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

1. A method for detecting, in a circuit, a state of supply of a load supplied by a variable supply voltage and coupled to at least one switch controlling the load, the method comprising:

measuring at least one logarithmic value representative of the variable supply voltage and at least one logarithmic value representative of a voltage across the load;

calculating a difference between said logarithmic values; and

detecting at least one of the state of the supply of the load and a state of the at least one switch controlling the load based on the calculated difference, wherein the detecting comprises comparing the calculated difference with a plurality of thresholds.

2. The method of claim 1 , wherein the difference is an analog voltage, and wherein the plurality of thresholds comprise predetermined characteristic operation thresholds of the circuit.

3. The method of claim 2 , wherein said analog voltage is calculated at times that are synchronized on the variable supply voltage.

4. The method of claim 1 , wherein the calculated difference is represented as an absolute value of an analog voltage, and wherein the plurality of thresholds comprise predetermined characteristic operation thresholds of the circuit.

5. The method of claim 4 , wherein said absolute value is averaged before being compared with the plurality of 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 a state of supply, by a variable supply voltage, of a load in series with at least one first switch, the circuit comprising:

means for measuring values of the variable supply voltage and of a voltage across the load and for making said measured values logarithmic; and

an element for calculating a difference between said logarithmic values to identify at least one defect in at least one of the load and the at least one first switch based on the calculated difference, wherein identifying the at least one defect comprises comparing the calculated difference with at least one threshold.

9. The circuit of claim 8 , further comprising a second switch that is in series with the load and the at least one first switch.

10. The circuit of claim 8 , further 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 , further comprising at least one comparator for comparing the calculated difference with the at least one threshold comprising at least one characteristic operation threshold of the circuit.

13. The circuit of claim 8 configured to operate at the variable supply voltage of different frequencies and/or different amplitudes.

14. A circuit for supervising a state of supply of a load supplied by a variable voltage, wherein the load is in series with at least one first switch coupled between at least two terminals of application of the variable supply voltage, the circuit comprising:

at least one first component for measuring first values of the variable voltage and second values of a voltage across the load and for making the first and second values logarithmic; and

at least one second component for calculating a difference between the first logarithmic values and the second logarithmic values to determine at least one of the state of the supply of the load and a state of the at least one first switch, wherein the determining comprises comparing the calculated difference with a plurality of thresholds.

15. The circuit of claim 14 , wherein the at least one first component comprises a plurality of diodes that make the first and second values logarithmic.

16. The circuit of claim 15 , wherein the plurality of diodes comprise:

a first and a second diodes coupled in anti-parallel between a first input terminal of the circuit and a terminal from the at least two terminals of application of the variable supply voltage; and

a third and a fourth diodes coupled in anti-parallel between a second input terminal of the circuit and a terminal of the load.

17. The circuit of claim 15 , wherein waveforms obtained on an output of the at least one second component are considerably flattened.

18. The circuit of claim 14 , wherein a first resistor is coupled in parallel with the load and a second resistor is coupled between the load and an input terminal of the circuit.

19. The circuit of claim 17 , wherein a value of the first resistor is higher than a value of the second resistor.

20. The circuit of claim 14 , wherein the at least one second component comprises an operational amplifier.

21. The method of claim 1 , wherein measuring the at least one logarithmic value representative of the variable supply voltage and the at least one logarithmic value representative of the voltage across the load comprises utilizing a plurality of diodes.

22. The method of claim 21 , wherein the plurality of diodes comprise:

a first and a second diodes coupled in anti-parallel between a first input terminal of the circuit and a terminal from at least two terminals of application of the variable supply voltage; and

a third and a fourth diodes coupled in-anti-parallel between a second input terminal of the circuit and a terminal of the load.