BACKGROUND OF THE INVENTION 
       [0001]    This application relates to an electric circuit wherein a protection device for a solid state circuit element is incorporated into a circuit, which works in harmony with an arc fault circuit interrupter (“AFCI”). 
         [0002]    In modern buildings, more electrical safety measures are being required. Recently, AFCIs have been required in building electric systems. An AFCI acts to disable an electric circuit should specific current patterns be detected. These patterns could include arcing and sparking resulting from a short-circuit. Once these patterns are recognized, the AFCI unit will de-energize the circuit. AFCI units typically de-energize a circuit within a mini-second timeframe. 
         [0003]    Solid state circuit elements are being incorporated to control the electric systems. Such solid state devices also need to be protected from a short-circuit current. In fact, a solid state device must be protected more quickly than the AFCI will de-energize the circuit. As an example, after a micro-second range, a solid state device could be damaged. 
       SUMMARY OF THE INVENTION 
       [0004]    In a disclosed embodiment of this invention, an electric circuit is provided with a solid state device having a protection switch. When the protection switch is closed, a parallel electric line which bypasses the solid state device is closed such that the circuit does supply the current to the AFCI, and such that the AFCI can act to de-energize the circuit. 
         [0005]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic view of an electric circuit in a normal operation mode. 
           [0007]      FIG. 2  shows a first step in addressing a short circuit. 
           [0008]      FIG. 3  shows a subsequent step. 
           [0009]      FIG. 4  shows a sample dimmer circuit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0010]    An electric circuit  20  is illustrated in  FIG. 1 . The electric circuit  20  is shown for powering a light bulb  22 . While light bulb  22  is shown, electric circuits for powering any number of items could benefit from this invention. An AFCI  24  may be a standard item and is incorporated into the circuit. The AFCI will operate to detect an arc fault or other short-circuit predictors and will de-energize the circuit when such an occurrence is detected. A control  26  includes a MOSFET implemented bi-directional switch  28 . This switch  28  is part of an overall control  30  for providing dimming of the power delivered to the light bulb  22 . One such dimmer circuit is disclosed in U.S. patent application Ser. No. 11/684,834, entitled “Dimming Circuit for Controlling Electrical Power,” filed on Mar. 12, 2007. While the solid state device is shown as a MOSFET switch, other solid state devices can benefit from this invention. Moreover, dimmer circuits other than the specifically disclosed dimmer circuit (see  FIG. 4 ) can also benefit from this application. 
         [0011]    The MOSFET  28  is provided with a parallel bypass line  32  having its own electromechanical bi-directional switch  34 . A line  36  downstream of the light bulb  22  communicates to a current sensing control  38 . The current sensing control communicates with a switch control  40 . When an undesirably high current is sensed, the switch control  40  acts to control the switches  28  and  34 , as shown in  FIGS. 2 and 3 . Initially, and during normal operation as shown in  FIG. 1 , the switch  28  is controlled by a power width modulation (PWM) signal and the switch  34  is opened. 
         [0012]    As a first step shown in  FIG. 2 , when an unusually high current is sensed, the switch  28  is opened. At this point, the switch  34  remains open. This now protects the solid state device  28 , and the remainder of the dimming circuit  30 . Soon thereafter, and as shown in  FIG. 3 , the switch  34  is closed. Now, the current can continue to flow to the AFCI  24 , and the AFCI  24  can act as designed to protect the remainder of the circuit. 
         [0013]    In this manner, the solid state device is protected while the AFCI is still allowed to perform its function. 
         [0014]    A sample dimmer circuit is shown in  FIG. 4 . Notably, the sample dimmer circuit  30  as shown in  FIG. 4  includes two MOSFETS  28 . The circuit of this application can have redundant bypass lines and switches associated with each of the MOSFETS. The microcontroller  30  provides a timing control signal input to the timing portion  41 . The timing control signal in one example comprises a pulse width modulation control signal. The timing control signal controls when the dimming portion  42  activates the MOSFET switches  46  of the power train portion  44  to control the amount of power supplied to a load  52 . The microcontroller  26  determines how to set the timing control signal based upon what setting a user selects (e.g., what dimming level is desired). In one example, the microcontroller  30  uses known techniques for providing the pulse width modulation input to achieve a desired corresponding amount of dimming. 
         [0015]    In the illustrated example, the power train portion  44  includes the MOSFETs  28  because they are efficient for certain power levels (e.g., up to about 600W). Another example is useful with higher powers and includes an IGBT in place of the MOSFETs  28 . 
         [0016]    One example load  22  is a light bulb. Controlling the light intensity of a bulb is one example use of the illustrated arrangement. In this example, the load  50  is plugged into a wall socket having terminals schematically represented at  52  and  54   
         [0017]    The MOSFETs  28  in one example operate according to a known reverse phase control strategy when the gate and source of each is coupled with a sufficient voltage to set the MOSFETs  28  into an operative state (e.g., turn them on) so that they allow power from a source  56  (e.g., line AC) to be supplied to the load  50 . In the reverse phase control example, the MOSFETs  28  are turned on at 0 volts and turned off at a high voltage. In another example a forward phase control strategy is used where the MOSFETs  28  turn on at a high voltage and off at 0 volts. Another example includes turning the MOSFETs  28  on at a non-zero voltage and turning them off at another non-zero voltage. 
         [0018]    The dimming portion  42  controls when the power train portion  44  is on and, therefore, controls the amount of power provided to the load  22 . Controlling the amount of power provided to a light bulb controls the intensity of light emitted by the bulb, for example. 
         [0019]    In this example, an isolated DC voltage source  60  is selectively coupled directly to the gate and source of the MOSFETs  28  for setting them to conduct for delivering power to the load. The isolated DC voltage source  60  has an associated floating ground  62 . A switch  64  responds to the timing control signal input  26  from the microcontroller and enters an operative state (e.g., turns on) to couple the isolated DC voltage source  60  to the MOSFETs  28 . In the illustrated example, the switch  64  comprises an opto-coupler component. Other examples include a relay switch or a transformer component for selectively coupling the isolated DC voltage source  60  to the MOSFETs  28 . 
         [0020]    In one example, the isolated DC voltage source  60  provides  12  volts. In another example, a lower voltage is used. The voltage of the isolated DC voltage source  60  is selected to be sufficient to turn on the MOSFETs  46  to the saturation region. 
         [0021]    One example includes using an isolated DC-DC converter to achieve the isolated DC voltage source  60 . Another example includes a second-stage transformer. Those skilled in the art who have the benefit of this description will realize what components will work best for including an isolated DC voltage source in their particular embodiment. 
         [0022]    The illustrated example includes voltage controlling components for controlling the voltage that reaches the gate and source of the MOSFETs  28 . The illustrated example includes resistors  66  and  68  and a zener diode  70 . The resistor  66  sets the turn on speed or the time it takes to turn on the MOSFETs  28 . The resistors  66  and  68  set the turn off speed or the time it takes to turn off the MOSFETs  28 . In one example, the resistor  68  has a much higher resistance compared to that of the resistor  66  such that the resistor  68  effectively sets the turn off time for the MOSFETs  28 . Selecting an off speed and on speed allows for avoiding oscillation of the MOSFETs  28  and avoiding generating heat if the MOSFETs  28  were to stay in a linear operation region too long. 
         [0023]    The zener diode  70  provides over voltage protection to shield the MOSFETs from voltage spikes and noise, for example. The zener diode  70  is configured to maintain the voltage provided to the MOSFET gate and source inputs at or below the diode&#39;s reverse breakdown voltage in a known manner. One example does not include a zener diode. 
         [0024]    One advantage to the disclosed example is that the MOSFETs can be fully controlled during an entire AC cycle without requiring a rectifier. The disclosed example is a more efficient circuit arrangement compared to others that relied upon RC circuitry and a rectifier for controlling the MOSFETs. 
         [0025]    As mentioned above, while a detailed description has been given of the  FIG. 4  circuit, this invention is not limited to any particular circuit. 
         [0026]    Also, while bi-directional switches are disclosed for AC applications, uni-directional switches can be used, as an example for DC applications, say for LED lighting. 
         [0027]    In general, it may often be in practice that the AFCI is incorporated into an existing circuitry within a building, and that the present invention would be incorporated as a solid state circuit protection system, which is connected into the existing building circuit having the AFCI. 
         [0028]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
An electric circuit includes a load, a solid state device, and a control for opening the circuit such that current will not flow through the solid state device, and for facilitating flow of current to bypass said solid state device and provide a current path to an arc fault circuit interrupter. A bypass includes a normally opened switch which is closed to provide current to the arc fault circuit interrupter.