Synchronous-rectified DC to DC converter with improved current sensing

Abstract

A DC to DC buck pulse width modulator converter circuit includes an input, a high side output and a low side output. A high side switch is electrically connected between a common output node and a voltage supply, and controls a flow of current therethrough dependent upon the high side output. A low side switch is electrically connected between the common output node and ground, and controls a flow of current therethrough dependent upon the low side output. A virtual ground amplifier includes a second input electrically connected to ground. A current feedback resistor is electrically connected intermediate the common output node and a first input of the virtual ground amplifier. A variable impedance component is electrically connected to an output of the virtual ground amplifier and to the first input of the virtual ground amplifier. The impedance of the variable impedance component is varied dependent upon the output of the virtual ground amplifier. A sample and hold circuit is electrically connected intermediate the input of the pulse width modulator converter circuit and the variable impedance component. The sample and hold circuit sources a virtual ground current through the variable impedance component, and samples the virtual ground current.

1. A power supply, comprising:
 a DC to DC buck pulse width modulator converter circuit having an input, a high side output and a low side output;    a high side switch electrically connected intermediate a common output node and a voltage supply, said high side switch configured for controlling a flow of current therethrough dependent at least in part upon said high side output;    a low side switch electrically connected intermediate said common output node and ground, said low side switch configured for controlling a flow of current therethrough dependent at least in part upon said low side output;    a virtual ground amplifier having a first input, a second input and an output, said second input electrically connected to ground potential;    a current feedback resistor electrically connected intermediate said common output node and said first input of said virtual ground amplifier;    a variable impedance component electrically connected to said output of said virtual ground amplifier and to said first input of said virtual ground amplifier, said variable impedance component configured to vary in impedance dependent at least in part upon said output of said virtual ground amplifier; and    a sample and hold circuit electrically connected intermediate said DC to DC buck pulse width modulator converter circuit and said variable impedance component, said sample and hold circuit configured to source a virtual ground current through said variable impedence component and to sample and hold said virtual ground current.    
     
     
       2. The power supply of  claim 1 , further comprising a system control circuit, said system control circuit electrically coupled to said sample and hold circuit, said system control circuit issuing a first control signal, said sample and hold circuit being configured to sample and hold said virtual ground current in response to said first control signal, said sample and hold circuit issuing a sample signal dependent at least in part upon said virtual ground current, said system control circuit selectively activating and deactivating at least one of said high side switch and said low side switch dependent at least in part upon said sample signal. 
     
     
       3. The power supply of  claim 2 , wherein said system control circuit issues a sync signal, said sync signal resetting at least one of said high side switch and said low side switch. 
     
     
       4. The power supply of  claim 2 , further comprising an overcurrent detector circuit electrically coupled to said sample and hold circuit and to said system control circuit, said overcurrent detector circuit configured for issuing an overcurrent signal when said sample signal exceeds a pre-determined threshold. 
     
     
       5. The power supply of  claim 4 , wherein said system control circuit is configured for shutting down said DC to DC buck pulse width modulator converter circuit in response to said overcurrent signal. 
     
     
       6. The power supply of  claim 5 , wherein said system control circuit is configured to restart said DC to DC buck pulse width modulator converter circuit a predetermined period of time after receiving said overcurrent signal. 
     
     
       7. The power supply of  claim 2 , further comprising a power supply output, a voltage feedback resistor electrically connected intermediate said power supply output and said input of said DC to DC buck pulse width modulator converter circuit. 
     
     
       8. The power supply of  claim 7 , wherein said system control circuit includes a current mirror, said current mirror sourcing a droop current, said droop current being dependent at least in part upon said virtual ground current, said droop current being electrically coupled to said input of said DC to DC buck pulse width modulator converter circuit to modify a feedback voltage across said voltage feedback resistor and thereby adjust an output voltage of said power supply dependent at least in part upon said droop current. 
     
     
       9. The power supply of  claim 1 , further comprising a negative current source, said system control circuit issuing a second control signal, said second control signal being electrically coupled to said negative current source, said negative current source sourcing a negative current in response to said second control signal, said negative current flowing into said first input of said virtual ground amplifier to thereby connect said current feedback resistor to ground when current through said current feedback resistor is negative. 
     
     
       10. The power supply of  claim 1 , wherein said variable impedance component comprises one of a field effect transistor and an NPN-type transistor. 
     
     
       11. The power supply of  claim 1  further comprising an inductor having a first end and a second end, said first end electrically connected to said common output node, said second end configured for being electrically connected to a load. 
     
     
       12. A method of sensing an output current in a power supply, said power supply comprising a DC to DC buck pulse width modulator converter circuit having an input, a high side output and a low side output, said method comprising the steps of:
 electrically connecting a high side switch intermediate a common output node and a voltage supply, said high side switch configured for controlling a flow of current therethrough dependent at least in part upon said high side output;  
 a low side switch electrically connected intermediate said common output node and ground, said low side switch configured for controlling a flow of current therethrough dependent at least in part upon said low side output;  
 directing a sensed current to a virtual ground node, said sensed current comprising a known portion of the output current when said low side switch is in an on condition, said sensed current flowing into said virtual ground node in a first direction;  
 sourcing a virtual ground current into said virtual ground node, said virtual ground current flowing into said virtual ground node in a second direction, said second direction being opposite to said first direction, said virtual ground current being substantially equal to said sensed current and thereby canceling said sensed current at said virtual ground node; and  
 sampling and holding a value of said virtual ground current.  
 
     
     
       13. The method of  claim 12 , comprising the further step of selectively activating and deactivating at least one of said high side switch and said low side switch dependent at least in part upon said sampling and holding step. 
     
     
       14. The method of  claim 12 , comprising the further step of selectively activating and deactivating at least one of said high side switch and said low side switch on at least one of a periodic and a random basis. 
     
     
       15. The method of  claim 12 , comprising the further steps of:
 comparing said sampled and held value of said virtual ground current to a predetermined maximum limit; and  
 shutting down said power supply when said virtual ground current exceeds said predetermined maximum limit.  
 
     
     
       16. The method of  claim 15 , comprising the further step of restarting said power supply a predetermined period of time after said shutting down step. 
     
     
       17. The method of  claim 12 , comprising the further step of adjusting an output voltage of said power supply dependent at least in part upon said sampled and held value of said virtual ground current. 
     
     
       18. A power supply, comprising:
 A DC to DC buck pulse width modulator converter circuit having an input, a high side output and a low side output;    a high side switch electrically connected intermediate a common output node and a voltage supply, said high side switch configured for controlling a flow of current therethrough dependent at least in part upon said high side output;    a low side switch electrically connected to said common output node and to ground through a sense resistor, said low side switch configured for controlling a flow of current therethrough dependent at least in part upon said low side output;    a virtual ground amplifier having a first input, a second input and an output, said second input electrically connected to ground potential;    a current feedback resistor electrically connected intermediate said sense resistor and said first input of said virtual ground amplifier;    a variable impedance component electrically connected to said output of said virtual ground amplifier and to said first input of said virtual ground amplifier, said variable impedance component configured to vary in impedance dependent at least in part upon said output of said virtual ground amplifier; and    a sample and hold circuit electrically connected intermediate said DC to DC buck pulse width modulator converter circuit and said variable impedance component, said sample and hold circuit configured to source a virtual ground current through said variable impedance component and to sample and hold said virtual ground current.    
     
     
       19. A method for controlling a DC/DC converter having an output voltage and sourcing an output current to a load, the method comprising:
   receiving a sensed current at a node, the sensed current representative of the output current when a low side circuit is in an on condition, the sensed current flowing into the node in a first direction;        sourcing a current into the node, the sourced current flowing into the node in a second direction, the second direction being opposite to the first direction, the sourced current also representative of the output current;        sampling and holding a value of the sourced current;        receiving a signal representative of the output voltage;        issuing an error signal dependent at least in part upon the signal representative of the output voltage, the sampled and held value of the sourced current and a first reference signal;        issuing a comparison signal, the comparison signal based at least in part upon the error signal and a second reference signal; and        issuing a control signal based at least in part upon the comparison signal, wherein the control signal selectively controls the DC/DC converter.     
     
     
       20. The method of  claim 19 , wherein receiving a sensed current comprises receiving a current through a sense resistor. 
     
     
       21. The method of  claim 19 , wherein receiving a sensed current comprises receiving a current through a sense resistor coupled between a node of the low side circuit and the node receiving the sensed current. 
     
     
       22. The method of  claim 19 , wherein sourcing a current into the node comprises sourcing a current through a variable impedance component. 
     
     
       23. The method of  claim 19 , wherein the second reference signal is a ramp signal. 
     
     
       24. The method of  claim 19 , wherein issuing a control signal comprises issuing a control signal with an SR latch. 
     
     
       25. The method of  claim 19 , and further including summing at least two of the signal representative of the output voltage, the sampled and held value of the sourced current and the first reference signal prior to issuing an error signal. 
     
     
       26. A method of sensing an output current in a power supply, the power supply comprising a DC to DC converter circuit having an input, a high side output and a low side output, the method comprising:
   receiving a sensed current at a node, the sensed current representative of the output current when a low side circuit is in an on condition, the sensed current flowing into the node in a first direction;        sourcing a current into the node, the sourced current flowing into the node in a second direction, the second direction being opposite to the first direction, the sourced current also representative of the output current; and      
       
         sampling and holding a value of the sourced current. 
       
     
     
       27. The method of  claim 26 , wherein receiving a sensed current comprises receiving a current through a sense resistor. 
     
     
       28. The method of  claim 26 , wherein receiving a sensed current comprises receiving a current through a sense resistor coupled between a node of the low side circuit and the node receiving the sensed current. 
     
     
       29. The method of  claim 26 , wherein sourcing a current into the node comprises sourcing a current through a variable impedance component. 
     
     
       30. A method of controlling an output current in a power supply, the power supply comprising a converter circuit having an input, a high side output coupled to a high side switch and low side output coupled to a low side switch, the method comprising:
   generating a sensed current that is representative of the load current;        directing the sensed current to a current sense node in a first direction;        sourcing a current into the current sense node, the sourced current flowing into the current sense node in a second direction, the second direction being opposite to the first direction, the sourced current being substantially equal to the sensed current and thereby canceling the sensed current at the current sense node;        sampling and holding a value of the sourced current; and        generating control signals for the high side and low side outputs based on the sourced current.     
     
     
       31. The method of  claim 30 , wherein generating a sensed current comprises generating a sensed current when the low side switch is in an on condition. 
     
     
       32. The method of  claim 30 , wherein generating control signals comprises generating signals for activating and deactivating at least one of the high side switch and the low side switch dependent at least in part upon the value of the sampling and holding of the sourced current. 
     
     
       33. The method of  claim 30 , wherein generating control signals comprises activating and deactivating at least one of the high side switch and the low side switch on at least one of a periodic and a random basis. 
     
     
       34. The method of  claim 30 , further comprising:
   comparing the sampled and held value of the sourced current to a selected value; and        shutting down the power supply when the sourced current exceeds the selected value.     
     
     
       35. The method of  claim 34 , further comprising restarting the power supply a selected period of time after shutting down the power supply. 
     
     
       36. The method of  claim 30 , wherein generating control signals comprises generating control signals to adjust an output voltage of the power supply dependent at least in part upon the sampled and held value of the sourced current.