Current detection and limiting method and apparatus

Abstract

An apparatus for detecting and controlling current. A current detector for generating a first value that represents an amount of current being delivered to a device. A current limit circuit for generating a second value that represents a maximum permitted current level from a current source. A current controller for controlling the amount of current drawn by the device if the first value exceeds the second value.

1 - 17 . (canceled) 
     
     
         18 . An apparatus for detecting and controlling current comprising:
 a current detector for generating a first value that represents an amount of current being delivered to a device;   a programmable current limit circuit for generating a variable value that represents a maximum permitted current level from a current source; and   a current controller for controlling the amount of current drawn by the device if the first value exceeds the variable value.   
     
     
         19 . The apparatus of  claim 18  wherein the first value is generated by a voltage drop across a resistor that is in line with the current being delivered to the device. 
     
     
         20 . The apparatus of  claim 18  wherein the programmable current limit circuit comprises:
 a resistor having a predetermined value; and 
 a variable bias current source coupled to the resistor, the variable bias current source providing a predetermined current. 
 
     
     
         21 . The apparatus of  claim 18  wherein the current controller for controlling the amount of current drawn by the device if the first value exceeds the variable value comprises a gain control for controlling a gain of a pre-amplifier 
     
     
         22 . The apparatus of  claim 18  wherein the programmable current limit circuit comprises:
 a resistor having a predetermined value; 
 a programmable bias current source coupled to the resistor, the programmable bias current source providing a first predetermined current; 
 a second bias current source coupled to the resistor, the second bias current source providing a second predetermined current; and 
 a switch for disconnecting the second bias current source if the first value exceeds the variable value. 
 
     
     
         23 . The apparatus of  claim 22  further comprising circuitry for reconnecting the second bias current source if the first value is lower than a third value. 
     
     
         24 . The apparatus of  claim 18  further comprising a second current controller for disconnecting the device if the first value exceeds a third value. 
     
     
         25 . The apparatus of  claim 18  wherein the current detector for generating the first value that represents the amount of current being delivered to the device comprises means for generating the first value that represents the amount of current being delivered to the device. 
     
     
         26 . The apparatus of  claim 18  wherein the programmable current limit circuit for generating the variable value that represents the maximum permitted current level from the current source comprises means for generating the variable value that represents the maximum permitted current level from the current source. 
     
     
         27 . The apparatus of  claim 18  wherein the current controller for controlling the amount of current drawn by the device if the first value exceeds the variable value comprises means for controlling the amount of current drawn by the device if the first value exceeds the variable value. 
     
     
         28 . The apparatus of  claim 18  wherein the maximum permitted current level from the current source is less than the maximum available current level from the current source. 
     
     
         29 . The apparatus of  claim 18  further comprising a second current controller for disconnecting the device if the first value exceeds a third value that represents a short circuit condition. 
     
     
         30 . The apparatus of  claim 18  wherein the device is a USB-connected audio device and the current limit circuit is a USB protective device. 
     
     
         31 . An apparatus for detecting and controlling current comprising:
 a current detector for generating a first value that represents an amount of current being delivered to a device;   a programmable current limit circuit for generating a variable value that represents a maximum permitted current level from a current source, the programmable current limit circuit comprising:
 a resistor having a predetermined value; 
 a programmable bias current source coupled to the resistor, the programmable bias current source providing a first predetermined current; 
 a second bias current source coupled to the resistor, the second bias current source providing a second predetermined current; 
 a switch for disconnecting the second bias current source if the first value exceeds the second value; and 
 circuitry for reconnecting the second bias current source if the first value is lower than a third value; 
   a current controller for controlling the amount of current drawn by the device if the first value exceeds the variable value, comprising a gain control for controlling a gain of a pre-amplifier;   a second current controller for disconnecting the device if the first value exceeds a fourth value; and   wherein the first value is generated by a voltage drop across a resistor that is in line with the current being delivered to the device.   
     
     
         32 . A method for detecting and controlling current comprising:
 generating a first voltage from a sense resistor in line with a current being provided to a device;   generating a variable voltage from a reference resistor in line with a variable bias current source; and   generating a control signal to reduce the current being provided to the device if the first voltage is greater than the variable voltage.   
     
     
         33 . The method of  claim 32  further comprising reducing a bias current of the variable bias current source by a variable amount after generating the control signal. 
     
     
         34 . The method of  claim 33  further comprising:
 generating a third voltage from the reference resistor and the reduced bias current; and 
 terminating the generation of the control signal to reduce the current being provided to the device if the first voltage is less than the third voltage. 
 
     
     
         35 . The method of  claim 33  further comprising:
 generating a third voltage from a second reference resistor in line with a second bias current source; and 
 generating a control signal to disable the device if the first voltage is greater than the third voltage. 
 
     
     
         36 . The method of  claim 33  further comprising:
 reducing a bias current of the variable bias current source after generating the control signal; and 
 increasing the bias current if the first voltage is less than a third voltage. 
 
     
     
         37 . The method of  claim 32  further comprising:
 reducing a bias current of the variable bias current source after generating the control signal; 
 generating a third voltage from the reference resistor and the reduced bias current; 
 terminating the generation of the control signal to reduce the current being provided to the device if the first voltage is less than the third voltage; and 
 increasing the bias current if the first voltage is less than the third voltage.