Switching converter with reduced dead-time
A switching converter with reduced dead-time and without reverse-recovery is disclosed. The switching converter includes a first power switch coupled to a second power switch, a mode detector and a controller. The mode detector is adapted to detect a mode of operation of the first power switch and the second power switch, and to identify a first period during which the first power switch is turned on and operates in a linear mode while the second power switch is turned off. The controller is adapted to bias the second power switch with a predetermined voltage during the first period to turn on the second power switch during a second period. In the second period the first power switch is operating in a saturation mode.
1. A switching converter comprising
a first power switch coupled to a second power switch at a switching node;
a mode detector adapted to detect a mode of operation of the first power switch and the second power switch, and to identify a first period during which the first power switch is turned on and operates in a linear mode while the second power switch is turned off; and
a controller adapted to bias the second power switch with a predetermined voltage during the first period to turn on the second power switch during a second period, wherein in the second period the first power switch is operating in a saturation mode.
2. The switching converter as claimed in claim 1 , wherein the predetermined voltage is less than a threshold voltage at which the second power switch starts drawing a current.
3. The switching converter as claimed in claim 1 , wherein the controller is adapted to turn on the second power switch before the switching node reaches a voltage level sufficient to forward bias a body diode of the second power switch.
4. The switching converter as claimed in claim 1 , wherein the mode detector comprises a first detector portion coupled to the first power switch and a second detector portion coupled to the second power switch.
5. The switching converter as claimed in claim 4 , wherein the first detector portion comprises
a reference voltage circuit adapted to generate a first voltage reference and a second voltage reference;
a first comparator adapted to compare a drive voltage for driving the first power switch with the first voltage reference to generate a first control signal; and
a second comparator adapted to compare the drive voltage with the second voltage reference to generate a second control signal.
6. The switching converter as claimed in claim 5 , wherein the first reference voltage follows a control voltage of the power switch when operating in a linear mode, and wherein the second reference voltage follows a control voltage of the power switch when operating in a saturation mode.
7. The switching converter as claimed in claim 5 , wherein the reference voltage circuit comprises a first current source and a second current source, the first current source being coupled to a first current mirror.
8. The switching converter as claimed in claim 7 , wherein the second current source is coupled to a second current mirror.
9. The switching converter as claimed in claim 7 , wherein the second current source is coupled to the first current mirror.
10. The switching converter as claimed in claim 5 , wherein the first detector portion comprises a bias circuit for generating the predetermined voltage.
11. The switching converter as claimed in claim 10 , wherein the bias circuit comprises an amplifier coupled to a diode.
12. The switching converter as claimed in claim 5 , wherein the second detector portion is implemented in the same fashion as the first detector portion.
13. The switching converter as claimed in claim 7 , wherein the first current source is adapted to generate a first current and the second current source is adapted to generate a second current, wherein the first current is greater than the second current.
14. The switching converter as claimed in claim 1 , wherein the first power switch is a high-side power switch and wherein the second power switch is a low-side power switch and wherein a voltage at the switching node becomes negative at some point during the second period.
15. The switching converter as claimed in claim 1 , wherein the first power switch is a low-side power switch and wherein the second power switch is a high-side power switch.
16. The switching converter as claimed in claim 15 , comprising an inductor coupled to the switching node, and wherein the controller is adapted to turn off the low-side power switch while an inductor current of the inductor is negative.
17. The switching converter as claimed in claim 15 , wherein the high-side power switch is turned on when the low-side power switch is in saturation to prevent the forward bias of the body diode of the high-side power switch.
18. A method of operating a switching converter having a first power switch coupled to a second power switch at a switching node; the method comprising
detecting a mode of operation of the first power switch and the second power switch;
identifying a first period during which the first power switch is turned on and operates in a linear mode while the second power switch is turned off; and
biasing the second power switch during the first period to turn on the second power switch during a second period,
wherein in the second period the first power switch is operating in a saturation mode.
19. The method as claimed in claim 18 , wherein the predetermined voltage is less than a threshold voltage at which the second power switch starts drawing a current.
20. The method as claimed in claim 18 , comprising turning on the second power switch before the switching node reaches a voltage level sufficient to forward bias a body diode of the second power switch.