Voice coil motor temperature sensing circuit to reduce catastrophic failure due to voice coil motor coil shorting to ground

Abstract

An electrical circuit includes: a controlled switch; one or more temperature sensors in thermal contact with the controlled switch; and a control unit configured to: receive a temperature signal from the one or more temperature sensors; compare the received temperature signal to a predetermined threshold; and in response to the received temperature signal exceeding the predetermined threshold, render the controlled switch inoperative.

What is claimed is: 
     
         1 . An electrical circuit, comprising:
 a plurality of controlled switches;   a plurality of temperature sensors in thermal contact with each of the plurality of controlled switches; and   a control unit configured to:
 calculate an average temperature for each of the plurality of controlled switches based on temperature signals received from the plurality of temperature sensors associated with each of the plurality of controlled switches; 
 compare the average temperature of each of the plurality of controlled switches to the average temperature of every other one of the plurality of controlled switches; 
 in response to a variation in the average temperature of any of the plurality of controlled switches greater than a predetermined amount compared to the average temperature of any other one of the plurality of controlled switches, render the plurality of controlled switches inoperative; and 
 in response to the variation in the average temperature exceeding the predetermined amount, record an over-temperature event. 
   
     
     
         2 . The electrical circuit of  claim 1 , wherein the predetermined amount of variation in the average temperature is variable based on operating conditions of the electrical circuit. 
     
     
         3 . The electrical circuit of  claim 2 , wherein the control unit is further configured to compare the variation in the average temperature to one or more threshold values stored in a memory. 
     
     
         4 . The electrical circuit of  claim 3 , wherein the one or more threshold values stored in the memory comprise a temperature profile for the plurality of controlled switches characterized over different operating conditions. 
     
     
         5 . The electrical circuit of  claim 1 , wherein the control unit is configured to record the over-temperature event in a designated portion of a non-volatile storage medium. 
     
     
         6 . The electrical circuit of  claim 1 , wherein the control unit is further configured to cause the electrical circuit to initiate one or more predetermined operations prior to rendering the plurality of controlled switches inoperative. 
     
     
         7 . The electrical circuit of  claim 1 , wherein the plurality of controlled switches are field effect transistors (FETs). 
     
     
         8 . A method for sensing an overcurrent condition in an electrical circuit, the method comprising:
 monitoring temperature of a plurality of circuit elements;   calculating an average temperature for each of the plurality of circuit elements;   comparing the average temperature of each of the plurality of circuit elements to the average temperature of every other one of the plurality of circuit elements;   in response to a variation in the average temperature of any of the plurality of circuit elements greater than a predetermined amount compared to the average temperature of any other one of the plurality of circuit elements, rendering the plurality of circuit elements inoperative, and   in response to the variation in the monitored temperature of any of the plurality of circuit elements exceeding the predetermined amount, recording an over-temperature event.   
     
     
         9 . The method of  claim 8 , wherein the predetermined amount of variation in the average temperature is variable based on operating conditions of the electrical circuit. 
     
     
         10 . The method of  claim 9 , further comprising comparing the variation in the average temperature to one or more threshold values stored in a memory. 
     
     
         11 . The method of  claim 10 , wherein the one or more threshold values stored in the memory comprise a temperature profile for the plurality of circuit elements characterized over different operating conditions. 
     
     
         12 . The method of  claim 8 , wherein the recording the over-temperature event comprises recording the over-temperature event in a designated portion of a non-volatile storage medium. 
     
     
         13 . The method of  claim 8 , further comprising, causing the electrical circuit to initiate one or more predetermined operations prior to rendering the one or more circuit elements inoperative. 
     
     
         14 . A data storage device (DSD), comprising:
 a plurality of field effect transistors (FETs) configured as an H-bridge circuit;   two or more temperature sensors integrated with each of the plurality of FETs; and   a control unit configured to:
 calculate an average temperature for each of the plurality of FETs based on temperature signals received from the two or more temperature sensors associated with each of the plurality of FETs; 
 compare the average temperature of each of the plurality of FETs to the average temperature of every other one of the plurality of FETs; 
 in response to a variation in the average temperature of any one of the plurality of FETs greater than a predetermined amount compared to the average temperature of any other one of the plurality of FETs, render the plurality of FETs inoperative; and 
 in response to the variation in the average temperature exceeding the predetermined amount, record an over-temperature event. 
   
     
     
         15 . The DSD of  claim 14 , wherein the predetermined amount of variation in the average temperature is variable based on operating conditions of the H-bridge circuit. 
     
     
         16 . The DSD of  claim 15 , wherein the control unit is further configured to compare the variation in the average temperature to one or more threshold values stored in a memory. 
     
     
         17 . The DSD of  claim 16 , wherein the one or more threshold values stored in the memory comprise a temperature profile for the plurality of FETs characterized over different operating conditions of the H-bridge circuit. 
     
     
         18 . The DSD of  claim 14 , wherein the control unit is configured to record the over-temperature event in a designated portion of a non-volatile storage medium. 
     
     
         19 . The DSD of  claim 14 , wherein the control unit is further configured to cause the DSD to initiate one or more predetermined operations prior to rendering the plurality of FETs inoperative. 
     
     
         20 . The DSD of  claim 19 , wherein at least one of the one or more predetermined operations is an emergency power-off retract of a read-write head actuator arm.