Method of operating a switching power converter
View Patent ↗A method of operating a switching power converter circuit having first and second transistors connected to an inductor, where a conduction control signal is selectively applied to the second transistor as a function of an operation of the first transistor during a conduction cycle. The decision on whether to provide a conduction control signal to the second transistor is made in one mode of operation as a function of the length of the first conduction control signal applied to the first transistor during the conduction cycle. In another mode of operation a comparison is made of the on-to-off conduction transition time of the second transistor to the length of time remaining in a conduction cycle after the first transistor ceases to conduct.
1. A method of operating a switching power converter circuit including an inductor, a first transistor having a terminal connected to the inductor, a diode having one terminal connected to the common connection between the first transistor and the inductor, a second transistor connected in parallel with the diode, each transistor having a control terminal for receiving a conduction control signal in a conduction cycle having a length, the method comprising:
providing a first conduction control signal to the control terminal of the first transistor during at least a portion of the conduction cycle to cause the first transistor to conduct; and
selectively providing a second conduction control signal to the control terminal of the second transistor as a function of an operation of the first transistor during the conduction cycle.
2. The method of claim 1 , wherein the function of an operation of the power converter considered in a decision to selectively provide the second conduction control signal to the second transistor is a length of the first conduction control signal applied to the first transistor during the conduction cycle.
3. The method of claim 2 , further comprising providing the second conduction control signal to the control terminal of the second transistor if an on-to-off conduction transition time of the second transistor is less than a length of time remaining in a conduction cycle after a cessation of conduction of the first transistor in the conduction cycle.
4. The method of claim 2 , further comprising:
measuring an on-to-off conduction transition time of the second transistor;
storing the measured on-to-off conduction time of the second transistor; and
providing the second conduction control signal to the control terminal of the second transistor if the amount of time remaining in a conduction cycle is greater than the stored on-to-off conduction time of the second transistor.
5. The method of claim 2 , further comprising:
storing an on-to-off conduction time of the second transistor; and
providing the second conduction control signal to the control terminal of the second transistor if the amount of time remaining in a conduction cycle after the first transistor ceases conduction is greater than the stored on-to-off conduction time of the second transistor.
6. The method of claim 1 , further comprising:
calculating a length of time required for a current in the inductor to cease flowing if the second transistor were not caused to conduct;
comparing an on-to-off conduction transition time of the second transistor with the length of time for the current in the inductor to cease flowing;
causing the second transistor to conduct if the on-to-off transition time of the second transistor is less than a length of time for the conduction of current in the inductor to cease if the second transistor was not caused to conduct.
7. A method of operating a switching power converter circuit including an inductor, a first transistor having a terminal connected to a terminal of the inductor, and a second transistor having a terminal connected to the common connection between the first transistor and the inductor, each transistor having a control terminal for receiving a conduction control signal in a conduction cycle having a length, the method comprising:
providing a first conduction control signal to the control terminal of the first transistor during at least a portion of the conduction cycle to cause the first transistor to conduct; and
selectively providing a second conduction control signal to the control terminal of the second transistor as a function of an operation of the first transistor during the conduction cycle.
8. The method of claim 7 , wherein the function of an operation of the power converter considered in a decision to selectively provide the second conduction control signal to the second transistor is a length of the first conduction control signal applied to the first transistor during the conduction cycle.
9. The method of claim 8 , further comprising providing the second conduction control signal to the control terminal of the second transistor if an on-to-off conduction transition time of the second transistor is less than a length of time remaining in a conduction cycle after a cessation of conduction of the first transistor in the conduction cycle.
10. The method of claim 8 , further comprising:
measuring an on-to-off conduction transition time of the second transistor;
storing the measured on-to-off conduction time of the second transistor; and
providing the second conduction control signal to the control terminal of the second transistor if the amount of time remaining in a conduction cycle is greater than the stored on-to-off conduction time of the second transistor.
11. The method of claim 8 , further comprising:
storing an on-to-off conduction time of the second transistor; and
providing the second conduction control signal to the control terminal of the second transistor if the amount of time remaining in a conduction cycle after the first transistor ceases conduction is greater than the stored on-to-off conduction time of the second transistor.
12. The method of claim 7 , further comprising:
calculating a length of time required for a current in the inductor to cease flowing if the second transistor were not caused to conduct;
comparing an on-to-off conduction transition time of the second transistor with the length of time for the current in the inductor to cease flowing;
causing the second transistor to conduct if the on-to-off transition time of the second transistor is less than a length of time for the conduction of current in the inductor to cease if the second transistor was not caused to conduct.
13. The method of claim 7 , further comprising:
determining a magnitude of a current flowing through the inductor during a conduction of the first transistor during a conduction cycle;
calculating an amount of power that would be consumed if the second transistor were provided the second conduction control signal in a portion of the conduction cycle after the first transistor ceases conduction;
calculating an amount of power that would be consumed if the second transistor were not provided the second conduction control signal; and
comparing the amounts of power that would be consumed for conduction and non-conduction of the second transistor; and
providing the second conduction control signal to the second transistor based on the results of the comparison.