Abstract:
A power stealing system having a switch and a circuit that takes power from equipment to operate control electronics. The system may be such that power stealing occurs while the equipment is not powered to avoid disruption or false signals in the electronics or equipment. The circuit may convey taken power to a storage device. The electronics may be powered by the storage device. The storage device may have a capacitor, a rechargeable battery, a non-chargeable battery, a solar cell, fuel cell, line power, and/or the like.

Description:
BACKGROUND 
   The invention pertains to control devices using power stealing and particularly pertains to thermostatic devices having power stealing circuitry. 
   SUMMARY 
   The invention is a control device doing power stealing in its operation. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a block diagram of a power stealing control device; and 
       FIGS. 2 ,  3 ,  4  and  5  are circuit diagrams of a power stealing control device. 
   

   DESCRIPTION 
   A control device having a power stealing mechanism is shown in  FIG. 1 . Power may be picked off of a supply for a thermostatic load  16 . Control of power may involve a switch  13  which may consist of a relay, FET, TRIAC, or the like. The switch  13  may be controlled by a controller  14  which may be a microcontroller. The switch  13  may permit a power-stealing circuit  11  to take power for the control device, such as thermostatic electronics, from power for the thermostatic load  16 . Then power from circuit  11  may be conveyed to a storage/power device  12 . Device  12  may have a capacitor, rechargeable battery, non-chargeable battery, solar cell, fuel cell, and/or the like. Some of the stored power may be provided to the controller  14  to sustain operation of it, and to switch  1   3  and circuit  11 . Line power may be available. 
   A circuit diagram of the power stealing electronics for a control device is shown in  FIGS. 2 ,  3 ,  4  and  5 . The circuit diagrams in these Figures reveal illustrative examples of implementing the present invention. With a switch  13  in a first position, line  21  is not connected to a line or terminal  23 . With switch  13  in a second position, then line  23  is connected to line  21 . 
   Switch  13  may be instead some solid state device such as a FET, TRIAC, or the like. Switch  13  in  FIGS. 2 ,  3 ,  4  and  5  may be, for example, a relay, a latching relay, or solid state device. The switch or relay  13  in  FIG. 2  may have solenoid  26  that is connected by a driver  33  to ground, since the end of the solenoid is connected to V SWITCH , and pull a contact arm  27  down to short terminals  21  and  23  to call or connect the load  16  to its power. Upon release or the grounding of the terminal of solenoid  26  to ground, the contact arm  27  may return to a normal position having a contact with line  22 . Then there may be an AC voltage across terminals  21  and  23  which are connected to rectifier  24  for rectification of the input to a DC output at terminals  35  and  36 . The voltage at terminals  21  and  23  may instead be DC and the rectifier  24  might not be needed. 
   The device in  FIG. 3  may have two solenoids  25  and  26  which can move a contact arm  27  from terminal  22  to terminal  23  or vice versa. Each solenoid may have a lead connected to a switch voltage V SWITCH    28 . Solenoids  25  and  26  also may have leads  31  and  32  connected to a driver  33  which may activate solenoid  25  or solenoid  26  by connecting lead  31  or  32  to a device ground  36 , respectively. Only one lead  31  or  32  should be grounded at one time. However, when arm  27  is moved to terminal  22  or to  23 , with an activation of solenoid  25  or  26 , respectively; the lead,  31  or  32 , need not be constantly grounded to maintain arm  21  in its last moved-to position. Also, if the switch voltage  28  is non-existent, then arm  27  may remain in its last position with neither solenoid activated. The grounding of lines  31  and  32  need be only temporary to change the position of relay arm  27 . Thus, no energy is needed to maintain either position of arm  27 . Because of this characteristic, the switch may be regarded as a latching relay. Driver  33  may change the position of the relay with a signal (or multiple signals) on line  34  from controller  14 . Controller  14  may be, for example, an eight bit microcontroller which has a part number ATmega48V-10, possibly available from a vendor such as Atmel Corporation. 
   When a voltage from a load  16  and its power supply with a load ground  40  (noted in  FIGS. 3 ,  4  and  5 ) is across the input lines  21  and  23  of rectifier  24 , then there may be a DC voltage at the output of rectifier  24  on line  35  relative to a device ground  36 . The rectifier output voltage on line  35  may go to the power stealing circuit  11 . Line  35  may be connected to an emitter of PNP transistor  37 . Transistor  37  may be, for example, a part number MMBT2907A, possibly available from a vendor such as Diodes Inc. Resistors  38  and  39  may have one end connected to line  35 . Resistors  38  and  39  may be about 10 megohms and 20 K ohms, respectively. The other end of resistor  39  may be connected to the base of transistor  37  and one end of a resistor  41 . Resistor  41  may be about 100 K ohms. The other end of resistor  41  may be connected to a collector of an NPN transistor  42 . Transistor  42  may be, for example, a part number MMBTA05LT1, such as an “ON Semiconductor™” device. The other end of resistor  38  may be connected to the base of transistor  42  and to one end of a resistor  43  of about 20 K ohms. The other end of resistor  43  may be a power-steal control line  47  that is connected to controller  14 . The collector of transistor  37  may be connected to one end of a resistor  44  of about 20 K ohms. The other end of resistor  44  may provide a power-steal output voltage (V PS ) line  46  of circuit  11 . The emitter of transistor  42  and an anode of a zener diode  45  may be connected to device ground  36 . The cathode end of diode  45  may be connected to line  46 . Diode  45  may be a 5.1 volt zener diode having, for example, a part number MMSZ4689, possibly available from Fairchild Semiconductor Corporation. Resistor  44  may be a current limiting resistor. 
   The output line V PS    46  of circuit  11  may go to a storage/power device  12 . Line  46  may be connected to an anode of a diode  48 . The cathode of diode  48  may be connected to the cathode of diode  49 . Diodes  48  and  49  may be a pair of Schottky diodes having a part number BAS70-05, which possibly is available from General Semiconductor, Inc., in Melville, N.Y. A capacitor  51  may at the same time be a storage device for power stealing by circuit  11  provided at V PS  terminal or line  46 . Capacitor  51  could be replaced by a rechargeable battery. The cathodes of diodes  48  and  49  may be connected to one end of the storage capacitor  51  which may be about 47 millifarads. This end of capacitor  51  may be regarded as a voltage terminal (V CC )  52 . V CC    52  may be connected to the controller  14 . Connected between V CC    52  and device ground  36  may be at least one 0.1 microfarad capacitor  53 . The other end of storage capacitor  51  may be connected to device ground  36 . 
   A resistor  54  of about 274 ohms may have one end connected to V CC  terminal  52  and the other end connected to the V SWITCH  terminal  28 . A capacitor  55  of about 1000 microfarads may be connected between V SWITCH  terminal  28  and device ground  36 . 
   A resistor  56  of about 274 ohms may have one end connected to the anode of diode  49  and another end connected to a battery voltage (V BATT ) terminal  57 . Terminal  57  may be connected to a positive terminal of a battery  58 . The negative terminal of battery  58  may be connected to the device ground  36 . Battery  58  may be an externally or internally chargeable storage battery, a non-chargeable battery, or a back-up voltage source at terminal  57 . The battery  58  may provide power to controller  14  and other components of the system electronics as may be needed. This battery  58  may be a primary source or secondary backup source, and in that place it may be a non-chargeable or chargeable battery, fuel cell, solar cell, or the like. 
   The V PS  terminal  46  may be connected to the cathode of a diode  61 . The anode of diode  61  may be connected to the cathode of a diode  62 . The anode of diode  62  may be connected to device ground  36 . Diodes  61  and  62  may have, for example, a part number BAV199 and be possibly available from a vendor such as Diodes Incorporated. The common connection between diodes  61  and  62  may be connected via a line  59  to the controller  14 . Line  59  may provide to controller  14  a status signal of line  23  to rectifier  24  via a resistor  63  of about 1.2 megohms. There may be a pull-down resistor  64  of about 1.2 megohms connected between line  21  of rectifier  24  and the device ground  36 . 
     FIG. 4  is similar to  FIG. 3  except it may have a single coil  30  latching switch  13  that uses different polarities in application of electrical power to the coil or actuator  30  to move and latch the switch contact  27  one way or the other, respectively.  FIG. 5  is similar to  FIGS. 2 ,  3  and  4  except that  FIG. 5  may incorporate a solid state switch as device  13 . The switch may of a latching topology or a non-latching topology. The switch may instead be another kind of device that accomplishes the appropriate circuit connections for the invention. 
   In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense. 
   Although the invention has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.