Temperature limited current driver

Abstract

A driver circuit includes a temperature sensor configured to generate a first voltage representative of current operating temperature of the driver circuit. The driver circuit also includes an amplifier configured to compare the first voltage to a second voltage representative of an upper threshold operating temperature, and to generate a control signal based upon the comparison. A variable current source is configured to generate a load current as a function of the control signal. The amplifier generates the control signal so as to cause the variable current source to generate the load current as having a magnitude equal to an upper threshold, when the first voltage is less than the second voltage.

1 . A driver circuit, comprising:
 a temperature sensor configured to generate a first voltage representative of current operating temperature of the driver circuit;   an amplifier configured to compare the first voltage to a second voltage representative of an upper threshold operating temperature, and to generate a control signal based upon the comparison; and   a variable current source configured to generate a load current as a function of the control signal;   wherein the amplifier generates the control signal so as to cause the variable current source to generate the load current as having a magnitude equal to an upper threshold when the first voltage is less than the second voltage.   
     
     
         2 . The driver circuit of  claim 1 , wherein the amplifier generates the control signal so as to cause the variable current source to generate the load current as having a magnitude that is a function of the first and second voltages. 
     
     
         3 . The driver circuit of  claim 1 , wherein the amplifier generates the control signal so as to cause the variable current source to generate the load current as having a variable magnitude that is a function of the first and second voltages. 
     
     
         4 . The driver circuit of  claim 3 , wherein the amplifier generates the control signal so as to cause the variable current source to generate the load current as having a magnitude that is decreasing until the first and second voltages are equal. 
     
     
         5 . The driver circuit of  claim 3 , wherein the amplifier generates the control signal so as to cause the variable current source to generate the control signal so as cause the variable current source to maintain the magnitude of the load current at a level at which the first and second voltages are equal. 
     
     
         6 . The driver circuit of  claim 1 , wherein the temperature sensor comprises a bipolar junction transistor. 
     
     
         7 . The driver circuit of  claim 1 , further comprising a voltage divider coupled between a bandgap voltage and ground, with the second voltage being generated at a center tap of the voltage divider. 
     
     
         8 . The driver circuit of  claim 7 , further comprising a bandgap voltage generator generating the bandgap voltage. 
     
     
         9 . A driver circuit, comprising:
 a temperature sensing circuit configured to generate a first voltage representative of current operating temperature of the driver circuit;   a voltage controlled current source configured to compare the first voltage to a second voltage representative of an upper threshold operating temperature, and to generate a control signal based upon the comparison; and   an output stage generating a load current as a function of the control signal;   wherein the voltage controlled current source generates the control signal so as to cause output stage to generate the load current as having a magnitude equal to an upper threshold when the first voltage is less than the second voltage.   
     
     
         10 . The driver circuit of  claim 9 , wherein the voltage controlled current source generates the control signal so as to cause the output stage to generate the load current as having a magnitude that is a function of the first and second voltages. 
     
     
         11 . The driver circuit of  claim 9 , wherein the voltage controlled current source generates the control signal so as to cause the output stage to generate the load current as having a variable magnitude that is a function of the first and second voltages. 
     
     
         12 . The driver circuit of  claim 11 , wherein the voltage controlled current source generates the control signal so as to cause the output stage to generate the load current as having a magnitude that is decreasing until the first and second voltages are equal. 
     
     
         13 . The driver circuit of  claim 11 , wherein the voltage controlled current source generates the control signal so as to cause the output stage to generate the control signal so as cause the output stage to maintain the magnitude of the load current at a level at which the first and second voltages are equal. 
     
     
         14 . The driver circuit of  claim 9 , wherein the temperature sensing circuit comprises a bipolar junction transistor having a collector coupled to a first supply voltage, a base coupled to a bandgap voltage, and an emitter coupled to the voltage controlled current source. 
     
     
         15 . The driver circuit of  claim 14 , further comprising a resistor coupled between the emitter of the bipolar junction transistor and ground, with the first voltage being generated across the resistor. 
     
     
         16 . The driver circuit of  claim 9 , wherein the voltage controlled current source comprises an operational transconductance amplifier having a non-inverting terminal coupled to the second voltage and an inverting terminal coupled to the first voltage. 
     
     
         17 . A method of generating a load current for driving a load, the method comprising:
 generating a first voltage representative of a current operating temperature;   comparing the first voltage to a second voltage representative of an upper threshold operating temperature; and   generating the load current having a magnitude depending upon a relationship between the first voltage and the second voltage.   
     
     
         18 . The method of  claim 17 , wherein the load current is generated as having a magnitude equal to an upper threshold when the first voltage is less than the second voltage. 
     
     
         19 . The method of  claim 17 , wherein the load current is generated as having a magnitude with a decreasing slope when the first voltage is greater than the second voltage. 
     
     
         20 . The method of  claim 17 , further comprising, when the first and second voltages are equal, the load current is generated as having a magnitude that remains at a level at which the first and second voltages are equal. 
     
     
         21 . The method of  claim 20 , wherein generating the load current as having a magnitude that remains at a level at which the first and second voltages are equal comprises continuously varying a magnitude of the load current such that the first and second voltages remain equal.