Capacitance determination in a switched mode power supply

1. A method of determining a measure of a total capacitance of one or more capacitive elements connected to an output of a switched mode power supply, comprising:

generating a voltage control signal to cause an output voltage controller to sweep a voltage (V out ) at the output of the switched mode power supply from an initial voltage value to a final voltage value;

generating a sampler control signal to control a current sampler to sample a current at the output only before or only after the output voltage has passed a threshold value (V start , V stop ) different from the initial and final values;

receiving sample values of the current at the output measured by the current sampler during the sweep of the output voltage; and

calculating an integrated current value representing a measure of the total capacitance using the received sample values, the threshold value being such as to reduce an error in the calculated integrated current value.

2. A method of determining a measure of a total capacitance of one or more capacitive elements connected to an output of a switched mode power supply, comprising:

generating a voltage control signal to cause an output voltage controller to sweep a voltage (V out ) at the output of the switched mode power supply from an initial voltage value to a final voltage value;

generating a sampler control signal to control a current sampler to sample a current at the output only after the output voltage has passed a first threshold value (V start ) and only before the output voltage has passed a second threshold value (V stop ) different from the first threshold value, the first and second threshold values both being different from the initial and final values;

receiving sample values of the current at the output measured by the current sampler during the sweep of the output voltage; and

calculating an integrated current value representing a measure of the total capacitance using the received sample values, the first and second threshold values being such as to reduce an error in the calculated integrated current value.

3. A method of determining a measure of a total capacitance of one or more capacitive elements connected to an output of a switched mode power supply, comprising:

generating a voltage control signal to cause an output voltage controller to sweep a voltage (V out ) at the output of the switched mode power supply from an initial voltage value to a final voltage value;

receiving sample values of a current at the output measured by a current sampler during the sweep of the output voltage;

processing the received sample values to select therefrom a subset of the sample values comprising current values measured only before or only after the output voltage has passed a threshold value (V start , V stop ) different from the initial and final values; and

calculating an integrated current value representing a measure of the total capacitance using the received sample values, the threshold value being such as to reduce an error in the calculated integrated current value, wherein the integrated current value is calculated using the selected subset of sample values.

4. A method of determining a measure of a total capacitance of one or more capacitive elements connected to an output of a switched mode power supply, comprising:

generating a voltage control signal to cause an output voltage controller to sweep a voltage (V out ) at the output of the switched mode power supply from an initial voltage value to a final voltage value;

receiving sample values of a current at the output measured by a current sampler during the sweep of the output voltage;

processing the received sample values to select therefrom a subset of the sample values comprising current values measured only after the output voltage has passed a first threshold value (V start ) and only before the output voltage has passed a second threshold value (V stop ) different from the first threshold value, the first and second threshold values both being different from the initial and final values; and

calculating an integrated current value representing a measure of the total capacitance using the received sample values, the first and second threshold values being such as to reduce an error in the calculated integrated current value, wherein the integrated current value is calculated using the selected subset of sample values.

5. The method according claim 4 , wherein the process of generating a voltage control signal comprises generating a voltage control signal to cause the output voltage controller to ramp the voltage (V out ) at the output of the switched mode power supply from the initial voltage value to the final voltage value.

6. The method according to claim 4 , wherein the process of generating a voltage control signal comprises generating a voltage control signal to sweep the output voltage (V out ) from an initial voltage value substantially equal to zero.

7. The method according to claim 4 , wherein the switched mode power supply comprises an output filter having a capacitor, and the method further comprises:

weighting the integrated current value with a weighting factor to give a weighted value;

calculating a load capacitance value by subtracting a capacitance value of said capacitor from the weighted value; and

setting at least one parameter of the switched mode power supply in dependence upon the calculated load capacitance value.

8. The method according to claim 4 , wherein each sample value used to calculate the integrated current value corresponds to the output current averaged over a switch period of the switched mode power supply.

9. A switched mode power supply controller for determining a measure of a total capacitance of one or more capacitive elements connected to an output of a switched mode power supply, comprising:

a signal generator operable to generate a voltage control signal for causing an output voltage controller to sweep a voltage (V out ) at the output of the switched mode power supply from an initial voltage value to a final voltage value;

a sampler control signal generator operable to generate a sampler control signal to control a current sampler to sample a current at the output only before or only after the output voltage has passed a threshold value (V start , V stop ) different from the initial and final values;

a receiver operable to receive sample values of the current at the output measured by the current sampler during the sweep of the output voltage (V out ); and

a current calculator operable to calculate an integrated current value representing a measure of the total capacitance using the received sample values, the threshold value being such as to reduce an error in the calculated integrated current value.

10. A switched mode power supply controller for determining a measure of a total capacitance of one or more capacitive elements connected to an output of a switched mode power supply, comprising:

a signal generator operable to generate a voltage control signal for causing an output voltage controller to sweep a voltage (V out ) at the output of the switched mode power supply from an initial voltage value to a final voltage value;

a sampler control signal generator operable to generate a sampler control signal to control a current sampler to sample a current at the output only after the output voltage has passed a first threshold value (V start ) and only before the output voltage has passed a second threshold value (V stop ) different from the first threshold value, the first and second threshold values both being different from the initial and final values;

a receiver operable to receive sample values of the current at the output measured by the current sampler during the sweep of the output voltage (V out ); and

a current calculator operable to calculate an integrated current value representing a measure of the total capacitance using the received sample values, the first and second threshold values being such as to reduce an error in the calculated integrated current value.

11. A switched mode power supply controller for determining a measure of a total capacitance of one or more capacitive elements connected to an output of a switched mode power supply, comprising:

a signal generator operable to generate a voltage control signal for causing an output voltage controller to sweep a voltage (V out ) at the output of the switched mode power supply from an initial voltage value to a final voltage value;

a receiver operable to receive sample values of a current at the output measured by a current sampler during the sweep of the output voltage (V out ); and

a current calculator operable to calculate an integrated current value representing a measure of the total capacitance using the received sample values,

wherein the current calculator is further operable to process the received sample values to select therefrom a subset of the sample values comprising current values measured only before or only after the output voltage has passed a threshold value (V start , V stop ) different from the initial and final values, the threshold value being such as to reduce an error in the calculated integrated current value, wherein the integrated current value is calculated using the selected subset of sample values.

12. A switched mode power supply controller for determining a measure of a total capacitance of one or more capacitive elements connected to an output of a switched mode power supply, comprising:

a signal generator operable to generate a voltage control signal for causing an output voltage controller to sweep a voltage (V out ) at the output of the switched mode power supply from an initial voltage value to a final voltage value;

a receiver operable to receive sample values of a current at the output measured by a current sampler during the sweep of the output voltage (V out ); and

a current calculator operable to calculate an integrated current value representing a measure of the total capacitance using the received sample values,

wherein the current calculator is further operable to process the received sample values to select therefrom a subset of the sample values comprising current values measured only after the output voltage has passed a first threshold value (V start ) and only before the output voltage has passed a second threshold value (V stop ) different from the first threshold value, the first and second threshold values both being different from the initial and final values and being such as to reduce an error in the calculated integrated current value, wherein the integrated current value is calculated using the selected subset of sample values.

13. The switched mode power supply controller according to claim 12 , wherein the signal generator is operable to generate a voltage control signal for causing the output voltage controller to ramp the voltage (V out ) at the output of the switched mode power supply from the initial voltage value to the final voltage value.

14. The switched mode power supply controller according to claim 12 , wherein the signal generator is operable to generate a voltage control signal to sweep the output voltage (V out ) from an initial voltage value substantially equal to zero.

15. The switched mode power supply controller according to claim 12 , wherein the switched mode power supply comprises an output filter having a capacitor, and wherein the current calculator is further operable to:

weight the integrated current value with a weighting factor to give a weighted value; and

calculate a load capacitance value by subtracting a capacitance value of said capacitor from the weighted value;

and wherein the switched mode power supply controller further comprises a parameter setting unit operable to set at least one parameter of the switched mode power supply in dependence upon the calculated load capacitance value.

16. The switched mode power supply controller according to claim 12 , wherein each sample value used to calculate the integrated current value corresponds to the output current averaged over a switch period of the switched mode power supply.

17. The switched mode power supply comprising a switched mode power supply controller according to claim 9 .