Patent Publication Number: US-2012025948-A1

Title: Power management circuitry for electronic door locks

Description:
BACKGROUND 
     The present invention is directed to an electronic door lock circuit, and in particular to power management circuitry to minimize power consumption by the electronic door lock circuit. 
     Electronic door locks are employed in a variety of applications, providing both security and flexibility in controlling access. A well-known example is the magnetic strip electronic door lock employed by a majority of hotels. 
     Electronic door locks differ from traditional locksets, in which a key mechanically determines whether a door should be unlocked, in that electronic door locks include a microcontroller that receives identification data from a keycard (e.g., magnetic strip card, or radio-frequency identification (RFID) card) and generates an output that determines whether the door should be unlocked. 
     For electronic door locks connected to line power, power consumption is not of much concern. For electronic door locks that rely on an isolated power source, such as one or more batteries, then power consumption by the electronic door lock becomes an important factor in determining how long batteries will last before needing replacement. Electronic door locks that require frequent battery changes will increase the maintenance cost associated with the locks. 
     A variety of work has been done to minimize the power consumed by the electronic door lock during the activation stage, in which the door lock circuitry (typically a microcontroller) reads data from a keycard and electrically activates a mechanism to unlock the door. In the time between activation stages, the microcontroller is maintained in a sleep state that minimizes power consumption, while still allowing the processor to be alerted, generally through the use of interrupts, to the presence of a keycard. 
     While operating the microcontroller in a sleep mode improves power consumption, the microcontroller continues to draw small amounts of current that over time represent a significant portion of the available battery power. 
     SUMMARY 
     A power management circuit is provided that conserves power for an electronic door lock system. The power management circuit includes an ON/OFF circuit, a load switch circuit and an electronic door lock circuit. The ON/Off circuit generates an enable signal in response to a detected keycard. The enable signal is provided to an enable pin of the load switch circuit. In response to a detected keycard, the load switch circuit is in an enabled state in which it provides power to the electronic door lock circuit. In response, the electronic door lock circuit reads identification data from the detected keycard and determines whether or not the door should be unlocked. Upon completing this task, the electronic door lock circuit generates a self turn-off signal that is provided in feedback to the ON/OFF circuit. In response, the enable signal provided to the load switch circuit is removed and the load switch circuit is disabled. In the disabled state, the load switch circuit prevents power from being provided (and therefore consumed) by the electronic door lock circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a power management circuit for an electronic door lock according to an embodiment of the present invention. 
         FIGS. 2A and 2B  are block diagrams illustrating other embodiments of the power management circuit for an electronic door lock according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a power management circuit that reduces the power consumed by electronic door lock circuitry. In particular, the present invention focuses on reducing power requirements during the period in which the electronic door lock circuitry is inactive (i.e., the period between activations in which the circuitry is responsible for reading data from a keycard and actuating an unlocking mechanism that allows the door to be opened). The present invention takes advantage of low-power alternatives to sensing the presence of keycard that does not require intervention from the electronic door lock circuitry (typically a microcontroller). This allows the door lock circuitry to be turned ‘off’, as opposed to being placed in a partially active sleep state, in the periods of time between activations. This reduces the total amount of power consumed by the electronic door lock circuitry. 
       FIG. 1  is a block diagram of power management circuit  10  according to an embodiment of the present invention. Power management circuit  10  includes ON/OFF circuit  12 , load switch circuit  14 , and electronic door lock circuit (hereinafter, “lock circuit”)  16 . A dc power source (e.g., a battery) labeled V batt  provides dc power to ON/OFF circuit  12  and load switch circuit  14 . In some embodiments the dc power provided by V batt  may only be provided to load switch circuit  14  in response to the keycard detection input indicating the presence of a keycard. In this embodiment, however, the dc power provided by V batt  is also provided to load switch circuit  14 . 
     Load switch circuit  14  is operated in one of two states, based on the input provided to the enable input “EN” of load switch  14 . In the first state, load switch circuit  14  is enabled (e.g., the ON/OFF signal provided to the enable pin “EN” is a logic high value) and acts to supply the dc input voltage provided by the dc source or a modified version of the dc input voltage to lock circuit  16 . In the second state, load switch circuit  14  is disabled (e.g., the ON/OFF signal provided to the enable pin “EN” is a logic low value) to prevent load switch circuit  14  from providing any dc power to lock circuit  16 . As a result, lock circuit  16  does not consume power during inactive periods of time when no keycard is present. In addition, the quiescent current (current consumed by load switch circuit  14  in the disabled state) is extremely low, even as compared with the current consumed by prior art lock circuits that operate in a sleep state between activation periods. Therefore, during inactive periods, power management circuit  10 , and in particular, load switch circuit  14  and lock circuit  16 , consume very little power. 
     In response to load switch circuit  14  being enabled (i.e., first state), a dc output voltage is provided to power lock circuit  16 . In one embodiment, lock circuit  16  may include a variety of components, such as a microcontroller, that are employed to electrically activate an unlocking mechanism in response to a matching keycard (represented by “keycard ID input”). The period of time in which lock circuit  16  responds to a presented keycard is referred to as the activation period. Following the activation period (e.g., unlock period, plus a relock period, plus a small duration of time between), lock circuit  16  generates a signal (labeled “End-of-Activation Signal”) that is provided as feedback to ON/OFF circuit  12 . In response, ON/OFF circuit  12  disables load switch circuit  14  (i.e., second state), thereby removing all power from lock circuit  16 . Power management circuit  10  remains in this low-power mode, in which lock circuit  16  consumes no power and load switch  14  consumes no or very little power, until a subsequent detection of a keycard. 
     The keycard detection input provided to ON/OFF circuit  12  may be electrical or mechanical nature. In one embodiment, a keycard (e.g., magnetic strip card) placed into the reader mechanically actuates a switch to generate the ON/OFF signal provided to load switch circuit  14 . In this embodiment, the only power consumed by power management circuit  10  is related to the quiescent current, if any, consumed by a disabled load switch circuit  14  (i.e., in the second operational state). In another embodiment, a proximity sensor or similarly electrical sensor device is used to detect the presence of a nearby keycard. This is typically employed in embodiments in which the keycard is never actually swiped through a reader (no mechanical action), but only held in close proximity to the reader for reading. In this embodiment, a small amount of power must be diverted to the proximity sensor for detecting the presence of the keycard. The benefit of this approach, however, is the proximity sensor or similar device is typically a lower voltage device than the microcontroller employed by door lock circuit  16 . Therefore, the power consumed by operating the low-voltage proximity sensor remains less than the power consumed by a traditional approach that requires the relatively higher voltage microcontroller (operating in a sleep mode) to be supplied with power. 
     Depending on the application and the type of keycard reader or sensor employed, load switch circuit  14  may provide power directly to a keycard reader or may provide power to electronic door lock circuit  16 , which in turn provides power to the keycard reader. A benefit of providing power directly to the keycard reader following the enablement of load switch circuit  14 , is the keycard reader is made operational very quickly following the detected keycard. In other embodiments however, electronic door lock circuit  16  provides power, based on the power received from load switch circuit  14 , to the keycard reader. The benefit of this approach, is electronic door lock circuit may selectively remove power from the keycard reader upon receiving the ID data provided by the keycard, thereby conserving the total amount of power consumed by power management circuit  10 . 
     In one embodiment, load switch  14  is implemented with a boost regulator that, when enabled, boosts the dc input voltage provided by V batt  to a higher voltage dc output. A benefit of this approach is a boost regulator is capable of being enabled and disabled the same as a load switch, and consumes very little power in the disabled state. In addition, a lower voltage dc power source, such as a single AA battery, may be employed despite higher voltage requirements from lock circuit  16 . For instance, a dc input voltage generated by a single AA battery (approximately 1.2-1.5 Volts (V)) is converted by a boost regulator to a dc output voltage of approximately 2-5 V as required by a microcontroller employed by lock circuit  16 . A benefit of employing the boost regulator is a lower voltage dc source (e.g., a single AA battery versus a higher voltage battery or several batteries connected in series to generate a higher voltage dc output) may be used in conjunction with devices, such as lock circuit  16 , that require higher operational voltage levels to operate. In addition, the reduction of power consumed by the circuit during inactive periods extends the battery life associated with the dc power source. In other embodiments, the boost regulator may be implemented with other power conversion circuits, such as a buck regulator or a buck-boost regulator. 
     In an exemplary embodiment, the dc power source V batt  includes a plurality of individual batteries (e.g., AA batteries) connected in parallel to provide additional energy to power management circuit  10 . In particular, this is useful in applications in which electronic door lock circuitry includes higher usage requirements. For example, for electronic door locks in which additional electrical energy is required to actuate the locking mechanism. In another embodiment, the dc power source V batt  includes a plurality of individual batteries connected in series with one another to provide a higher voltage dc input. This embodiment is useful in applications that do not employ a boost regulator, such that the voltage provided by dc source V batt  is sufficient to operate lock circuit  16  as well as any additional components. 
       FIGS. 2A and 2B  are block diagrams illustrating other embodiments of a power management circuit according to the present invention. The difference between the embodiments described with respect to  FIGS. 2A and 2B  is in how power is distributed to components included with the power management circuit. 
       FIG. 2A  is a block diagram of power management circuit  20   a  that includes ON/OFF circuit  22   a,  boost regulator  24   a,  and microcontroller  26   a.  Reader  28   a  is included in this view to highlight the consequence of providing power sequentially from boost regulator  24   a  to microcontroller  26   a,  and from microcontroller  26   a  to reader  28   a.    
     ON/OFF circuit  22   a  includes diode D 1 , mechanically activated switch  30   a , and resistor R 1 . Dc power source V batt  is connected through diode D 1  and switch  30   a  to the enable pin of boost regulator  24   a.  Switch  30   a  is maintained as an open circuit if no keycard is present within reader  28   a  (typically a slide-type magnetic reader), thereby preventing power from being supplied to the enable (EN) pin of boost regulator  24   a.  In response to the presence of a keycard, switch  30   a  is mechanically closed to supply power to the enable pin of boost regulator  24   a,  resulting in boost regulator transitioning from a disabled state to an enabled state. 
     In response to the enable signal provided by the activation of switch  30   a , boost regulator  24   a  generates a dc output voltage (of higher voltage than the dc input voltage provided by V batt ) that is provided to microcontroller  26   a.  As microcontroller  26   a  becomes operational, one of the functions it performs is to provide a dc output (via output pin ‘Vout 1 ’) to other components, such as reader  28   a.  In addition, microcontroller  26   a  provides a dc output (via output pin ‘Vout 2 ’) that is provided as feedback to the enable pin of boost regulator  24   a  to ensure that after the keycard has been removed from reader  28   a  (causing switch  30   a  to open), boost regulator  24   a  will remain in the enabled state throughout the remainder of the activation period. Reader  28   a  provides microcontroller  26   a  with keycard ID data (labeled ‘ID Data’) that is employed by microcontroller  26   a  to determine whether the door should be unlocked. In response to matching ID data, microcontroller  26   a  generates an activation output that causes the door to be unlocked. Upon receiving complete ID data from reader  28   a  (but before the end of the activation period), microcontroller  26   a  may conserve power by removing power (provided via output pin Vout 1 ) to reader  28   a.  In this way, the amount of power consumed by reader  28   a  is reduced, and additional power is conserved by power management circuit  20   a.    
     At the end of the activation period, microcontroller  26   a  provides a self turn-off signal by removing the dc output previously provided in feedback to the enable pin of boost regulator  24   a.  In response, boost regulator  24   a  is disabled such that no dc power is provided to microcontroller  26   a  (or other passive components employed by the electronic door lock circuit). Power management circuit  20   a  remains in this state until a subsequent activation period is detected by the mechanical actuation of switch  30   a.  In this embodiment, resistor R 2  is a pull-up resistor that prevents large currents from flowing into the enable pin of boost regulator  24   a.    
     Benefits of this embodiment include extremely low power consumption in between activation periods. In particular, because ON/OFF circuit  22   a  is mechanically activated, keycard detection does not require any power consumption. Furthermore, as discussed above, boost regulator  24   a  consumes very little power when operating in the disabled mode, and microcontroller  26  and associated components associated with electronic door lock circuitry consume no power during non-activation periods. 
     In addition, microcontroller  26   a  may include storage capacity (e.g., random access memory, hardware registers, etc.) that allows the microcontroller, prior to generating the self turn-off signal, to store key variables associated with the operation of the electronic door lock. For example, the variables may be associated with the operating state of the microcontroller. In a subsequent activation, microcontroller  26   a  employs the stored variables to decrease the start-up time associated with the microcontroller and to improve the continuity associated with the microcontroller between subsequent activations. 
       FIG. 2B  is a block diagram of power management circuit  20   b  that includes ON/OFF circuit  22   b,  boost regulator  24   b,  and microcontroller  16   b.  Power management circuit  20   b  operates in the same way as power management circuit  20   a  described with respect to  FIG. 2A . The difference between the two embodiments is the manner in which the attached keycard reader receives power from the circuit. 
     In  FIG. 2A , dc power provided by boost regulator  24   a  is provided to microcontroller  26   a,  with microcontroller  26   a  providing subsequent power to reader  28   a . The benefit of this approach is microcontroller  26   a  is able to remove power to reader  28   a  immediately upon receiving ID data from the reader (as opposed to waiting for the end of the activation period). In this way, the amount of power consumed by reader  28   a  is minimized. However, this embodiment requires microcontroller  28   a  to, in essence, boot up before power is provided to reader  28   a,  adding additional time delays between the moment when the presence of the keycard mechanically closes switch  30   a  and the moment when reader  28   a  has received sufficient power from microcontroller  26   a  to read ID data from the keycard. 
     In the embodiment shown in  FIG. 2B , dc power provided by boost regulator  24   b  is simultaneously provided to both microcontroller  26   b  and reader  28   b.  The benefit of this approach is reader  28   b  becomes operational more quickly because it does not require reader  26   b  to wait until microcontroller  26   b  is operational. However, the drawback of this approach is that microcontroller  26   b  cannot remove power to reader  28   b  upon receiving ID data. That is, reader  28   b  will remain active, and therefore will continue to consume power, until the activation period ends and the self turn-off signal provided in feedback by microcontroller  26   b  to the enable pin of boost regulator  24   b  causes power to be removed from both microcontroller  26   b  and reader  26   b  (as well as all other passive components). 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.