Abstract:
A power distribution system and method has a controller and at least one semiconductor switch. The power distribution system additionally has an on status detector which detects the status of the semiconductor switches, and an overcurrent status circuit which checks for overcurrent conditions.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates generally to power distribution systems, and more specifically to overcurrent protection in DC power distribution systems. 
         [0002]    In power distribution systems where DC power is distributed to multiple different loads, it is known to use a set of switches/relays in conjunction with a power system controller to control the power flowing to each load. In order to facilitate operation and power distribution to all of the loads, a controller, which is capable of controlling the state of each of the switches/relays in the system, is typically utilized. 
         [0003]    Initially, systems designed in this way used mechanical relay switches. However, mechanical relay systems suffered from reliability problems. In order to improve reliability, many applications now use semiconductor switches instead of mechanical relays due to a longer life-span of the semiconductor switches. Use of semiconductor switches has the additional benefit of reducing the size of the circuit as well as reducing the weight. 
         [0004]    Use of semiconductor switches necessitates a different style of controller than the controller used for mechanical relay switches. Existing semiconductor switch controllers are expensive to construct and maintain, are larger than desirable for use in many systems, such as aircraft power systems, and do not readily scale for different sized loads and trip currents. 
       SUMMARY OF THE INVENTION 
       [0005]    Disclosed is a control circuit for controlling a semiconductor switch. The control circuit has a controller, a current shunt, an on status detector, an overcurrent detector. The on status detector is connected to a semiconductor in the semiconductor array, and monitors the on status of the semiconductor switch. The overcurrent detector monitors for the presence of an overcurrent. Each of the overcurrent detector and the on/off state detector additionally has an output signal indicating the state of the monitored semiconductor in the case of the on status circuit, and the overcurrent status in the case of the overcurrent detector. 
         [0006]    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 
         [0007]      FIG. 1A  is a schematic diagram of an example semiconductor control circuit. 
           [0008]      FIG. 1B  is a schematic diagram of an example semiconductor control circuit having opto-coupler interface connections. 
           [0009]      FIG. 2A  is a circuit diagram illustrating an example overcurrent status circuit. 
           [0010]      FIG. 2B  is a circuit diagram illustrating an example overcurrent status circuit having an opto-coupler connection. 
           [0011]      FIG. 3A  is a circuit diagram illustrating an example semiconductor on status circuit. 
           [0012]      FIG. 3B  is a circuit diagram illustrating an example semiconductor on status circuit having an opto-coupler connection. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    When controlling power to multiple DC loads using multiple semiconductor switches in a DC power distribution system, it is necessary for a controller to be able to monitor the state of each semiconductor switch and appropriately respond to any overcurrent conditions.  FIG. 1  illustrates a box diagram of an electric circuit capable of controlling and monitoring a semiconductor switch  150 . The circuit of  FIGS. 1A and 1B  could be adapted to control and monitor multiple semiconductor switches using methods known in the art. 
         [0014]    The example of  FIGS. 1A and 1B  have a controller  110  connected to a first input power line  112  and to a neutral line  114 . The controller  110  additionally has a control output  116  which connects to an overcurrent detection circuit  120 , a current limiting circuit  130 , and a semiconductor switch  150 . The overcurrent detection circuit  120  is connected to the input power line  112 , a current limiting circuit  130 , a current shunt circuit  140 , and an overcurrent status circuit  170 . The current limit circuit  130  is also connected to the input power line  112 . The semiconductor switch  150  has a gate input which accepts the control signal  116  and has a power input connected to the current shunt  140 , and a power output connected to the output voltage signal  118  and to an on status circuit  160 . 
         [0015]    The solid state controller  110  of  FIG. 1  controls the state of the semiconductor switch  150  by using a control signal, an output from the solid state controller  110  on the control signal output line  116 . The control signal line  116  voltage is either 10-15V below the input power line  112  voltage, placing the semiconductor switch  150  in an on state, or the control signal line  116  voltage is equal to the power line  112  voltage placing the semiconductor switch  150  in an off state. When the control signal line  116  voltage is 10-15V below the input power line  112  voltage, the semiconductor switch  150  is turned on, and power is allowed to flow from the current shunt  140  through the semiconductor switch  150  to the output voltage  118 . Additionally, power simultaneously flows through the semiconductor switch  150  to the on status detection circuit  160 . 
         [0016]    When the on status circuit  160  detects power flowing from the semiconductor switch  150 , the on status circuit  160  begins outputting a semiconductor switch on signal  380  (illustrated in  FIGS. 3A and 3B ) which can used to monitor the status of the semiconductor switch system or for any other purpose. When the semiconductor switch  150  turns off, and thus ceases allowing power to flow through the semiconductor switch  150 , the on status detection circuit  160  will no longer detect power, and therefore will cease sending the semiconductor switch on signal. In  FIG. 1B , the on status circuit  160  has an additional connection  162  to the power line  112 . The connection  162  allows the isolated on status circuit  160  to receive power for the optical isolation. 
         [0017]    When an overcurrent condition occurs, the semiconductor switch  150 , the current shunt  140 , and the output wiring are subject to potential damage if the overcurrent condition is allowed to continue indefinitely. To protect the semiconductor switch  150 , the current shunt  140 , and any output wiring from damage, the example of  FIG. 1  includes an overcurrent detection circuit  120  and an overcurrent status circuit  170 . 
         [0018]    The overcurrent detection circuit  120  detects the current through the current shunt  140 . When the overcurrent detection circuit  120  detects a current that exceeds a preset threshold, it determines that an overcurrent condition is present in the circuit. When an overcurrent has been detected, the overcurrent detection circuit  120  clamps the control signal line  116  to about 1.5V less than the power line  112  voltage causing the semiconductor switch  150  to be latched off. After detecting an overcurrent condition, the overcurrent detection circuit  120  also outputs a signal to the overcurrent status circuit  170 . Once the overcurrent status circuit  170  receives a signal from the overcurrent detection circuit  120 , the overcurrent status circuit  170  switches on and begins outputting an overcurrent detected signal. 
         [0019]    The overcurrent detected signal can be used to monitor the status of the semiconductor switch system and detect when an overcurrent event has occurred. The semiconductor switch  150  will remain latched off by the overcurrent detection circuit  120  until the input to the control circuit  110  is removed. Once the input signal has been removed, the overcurrent latch is removed, and the control circuit  110  can be commanded to turn the output on again. If the overcurrent condition still exists, the overcurrent detection circuit  120  will again detect the condition and latch the semiconductor switch  150  off. 
         [0020]    The current limit circuit  130  detects the current through the current shunt  140 . When the current limit circuit  130  detects that the current reaches a preset threshold, the current limit circuit  130  changes the voltage on the control signal line  116  to control and limit the current through the semiconductor switch  150 . The preset threshold for the current limit is higher than the preset threshold for the overcurrent detection circuit ensuring that if the current limit is reached, the overcurrent detection circuit will latch off the semiconductor switch  150 . 
         [0021]      FIGS. 2A and 2B  illustrate example circuits which could be used for the overcurrent status circuit  170  in the example of  FIG. 1 .  FIG. 2A  utilizes a pair of resistors  210 ,  220  to condition the overcurrent detected signal and a transistor  230  which switches on in the presence of an overcurrent detected signal. When the transistor  230  switches on a connection is made between the status indicator  240  and the neutral line. The connection allows current to travel through the status indicator  240 , which in turn indicates that an overcurrent condition is present in the circuit. 
         [0022]    The example of  FIG. 2B  performs the same function as the example of  FIG. 2A , however it includes an opto-coupler  260  for optically isolating the overcurrent present signal from the overcurrent detection circuit  170 , as well as from the remainder of the circuit. When the transistor  230  in the example of  FIG. 2B  turns on, current flows from input power line  112  through two resistors  270 ,  250  and the input side of the opto-coupler  260 . The first resistor  270  conditions the current to a level compatible with an opto-coupler  260 . The second resistor  250  is placed in parallel with the opto-coupler  260  and provides noise immunity for opto-coupler  260 . When transistor  230  is on, current flows through the primary side of the opto-coupler  260 , and the transistor output of the opto-coupler  260  is on. The opto-coupler  260  output is the overcurrent status signal, and is isolated from the remainder of the circuit via a light gap within the opto-coupler  260 . 
         [0023]      FIGS. 3A and 3B  illustrate example on status circuits  160  which could be used in the example of  FIG. 1 .  FIG. 3A  illustrates one example on status circuit  160 , which utilizes two resistors  310 ,  320  and a diode  330  in conjunction with a transistor  340  to produce an on status signal. When the semiconductor switch  150  of  FIG. 1  is in an on condition, current will pass through the semiconductor switch  150  into the on status circuit  160 . Once in the on status circuit  160 , current passes through the first resistor  310  and is then split between two paths. The first current path provides a control signal to the transistor  340  and the second current path returns to ground through the second resistor  320 . This circuit configuration is operable to turn the transistor  340  on whenever the semiconductor  150  is on, thereby allowing current to flow through the on status indicator line  380 , and provides an on status indicator in the same manner as the overcurrent status circuit  170  described above. 
         [0024]      FIG. 3B  operates in a similar fashion to the example of  FIG. 3A , with the additional inclusion of an opto-coupler  350  for optically isolating the on status indicator line  380  from the remainder of the circuit. As in the overcurrent status circuit  160 , a first resistor  360  conditions the current to be compatible with the opto-coupler  350 . A second resistor  370  is placed in parallel with the opto-coupler  350  and provides noise immunity for the opto-coupler  350 . When transistor  340  is on, current flows through the primary side of the opto-coupler  350 , and the transistor output of the opto-coupler  350  is on. The opto-coupler  350  output is the overcurrent status signal, and is isolated from the remainder of the circuit via a light gap within the opto-coupler. 
         [0025]    It is known that alternate designs could be used for the on status circuit as well as for the overcurrent status circuit, and fall within the above disclosure. Additionally 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.