Highly Accurate Over Current Fault Protection for Battery Packs

Abstract

This disclosure relates generally to the field of providing highly accurate over current fault protection in charging systems and, more particularly, to systems in which the charge over current protection (COCP) and discharge over current protection (DOCP) circuitry in electronic devices are particularly resilient to variations in field-effect transistor (FET) resistance with temperature, gate drive, and/or process shift; variations in printed circuit board (PCB) resistance; and variations in integrated circuit (IC) trip voltages. Through the use of novel circuit designs disclosed herein that effectively “bypass” the traditional “power FETs” that control the current flow to the battery pack(s) of the electronic device using a novel “sense FET” concept, the major sources of error in current sensing may be eliminated without compromising any safety features of the electronic device, thus allowing for more accurate over current fault protection systems for battery packs across a wide range of operating conditions and temperatures.

What is claimed is: 
     
         1 . A battery pack comprising:
 at least one cell;   a power switching circuit comprising one or more switching devices configured to selectively enable or disable current flow through the at least one cell;   a protection circuit having one or more inputs configured to measure one or more electrical parameters of the battery pack and one or more outputs configured to control the power switching circuit responsive to the one or more measured electrical parameters; and   a sensing circuit coupled to the one or more inputs of the protection circuit so as to permit the protection circuit to measure the one or more electrical parameters bypassing the power switching circuit.   
     
     
         2 . The battery pack of  claim 1  further comprising a current sensing resistor coupled in series with the at least one cell, wherein the one or more inputs of the protection circuit comprise a first input coupled to a first terminal of the current sensing resistor and a second input coupled to a second terminal of the current sensing resistor by the sensing circuit, the first and second inputs being configured to measure current through the at least one cell. 
     
     
         3 . The battery back of  claim 2  wherein the protection circuit is further configured to disable current flow through the at least one cell responsive to an overcurrent condition sensed via the current sensing resistor. 
     
     
         4 . The battery pack of  claim 2  wherein the sensing circuit comprises one or more switching devices coupled to the protection circuit and configured to operate in conjunction with corresponding one or more switches of the power switching circuit. 
     
     
         5 . The battery pack of  claim 1  wherein the one or more inputs of the protection circuit comprise first and second inputs configured to measure a voltage of the at least one cell. 
     
     
         6 . The battery pack of  claim 5  wherein the protection circuit is further configured to disable current flow through the at least one cell responsive to an unacceptable cell voltage level. 
     
     
         7 . The battery pack of  claim 1  wherein the sensing circuit comprises one or more switching devices coupled to the protection circuit and configured to operate in conjunction with corresponding one or more switches of the power switching circuit. 
     
     
         8 . A battery pack comprising:
 at least one cell;   a first power switching circuit coupled in series with the at least one cell and configured to selectively enable or disable current flow through the at least one cell responsive to an overcurrent protection circuit;   a first sensing circuit coupled a current sensing resistor in series with the at least one cell and to one or more inputs of the overcurrent protection circuit so as to permit the overcurrent protection circuit to bypass the power switching circuit to measure current through the at least one cell;   a second power switching circuit coupled in series with the at least one cell and configured to selectively enable or disable current flow through the at least one cell responsive to an overtemperature protection circuit; and   a second sensing circuit coupled to a temperature cutoff device in series with the at least one cell and to one or more inputs of the overtemperature protection circuit so as to permit the overtemperature protection circuit to bypass the second power switching circuit to measure current through the temperature cutoff device.   
     
     
         9 . The battery back of  claim 8  wherein the overcurrent protection circuit is configured to disable current flow through the at least one cell responsive to an overcurrent condition sensed via the current sensing resistor. 
     
     
         10 . The battery pack of  claim 8  wherein the overtemperature protection circuit is configured to disable current flow through the at least one cell responsive to an overtemperature condition sensed via the temperature cutoff device. 
     
     
         11 . The battery pack of  claim 8  wherein the first and second power switching circuits each comprise respective first and second switching devices, the first switching devices being connected to selectively enable or disable current in a first direction and the second switching device being connected so as to selectively enable or disable current in a second direction opposite the first direction. 
     
     
         12 . The battery pack of  claim 11  wherein the first and second sensing circuits each comprise first and second switching devices configured to operate in conjunction with corresponding first and second switches of the respective first and second power switching circuits. 
     
     
         13 . The battery pack of  claim 12  wherein at least one of the overcurrent protection circuit and the overtemperature protection circuit comprise one or more inputs configured to measure a voltage of the at least one cell. 
     
     
         14 . The battery pack of  claim 13  wherein the at least one of the overcurrent protection circuit and the overtemperature protection circuit comprising one or more inputs configured to measure a voltage of the at least one cell is further configured to disable current flow through the at least one cell responsive to an unacceptable cell voltage level. 
     
     
         15 . A battery pack comprising:
 at least one cell;   a first protection circuit having one or more inputs configured to measure one or more electrical parameters of the battery pack;   first means for selectively enabling or disabling current flow through the at least one cell responsive to the protection circuit; and   first means for permitting the protection circuit to bypass the power switching circuit to measure the one or more electrical parameters.   
     
     
         16 . The battery pack of  claim 15  wherein the first means for selectively enabling or disabling current flow through the at least one cell responsive to the protection circuit comprises a power field effect transistor (FET) circuit having a first FET configured to selectively enable or disable current in a first direction and a second FET configured to selectively enable or disable current in a second direction opposite the first direction. 
     
     
         17 . The battery pack of  claim 15  wherein the first means for permitting the protection circuit to bypass the power switching circuit to measure the one or more electrical parameters comprises:
 a current sensing resistor coupled in series with the at least one cell; 
 a sense field effect transistor (FET) circuit having a first FET configured to selectively pass or block current in a first direction and a second FET configured to selectively pass or block current in a second direction opposite the first direction; 
 wherein a first terminal of the sense FET circuit is coupled to a first terminal of the current sensing resistor and a second terminal of the sense FET circuit is coupled to the first protection circuit. 
 
     
     
         18 . The battery pack of  claim 15  further comprising:
 a second protection circuit having one or more inputs configured to measure one or more electrical parameters of the battery pack; 
 second means for selectively enabling or disabling current flow through the at least one cell responsive to the protection circuit; and 
 second means for permitting the protection circuit to bypass the power switching circuit to measure the one or more electrical parameters. 
 
     
     
         19 . The battery pack of  claim 18  wherein the first means for selectively enabling or disabling current flow through the at least one cell responsive to the protection circuit comprises a power field effect transistor (FET) circuit having a first FET configured to selectively enable or disable current in a first direction and a second FET configured to selectively enable or disable current in a second direction opposite the first direction. 
     
     
         20 . The battery pack of  claim 18  wherein the first means for permitting the protection circuit to bypass the power switching circuit to measure the one or more electrical parameters comprises:
 a current sensing resistor coupled in series with the at least one cell; 
 a sense field effect transistor (FET) circuit having a first FET configured to selectively pass or block current in a first direction and a second FET configured to selectively pass or block current in a second direction opposite the first direction; 
 wherein a first terminal of the sense FET circuit is coupled to a first terminal of the current sensing resistor and a second terminal of the sense FET circuit is coupled to the first protection circuit.