Abstract:
An electronic digital thermostat adapted for installation in locations with or without an external power supply preferably includes a compartment for receiving a replaceable internal power supply, such as a batteries, for powering the thermostat if an external power supply is not available, and a connector for connecting the thermostat to an external power supply for powering the thermostat when the external power supply is available. The thermostat is configured to preferentially draw power from an external power supply connected to the thermostat, if power from an external power supply is available, and draw power from an internal power supply connected to the thermostat, if power from an external power supply is not available. An additional power backup, such as a capacitor, may be provided to maintain power to the thermostat for short durations when power is unavailable from both the internal power supply and the external power supply.

Description:
FIELD OF THE INVENTION 
     This invention relates to thermostats and, more particularly, to a digital thermostat having dual power options adapted for installation in locations with or without an external power supply. 
     BACKGROUND OF THE INVENTION 
     Thermostats for controlling climate control systems generally fall into two broad categories: (1) mechanical thermostats and (2) electronic digital thermostats. A typical mechanical thermostat, such as for a multi-stage thermostat application, is connected to an alternating current (AC) power supply, normally a transformer. However, mechanical thermostats do not require continuous electrical power. 
     On the other hand, a typical digital thermostat, such as one that is multi-stage, requires continuous power for thermostat components such as a microcomputer and thermostat control circuit. These component parts require power at all times. Therefore, digital thermostats need additional connections to a power supply, such as a transformer, to satisfy these power requirements. 
     Thus, when replacing a mechanical multi-stage thermostat with a digital multi-stage thermostat, an additional wire is usually required to power and maintain operation of the digital thermostat. When replacing one digital thermostat with another digital thermostat, the additional power connection wire is normally present. 
     When installing a digital thermostat for a new application, such as when building a new house, providing continuous power for the digital thermostat by adding the necessary extra power wire is relatively easy. However, in retrofit applications, and specifically, when replacing a mechanical thermostat with a digital thermostat, providing an additional wire for electrical power can be difficult, time consuming and costly. 
     Therefore, what has been needed is a digital thermostat having multiple power capabilities that is adapted for both new installations and for retrofit installations (when an external power supply is not available, because all necessary connections are not present). 
     SUMMARY OF THE INVENTION 
     The thermostat of the present invention provides dual power supply compatibility allowing for installation and operation in both new and retrofit applications. The thermostat is adapted to draw power from either an external AC power supply (i.e., transformer) or an internal replaceable power supply (e.g., replaceable batteries). If the thermostat is connected to an external power supply, the replaceable internal power supply may provide extended duration back-up power in the event of external power failure. 
     According to one aspect of the present invention, an electronic thermostat for controlling the operation of a climate control system is adapted for installation in locations with or without an external power supply. The thermostat includes a thermostat circuit, a compartment for receiving a replaceable internal power supply, a connector for connecting the thermostat circuit to the replaceable internal power supply in the compartment, for powering the thermostat circuit, and a connector for connecting the thermostat circuit to the external power supply for powering the thermostat. The electronic thermostat is further configured such that the thermostat preferentially draws power from the external power supply connected to the thermostat, if power from the external power supply is available, and from the internal power supply connected to the thermostat, if power from the external power supply is not available. The replaceable internal power supply is preferably at least one replaceable battery. 
     Additionally, the electronic thermostat is preferably provided with an energy reduction device adapted to reduce energy consumption of the thermostat when power from the external power supply is not available, with the thermostat drawing power from the internal power supply. Further, an energy storage device can be provided for powering the thermostat for a short duration if power from both the external power supply and the internal power supply are not available. The energy storage device may be a capacitor or super-capacitor. A programmed memory storage device may also be provided to the electronic thermostat for maintaining thermostat program information when power from both the external power supply and the internal power supply are not available. The programmed memory device may be an electrically erasable programmable read only memory. 
     According to another aspect of the present invention, an electronic digital thermostat for controlling a climate control system is preferably powered by at least one of the following: a replaceable internal power supply, which is preferably at least one battery, and an external power supply. The thermostat includes a compartment for receiving the replaceable internal power supply, a connector for connecting the thermostat to the internal power supply in the compartment for powering the thermostat, and a connector for connecting the thermostat to the external power supply for powering the thermostat. The thermostat is preferably configured such that the thermostat preferentially draws power from the external power supply connected to the thermostat, if power from the external power supply is available, and from the internal power supply connected to the thermostat, if power from the external power supply is not available. The thermostat further comprises an energy reduction device, which may reduce energy consumption of the thermostat, when power from an external power supply is not available. In this event, when power becomes unavailable from the external power supply, the thermostat draws a reduced amount of power from the internal power supply. The internal power supply preferably is configured to provide power for more than a short duration, with the thermostat operating normally for an extended period of time using the internal power supply. 
     Further, an energy storage device, preferably a super capacitor, may be provided for powering the thermostat for a short duration if power from both the external power supply and the internal power supply are not available. A programmed memory storage device, such as an electrically erasable programmable read only memory, may also be provided for maintaining thermostat program information when power from both the external power supply and the internal power supply are not available. 
     According to still another aspect of the present invention, a method of powering an electronic thermostat includes providing power to the electronic thermostat in locations with or without an external power supply. The method comprises the steps of powering the thermostat from an external power supply connected to the thermostat, if power from the external power supply is available, and powering the thermostat from an internal power supply connected to the thermostat, if power from the external power supply is not available. Additional steps may include powering the thermostat from an energy storage device or storing thermostat program information in a programmed memory storage device if power from both the external power supply and the internal power supply are not available. 
     Therefore, the present invention provides numerous novel features and advantages over prior thermostats. In particular, the invention provides a thermostat, and preferably, a digital multi-stage thermostat that can be powered by a replaceable internal power supply or an external power supply. This provides adaptability for both new installations and retrofit installations of existing thermostats (in particular, replacement of mechanical thermostats with digital thermostats). The adaptability provides ease in installation and savings in both labor and cost when retrofitting an existing system. 
     These and other features and advantages will be in part apparent and in part pointed out in a more detailed description of the various embodiments and aspects of the invention as set out below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front plan view of a thermostat constructed according to the principles of the present invention; 
     FIG. 2 a  is an exploded view of the liquid crystal display of the thermostat of FIG. 1; 
     FIG. 2 b  is an exploded view of an alternate liquid crystal display of the thermostat of FIG. 1; 
     FIG. 3 is a perspective view of the base of the thermostat of FIG. 1; 
     FIG. 4 is a rear plan view of the thermostat of FIG. 1; 
     FIG. 5 is a schematic wiring diagram of a typical mechanical multi-stage thermostat; 
     FIG. 6 is a schematic wiring diagram of a typical digital multi-stage thermostat; and 
     FIG. 7 is a schematic wiring diagram of the thermostat of FIG. 1 showing a thermostat control circuit constructed according to the principles of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A thermostat adapted for drawing power from a replaceable internal power supply, or an external power supply, is designated generally by reference numeral  30  in FIGS. 1 and 3. The thermostat  30  is of the type for use in connection with a climate control system, such as a heating/cooling system. 
     In the preferred embodiment, the thermostat  30  is a multi-stage electronic digital thermostat having a housing  32  with a removable front face  34  and a thermostat base  36 . The thermostat base  36  is provided with a liquid crystal display (LCD)  38 , a compartment  40  with connectors  42  for connection to a replaceable internal power supply  43 , and a user input pad  44  on a front panel  46 . Additionally, mounting holes  48  are provided to the thermostat base  36  for mounting the thermostat  30  to a wall or other desirable location using screws  50  or other suitable connectors. 
     A selector switch  52  and an energy management control  54  are provided on a back face  56  of the thermostat base  36 . Depending upon the setting of the selector switch  52 , the thermostat  30  may be connected to either a heater or heat pump system. The energy management control  54  provides for powering a heating system up to 30 minutes before a programmed setting of the thermostat  30  to gradually raise the room temperature to the programmed set point temperature in an efficient stage of heat. Additionally, a reset button  55  may also be provided on the front panel  46  to clear and reset the user programmed information of the thermostat  30 . 
     The LCD display  38 , as shown in FIGS. 2 a  and  2   b,  preferably alternately displays the current time and room temperature on characters  58 , displays the day of the week on characters  60 , displays the mode of operation of the thermostat  30 , such as HEAT or COOL, on characters  62 , displays the current programmed set temperature on characters  64 , and may indicate a HOLD mode on characters  66 . 
     In general, the up arrow button  68  and down arrow button  70  are pressed to select or set certain features or functions of the thermostat  30  (e.g., raise and lower the programmed set temperature, respectively). The SET TIME button  72  is used to set the current time of day, the VIEW PRGM button  74  is used to view the current programmed information, the RUN PRGM button  76  activates the function being programmed and the HOLD TEMP button  78  maintains the temperature at a specific setting. 
     A fan switch  80  is provided to select between a continuous fan operation mode when “FAN ON” is selected and an automatic programmed mode of operation when AUTO is selected. A SYSTEM switch  82  is provided to select a cooling mode (COOL), a heating mode (HEAT) or a disabled or off mode (OFF). 
     The thermostat  30  may also be provided with additional features and functions such as toggling the temperature display between Celsius and Fahrenheit by pressing the SET TIME button  72  and HOLD TEMP button  78  simultaneously. It should be appreciated by one skilled in the art that additional features and functions may be added to the thermostat  30  without departing from the scope of the invention. 
     When reference is made to pressing or using a button or using a switch, it should be understood by one skilled in the art that that this refers to a user pressing the button or moving the switch that corresponds to the specific programming function desired. The buttons may be actual depressible buttons or simply pressure or contact sensitive buttons or another suitable input device. The switches may be sliding or toggle switches or another suitable input device. The LCD display  38  displays programming information that is manually entered by a user pressing the desired button or selecting the function by using a switch. 
     The thermostat  30  of the present invention is also preferably provided with a cover  84  hingedly attached to the bottom side of thermostat  30  on the front panel  46 , as shown in FIG.  1 . This allows a user to close the cover  84  over the user input pad  44 , thereby hiding the buttons and switches, preventing inadvertent operation of the buttons and switches, and protecting the buttons and switches from exterior elements, such as dirt and dust. 
     The thermostat  30 , to this point has been described with reference to conventional component parts, such as the series 1F80 thermostats sold by White-Rodgers Division of Emerson Electric Co. It should be apparent to one skilled in the art that the thermostat  30 , heretofore described, may be modified and variations may be provided, such that the novel features described below may be incorporated with the thermostat  30  as well as any digital thermostat for controlling operation of a climate control system. 
     Generally, multi-stage mechanical thermostats, such as those for light commercial applications, do not require continuous power and therefore are not hardwired to both sides (i.e., 24 volt (or hot) and common or neutral) of a transformer for delivering electrical power. Thus, as shown in the schematic wiring diagram in FIG. 5, a typical mechanical multi-stage thermostat is connected to an AC power supply, which is usually a transformer  98 , with one wire  86  (24 volt) connected to a thermostat terminal RC  88  and another wire  90  (common or neutral) connected to a common side  92  of the heating/cooling relays. This typical mechanical multi-stage thermostat as shown in FIG. 5 does not consume or require continuous power, and therefore only wire  86  is required to be connected to the thermostat. 
     A digital multi-stage thermostat, shown in a schematic wiring diagram in FIG. 6, has continuous power requirements for some of its component parts, including a microcomputer and a thermostat control circuit  94 . Typically, wire  96  (24 volt) is connected from the transformer  98  to a thermostat terminal R  100  and wire  102  (common or neutral) is connected from the transformer  98  to a thermostat terminal C  104  to provide continuous power to the thermostat  30 . Thus, both sides of the transformer  98  (i.e., system hot (24 volt) and neutral) are needed to power the thermostat  30  and must be connected directly to the thermostat  30 . 
     When replacing a mechanical (multi-stage) thermostat with a digital (multi-stage) thermostat, another power line connection, such as wire  102  (common or neutral), is required to provide continuous power to operate the thermostat. In most replacement situations, this means that a separate power supply line must be installed, increasing the complexity and the expense of the replacement installation. However, the thermostat  30  of the present invention is provided with compartment  40  to provide for connection to a replaceable internal power supply  43 , such as standard AA alkaline batteries, thus eliminating the need to provide a new power line. 
     Where there is a power supply line such as wire  102 , the thermostat  30  of the present invention operates with DC regulated power provided from the transformer  98  through a linear regulator. However, if a power supply is not present and a new one is not installed, the thermostat is powered by the replaceable internal power supply. 
     It should be understood that when reference is made to a situation where there is no external power supply, this means that no external power is available to provide continuous power (i.e., the extra power line connection (neutral or common) is not present). However, power is still present from the transformer to provide power to, for example, the heating/cooling relays through other parts of the thermostat (e.g., thermostat relay contacts). 
     If both power lines  96  and  102  are present, power from an external power supply is provided such that terminal R 100  is connected to 24 volt (hot) and terminal C  104  is connected to the neutral or common side of the 24 volt power supply. As shown in FIG. 7, a linear regulator LR is connected to the transformer  98  through terminal R 100 . This provides power to the thermostat  30  and back biases or reverse biases a diode D between the regulated external power supply and the replaceable internal power supply  43 , resulting in no power being provided to the thermostat  30  from the replaceable internal power supply  43 . However, when wire  102  is not present (e.g., an external power supply is not present and a new one is not installable, or in the event of external power supply failure), no power is provided to the diode from the external power supply through the linear regulator, the diode is forward biased, and power (about 4.5 volts) is supplied to the thermostat  30  by the replaceable internal power supply  43 , which is preferably 3 AA batteries. 
     An energy storage device, such as a capacitor or super-capacitor, may be provided as a backup for all or some of the power requirements of the thermostat  30  for short time durations. Additionally, a programmed memory storage device, such as an electrically erasable programmable read only memory, may also be provided so that the thermostat  30  maintains user programmed information upon the loss of power. One such device is a 24C02N E 2 PROM sold by Atmel Corporation. 
     Additional features may be provided to the thermostat  30  to conserve power or alert a user to a low power condition. For example, an energy reduction device may be provided, such that a real time clock may be programmed either to stop, consume the lowest amount of microcontroller run current, or run continuously (with batteries or a capacitor) in the event of external power failure from the transformer  98  connected to the thermostat  30  by wire  102 . Additionally, the LCD display  38  may be provided such that it blanks out and displays only “LOW BATTERY” when the replaceable internal power supply has reached a predetermined low level. Additionally, when this “LOW BATTERY” condition exceeds a certain predetermined time period, for example four weeks, the thermostat  30  may be preprogrammed to alert the user as to this “LOW BATTERY” condition, by raising the set point temperature during the summer or lowering the set point temperature during the winter by a predetermined set amount, such as 10 degrees Fahrenheit, until threshold temperatures are reached, for example 90 degrees Fahrenheit and 60 degrees Fahrenheit, respectively. Such a feature is disclosed in U.S. Pat. No. 5,251,813, owned by Emerson Electric Co., which disclosure is expressly incorporated herein by reference. 
     While the present invention has been described by reference to specific embodiments, it should be understood and apparent to those skilled in the art that modifications and variations of the invention may be constructed without departing from the scope of the invention. However, these changes are included within the teaching of the disclosure, and it is therefore intended that the invention be limited only by the scope of the claims appended hereto, and their equivalents.