Abstract:
A power supply unit for use with thermostats or other like devices requiring power. A power supply unit may be designed to keep electromagnetic interference emissions at a minimum, particularly at a level that does not violate governmental regulations. A unit may be designed so that there is enough power for a triggering a switch at about a cross over point of a waveform of input power to the unit. Power for triggering may come from a storage source rather than line power to reduce emissions on the power line. Power for the storage source may be provided with power stealing. Power stealing may require switching transistors which can generate emissions. Gate signals to the transistors may be especially shaped to keep emissions from transistor switching at a minimum.

Description:
BACKGROUND 
       [0001]    The present disclosure pertains to thermostats and particularly to various kinds of power supplies for thermostats. 
       SUMMARY 
       [0002]    The disclosure reveals a power supply unit for use with thermostats or other like devices requiring power. A power supply unit may be designed to keep electromagnetic interference emissions at a minimum, particularly at a level that does not violate governmental regulations. A unit may be designed so that there is enough power for triggering a switch at about a cross over point of a waveform of input power to the unit. Power for triggering may come from a storage source rather than line power to reduce emissions on the power line. Power for the storage source may be provided with power stealing. Power stealing may require switching transistors which can generate emissions. Gate signals to the transistors may be especially shaped to keep emissions from transistor switching at a minimum. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0003]      FIGS. 1 and 2  are diagrams of a thermostat power supply unit for low and high power, respectively; 
           [0004]      FIGS. 3 and 4  are diagrams of a thermostat power supply having a gate driving circuit for low and high power, respectively; 
           [0005]      FIGS. 5 and 6  are diagrams of a thermostat power supply having an active trigger circuit for low and high power, respectively; 
           [0006]      FIG. 7  is a diagram of various waveforms applicable to the active trigger circuit; 
           [0007]      FIGS. 8 and 9  are more detailed diagrams of the thermostat power supply for low and high power, respectively; 
           [0008]      FIG. 10  is a diagram of a power steal switching transistors circuit; 
           [0009]      FIG. 11  is a diagram of an energy storage module and a linear regulator; 
           [0010]      FIG. 12  is a diagram of a triac and an RC network; 
           [0011]      FIG. 13  is a diagram of a half wave zero crossing detect circuit; 
           [0012]      FIG. 14  is a diagram of a gate signal shaping circuit; 
           [0013]      FIG. 15  is a diagram of a transistor reverse wave protection circuit; 
           [0014]      FIG. 16  is a diagram of a negative current source; 
           [0015]      FIG. 17  is a diagram of triac gate triggering signal source; 
           [0016]      FIG. 18  is a diagram of triac and AC-DC converter; 
           [0017]      FIG. 19  is a diagram of an energy storage module and a DC-DC converter; 
           [0018]      FIG. 20  is diagram of another half wave zero crossing detect circuit; and 
           [0019]      FIG. 21  is a diagram of another gate signal shaping circuit. 
       
    
    
     DESCRIPTION 
       [0020]    The present system and approach may incorporate one or more processors, computers, controllers, user interfaces, wireless and/or wire connections, and/or the like, in an implementation described and/or shown herein. 
         [0021]    This description may provide one or more illustrative and specific examples or ways of implementing the present system and approach. There may be numerous other examples or ways of implementing the system and approach. 
         [0022]    A triac  12  or bypass circuit  18  and a MOSFET power steal  14  combination may be noted ( FIG. 1 ). Two-wire devices may need power stealing functionality to supply their electronics, and conditioned triac triggering functionality to comply with FCC title 47 part 15 sub B, EMI conducted emissions regulations. 
         [0023]    The triggering functionality need may involve using active triggering which in turn requires high power in order to deliver consistent and reliable performance at a triac gate. Active triggering may be defined as the ability to store energy and supply it to trigger the triac  12  near zero-crossing when a power line&#39;s energy is not sufficient. 
         [0024]    One way of supplying high power to the electronics may be a use of a serial MOSFETs power stealing approach. Another approach may be to delay the triac trigger, but this approach might not comply with FCC regulations. 
         [0025]    Current transformers may also be used but they might not be able, in the load range and size available, to supply the high power requirement for the active triac triggering and thus not comply with FCC regulations. 
         [0026]    A thermostat device may have two states. First, the ON state  22  ( FIG. 1 ) is when a heating demand is ON while the entire device is operating with triac  12  ON. Second, the OFF state  23  may be when the heating demand is OFF while the device remains in operation with triac  12  OFF. 
         [0027]    A triac  12  and MOSFET  14  combination for the ON state  22  does not appear to have been done or been used in a thermostat. 
         [0028]    For the OFF state  23 , a triac bypass circuit  18  may be needed to supply power to thermostat electronics. Depending on power requirements, bypass circuit  18  may be an AC-DC converter for high power such as for RF applications, an RC (resistor-capacitor) network for moderate or low power, or an R (resistor) only network for rather low power. 
         [0029]    Virtually any kind of a bypass supply approach may be used because the triac triggering approach can be independent of the bypass supply approach which is not necessarily the case in a related art OFF state supply approach of an R network with a current transformer or triac trigger being delayed. 
         [0030]    The present thermostat topology may be a key combination for FCC compliance. It may provide a solution for in-line line-volt thermostats. 
         [0031]    Bypass circuit  18  may be scaled to accommodate a full range of thermostats&#39; energy requirements such as RF energy hungry applications (e.g., wifi, zigbee, RF host modules, and so forth), RF moderate or low energy applications (e.g., RF client modules, and so forth), and the usual programmable or non-programmable thermostats. Also, the triac switch component  12  may be changed to an SCR (thyristor) or a relay with minor adjustments to circuitry. 
         [0032]    A MOSFET gate driving circuit  28  for transition softening may be noted in  FIGS. 3 and 4 . Two-wire devices may need power stealing functionality to supply their electronics. When this power stealing is done with serial MOSFETs  14 , they may need to be triggered in such a way that turning MOSFETs ON/OFF complies with FCC regulations. 
         [0033]    By having a circuit  28  that may control the rate of charge and discharge of the MOSFET gates, the gate switching behaviors may be controlled, and thus control the current and voltage transition generated by the power steal module  14 . Such control may enable one to reduce EMI conducted emissions. 
         [0034]    A circuit  28  may do a positive zero crossing power steal and use two current limiting devices to control the rate of charge and discharge of the MOSFET gates, respectively. The circuit may also use latching circuitry enabled by a voltage level detector, to keep the MOSFETs state until the next power steal. 
         [0035]    Some approaches may use a current transformer or the triac itself to do the power steal. In both cases, the triac transition cannot necessarily be controlled in such a way that will comply with FCC regulations. The MOSFET transition may need to be smoothed. The present circuit may soften a MOSFET transition. In this case, one may use the circuit to reduce EMI conducted emissions produced by a current zero crossing power stealing circuit using MOSFETs. 
         [0036]    An active triac  12  may be noted. In order to comply with FCC emission regulations, triac triggering may need to be controlled in such a way that EMI noise emitted on the AC main lines is kept low. This functionality may be accomplished by an active triggering. 
         [0037]    Active triac triggering may be done with the present approach in thermostats. The approach may result in reduced EMI conducted emissions generated by triac  12 . Active triggering may be defined as the ability to store energy and supply the energy to trigger triac  12  near zero-crossing when power line&#39;s energy is not sufficient. Previously, passive triggering may have been used, which meant triggering triac  12  with energy directly from a power line  13 . 
         [0038]    Active triac triggering may be done from a continuous or pulsed DC source. Triac  12  may work in quadrants II and III. The triggering may also be done from an alternating continuous or pulsed DC source. Triac  12  may work in quadrants I and III. 
         [0039]    To activate the circuit, a command signal or drive  34  may be applied at an input of an active trigger circuit  33  as illustrated in  FIGS. 5-7 . Command signal  34  may be synchronized with the current zero crossing from AC line  13 . The shape of an active triggering signal  36  may depend on the shape of the input command signal  34  and on the logic of active trigger circuit  33 . 
         [0040]    For triac quadrants I and III, the practice may be to alternate the trig  36  between positive and negative signals as shown by the signal profiles  42  and  43 . Command signal  34  may be continuous or pulsed as shown by signal profiles  44  and  45 , respectively. 
         [0041]    For triac quadrants II and III, the practice may be to provide a negative trig signal  36  as shown by signal profiles  46  and  47 . The command signal  34  to active trigger circuit  33  may be continuous or pulsed as shown by signal profiles  44  and  45 , respectively. 
         [0042]    A choice of active triggering circuits may depend on the thermostat complexity combined with the energy consumption needed. An alternating DC source may be more complex. Pulse triggering may consume less power. The noted active triggering approaches may reduce EMI conducted emissions produced by the triac. 
         [0043]      FIG. 1  is a diagram of a power supply unit  11  for a thermostat needing low power. Unit  11  may have a triac or SCR module  12  having an input connected to a line voltage  13 . Module  12  may have a relay or some triggerable switch. A MOSFET power steal module  14  may have an input connected to an output of module  12  via line  21 . An output of module  14  may be connected to a load voltage line  15 . A source  10  may provide AC power on line voltage  13  and line  16 . Line  16  may be connected to one end of an electric baseboard  17 . Another end of baseboard  17  may be connected to line  15 . 
         [0044]    A bypass circuit  18  may have an input connected to line voltage  13 . An output of circuit  18  may be a circuit low voltage line  21  connected to an input of stealing circuit  19 . Unit  11  layout may be divided into three areas including an on state area  22 , an off state area  23 , and an always active area  24 . Modules  12  may be in area  22 . Circuit  18  may be in area  23 , and circuit  19  and  14  may be in area  24 . A component of the triac or SCR module  12  may be a triac. Components of the MOSFET power steal module  14  may incorporate power steal switching MOSFETs. A component of bypass circuit  18  may be an RC network. A component of stealing circuit  19  may be for energy storage. 
         [0045]      FIG. 2  is a diagram of a power supply unit  31  for a thermostat needing more power like RF applications. Unit  31  may be similar to unit  11  of  FIG. 1  except that the component of circuit  18  may instead be an AC-DC converter and the MOSFET power steal module is in the area  22 . 
         [0046]      FIG. 3  is a diagram of a power supply unit  41  for a thermostat needing low power. Unit  41  may be similar to unit  11  of  FIG. 1  except that unit  41  may incorporate a zero crossing (ZC) detection module  26  in area  22 . An input of module  26  may be connected to line voltage  13 . An output from module  26  may be a ZC signal on a line  27  to an input of a gate driving circuit  28 . Also to an input of circuit  28  may be the circuit low voltage on line  21 . An output from circuit  28  may go to an input of module  14  via a line  29 . Module  26  may incorporate a half wave ZC detect component. Circuit  28  may incorporate a MOSFET gate signal shaping component. 
         [0047]      FIG. 4  is a diagram of a power supply unit  51  for a thermostat needing high power for RF applications. Unit  51  may be similar to unit  41  of  FIG. 3  except that the component of circuit  18  may instead be an AC-DC converter and the MOSFET power steal module is in the area  22 . 
         [0048]      FIG. 5  is a diagram of a power supply unit  61  for a thermostat using low power. Unit  61  may be similar to unit  41  of  FIG. 3  except that unit  61  does not necessarily incorporate the gate driving circuit  28  and may incorporate a microcontroller  32  and an active trigger module  33  in area  22 . ZC signal may go on line  27  to an input of microcontroller  32 . A drive signal on a line  34  may go to an input of active trigger module  33 . Stored energy may proceed from an output of circuit  19  to an input of module  33  via a line  35 . A trig signal from an output of module  33  may proceed along a line  36  to an input of module  12 . 
         [0049]      FIG. 6  is a diagram of a power supply unit  71  for a thermostat needing high power. Unit  71  may be similar to unit  61  of  FIG. 5  except that the component of circuit  18  may be an AC-DC converter and the MOSFET power steal module is in the area  22 . Units  61  and  71  may be expanded to incorporate the gate driving circuit  28  arrangement of units  41  and  51 . 
         [0050]      FIG. 8  is a diagram of a low power version of a power supply unit  81  having resemblances to units  11 ,  31 ,  41 ,  51 ,  61  and  71  of  FIGS. 1-6 , respectively. An RC network of a bypass circuit  18  may output current along connection  21  to power stealing switching MOSFETs. Power steal module  14  along connection  52  may provide stolen energy (Vrect) to energy storage module or stealing circuit  19 . A connection  53  may provide energy at a level (Vrect) 10 or 15 Vdc to a linear regulator and super cap circuit  54 , the gate driving circuit of MOSFET signal shaping circuit  28 , a DC-DC negative current source  55  of active trigger module  33 , and a backlight circuit  56 . 
         [0051]    Regulator and super cap circuit  54  may provide 3 Vdc power along connection  57  to a processor and other circuits  58 . Zero crossing detector  26  having an input along connection  66  from bypass circuit  18  and a half wave ZC detect of detector  26  may provide a zero crossing signal along a connection  27  to a CPU  32 . A drive signal from CPU  32  along a connection  34  may go to a triac gate triggering signal circuit  59  of active trigger module  33 . The DC-DC negative current source  55  may provide energy at Vo with a current of a negative 300 mA along a connection  61  to the triac gate triggering signal circuit  59 . 
         [0052]    A zero crossing signal may go on connection  62  from detector  26  to the gate signal shaping circuit  28 . A MOSFET reverse wave protection circuit  63  may have an input from line  13  and a protect signal output on connection  64  to circuit  28 . 
         [0053]      FIG. 9  is a diagram of a high power version of a power supply unit  91  which appears similar to unit  81  of  FIG. 8 . Line power  13  of other units may be presented as two lines  1  and  2  at unit  91 . Power  71  of line  1  may be provided to power steal module  14  and MOSFET reverse wave protection circuit  63 . Power  72  of line  2  may be provided to bypass circuit  18  and half wave ZC detector of circuit  26 . 
         [0054]    In contrast to unit  81 , bypass circuit  18  of unit  91  may have an AC-DC converter in lieu of an RC network. AC-DC converter may supply energy (Vrect) on connection  21  to energy storage module  19 . In lieu of linear regulator and super cap circuit  54 , unit  91  may have a DC-DC converter  67 . An output of converter  67  may be 3 Vdc to processor and circuits  58  and RF Redlink™ module  68 . RF Redlink™ module  68  may also be a Wifi module or any other RF protocol. Another distinction between units  81  and  91  may be connection  36  being extended as an input to gate signal shaping circuit  28 . 
         [0055]      FIGS. 10-17  are diagrams for circuitry of various parts of unit  81 .  FIG. 10  is a diagram of power steal switching MOSFETs  14  showing a line  1 , which may be of power  13  and be designated as line  71 . Also, there may be connections  29  and  52 , and ground terminal  75 .  FIG. 11  is a diagram of energy storage module  19  and linear regulator  54 . Also shown are connections  52 ,  53  and  57 , and ground terminal  75 . 
         [0056]      FIG. 12  is a diagram of a triac circuit  12  and an RC network of bypass circuit  18  along with line  2 , which may be of power  13  and designated as line  72 . Also there may be connections  66  and  36 , and ground terminal  75 .  FIG. 13  is a diagram of a half wave ZC detect circuit  26  along with connections Vrect  53 , a connection  66 , crossing connection  62 , CPU ZC connection  27 , and ground terminal  75 . 
         [0057]      FIG. 14  is a diagram of the gate signal shaping circuit  28 . Also shown are connections  53 ,  62 ,  64  and  29 , and ground terminal  75 .  FIG. 15  is a diagram of a MOSFET reverse wave protection circuit  63  showing connection  53 , line  71 , connection  64  for the protect signal, and a ground terminal  75 . 
         [0058]      FIG. 16  is a diagram of the DC-DC negative current source  55  having an output on connection  61 , a voltage connection  53  and a ground connection  75 .  FIG. 17  is a diagram of triac gate triggering signal circuit  59  showing a connection  61 , a drive connection  34 , a triac gate signal connection  36  and a ground connection  75 . 
         [0059]    Power supply unit  91  of the high power version may be essentially the same as power supply unit  81  of the low power version. The following noted Figures may reveal some differences between the units.  FIG. 18  is a diagram of a high power version of bypass circuit  18  having an AC-DC converter in lieu of an RC network as shown in  FIG. 12 . The AC-DC converter may be connected to a crossing signal on connection  62 , a voltage connection  53 , a line  72  connection from an output of triac  12 , an energy output on connection  21  and a ground connection  75 .  FIG. 19  is a diagram of a DC-DC converter  67  in lieu of the linear regulator of  FIG. 11 . Converter  67  may have a connection  53  from the energy storage module  19 , an output on connection  57  and a ground connection  75 . 
         [0060]      FIG. 20  is a diagram of a half wave ZC detect circuit  26  for the unit  91  high power version in lieu of circuit  26  of  FIG. 13 . The design of circuit  26  in  FIG. 20  may be different from circuit  26  in  FIG. 13  in that circuit  26  of  FIG. 20  is designed to accommodate a line  72  connection. 
         [0061]    Circuit  26  may have output lines on connection  62  and  27 . Circuit  26  may have a voltage connection  53  and a ground connection  75 . 
         [0062]      FIG. 21  is a diagram of gate shaping signal circuit  28  for the unit  91  high power version in lieu of circuit  28  of  FIG. 14 . The design of circuit  28  in  FIG. 21  may be different from circuit  28  in  FIG. 14  in that circuit  28  of  FIG. 21  is designed to accommodate a drive signal on connection  36 . Circuit  28  may also have input lines on connections  53 ,  62  and  64 . There may also be a gate signal output on connection  29 . Circuit  28  may have a ground connection  75 . 
         [0063]    A thermostat power supply may incorporate a first terminal for connection to a first line of a power source, a triac having a first input connected to the first terminal, a bypass circuit having a first input connected to the first terminal, a stealing circuit having an input connected to an output of the bypass circuit, a power steal module having an input connected to an output of the triac and an output connected to an output of the stealing circuit, a second terminal for connection to a load, a zero crossing detection module having an input connected to the first terminal, and a gate driving circuit having an input connected to an output of the zero crossing detection module, and an output connected to a second input of the power steal module. 
         [0064]    The power steal module may be for stealing energy from the first terminal. The stealing circuit may be for storing stolen energy from the power steal module. The power steal module may incorporate one or more MOSFETs that switch on and off for stealing energy. The gate driving circuit may provide gate signals to the one or more MOSFETs for switching the one or more MOSFETs on and off. 
         [0065]    The gate driving circuit may shape the gate signals to reduce EMI emissions from the one or more MOSFETs due to switching the one or more MOSFETs on and off. The zero crossing detection module may provide a signal to the gate driving circuit for determining times that the gate signals are to switch the one or more MOSFETs on and off relative to a zero crossing point of a waveform on the first line of the power source. 
         [0066]    A power unit may incorporate a first terminal for connection to a power source, a triggerable switch having an input connected to the first terminal, a bypass circuit having an input connected to the first terminal, a storage having an input connected to an output of the bypass circuit, a power steal module having an input connected to an output of the triggerable switch and having an output connectable to a second terminal, a second terminal for connection to a load connected to the power source, a zero crossing detector having an input connected to the first terminal, and a gate driving circuit having an input connected to the zero crossing detector, and having an output connected to the power steal module. 
         [0067]    The power steal module may incorporate one or more transistors that switch on and off to let current flow as deemed to the second terminal. The gate driving circuit may provide signals to the one or more transistors that switch on and off according to the signals which are adjusted in shape to result in the switch on and off of current to obtain minimized EMI emissions from switched current. The minimized EMI emissions are to comply with applicable government regulations. The one or more transistors may be MOSFETs. 
         [0068]    The power steal module and/or gate driving circuit may further incorporate MOSFETs as the one or more transistors, one or more current limiting devices to control a rate of charge and discharge of one or more gates of the MOSFETs, and latching circuitry enabled by a voltage level detector to keep a state of the MOSFETs from a previous power steal to a subsequent power steal. 
         [0069]    The unit may further incorporate a MOSFET wave protection module having an input connected to the first terminal and an output connected to an input of the gate signal generator. The gate signal generator may provide the signals to the one or more transistors according to timing derived from the zero crossing detector. 
         [0070]    A thermostat power system may incorporate a first terminal for connection to a power supply and load arrangement, a second terminal for connection to the power supply and load arrangement, a triggerable switch, having an input, connected to the first terminal, a bypass circuit having an input connected to the first terminal, an energy storage module having an input connected to an output of the bypass circuit, a power steal module having an input connected to an output of the triggerable switch, and a driving circuit for a control signal having an output connected to a second input of the power steal module. The control signal may minimize EMI emissions from the power steal module. 
         [0071]    The system may further incorporate a wave zero crossing detector having an input connected to the first terminal and an output connected to an input of the driving circuit. 
         [0072]    The control signal from the driving circuit may goes to a gate of one or more transistors to turn on or off the one or more transistors to steal power. The turn on or off of the transistors may cause EMI emissions. The driving circuit adjusts a shape of the control signal to turn on or off the transistors in a manner to minimize EMI emissions. The one or more transistors may be MOSFETs. 
         [0073]    The driving circuit may provide a control signal that is timed according to a signal from the wave zero crossing detector to turn on or off the transistors in a manner to minimize EMI emissions. 
         [0074]    The triggerable switch may be selected from a group consisting of a triac, an SCR and a relay. 
         [0075]    The system may further incorporate a reverse wave protection module having an input connected to the first terminal and an output connected to a second input of the driving circuit. 
         [0076]    A power supply unit for a heating, ventilation and air conditioning thermostat, may incorporate a first terminal for connection to a line of a power source, a second terminal for connection to a load, a bypass circuit having an input connected to the first terminal, a triac having an input connected to the first terminal, a stealing circuit having an input connected to an output of the bypass circuit and having an output connected to the second terminal, a power steal module having an input connected to an output of the triac, and a trigger circuit having an output connected to a second input of the triac. 
         [0077]    The unit may further incorporate a zero crossing detection circuit having an input connected to the first terminal and an output connected to an input of the trigger circuit. 
         [0078]    The unit may further incorporate a zero crossing detection circuit having an input connected to the first terminal, and an interface circuit having an input connected to an output of the zero crossing detection circuit and having an output connected to an input of the trigger circuit. 
         [0079]    A second output of the stealing circuit may be connected to a second input of the trigger circuit. An output of the trigger circuit may be connected to a second input of the triac. The stealing circuit may incorporate energy storage. Stored energy may go from the second output of the stealing circuit to the second input of the triac. 
         [0080]    A zero crossing signal may go from the zero crossing detection circuit to the input of the interface circuit. A zero crossing drive signal may go from the output of the interface circuit to the input of the trigger circuit. 
         [0081]    The zero crossing detection circuit may incorporate a half wave zero crossing detector. The trigger circuit may incorporate a DC-DC negative current source having an input connected to the second output of the stealing circuit, and a triac gate triggering signal circuit having an input connected to an output of the DC-DC negative current source. 
         [0082]    The unit may further incorporate a DC-DC converter connected to the second output of the stealing circuit. The bypass circuit may incorporate an AC-DC converter. 
         [0083]    The unit may further incorporate a linear regulator connected to the second output of the stealing circuit. The bypass circuit may incorporate an RC network. 
         [0084]    A power system for thermostats, may incorporate a first terminal connected to a line of a power supply, a bypass circuit having an input connected to the first terminal, a triggerable switch having an input connected to the first terminal, a power steal module having an input connected to an output of the bypass circuit, a zero crossover detector having an input connected to an output of the bypass circuit, a energy storage module having an input connected to an output of the power steal module, and a trigger circuit having an input connected to an output of a zero crossover detector and having an output connected to a second input of the triggerable switch. 
         [0085]    The trigger circuit may incorporate a processor. The processor may have an input connected to the output of the zero crossover detector and an output connected to the second input of the triggerable switch. The processor may determine a drive signal for the triggerable switch from a zero crossing signal of the output of the zero crossover detector and from a set of instructions. 
         [0086]    Power may be taken from the energy storage module and used to trigger the triggerable switch near a zero crossing of energy on the line of the power supply as effected by the processor and a line pattern according to a working quadrant of the triggerable switch. 
         [0087]    The system may further incorporate a gate signal shaper having an input connected to an output of the zero crossover detector and having an output connected to the power steal module. The power steal module may incorporate one or more MOSFETs. 
         [0088]    An output of the gate signal shaper may be a gate signal having a shape that switches the one or more MOSFETs on or off in a manner to minimize EMI emissions from switching stolen power by the one or more MOSFETs. 
         [0089]    The system may further incorporate a MOSFET reverse wave protection circuit having an input connected to the first terminal and an output connected to a second input of the gate signal shaper. 
         [0090]    The power steal module may steal power from the first terminal or an output of the bypass circuit. The power steal module may provide stolen power to the energy storage module. 
         [0091]    A thermostat power system may incorporate a triggerable switch having an input connected to a first terminal, a bypass circuit having an input connected to the first terminal, an energy storage module having an input connected to an output of the bypass circuit and an output connected to a second terminal, a power steal circuit having an input connected to an output of the triggerable switch, and an active trigger module having an input connected to an output of a wave position detector, having an output connected to the triggerable switch, and having an input connected to a second output of the energy storage module. The first terminal and second terminal may be for connection to an AC power line and load arrangement. 
         [0092]    The power steal circuit may incorporate transistors. A trig signal may be sent at certain times, according to information at the output of the wave position detector, from the output of the active trigger module to a second input of the triggerable switch. A signal from the output of the triggerable switch to the input of the power steal circuit may turn the transistors on or off. The active trigger module may take energy at the second input from the second output of the energy storage to trigger the triggerable switch near a zero crossing of the power line when energy directly from the power line is insufficient to trigger the triggerable switch. 
         [0093]    A power supply unit for a heat, ventilation and air conditioning thermostat, may incorporate a triac having an input, a gate and an output, a bypass circuit having an input connected to the input of the triac, a stealing circuit having an input connected to an output of the bypass circuit, and a MOSFET power steal module having an input connected to the output of the triac. The input of the triac and an output of the MOSFET power steal module may be primary terminals for connection in a power circuit. 
         [0094]    The power circuit may incorporate a power source connected in series with an electrical load. The electrical load may be an electric heating mechanism. 
         [0095]    The stealing circuit may incorporate an energy storage module. The MOSFET power steal module may steal energy and the energy may go to the energy storage module. The energy may be used to trigger the triac at a zero crossing of line voltage from the power source. 
         [0096]    The unit may further incorporate a gate signal shaper connected to the MOSFET power steal module. The gate signal shaper may provide a gate signal that results in a soft transition of turning on and off of the MOSFETs. 
         [0097]    The unit may further incorporate a half wave zero cross detect module connected to the line voltage, to a gate signal shaper, and to a triac gate triggering module. 
         [0098]    Power supply electronics for a thermostat, may incorporate a first terminal for connection to a first line of a power source, a bypass circuit having an input connected to the first terminal, a triac having an input connected to the first terminal, a second terminal for connection to a load, a stealing circuit having an input connected to an output of the bypass circuit and an output connected to the second terminal, and a power steal module having an input connected to the output of the triac and an output connected to the second terminal. 
         [0099]    The power steal module may incorporate one or more MOSFETs that are switched on to steal power. The stealing circuit may incorporate an energy storage unit. Stolen power goes to the energy storage unit. 
         [0100]    The bypass circuit may incorporate an RC network, or an AC-DC converter. 
         [0101]    The electronics may further incorporate a linear regulator and a super capacitor connected to an output of the energy storage unit. 
         [0102]    The electronics may further incorporate a DC-DC converter connected to an output of the energy storage unit. 
         [0103]    If the power steal module incorporates two or more MOSFETs, then a serial MOSFETs power stealing approach may be effected. 
         [0104]    A thermostatic power supply may incorporate a bypass circuit, a first terminal for connection to a power source, a second terminal for connection to a load, a bypass circuit having an input connected to the first terminal, an energy storage module having an input connected to the bypass circuit and an output connected to the second terminal, a triggerable switch having an input connected to the first terminal, and a power steal module having an input connected to an output of the triggerable switch and an output connected to the second terminal. 
         [0105]    The supply may further incorporate a DC-DC converter having an input connected to the output of the energy storage module. The bypass circuit may incorporate an AC-DC converter. 
         [0106]    The supply may further incorporate a linear regulator having an input connected to the output of the energy storage module. The bypass circuit may incorporate an RC network. 
         [0107]    The supply may further incorporate a super capacitor connected to the linear regulator. The triggerable switch may be selected from a group consisting of a triac, SCR and a relay. The power steal module may incorporate one or more switching MOSFETs. 
         [0108]    In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense. 
         [0109]    Although the present system and/or approach 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 specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the related art to include all such variations and modifications.