Switched mode power supply control

1. A method of controlling a switch that is used to charge a capacitor that provides an output voltage (Vo), the switch having an inductor on an input side of the switch between a power source (Vi) and the switch, the method comprising:

initiating a switching cycle (k) including turning on the switch;

sensing a voltage (Vsns) representing current through the inductor;

using a reference voltage (Vref) as a basis for turning off the switch during the switching cycle (k) when Vsns exceeds Vref; and

setting an initial value of Vref at a beginning of the switching cycle based on at least one feature of an activation of the switch during at least one previous switching cycle (k−n) and reducing Vref during the switching cycle.

2. The method of claim 1 , comprising reducing Vref during the switching cycle using a rate such that Vref will be approximately equal to a voltage (Vpeak) corresponding to a preselected peak current threshold of the inductor at a time when Vsns equals Vpeak.

3. The method of claim 2 , wherein reducing Vref comprises using feedback information regarding a gate voltage of the switch during the switching cycle.

4. The method of claim 1 , wherein the at least one feature of the activation of the switch is based upon at least a duty cycle on time of the switch during the previous switching cycle (k−n).

5. The method of claim 4 , wherein the at least one feature of the activation of the switch is based on integrating a gate voltage (Vgate) of the switch over the on time of the switch during the previous switching cycle.

6. The method of claim 5 , comprising determining the on time of the switch during the previous switching cycle by detecting a peak of an integration of Vgate during the previous switching cycle.

7. The method of claim 1 , comprising determining the at least one feature of the activation of the switch for each of a plurality of previous switching cycles (k−n), wherein n=1, 2, . . . m;

averaging the determined at least one feature of the plurality of previous switching cycles (k−n); and

using the averaged at least one feature for setting the initial value of Vref.

8. The method of claim 1 , comprising

predetermining a desired peak current for the inductor; and

turning off the switch during the switching cycle (k) when the current through the inductor equals or exceeds the desired peak current for the inductor.

9. The method of claim 1 , comprising using the switch to control power to a fuel injector.

10. A switch control device, comprising:

a switch that is used to charge a capacitor that provides an output voltage (Vo);

an inductor on an input side of the switch between a power source and the switch;

a switching cycle control element that initiates activation of the switch at the beginning of a switching cycle (k);

a comparator that provides an indication of a relationship between a voltage (Vsns) representing current through the inductor and a reference voltage (Vref), the switching cycle control element turning off the switch during the switching cycle (k) based on the indication from the comparator when Vsns exceeds Vref;

at least one feedback loop that provides an indication of at least one feature of an activation of the switch during at least one previous switching cycle (k−n), wherein Vref is set to an initial value at a beginning of the switching cycle (k) based on the indication of the at least one feature during the previous switching cycle and Vref is reduced during the switching cycle.

11. The device of claim 10 , wherein

Vref is reduced during the switching cycle from the initial value at a rate such that Vref will be approximately equal to a voltage (Vpeak) corresponding to a preselected peak current threshold of the inductor at a time when Vsns equals Vpeak; and

the switching cycle control element turns off the switch when Vsns exceeds Vref.

12. The device of claim 11 , comprising a second feedback loop that provides information regarding a gate voltage of the switch during the switching cycle; and

wherein Vref is reduced at a rate based on the information regarding the gate voltage of the switch during the switching cycle.

13. The device of claim 10 , wherein the at least one feature of the activation of the switch is based upon at least a duty cycle ON-time of the switch during the previous switching cycle (k−n).

14. The device of claim 13 , wherein

the at least one feedback loop comprises an integrator that is configured to integrate a gate voltage (Vgate) of the switch over the on time of the switch during the previous switching cycle; and

the at least one feature of the activation of the switch is based on an output of the integrator.

15. The device of claim 14 , wherein

the at least one feedback loop comprises a peak detector configured to detect a peak of an integration of Vgate during the previous switching cycle; and

the detected peak of Vgate indicates an end of the on time of the switch during the previous switching cycle.

16. The device of claim 10 , wherein

the at least one feedback loop determines the at least one feature of the activation of the switch for each of a plurality of previous switching cycles (k−n), wherein n=1, 2, . . . m;

the at least one feedback loop is configured to determine an average of the determined at least one feature of the plurality of previous switching cycles (k−n); and

the averaged at least one feature is used for setting the initial value of Vref.

17. The device of claim 10 , wherein

the inductor has a predetermined desired peak current; and

the switching control element turns off the switch during the switching cycle (k) when a current through the inductor equals or exceeds the desired peak current for the inductor.

18. The device of claim 10 , comprising a load that is powered by the output of the switch.

19. The device of claim 18 , wherein the load comprises a fuel injector.