Voltage converter
A DC voltage converter, comprising: a multi-ratio capacitive converter; a linear voltage regulator in series with the multi-ratio capacitive converter; and a controller; the controller arranged to control the ratio of the multi-ratio capacitive converter dependent upon the voltage difference across the linear voltage regulator.
1. A DC voltage converter, comprising:
a multi-ratio capacitive converter;
a linear voltage regulator in series with the multi-ratio capacitive converter; and
a controller;
the controller arranged to control the ratio between the input voltage of the multi-ratio capacitive converter and the output voltage of the multi-ratio capacitive converter dependent upon the voltage difference between the output voltage of the linear voltage regulator and the input voltage of the linear voltage regulator.
2. A DC voltage converter according to claim 1 , wherein the controller controls the ratio of the multi-ratio capacitive converter such as to maintain the voltage difference across the linear voltage regulator within a predetermined voltage window.
3. A DC voltage converter according to claim 1 , wherein the predetermined voltage window is between a minimum voltage which is the drop-out voltage or close to and above the drop-out voltage of the linear voltage regulator, and a maximum voltage.
4. A DC voltage converter according to claim 3 , wherein the maximum voltage is dependent on the ratio of the multi-ratio capacitive converter.
5. A DC voltage converter according to claim 1 , wherein the controller controls the ratio of the multi-ratio capacitive converter such as to minimise the voltage difference across the linear voltage regulator.
6. A DC voltage converter according to claim 1 , wherein the controller controls the ratio of the multi-ratio capacitive converter such as to control the voltage difference across the linear voltage regulator to be close to and above the drop-out voltage of the linear voltage regulator.
7. A DC voltage converter according to any of claim 1 , wherein the controller comprises an analogue to digital converter and a digital processor.
8. A DC voltage converter according to claim 1 , wherein the controller comprises an internal state machine.
9. A DC voltage converter according to claim 1 , wherein the multi-ratio capacitive converter has four different ratios.
10. A DC voltage converter according to claim 1 , further comprising means for accommodating ripple on the output of the multi-ratio capacitive converter.
11. A method of converting DC voltage, the method comprising:
inputting an input voltage to a multi-ratio capacitive converter;
the multi-ratio capacitive converter converting the input voltage to an intermediate voltage;
feeding the intermediate voltage to a linear voltage regulator and also to a controller;
the linear voltage regulator regulating the intermediate voltage to an output voltage;
feeding the output voltage to the controller and also providing the output voltage as the overall output voltage; and
the controller controlling the ratio of between the input voltage of the multi-ratio capacitive converter and the intermediate voltage of the multi-ratio capacitive converter dependent upon the difference between the output voltage of the linear voltage regulator and the intermediate voltage of the multi-ratio capacitive converter.
12. A method according to claim 11 , wherein the controller controls the ratio of the multi-ratio capacitive converter such as to maintain the difference between the output voltage and the intermediate voltage within a predetermined voltage window.
13. A method according to claim 12 , wherein the predetermined voltage window is between a minimum voltage which is the drop-out voltage or close to and above the drop-out voltage of the linear voltage regulator, and a maximum voltage.
14. A method according to claim 11 , wherein the controller controls the ratio of the multi-ratio capacitive converter such as to minimise the difference between the output voltage and the intermediate voltage.
15. A method according to claim 11 , wherein the controller controls the ratio of the multi-ratio capacitive converter such as to control the difference between the output voltage and the intermediate voltage to be close to and above the drop-out voltage of the linear voltage regulator.