Abstract:
An electronic circuit breaker includes controllable contacts adapted to connect a power source to at least one load, and a microcontroller for monitoring the flow of power to the load, detecting different types of fault conditions and automatically opening the contacts in response to a fault. A primary power supply of the breaker receives power from the line source when the contacts are closed, and supplies power to the control circuitry. Fault indicators in the microcontroller indicate the type of fault that caused the contacts to open. A secondary power supply provides power to the control circuitry when the contacts are open and a switch is closed.

Description:
FIELD OF THE INVENTION 
     This invention relates to electronic circuit breakers and particularly to an improved circuit breaker having fault indication and a secondary power supply for the fault indication while the circuit breaker is open. 
     BACKGROUND 
     Today&#39;s residential electronic circuit breakers (AFCI) monitor and protect against many different types of fault conditions. When a circuit breaker trips, it is advantageous to know what type of fault the circuit breaker interrupted in order to accurately and rapidly correct the fault condition. The electronic modules in such circuit breakers are capable of indicating the interrupted fault only when the electronics are powered. Normally this requires re-closing the circuit breaker to power the electronic module. However, re-closing the circuit breaker to indicate the cause of the interrupted fault also means re-energizing the fault if the fault is still present. In order to safely re-close the circuit breaker, an electrician must open the load center and remove the line load and neutral load wires from the circuit breaker. It would be desirable to have a secondary means of powering the electronic module to allow the electronic module to indicate the interrupted fault, without the need to re-energize the fault at levels that would be considered hazardous, thus eliminating the need to remove the load wires from the circuit breaker. 
     BRIEF SUMMARY 
     In accordance with one embodiment, an electronic circuit breaker includes controllable mechanical contacts adapted to connect an AC power source to at least one load, and control circuitry for monitoring the flow of power from the AC power source to the load, detecting different types of fault conditions and automatically opening the contacts in response to the detection of a fault condition. A primary power supply receives power from the AC power source when the contacts are closed, and supplying power to the control circuitry. Fault indicators controlled by the control circuitry indicate the type of fault condition causing the control circuitry to open the contacts, and a secondary power supply supplies power to the control circuitry when the contacts are open and a manually operated switch is closed. By supplying the control circuitry with power from a secondary supply while the breaker contacts are open, this breaker system avoids any need to close the circuit breaker onto a hazardous fault to determine the reason the circuit breaker tripped. It also avoids any need to remove branch circuit wiring from the circuit breaker, or to re-open the circuit breaker from a load center, to indicate the cause of a trip, to update firmware, or to perform diagnostics. 
     In one implementation, the manually operated switch is connected to the AC power source on the source side of the controllable mechanical contacts, and the other side of the switch is coupled to the control circuitry so that the closing of the switch couples the AC power source to the control circuitry for supplying power to the control circuitry when the contacts are open. A rectifier may be coupled to the manually operated switch and to the control circuitry for converting power from the AC power source to DC power for the control circuitry. 
     The control circuitry preferably includes a microcontroller adapted to receive power via the contacts when the contacts are closed or via the manually operated switch when the contacts are open. The microcontroller is programmed to detect fault conditions, to open the contacts in response to the detection of a fault condition, and to automatically switch between a fault-protection mode of operation when the contacts are closed, or a fault-indicating mode of operation when the contacts are open. The microcontroller may be programmed to detect the coupling of the AC power source to the microcontroller via the contacts, and to automatically switch to the fault-indicating mode when the AC power source is not coupled to the microcontroller via the contacts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a portion of the electrical circuitry in a circuit breaker that is capable of indicating the type of fault that causes the circuit breaker to trip. 
         FIG. 2  is a flow diagram of a routine executed by the microcontroller in the circuitry of  FIG. 1  for activating a secondary power supply for supplying power to the microcontroller and a fault indicator while the circuit breaker is tripped. 
     
    
    
     DETAILED DESCRIPTION 
     Although the invention will be described in connection with certain preferred embodiments, it will be understood that the invention is not limited to those particular embodiments. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims. 
       FIG. 1  illustrates a circuit breaker that monitors the electrical power supplied to one or more loads  11  from a line power source  10  such as a 120-volt AC power source. During normal operation, i.e., in the absence of a fault, the source  10  supplies AC power to the load  11  through controllable mechanical contacts, i.e., normally closed breaker contacts  12  in a trip circuit  13  which automatically opens to protect the load  11  as known in the art. In addition, DC power is supplied to a microcontroller  14  in the breaker from a primary power source that includes a full wave rectifier  15  (such as a diode bridge), a pre-voltage regulator circuit  16  and a voltage regulator  17 . The diode bridge  15  rectifies AC power from the source  10  to produce a DC output supplied to the pre-voltage regulator circuit  16 . The pre-voltage regulator circuit  16  in turn supplies power to the voltage regulator  17 , which supplies the microcontroller  14  with a regulated DC input voltage. A push-to-test button  18  is connected to a PTT input of the microcontroller  14  to permit manually initiated testing of various parameters of the circuit breaker, as described, for example, in U.S. Pat. No. 7,151,656, which is assigned to the assignee of the present invention. 
     When a fault is detected by the circuit breaker, the microcontroller  14  generates a trip signal that is supplied to the trip circuit  13  to automatically opening the breaker contacts  12  to interrupt the flow of electrical current to the load. The microcontroller also stores information identifying the reason for the trip, such as the detection of a ground fault or an arcing fault. When the user desires to retrieve the stored information following a trip, it is necessary to supply power to the microcontroller  14  to enable the microcontroller to retrieve the stored information and to display or otherwise communicate that information to the user. If the AC power source  10  is re-connected to the rectifier  15  by re-closing the breaker contacts  12 , there is a risk of re-energizing the fault that caused the trip. Thus, the microcontroller  14  is preferably powered without closing the breaker contacts  12 , to avoid re-energizing the fault that caused the trip in the first place. 
     In the illustrative circuit, a secondary power supply can be coupled to the microcontroller  14 , while the breaker contacts  12  are open, by pushing the push-to-test button  18  to couple the line side of the AC power source  10  to the input of the voltage regulator  17 . From the PTT switch that is closed by pressing the PTT button  18 , the AC signal from the source  10  passes through a current-limiting resistor R 1  and then is clamped by a zener diode Z 1 . A half-wave rectifier formed by a diode D 1  allows current to flow from the node N 1  between the diode D 1  and the resistor R 1  to the input of the voltage regulator  17 , and this current is sufficient to charge an input capacitor C 1  and power the voltage regulator  17 . The voltage regulator  17  then provides the microcontroller  14  with the necessary voltage and current to enable the microcontroller  14  to retrieve and display the type of fault that caused the trip. The same signal supplied to the diode D 1  is also supplied to the PTT input of the microcontroller via resistor R 2 , so that the microcontroller  14  can detect when the PTT switch has been closed. 
     Thus, to check on what type of fault caused the circuit breaker to trip, a user simply pushes the PTT button  18  to temporarily couple the AC power source to the voltage regulator  17  via resistor R 1  and diode D 1 . The regulator  17  supplies power from C 1  to the microcontroller  14  so that information identifying the type of fault that caused the trip is retrieved by the microcontroller  14  and displayed to the user, e.g., by indicator lights  19  or any other desired type of indicator. The user continues to press the PTT button  18  until the displayed fault indication is understood, and then the user releases the PTT button  18  to power down the microcontroller  14 . 
     Referring to  FIG. 2 , upon being powered by either power source, the firmware initializes to a low-power state at step  20  until it determines which mode of operation it should enter. During this low-power state, the firmware monitors for the primary power supply (i.e., a standard voltage monitoring circuit) at step  21 , and step  21  determines whether the primary power supply is present. If the answer is affirmative, the microcontroller proceeds to step  23  where the normal operating mode is initialized. If the answer at step  22  is negative, the system advances to step  24  to monitor for a user input (i.e., closing of the PTT switch), and step  25  determines whether the user input is present. If the answer at step  25  is negative, the system proceeds to step  23  where the normal operating mode is initialized. An affirmative answer at step  25  advances the system to a pair of concurrent states represented by steps  26  and  27  in one path and step  28  in a parallel path. Step  26  monitors for the primary power supply, and step  27  determines whether the primary power supply is present. If the answer at step  27  is negative, the system returns to step  26 , and this loop continues as long as the primary power supply is not detected. Meanwhile, in the parallel path, step  28  initiates the alternate mode of operation, and the system then advances to step  29  to finish the alternate operation, which is to indicate the type of fault that caused a trip. 
     It can be seen from  FIG. 2  that the firmware enters the alternate mode only when (1) no power from the primary power supply is detected and (2) a closed PTT switch is detected. The firmware enters, or remains in, the normal operating mode whenever power from the primary power supply is detected, regardless of whether the PTT switch is open or closed. 
     During the normal operating mode, in which the microcontroller  14  is supplied with power from the primary power supply (via the closed breaker contacts  12 ), the firmware in the microcontroller  14  records the cause of an electronic trip event in the module&#39;s internal memory, prior to issuing the trip signal that causes the breaker contacts to open. During the alternate mode of operation, in which the microcontroller  14  is supplied with power from the secondary power supply, the firmware recalls a record of trip events from the memory and displays that information to the user. While in the alternate mode, the firmware continuously monitors for the primary power supply, and switches back to the normal operating mode when power from the primary power supply is detected. With the addition of a communication/storage port, the alternate mode of operation can also perform a self-update feature and/or circuit diagnostics. 
     By supplying the microcontroller  14  with power from a secondary supply while the breaker contacts  12  are open, the system described above avoids any need to close the circuit breaker onto a hazardous fault to determine the reason the circuit breaker tripped. It also avoids any need to remove branch circuit wiring from the circuit breaker, or to re-open the circuit breaker from a load center, to indicate the cause of a trip, to update firmware, or to perform diagnostics. 
     While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.