Electronic lock with power failure control circuit

A system for shutting down and restarting an electronic lock under power failure conditions comprising:

• a microcontroller including a stored control program having a plurality of microcontroller executable instructions;
• a lock actuator output adapted for connection to a lock actuator, the lock actuator output being connected to the microcontroller and the microcontroller sending a signal to the lock actuator output to switch the lock actuator between a locked and an unlocked state;
• a primary power supply input adapted for connection to a primary source of electrical power;
• an auxiliary power supply having at least one supercapacitor for providing auxiliary power and a supercapacitor monitoring and charging circuit connected to the microcontroller;
• an electrically controllable switch circuit connected to the primary power supply input and the auxiliary power supply to supply auxiliary power during a power failure condition;
• a power monitor circuit having a comparator, the power monitor circuit being connected to the primary power supply input to detect the power failure condition, the power monitor circuit also being connected to the microcontroller to signal a normal power condition and a power failure condition, the power monitor circuit also being connected to the electrically controllable switch circuit and the power monitor circuit switching the electrically controllable switch circuit to selectively connect a power output of the electrically controllable switch circuit between the primary source of electrical power and the auxiliary power supply to provide power to the microcontroller and the lock actuator upon detection of the power failure condition;
• wherein the power monitor circuit includes a lower voltage threshold and determines the power failure condition by comparing a voltage at the primary power supply input to the lower voltage threshold, wherein the power monitor circuit includes an upper voltage threshold and signals the microcontroller to stop executing the microcontroller executable instructions for a power failure state and begin executing the microcontroller executable instructions for a normal power state when the voltage at the primary power supply input raises above the upper voltage threshold for a preset period of time after the power failure condition occurred, and wherein the lower voltage threshold and the upper voltage threshold relate by hysteresis to prevent oscillation at or near transition points between the power failure state and the normal power state whereby upon detecting the power failure condition the electrically controllable switch circuit receives power from the auxiliary power supply to reduce power load on and enable recovery of the primary power supply input, and once the primary power supply input has recovered the electrically controllable switch circuit switching power back to the primary power supply input;
• and
• a visual indicator operable by the microcontroller to indicate the power failure condition;
• wherein the microcontroller executable instructions including:
• a normal power loop, corresponding to the normal power state, of the microcontroller executable instructions organized as a cooperative multitasking loop of tasks and executed by the microcontroller to operate the electronic lock in normal power conditions, the normal power loop including:
• an instruction for checking to determine if the power monitor circuit has signaled the detection of the power failure condition;
• an instruction for checking to determine if the at least one supercapacitor of the auxiliary power supply is fully charged;
• an instruction for turning on the supercapacitor monitoring and charging circuit to charge the at least one supercapacitor when the at least one supercapacitor is not fully charged;
• and
• an instruction for turning off the supercapacitor monitoring and charging circuit when the at least one supercapacitor is fully charged;
• a power failure loop, corresponding to the power failure state, of the microcontroller executable instructions;
• the microcontroller executing the power failure loop after the power monitor circuit has signaled the detection of the power failure condition, the power failure loop including:
• an instruction for checking to determine if the power monitor circuit has signaled the power failure condition,
• an instruction for resetting the microcontroller after the power monitor circuit determines the primary power supply input returned if the voltage of the primary power supply input raises above the upper voltage threshold for the preset period of time;
• at least one instruction for turning on the visual indicator to signal the power failure condition after the power monitor circuit has signaled the detection of the power failure condition;
• at least one instruction for sending a signal to the lock actuator output to switch the lock actuator to a desired locked or unlocked state in response to the power failure condition after the power monitor circuit has signaled the detection of the power failure condition.

A method for shutting down and restarting an electronic lock under power failure conditions comprising:

• monitoring a primary power supply input of the electronic lock with a power monitor and comparator circuit to detect a power failure condition and a normal power condition by comparing a voltage of the primary power supply input to a lower voltage threshold and an upper voltage threshold;
• wherein the electronic lock comprising:
• a lock including a latchbolt movable between an extended and a retracted position, the lock having a locked state and an unlocked state, the latchbolt being prevented from moving to the retracted position when the lock is in the locked state;
• a lock control circuit including a microcontroller and a memory having a stored control program including microcontroller executable instructions for a power failure state corresponding to the power failure condition and microcontroller executable instructions for a normal power state corresponding to the normal power condition;
• the primary power supply input connected to the lock control circuit and adapted for connection to a primary source of electrical power;
• an electrically powered lock actuator connected to the microcontroller, the lock actuator being responsive to a signal from the microcontroller to move the lock between the locked state and the unlocked state;
• the power monitor and comparator circuit having an input connected to the primary power supply input to detect the power failure condition, the power monitor and comparator circuit generates a control output to the electrically controllable switch circuit and a signal output connected to the microcontroller in response to the power failure condition, the power monitor and comparator circuit signaling the microcontroller via a power failure signal applied to the signal output when the power failure condition is detected at the primary power supply input;
• wherein the power monitor and comparator circuit includes the lower voltage threshold and determines the power failure condition by comparing a voltage at the primary power supply input to the lower voltage threshold, wherein the power monitor and comparator circuit includes the upper voltage threshold and signals the microcontroller to stop executing the microcontroller executable instructions for the power failure state and begin executing the microcontroller executable instructions for the normal power state when the voltage at the primary power supply input raises above the upper voltage threshold after the power failure condition occurred, and wherein the lower voltage threshold and the upper voltage threshold related by hysteresis to prevent oscillation at or near transition points between the power failure state and the normal power state whereby upon detecting the power failure condition the electrically controllable switch circuit receives power from the auxiliary power supply to reduce power load on and enable recovery of the primary power supply input, and once the primary power supply input has recovered the electrically controllable switch circuit switching power back to the primary power supply input;
• an auxiliary power supply having an auxiliary power output;
• the electrically controllable switch circuit having a primary power input connected to the primary power supply input, an auxiliary power input connected to the auxiliary power output of the auxiliary power supply, a power output connected to the microcontroller to provide power to the microcontroller and the lock actuator, and a control input connected to the control output of the power monitor and comparator circuit, the power monitor circuit controlling the electrically controllable switch circuit to selectively connect the power output between the primary source of electrical power and the auxiliary power supply;
• and
• a visual indicator operable by the microcontroller to indicate the power failure condition;
• executing tasks, by the microcontroller of the electronic lock, in a loop during the normal power condition;
• switching to the auxiliary power supply having at least one supercapacitor in the power failure condition to supply power to the electronic lock from the at least one supercapacitor during the power failure condition;
• setting the electronic lock to a desired locked or unlocked state after detecting the power failure condition;
• repeatedly monitoring a charge level of the at least one supercapacitor during the normal power condition;
• turning on a supercapacitor charger during the normal power condition when the charge level of the at least one supercapacitor is below a desired level;
• turning off the supercapacitor charger during the normal power condition when the charge level of the at least one supercapacitor has reached a desired level;
• turning on the visual indicator during the power failure condition;
• and
• resetting the electronic lock after the power failure condition has been detected if the normal power condition is subsequently detected for a predetermined period of time.