Apparatus and method for driving a power stage
A method and apparatus for driving a power stage is presented. In particular, the power stage is a half-bridge. In the method, there is a first power switch coupled to a second power switch via a switching node. The method steps include sensing a first control-terminal voltage of one of the first power switch and the second power switch and turning on the first power switch based on the first control-terminal voltage and sensing a second control-terminal voltage of one of the first power switch and the second power switch and turning on the second power switch based on the second control-terminal voltage. Optionally, the first power switch is turned on when the first control-terminal voltage has reached a first threshold value, and the second power switch is turned on when the second control-terminal voltage has reached a second threshold value.
1. A method of driving a power stage comprising a first power switch coupled to a second power switch via a switching node; the method comprising:
providing a first sensing resistance coupled to a control terminal of the first power switch and a second sensing resistance coupled to a control terminal of the second power switch;
sensing a first control-terminal voltage of one of the first power switch and the second power switch, comparing the first control-terminal voltage with a first reference value and generating a first control signal based on the comparison to turn on the first power switch;
sensing a second control-terminal voltage of one of the first power switch and the second power switch, comparing the second control-terminal voltage with a second reference value and generating a second control signal based on the comparison to turn on the second power switch.
2. The method as claimed in claim 1 , wherein the first power switch is turned on when the first control-terminal voltage has reached a first threshold value; and wherein the second power switch is turned on when the second control-terminal voltage has reached a second threshold value.
3. The method as claimed in claim 1 ,
wherein the first power switch comprises a first parasitic capacitor associated with a first parasitic current, and
wherein the second power switch comprises a second parasitic capacitor associated with a second parasitic current.
4. The method as claimed in claim 3 , wherein the first control-terminal voltage is a function of the first parasitic current and the first sensing resistance; and wherein the second control-terminal voltage is a function of the second parasitic current and the second sensing resistance.
5. The method as claimed in claim 3 , wherein the switching node has a switching voltage; and wherein the first and second parasitic currents are function of a time derivative of the switching voltage.
6. The method as claimed in claim 1 , wherein the switching node has a switching voltage that varies between a first value and a second value during a transient period; and wherein the first control-terminal voltage and the second control-terminal voltage are sensed at some point during the transient period.
7. A driver for use with a power stage, the power stage comprising a first power switch coupled to a second power switch via a switching node; the driver comprising a first sensing resistance coupled to a control terminal of the first power switch and a second sensing resistance coupled to a control terminal of the second power switch; the driver being adapted
to sense a first control-terminal voltage of one of the first power switch and the second power switch, to compare the first control-terminal voltage with a first reference and to generate a first control signal based on the comparison to turn on the first power switch;
to sense a second control-terminal voltage of one of the first power switch and the second power switch; to compare the second control-terminal voltage with a second reference and to generate a second control signal based on the comparison to turn on the second power switch.
8. The driver as claimed in claim 7 , wherein driver is adapted to turn on the first power switch when the first control-terminal voltage has reached a first threshold value; and to turn on the second power switch when the second control-terminal voltage has reached a second threshold value.
9. The driver as claimed in claim 7 ,
wherein the first power switch comprises a first parasitic capacitor associated with a first parasitic current, and
wherein the second power switch comprises a second parasitic capacitor associated with a second parasitic current.
10. The driver as claimed in claim 9 , wherein the first control-terminal voltage is a function of the first parasitic current and the first sensing resistance; and wherein the second control-terminal voltage is a function of the second parasitic current and the second sensing resistance.
11. The driver as claimed in claim 9 , wherein the switching node has a switching voltage; and wherein the first and second parasitic currents are function of a time derivative of the switching voltage.
12. The driver as claimed in claim 7 , further comprising:
a first comparator to compare the first control-terminal voltage with the first reference and to provide a first comparison signal;
a second comparator to compare the second control-terminal voltage with the second reference and to provide a second comparison signal;
a controller coupled to the first comparator and the second comparator; the controller being adapted to provide the first control signal to turn the first power switch on and the second control signal to turn the second power switch on; wherein the first control signal is based on the first comparison signal; and wherein the second control signal is based on the second comparison signal.
13. The driver as claimed in claim 12 , wherein the switching node has a switching voltage, the switching voltage increasing from a first value to a second value during a first transient period, and decreasing from the second value to the first value during a second transient period; and
wherein the first comparator is adapted to compare the first control-terminal voltage with the first reference at some point during the first transient period; and
wherein the second comparator is adapted to compare the second control-terminal voltage with the second reference at some point during the second transient period.
14. The driver as claimed in claim 12 , wherein the first comparator comprises a first transistor coupled to the first reference; and wherein the second comparator comprises a second transistor coupled to the second reference.
15. The driver as claimed in claim 12 , wherein the first comparator is coupled to the first sensing resistor; and wherein the second comparator is coupled to the second sensing resistor.
16. The driver as claimed in claim 15 , wherein the first sensing resistor is provided between the switching node and a control-terminal terminal of the first power switch; and wherein the second sensing resistor is provided between a ground terminal and a control-terminal terminal of the second power switch.
17. A power circuit comprising:
a power stage comprising a first power switch coupled to a second power switch via a switching node; and
a driver, the driver comprising a first sensing resistance coupled to a control terminal of the first power switch and a second sensing resistance coupled to a control terminal of the second power switch; the driver being adapted
to sense a first control-terminal voltage of one of the first power switch and the second power switch, to compare the first control-terminal voltage with a first reference and to generate a first control signal based on the comparison to turn on the first power switch;
to sense a second control-terminal voltage of one of the first power switch and the second power switch, to compare the second control-terminal voltage with a second reference and to generate a second control signal based on the comparison to turn on the second power switch.
18. The power circuit as claimed in claim 17 , wherein the power circuit is made at least in part of a III/V semiconductor.
19. The power circuit as claimed in claim 17 ,
wherein the first power switch comprises a first parasitic capacitor associated with a first parasitic current, and
wherein the second power switch comprises a second parasitic capacitor associated with a second parasitic current.
20. The power circuit as claimed in claim 19 , wherein the first control-terminal voltage is a function of the first parasitic current and the first sensing resistance; and wherein the second control-terminal voltage is a function of the second parasitic current and the second sensing resistance.
21. The power circuit as claimed in claim 19 , wherein the switching node has a switching voltage; and wherein the first and second parasitic currents are function of a time derivative of the switching voltage.
22. The power circuit as claimed in claim 17 , wherein the driver comprises:
a first comparator to compare the first control-terminal voltage with the first reference and to provide a first comparison signal;
a second comparator to compare the second control-terminal voltage with the second reference and to provide a second comparison signal;
a controller coupled to the first comparator and the second comparator; the controller being adapted to provide the first control signal to turn the first power switch on and the second control signal to turn the second power switch on; wherein the first control signal is based on the first comparison signal; and wherein the second control signal is based on the second comparison signal.
23. The power circuit as claimed in claim 22 , wherein the switching node has a switching voltage, the switching voltage increasing from a first value to a second value during a first transient period, and decreasing from the second value to the first value during a second transient period; and
wherein the first comparator is adapted to compare the first control-terminal voltage with the first reference at some point during the first transient period; and
wherein the second comparator is adapted to compare the second control-terminal voltage with the second reference at some point during the second transient period.