Current regulation in motors

Abstract

A motor controller that includes a processing device and a drive circuit. The drive circuit may include a plurality of switches, a motor winding, and a current sensor coupled together in an H-bridge configuration. The processing device is configured to cause a drive current to drive through the motor winding for a minimum amount of time. The processing device is also configured to compare the current through the current sensor to a threshold value at the minimum amount of time. The processing device is also configured to, based on the current being at or above the threshold value at the minimum amount of time, stop the drive current for an off period of time and cause a first decay of the current for a first percentage of the off period of time and a first slow decay for a second percentage of the off period of time.

What is claimed is: 
     
         1 . A process of operating a drive circuit that includes:
 a voltage source;   a ground;   a sense resistor having a first node and a second node connected to the ground;   a first transistor having a first node connected to the voltage source, a second node, and a gate;   a second transistor having a first node connected to the second node of the first transistor, a second node connected to the first node of the sense resistor, and a gate;   a third transistor having a first node connected to the voltage source, a second node coupled to the second node of the first transistor and the first node of the second transistor, and a gate;   a fourth transistor having a first node connected to the second node of the third transistor and coupled to the second node of the first transistor and the first node of the second transistor, a second node connected to the first node of the sense resistor, and a gate; and   a processing device coupled to the gates of the first, second, third, and fourth transistors;   
       the process comprising:
 causing a drive current to flow through the first and fourth transistors for a minimum on period of time; 
 sensing a current flow through the sense resistor at the end of the on period of time; 
 comparing the current flow through the sense resistor to a threshold; 
 causing no current to flow through the first transistor during an off period of time following the on period of time; 
 during the off period of time, causing a fast decay current to flow through the second and third transistors for a first duration of time and causing a slow decay current to flow through the second and fourth transistors for a second duration of time; and 
 varying the first duration of time and the second duration of time based on the comparison of the sensed current flow to the threshold level for a current cycle and an immediate previous cycle. 
 
     
     
         2 . The process of  claim 1  including repeating the process for cycles and in which the varying includes shortening the first duration and lengthening the second duration for that cycle based on sensing a drive current below the threshold for a cycle. 
     
     
         3 . The process of  claim 1  including repeating the process for cycles and in which the varying includes reducing the first duration to zero and lengthening the second duration to the off period for a cycle based on the drive current being below the threshold level for that cycle. 
     
     
         4 . The process of  claim 1  including repeating the process for cycles and in which the varying includes causing the first duration to be equal to the minimum on time for a cycle. 
     
     
         5 . The process of  claim 1  including repeating the process for cycles and in which the varying includes lengthening the first duration and shortening the second duration for a cycle based on the drive current being above the threshold level for that cycle and an immediate previous cycle. 
     
     
         6 . The process of  claim 1  including changing the threshold level. 
     
     
         7 . A process of operating a drive circuit comprising:
 in one cycle, causing a drive current to flow through first and second transistors for a minimum on period of time and causing no current to flow through the first transistor during an off period of time following the on period of time;   sensing the drive current through the first transistor at the end of the on period of time;   comparing the sensed drive current to a threshold;   during the off period of time, causing a fast decay current to flow through a third transistor and a fourth transistor for a first duration of time and causing a slow decay current to flow through the second and third transistors for a second duration of time; and   varying the first duration of time and the second duration of time based on the comparison of the sensed drive current to the threshold level for a current cycle and an immediate previous cycle.   
     
     
         8 . The process of  claim 7  including repeating the process for cycles and in which the varying includes shortening the first duration and lengthening the second duration for that cycle based on sensing a drive current below the threshold for a cycle. 
     
     
         9 . The process of  claim 7  including repeating the process for cycles and in which the varying includes reducing the first duration to zero and lengthening the second duration to the off period for a cycle based on the drive current being below the threshold level for that cycle. 
     
     
         10 . The process of  claim 7  including repeating the process for cycles and in which the varying includes causing the first duration to be equal to the minimum on time for a cycle. 
     
     
         11 . The process of  claim 7  including repeating the process for cycles and in which the varying includes lengthening the first duration and shortening the second duration for a cycle based on the drive current being above the threshold level for that cycle and an immediate previous cycle. 
     
     
         12 . The process of  claim 7  including changing the threshold level. 
     
     
         13 . A circuit comprising:
 a voltage source;   a ground;   a sense resistor having a first node and a second node connected to the ground;   a first transistor having a first node connected to the voltage source, a second node, and a gate;   a second transistor having a first node connected to the second node of the first transistor, a second node connected to the first node of the sense resistor, and a gate;   a third transistor having a first node connected to the voltage source, a second node coupled to the second node of the first transistor and the first node of the second transistor, and a gate;   a fourth transistor having a first node connected to the second node of the third transistor and coupled to the second node of the first transistor and the first node of the second transistor, a second node connected to the first node of the sense resistor, and a gate; and   a processing device coupled to the gates of the first, second, third, and fourth transistors, the processing device including instructions for:   in one cycle, causing a drive current to flow through first and fourth transistors for a minimum on period of time and causing no current to flow through the first transistor during an off period of time following the on period of time;   sensing the drive current through the first transistor at the end of the on period of time;   comparing the sensed drive current to a threshold;   during the off period of time, causing a fast decay current to flow through a third transistor and a fourth transistor for a first duration of time and causing a slow decay current to flow through the second and third transistors for a second duration of time; and   varying the first duration of time and the second duration of time based on the comparison of the sensed drive current to the threshold level for a current cycle and an immediate previous cycle.   
     
     
         14 . The process of  claim 13  in which the instructions include repeating the process for cycles and in which the varying includes shortening the first duration and lengthening the second duration for that cycle based on sensing a drive current below the threshold for a cycle. 
     
     
         15 . The process of  claim 13  in which the instructions include repeating the process for cycles and in which the varying includes reducing the first duration to zero and lengthening the second duration to the off period for a cycle based on the drive current being below the threshold level for that cycle. 
     
     
         16 . The process of  claim 13  in which the instructions include repeating the process for cycles and in which the varying includes causing the first duration to be equal to the minimum on time for a cycle. 
     
     
         17 . The process of  claim 13  in which the instructions include repeating the process for cycles and in which the varying includes lengthening the first duration and shortening the second duration for a cycle based on the drive current being above the threshold level for that cycle and an immediate previous cycle. 
     
     
         18 . The process of  claim 13  in which the instructions include changing the threshold level.