Detection of the supply state of a load supplied by a variable voltage

Abstract

A method and a circuit for detecting the state of supply of a load by a variable voltage, including measuring the difference between values representative of the variable supply voltage and of a voltage across the load.

1 . A method for detecting the state of supply of a load by a variable voltage, comprising: 
 measuring logarithmic values representative of the variable supply voltage and of a voltage across the load; and    calculating the difference between said logarithmic values.    
   
   
       2 . The method of  claim 1 , wherein an analog voltage representing said difference is compared with predetermined characteristic operation thresholds of the circuit.  
   
   
       3 . The method of  claim 2 , wherein times when said analog voltage is taken into account are synchronized on the variable supply voltage.  
   
   
       4 . The method of  claim 1 , wherein an absolute value of an analog voltage representing said difference is compared with predetermined characteristic operation thresholds of the circuit.  
   
   
       5 . The method of  claim 4 , wherein said absolute value is averaged before being compared with said thresholds.  
   
   
       6 . The method of  claim 1 , wherein the variable supply voltage is an A.C. voltage.  
   
   
       7 . The method of  claim 1 , wherein the variable supply voltage is a non-D.C. unipolar voltage.  
   
   
       8 . A circuit for supervising the state of supply of a load by a variable voltage in series with at least one first switch, comprising: 
 means for measuring values representative of the variable voltage and a voltage across the load and for making logarithmic said values; and    an element for calculating a difference between said logarithmic values.    
   
   
       9 . The circuit of  claim 8 , wherein a second switch is in series with the load and the first switch.  
   
   
       10 . The circuit of  claim 8 , comprising an element for calculating an absolute value of an output voltage of said element for calculating the difference.  
   
   
       11 . The circuit of  claim 10 , wherein said absolute value is averaged.  
   
   
       12 . The circuit of  claim 8 , comprising at least one comparator with at least one characteristic operation threshold of the assembly.