, thus resulting in extremely low active energy consumption of low-voltage capacitive power unit  10  as a whole. 
     It should be pointed out that, unlike known capacitive pump circuits, in which the Zener diode must be reverse-biased during the positive half-wave of the main supply voltage to regulate the output voltage, capacitive dividing circuit  28 , preferably, serves solely to store energy by which to generate a signal and preferably and advantageously a pulse signal corresponding to low-voltage enabling signal S 2  and of sufficient minimum energy to activate bistable relay  21 . 
     In other words, capacitive dividing circuit  28  does not need to regulate the output voltage V C3 , but simply to generate a signal S 2 , preferably a pulse signal S 2 , to energize the coil of bistable relay  21 . Once activated, in fact, bistable relay  21  is designed to stay permanently in the last switch position, with no need for a constant, continuous electric input signal. 
     The circuit architecture achieved by capacitive dividing circuit  28  supplying bistable relay  21  with an enabling pulse signal S 2  therefore greatly reduces the active energy dissipated by device  7 , on account of the power/energy used by device  7  being predominantly reactive. 
     In the example shown, capacity C 1  of first capacitor  37  and C 2  of second capacitor  38  may be designed to satisfy the equation:
 
 V   A *(2* C 1)/( C 2+ C 1)−0.7 =V   C2   ≦VZ   a)
 
where V A  is the peak value of main supply voltage V A ; V C2  is the voltage at the terminals of second capacitor  38 ; and VZ is the Zener voltage.
 
     In the  FIGS. 1 and 2  example, device  7  also comprises an EMC Filter  70  (Electro Magnetic Compatibility Filter) connected between bistable relay  21  and low-voltage power unit  6 . 
     EMC Filter  70  has terminals  71 ,  72  connected respectively to power terminals  16  and  17  of the low-voltage power unit  6  and comprises a capacitor  73  and bleeder resistor  74  designed to discharge the capacitor  73 . 
     Preferably, capacitor  73  and bleeder resistor  74  are connected in parallel to each other between terminals  71  and  72 . 
     In accordance with a variation of the present invention shown in  FIG. 3 , EMC Filter  70  is interposed between electrical power network  3  and low-voltage capacitive power unit  10 , i.e. upstream of the bistable relay  21 . However in another alternative not shown, the EMC Filter  70  can be interposed between the low-voltage capacitive power unit  10  and the bistable relay  21 . 
     Preferably, according to the variation shown in  FIG. 3 , terminals  71 ,  72  of the EMC Filter  70  are connected respectively to terminals  24 ,  25  of the Low-voltage capacitive power unit  10 . 
     Operation of device  7  to reduce the energy consumption of appliance  1  will now be described, assuming appliance  1  is running, i.e. is not on standby mode, and bistable relay  21  is therefore in the closed position. 
     The appliance  1  may be operable to automatically switch to standby mode after wash/dry cycle has been completed/ended, and/or, for example, when electronic device  5  does not receive any new user-commands within a prearranged time. 
     Main electronic control unit  5  generates signal S 1  to open switch  4  and disconnect loads  2  from electrical power network  3 , preferably when wash/dry cycle has been completed/ended and at the same time or later within a prearranged time generates disabling signal S 3 , which preferably is in the form of a pulse-type low-voltage signal. 
     Disabling signal S 3  switches bistable relay  21  from closed to open, thus turning off low-voltage power unit  6  and main electronic control unit  5  at the same time. 
     It should be pointed out that, at this stage, unlike the energy consumption reducing systems of known appliances, the total energy consumption of low-voltage power unit  6  and main electronic control unit  5  is advantageously nil. 
     This condition continues pending user operation/actuation of control device  11 . 
     In practice, user operation/actuation of control device  11  supplies enabling signal S 2  to bistable relay  21 , which switches from open to closed to connect low-voltage power unit  6  to electrical power network  3  and so turn on main electronic control unit  5 . 
     Main electronic control unit  5  may also be operable to advantageously enable the user to turn off the appliance  1  by means of the control device  11 . 
     Main electronic control unit  5  is, for this purpose designed, to detect whether user operates/actuates control device  11  while the appliance is running. 
     Main electronic control unit  5  is, for this purpose designed, to detect whether user operates/actuates control device  11  while the appliance is running 
     Device  7  may comprise a sensing device  44  for detecting low-voltage enabling signal S 2  at second control input  20  of bistable relay  21 . 
     Sensing device  44  may, for example, comprise a current/voltage measuring sensor for generating a logic signal indicating the presence/absence of low-voltage enabling signal S 2  at second control input  20  of bistable relay  21 . 
     Preferably, main electronic control unit  5  is designed to detect whether user operates control device  11  on the basis of the logic state of the signal generated by sensing device  44 . If user operates control device  11  while the appliance is running, main electronic control unit  5  detects the logic state change of the signal generated by sensing device  44  corresponding to the presence of low-voltage enabling signal S 2 . 
     In this case, main electronic control unit  5  determines the logic state signal change and generates signal S 1  to open switch  4  and disconnect loads  2  from electrical power network  3 , and at the same time generates disabling signal S 3 , which preferably is in the form of a pulse-type low-voltage signal. 
     Preferably, main electronic control unit  5  may be operable to generate signals S 1  and S 3  when signal/s generated by sensing device  44  meet/s prearranged conditions. 
     In accordance with a different embodiment, prearranged conditions may be met when the signal stays in a logic state for certain time interval. 
     In accordance with an embodiment, a prearranged condition may be met when the logic state of the signal generated by sensing device  44  changes a prearranged number of times within a certain temporal time interval. 
     Main electronic control unit  5  may also be designed to advantageously detect power failure. 
     Preferably, main electronic control unit  5  may be operable to determine power failure of appliance  1 , when low voltage V B  is restored by the low-voltage main power unit in the absence of low-voltage enabling signal S 2 . 
     If power failure occurs while the appliance is running, switching means  8  remain closed, connecting low-voltage main power unit  6  to electrical power network  3 ; and, when power is restored, low-voltage main power unit  6  is again powered to turn on main electronic control unit  5 . 
     In this case, main electronic control unit  5  determines whether it was turned on by power being restored, or by the user switching bistable relay  21 . 
     In the example shown, main electronic control unit  5  determines whether the logic state of the signal generated by sensing device  44  corresponds to the presence of low-voltage enabling signal S 2 . 
     If the logic signal generated by sensing device  44  indicates no low-voltage enabling signal S 2 , main electronic control unit  5  determines a power failure, and so controls loads  2  according to a program for reactivating the wash/dry cycle interrupted by the power failure. 
     Conversely, if the logic signal generated by sensing device indicates the presence of low-voltage enabling signal S 2 , main electronic control unit  5  determines no power failure, and so controls loads  2  according to a specific program for reactivating the user-selected wash cycle. 
     However alternative embodiments can be envisaged to enable the main electronic control unit  5  to determine whether it was turned on by power being restored, or by the user switching bistable relay  21 , for example the main electronic control unit can memorize at least the last step of the operating cycle running before the power failure, so that when the power is again available, the control unit  5  can recognize that an interruption has occurred and control the loads  2  accordingly for reactivating, for example, the wash/dry cycle interrupted by the power failure or the control unit  5  can proceed with specific program sequences envisaged in case of operating cycle interruption. 
     Electric household appliance  1  described has the following advantages: 
     Firstly, total standby energy consumption of the low-voltage power unit and main electronic control unit  5  is nil. 
     Secondly, using a bistable relay controlled by two distinct pulse signals enables use of a low-voltage capacitive power unit with simpler circuitry than conventional capacitive pumps. In fact, unlike conventional capacitive pumps, in which the Zener diode is reverse-biased to regulate the output voltage, appropriately designing the first and second capacitors of the capacitive dividing circuit, previously described, prevents reverse biasing of the Zener diode, which therefore simply acts as a voltage limiter. 
     Thirdly, the configuration of the capacitive dividing circuit greatly reduces active power consumption in standby mode. That is, as stated, the current circulating in the capacitive dividing circuit has a predominantly capacitive component which obviously dissipates reactive power. 
     Finally, using a bistable relay that permanently maintains its operating state enables power failure detection by the electronic control unit. 
     Clearly, changes may be made to the electric household appliance as described and illustrated herein without, however, departing from the scope of the present invention. 
     For example in another alternative, depicted as an example in  FIG. 4 , the electric household appliance comprises display means, a voltage supply control unit for supplying an electric voltage to said display means and sensor switching means which turn on/off the low-voltage power unit according to detection of user within a given distance from the appliance, electric household appliance further comprises a device for reducing energy consumption of the electric household appliance comprising low-voltage capacitive power means designed to supply a low-voltage to said sensor switching means. 
     Preferably, the low-voltage capacitive power means comprises a capacitive dividing circuit comprising a first and second input terminal connected to a first and second power line at a first and second predetermined potential respectively; a first and second output terminals generating said low-voltage; first and second charge-accumulating means connected between said first and second input terminal; and at least one voltage limiter connected parallel to said second charge-accumulating means and designed to switch from a non-conducting to a conducting state when subjected to a voltage above a predetermined breakdown voltage; said first and second charge-accumulating means being so designed that the voltage at the terminals of said second charge-accumulating means is below said predetermined breakdown voltage. 
     Preferably, the capacitive dividing circuit comprises third charge-accumulating means connected between said first and second output terminal. 
     Preferably, the voltage limiter comprises a Zener diode having the anode and cathode terminals connected respectively to the input terminal of said capacitive dividing circuit and to a node between said first and second charge-accumulating means. Preferably, the first, second, and third charge-accumulating means respectively comprise a first, second, and third capacitor designed according to the equation:
 
 V   A *(2 *C 1)/( C 2+ C 1)−0.7= V   C2   ≦VZ  
 
where V A  is the peak value of the main supply voltage; V C2  is the voltage at the terminals of the second capacitor; and VZ is the Zener voltage.
 
Preferably, the low-voltage capacitive power means comprise voltage regulating means interposed between said capacitive dividing circuit and said sensor switching means.
 
     More in detail, the  FIG. 4  embodiment relates, for example, to an oven  50  comprising a display  52 , preferably, though not necessarily a clock display; a device  51  for reducing energy consumption of display  52  when oven  50  is on standby and unattended by the user; and preferably, though not necessary, a voltage power unit  80  having an input connected to electrical power network  3  to receive main supply voltage V A , and an output connected to display  52  to supply it with a secondary supply voltage V B . 
     In  FIG. 4 , device  51  for reducing energy consumption of display  52  comprises switching means  81 , which are located along at least one of the power lines  82  connecting voltage power unit to phase line F and neutral line N of electrical power network  3 , and operate between a closed state—in which they close power line  82  to connect voltage power unit  80  to electrical power network  3  and so turn on voltage power unit  80  and display  52 —and an open state—in which they open power line  82  to disconnect voltage power unit  80  from electrical power network  3  and so turn voltage power unit  80  and display  52  off completely. 
     Preferably, switching means  81  are switched from the open to the closed state by a low-voltage enabling signal S 2 , or from the closed to the open state by a disabling signal S 3 . 
     Device  51  also comprises a low-voltage capacitive power unit  83  input-connected to electrical power network  3  to receive main supply voltage V A , and designed to generate a low voltage V 2  at the output. 
     Device  51  also comprises a proximity sensor  90  for detecting the presence or absence of the user within a given distance from oven  50 . 
     Preferably, proximity sensor  90  is connected to the output of low-voltage capacitive power unit  83 , preferably, though not necessary, via a known voltage regulating device  84 , and is designed to output enabling signal S 2  when the user is within a given distance from oven  50 , and, conversely, to output a disabling signal S 3  when the user is not within a given distance from oven  50 . 
     Switching means  81  are designed to switch from the closed to the open state on receiving disabling signal S 3  when user is not within a given distance from oven  50 , and to switch from the open to the closed state on receiving low-voltage enabling signal S 2  when the user is within a given distance from oven  50 . 
     In the  FIG. 4 , switching means  81  comprise two input terminals  92 ,  93  connected respectively to phase line F and neutral line N of electrical power network  3 ; and two output terminals  94 ,  95  supplying supply voltage V A  to corresponding power terminals  96 ,  97  of voltage power unit  80 . 
     Switching means  81  also comprise a first control input  100  connected to a first output of proximity sensor  90  to receive disabling signal S 3 ; and a second control input  98  connected to a second output terminal of proximity sensor  90  to receive enabling signal S 2 . 
     Preferably, switching means  81  comprise a bistable relay  101 , which has an electric contact  102  movable between a first position associated with said open state and in which it opens power line  82  connecting voltage power unit  80  to electrical power network  3 , and a second position associated with said closed state and in which it closes power line  82  to connect voltage power unit  80  to electrical power network  3 . 
     Bistable relay  101  also comprises an electromagnetic device  103  comprising, for example, two coils for moving movable electric contact  102  from the first to the second position on the basis of enabling signal S 2 , or from the second to the first position on the basis of disabling signal S 3 . 
     In the  FIG. 4  example, electric contact  102  is interposed between input terminal  92  and output terminal  94 , so as to open/close them on command. And electromagnetic device  103  has a terminal connected to second control input  98  to receive low-voltage enabling signal S 2 ; a terminal connected to first control input  100  to receive disabling signal S 3 ; and a terminal connected to input terminal  93 . 
     Low-voltage capacitive power unit  83  has a terminal  104  connected to phase line F; a terminal  105  connected to neutral line N; a terminal  106  connected to proximity sensor device  90 ; and a terminal  107  at a predetermined reference potential V REF  preferably, though not necessarily, corresponding to the neutral potential. 
     Low-voltage capacitive power unit  83  substantially comprises a capacitive dividing circuit  108 ; whereas regulating device  84 , when envisaged, is interposed between capacitive dividing circuit  108  and proximity sensor  90 . 
     In the  FIG. 4  circuit example, capacitive dividing circuit  108  comprises two input terminals  110 ,  111  connected respectively to terminals  104 ,  105  to receive main supply voltage V A ; and two output terminals  112 ,  113  at a potential V C3  and reference potential V REF  respectively. 
     Regulating device  84  comprises an input terminal  114  connected to output terminal  112  of capacitive dividing circuit  108 ; and an output terminal  115  connected to proximity sensor  90  to supply low-voltage V 2 . 
     Preferably, capacitive dividing circuit  108  comprises a capacitive divider  116  connected between input terminals  110  and  111  and comprising a first capacitor  117  and a second capacitor  118  connected in series between input terminals  110  and  111  via a common node  119 . 
     Capacitive dividing circuit  108  also comprises a Zener diode  120  with the anode terminal connected to input terminal  111 , and the cathode terminal connected to node  119 ; a third, preferably electrolytic, capacitor  121  connected between output terminals  112  and  113 ; and a diode  122  with the anode terminal connected to node  119 , and the cathode terminal connected to output terminal  112 . 
     In the  FIG. 4  embodiment, device  51  can also comprises an EMC Filter  200  (Electro Magnetic Compatibility Filter) which is interposed between bistable relay  101  and voltage power unit  80 . 
     EMC Filter  200  has two terminals which are connected respectively to power terminals  96  and  97  of the voltage power unit  80  and comprises a capacitor  203  and a bleeder resistor  204  designed to discharge the capacitor  203 . 
     Preferably, capacitor  203  and bleeder resistor  204  are connected in parallel to each other. 
     In accordance with a variation of the present invention (not shown), EMC Filter  200  is interposed between electrical power network  3  and low-voltage capacitive power unit  83 , i.e. upstream the bistable relay  21 . 
     Preferably, according to a variation, terminals of the EMC Filter  200  are connected respectively to terminals  104 ,  105  of the low-voltage capacitive power unit  83 . 
     In use, when capacitive dividing circuit  108  is powered by the negative half-wave of supply voltage V A , Zener diode  120  conducts to only circulate a current I 1  through first capacitor  117 , thus excluding second capacitor  118  and third capacitor  121 , which is therefore not charged at this stage. 
     It should be pointed out that, in the  FIG. 4  example, the capacity C 1  of first capacitor  117  and the capacity C 2  of second capacitor  118  of capacitive divider  116  are advantageously such that, during the positive half-wave of supply voltage V A  to terminals  110  and  111 , the voltage V C2  at the terminals of second capacitor  118  is lower than the Zener voltage VZ of Zener diode  120 , which is therefore never reverse-biased. 
     Preferably, when capacitive dividing circuit  108  is powered by the positive half-wave of supply voltage V A , capacitive divider  116  divides supply voltage V A  to generate, at the terminals of second capacitor  118 , voltage V C2 , which is lower than Zener voltage VZ of Zener diode  120 , so that, at this stage, Zener diode  120  remains off, and third capacitor  121  is charged with voltage V C3 . 
     It should be pointed out that first capacitor  117 , second capacitor  118 , and third capacitor  121  together define a reactive circuit, which is supplied as a whole with a current I 1  having a predominantly capacitive component, which advantageously provides/uses mainly reactive power. 
     Preferably, keeping Zener diode  120  off during the positive half-wave of main supply voltage V A , a current I 1  with a highly capacitive component is circulated, so the power dissipated by capacitive dividing circuit  108  is predominantly characterized by a reactive power component, and advantageously by a negligible active power component, thus resulting in extremely low active energy consumption of low-voltage capacitive power unit  83  as a whole. 
     It should be pointed out that, unlike known capacitive pump circuits, in which the Zener diode  120  must be reverse-biased during the positive half-wave of the main supply voltage to regulate the output voltage, capacitive dividing circuit  108  serves solely to store sufficient minimum energy by which to supply the proximity sensor  90 . 
     The circuit architecture achieved by capacitive dividing circuit  108  supplying proximity sensor  90  therefore greatly reduces the active energy dissipated by device  51 , on account of the power/energy provided/used by device  51  being predominantly reactive. 
     In the example shown, capacity C 1  of first capacitor  117  and C 2  of second capacitor  118  may be designed to satisfy the equation:
 
 V   A *(2 *C 1)/( C 2+ C 1)−0.7= V   C2   ≦VZ   a)
 
where V A  is the peak value of main supply voltage V A ; V C2  is the voltage at the terminals of second capacitor  118 ; and VZ is the Zener voltage.
 
     In actual use, when the user is within a given distance from oven  50 , proximity sensor  90  generates enabling signal S 2  to switch movable electric contact  102  of bistable relay  101  into the second operating position and so turn on voltage power unit  80  and display  52 . 
     Conversely, when the user is not within a given distance from oven  50 , proximity sensor  90  generates disabling signal S 3  to switch movable electric contact  102  into the first operating position and so turn off voltage power unit  80  and display  52 . 
     In another alternative, depicted as an example in  FIG. 5 , the electric household appliance comprises display means, voltage power means connected to an electrical power network to receive a main supply voltage to supply a voltage to said display means, a device for reducing energy consumption comprising:
         switching means which are switched by a enabling signal to a closed state connecting said voltage power means to the electrical power network to turn on the voltage power means and said display means;   a proximity sensor generating said enabling signal when detects a user within a given distance from the appliance; and   low-voltage capacitive power means which supply a low-voltage to supply said proximity sensor.       

     Preferably, the proximity sensor outputs a disabling signal when does not detect a user within said given distance from the appliance; said switching means being switched by the disabling signal to an open state disconnecting voltage power means from the electrical power network to turn the voltage power means and said display means off completely. 
     Preferably, the switching means comprise a bistable relay. 
     Preferably, the bistable relay comprises at least one movable electric contact movable between a first position associated with said open state and wherein it opens a power line connecting said voltage power means to a electrical power network, and a second position associated with said closed state and wherein it closes said power line. 
     Preferably, the bistable relay comprises electromagnetic means designed to move said movable electric contact from the first to the second position on the basis of the enabling signal, or to move the movable electric contact from the second to the first position on the basis of the disabling signal. 
     Preferably, the low-voltage capacitive power means comprises a capacitive dividing circuit comprising a first and second input terminal connected to a first and second power line at a first and second predetermined potential respectively; a first and second output terminals generating said low-voltage; first and second charge-accumulating means connected between said first and second input terminal; and at least one voltage limiter connected parallel to said second charge-accumulating means and designed to switch from a non-conducting to a conducting state when subjected to a voltage above a predetermined breakdown voltage; said first and second charge-accumulating means being so designed that the voltage at the terminals of said second charge-accumulating means is below said predetermined breakdown voltage. 
     Preferably, the capacitive dividing circuit comprises third charge-accumulating means connected between said first and second output terminal. 
     Preferably, the voltage limiter comprises a Zener diode having the anode and cathode terminals connected respectively to the input terminal of said capacitive dividing circuit and to a node between said first and second charge-accumulating means. 
     Preferably, the first, second, and third charge-accumulating means respectively comprise a first, second, and third capacitor designed according to the equation:
 
 V   A *(2 *C 1)/( C 2+ C 1)−0.7 =V   C2   ≦VZ  
 
where V A  is the peak value of the main supply voltage; V C2  is the voltage at the terminals of the second capacitor; and VZ is the Zener voltage.
 
     Preferably, the low-voltage capacitive power means comprise voltage regulating means interposed between said capacitive dividing circuit and said sensor switching means. 
     Preferably, the electric household appliance comprises an EMC Filter which is interposed between outputs of said switching means and input of said voltage power means. 
     Preferably, the electric household appliance comprises an EMC Filter being connected to the first and second input terminal of said capacitive dividing circuit. 
     More in detail,  FIG. 5  shows an alternative device  130  for reducing energy consumption of a display  131  of an oven  50 , for example, and which is similar to device  51 , and the component parts of which are indicated, where possible, using the same reference numbers as for the corresponding parts of device  51 . 
     Device  130  differs from device  51  by display  131  being connected by a power control unit  132  to the electrical power network  3  to receive supply voltage. 
     Moreover, device  130  has not switching means. 
     In detail, power control unit  132  comprises control inputs  133  and  134  connected respectively to outputs  135  and  136  of the proximity sensor  90  to receive enabling signal S 2  and disabling signal S 3 , and is operable to be switched from a no-power supply state to a power supply state by the enabling signal S 2 , or from the power supply state to the no-power supply state by the disabling signal S 3 . 
     More specifically, on receiving disabling signal S 3  power control unit  132  cuts off electrical power supply to display  131 . In other words, disabling signal S 3  commands power control unit  132  so as to turning off to display  131 . 
     On receiving enabling signal S 2 , power control unit  132  supply electrical power to turn on the display  131 .