Switching slew rate control for gate drivers
Switching circuits, half-bridge power converters, and methods for operating a switching circuit including a switching transistor coupled to a load. The method includes applying, with a driver, a gate voltage to the switching transistor. The method also includes generating, with a feedback capacitor, a feedback current based on a change in a voltage sensed at a drain terminal of the switching transistor when the switching transistor turns on. The method further includes applying the feedback current to the driver to limit the gate voltage applied to the switching transistor. The method also includes adjusting, with a controller, a switching slew rate of the switching transistor by draining an amount of the feedback current.
1. A method for operating a switching circuit including a switching transistor coupled to a load, the method comprising:
applying, with a driver, a gate voltage to the switching transistor;
generating, with a feedback capacitor, a feedback current based on a change in a voltage sensed at a drain terminal of the switching transistor when the switching transistor turns on;
applying the feedback current to the driver to limit the gate voltage applied to the switching transistor; and
adjusting, with a controller, a switching slew rate of the switching transistor by draining an amount of the feedback current.
2. The method of claim 1 , adjusting the switching slew rate of the switching transistor further includes draining the amount of the feedback current with a control transistor included in the controller.
3. The method of claim 1 , wherein the gate voltage is a first gate voltage, wherein applying the gate voltage to the switching transistor further includes:
applying, with a voltage follower transistor included in the driver, the first gate voltage to the switching transistor,
applying, with a gate capacitor included in the driver, a second gate voltage to the voltage follower transistor, and
applying, with a current source included in the driver, a constant current to the gate capacitor,
wherein the feedback current interferes with the constant current.
4. The method of claim 1 , further comprising adjusting the feedback current with a biasing transistor.
5. The method of claim 1 , wherein the switching transistor includes a gallium nitride transistor.
6. A switching circuit, comprising:
a switching transistor coupled to a load;
a driver including:
a voltage follower transistor configured to apply a gate voltage to the switching transistor,
a gate capacitor coupled to a gate terminal of the voltage follower transistor, and
a current source configured to apply a constant current to the gate capacitor;
a feedback capacitor coupled to a drain terminal of the switching transistor to generate a feedback current based on a change in a voltage sensed at the drain terminal of the switching transistor when the switching transistor turns on, wherein the feedback current interferes with the constant current and limits the gate voltage applied to the gate terminal of the switching transistor; and
a controller configured to adjust a switching slew rate of the switching transistor by draining an amount of the feedback current.
7. The switching circuit of claim 6 , wherein the gate voltage is a first gate voltage, wherein the controller includes a control transistor, and wherein the amount of the feedback current drained by the controller is set based on a second gate voltage of the control transistor.
8. The switching circuit of claim 7 , wherein the switching circuit further comprising a resistor coupled to the control transistor to set the second gate voltage of the control transistor.
9. The switching circuit of claim 6 , wherein the switching transistor, the feedback capacitor, the driver, and the controller are positioned within a chip housing, wherein the controller is coupled to a control terminal of the chip housing, and wherein the controller is further configured to:
receive an external control signal via the control terminal, and
adjust the switching slew rate of the switching transistor based on the external control signal.
10. The switching circuit of claim 6 , further comprising a biasing transistor configured to adjust the feedback current.
11. The switching circuit of claim 6 , wherein the switching transistor includes a gallium nitride transistor.
12. A half-bridge power converter, comprising:
a first switching circuit coupled to a load; and
a second switching circuit including:
a switching transistor coupled to the load,
a driver configured to apply a gate voltage to the switching transistor,
a feedback capacitor coupled to a drain terminal of the switching transistor to generate a feedback current based on a change in a voltage sensed at the drain terminal of the switching transistor when the switching transistor turns on, wherein the feedback current limits the gate voltage applied to a gate terminal of the switching transistor, and
a controller configured to adjust a switching slew rate of the switching transistor by draining an amount of the feedback current.
13. The half-bridge power converter of claim 12 , wherein the gate voltage is a first gate voltage, wherein the controller includes a control transistor, and wherein the amount of the feedback current drained by the controller is based on a second gate voltage of the control transistor.
14. The half-bridge power converter of claim 13 , wherein the second switching circuit further includes a resistor coupled to the control transistor to set the second gate voltage of the control transistor.
15. The half-bridge power converter of claim 12 , wherein the switching transistor, the feedback capacitor, the driver, and the controller are positioned within a chip housing, wherein the controller is coupled to a control terminal of the chip housing, and wherein the controller is further configured to:
receive an external control signal via the control terminal, and
adjust the switching slew rate of the switching transistor based on the external control signal.
16. The half-bridge power converter of claim 12 , wherein the driver includes:
a voltage follower transistor configured to apply the gate voltage to the switching transistor,
a gate capacitor coupled to a gate terminal of the voltage follower transistor, and
a current source configured to apply a constant current to the gate capacitor,
wherein the feedback current interferes with the constant current.
17. The half-bridge power converter of claim 12 , wherein the second switching circuit further includes a biasing transistor configured to adjust the feedback current.
18. The half-bridge power converter of claim 12 , wherein the switching transistor includes a gallium nitride transistor.
19. The half-bridge power converter of claim 12 , wherein the load includes an inductor and a capacitor coupled in a series configuration between the drain terminal of the switching transistor and a reference terminal.
20. The half-bridge power converter of claim 12 , wherein the first switching circuit is coupled between a high voltage supply and the load, wherein the drain terminal of the switching transistor is coupled to the load, and wherein a source terminal of the switching transistor is coupled to a reference terminal.