Power-efficient sync-rectifier gate driver architecture

1. An alternating current to direct current (AC-DC) power supply comprising:

a synchronous rectifier field effect transistor (FET);

a transformer of the AC-DC converter, the transformer being coupled to the synchronous rectifier FET; and

a secondary-side controller coupled to the synchronous rectifier FET, wherein the secondary-side controller is to control a primary-side FET across a galvanic isolation barrier, wherein the secondary-side controller comprises a synchronous rectifier gate driver (SRGD) coupled to a gate of the synchronous rectifier FET, wherein the SRGD is to drive the synchronous rectifier FET using a capacitor and an adaptive slew rate, wherein the capacitor is adiabatically charged and discharged.

2. The AC-DC power supply of claim 1 , wherein the secondary-side controller further comprises the capacitor coupled to the SRGD, and wherein the SRGD comprises:

a voltage generator circuit coupled to a first plate of the capacitor and a second plate of the capacitor;

a gate driver circuit coupled to the first plate of the capacitor and the gate of the synchronous rectifier FET; and

a phase and slew rate controller circuit coupled to the voltage generator circuit and coupled to the gate driver circuit.

3. The AC-DC power supply of claim 2 , wherein the voltage generator circuit comprises:

a first pull-up element coupled to the first plate and coupled to a first node at a first voltage level;

a second pull-up element coupled to the first pull-up element and coupled to the second plate, and further coupled to the first node; and

a first pull-down element coupled to the second pull-up element, the second plate, and a second node at a second voltage level, wherein the second voltage level is lower than the first voltage level.

4. The AC-DC power supply of claim 2 , wherein the gate driver circuit comprises:

a first pull-up element coupled between the first plate and the gate of the synchronous rectifier FET;

a second pull-up element coupled between a first node at a first voltage level and the gate of the synchronous rectifier FET and further coupled to the first pull-up element; and

a first pull-down element coupled to the first pull-up element, the second pull-up element, and the gate of the synchronous rectifier FET, and further coupled to a second node at a second voltage level, wherein the second voltage level is lower than the first voltage level.

5. The AC-DC power supply of claim 2 , wherein the phase and slew rate controller comprises a drive strength and slew rate controller, and wherein the voltage generator circuit comprises:

a first node coupled to the second plate;

a first pull-down element coupled to the first node;

a first switch coupled between the first pull-down element, the drive strength and slew rate controller, and further coupled to a second node at a first voltage level;

a first pull-up element coupled to the first node;

a second switch coupled between the first pull-up element and the drive strength and slew rate controller;

a third switch coupled between the drive strength and slew rate controller and a third node, wherein the third node is coupled between the second switch and the third switch, and wherein the third node is at a second voltage level greater than the first voltage level, and is coupled to the gate driver circuit; and

a fourth switch coupled between a level shifter and a second pull-up element.

6. The AC-DC power supply of claim 5 , wherein the phase and slew rate controller comprises an adaptive bias controller, and wherein the gate driver circuit comprises:

a fourth node coupled to the first plate;

a fifth switch coupled between a third pull-up element and the adaptive bias controller, wherein the third pull-up element is coupled to the fourth node;

a fourth pull-up element coupled to the gate of the synchronous rectifier FET, wherein the fifth switch is coupled between the third pull-up element and the fourth pull-up element;

a sixth switch coupled between the level shifter and a fifth pull-up element, wherein the fifth pull-up element is coupled to the gate of the synchronous rectifier FET;

a seventh switch coupled between the drive strength and slew rate controller and the third node at the second voltage level; and

an eighth switch coupled between the drive strength and slew rate controller and the gate of the synchronous rectifier FET and further coupled to the first node at the first voltage level.

7. The AC-DC power supply of claim 2 , wherein the phase and slew rate controller circuit comprises a drive strength and slew rate controller, an adaptive bias controller, and a phase and drive strength controller, and is to provide a control signal to control the voltage generator circuit and the gate driver circuit, and the drive strength and slew rate controller is to control a delay of the control signal.

8. The AC-DC power supply of claim 2 , wherein the phase and slew rate controller circuit comprises a drive strength and slew rate controller and an adaptive bias controller, and wherein the drive strength and slew rate controller is to control a delay of a control signal to control the gate driver circuit and the adaptive bias controller is to generate a boosted voltage at the gate of the synchronous rectifier FET, wherein the boosted voltage is greater than a supply voltage of the secondary-side controller.

9. The AC-DC power supply of claim 2 , wherein the phase and slew rate controller circuit is a control block coupled to the voltage generator circuit and coupled to the gate driver circuit, and is configured to generate a control signal to enable one of a first phase, a second phase, a third phase, or a fourth phase of operation of the SRGD and wherein the phase and slew rate controller is to:

in the first phase:

maintain the second plate of the capacitor at a first voltage level;

maintain the first plate of the capacitor at a second voltage level, higher than the first level; and

charge the gate of the secondary-side FET to the second voltage level;

in the second phase:

charge the second plate of the capacitor to the second voltage level;

charge the first plate of the capacitor to a third voltage level, higher than the second voltage level; and

charge the gate of the secondary-side FET to the third voltage level;

in the third phase:

discharge the second plate of the capacitor to the first voltage level;

discharge the first plate of the capacitor to the second voltage level; and

discharge the gate of the secondary-side FET to the second voltage level; and

in the fourth phase:

maintain the second plate of the capacitor at the first voltage level;

maintain the first plate of the capacitor at the second voltage level; and

discharge the gate of the secondary-side FET to the first voltage level.

10. The AC-DC power supply of claim 2 , wherein the phase and slew rate controller comprises a drive strength and slew rate controller comprising:

a current generator to generate a current which is inversely proportional to a drive strength of the synchronous rectifier FET; and

a delay-based slew generator comprising a plurality of current inverters positioned in a cascaded pattern to generate a delay of a control signal based on the current.

11. The AC-DC power supply of claim 2 , wherein the phase and slew rate controller comprises an adaptive bias controller comprising:

a comparator to compare a voltage of a control signal to a supply voltage of the secondary-side controller; and

an adaptive bias generator to generate a voltage level on the gate of the synchronous rectifier FET wherein the voltage level is greater than the supply voltage.

12. An alternating current to direct current (AC-DC) power adapter device comprising:

a USB-C connector;

a transformer coupled between AC terminals and DC terminals, the transformer to convert AC power on the AC terminals to DC power on the DC terminals with galvanic isolation between the AC terminals and the DC terminals;

a primary-side controller coupled to the transformer;

a secondary-side controller coupled to the transformer; and

a synchronous rectifier field effect transistor (FET), wherein the secondary-side controller comprises a synchronous rectifier gate driver (SRGD) coupled to a gate of the synchronous rectifier FET, wherein the SRGD is to drive the synchronous rectifier FET using a capacitor and an adaptive slew rate, and wherein the capacitor is adiabatically charged and discharged.

13. The AC-DC power adapter device of claim 12 , wherein the secondary-side controller further comprises the capacitor coupled to the SRGD and wherein the SRGD comprises:

a voltage generator circuit coupled to a first plate of the capacitor and a second plate of the capacitor;

a gate driver circuit coupled to the first plate of the capacitor and the gate of the synchronous rectifier FET; and

a phase and slew rate controller circuit coupled to the voltage generator circuit and coupled to the gate driver circuit.

14. The AC-DC power adapter device of claim 13 , wherein the voltage generator circuit comprises:

a first pull-up element coupled to the first plate and coupled to a first node at a first voltage level;

a second pull-up element coupled to the first pull-up element and coupled to the second plate, and further coupled to the first node; and

a first pull-down element coupled to the second pull-up element, the second plate, and a second node at a second voltage level, wherein the second voltage level is lower than the first voltage level.

15. The AC-DC power adapter device of claim 13 , wherein the gate driver circuit comprises:

a first pull-up element coupled between the first plate and the gate of the synchronous rectifier FET;

a second pull-up element coupled between a first node at a first voltage level and the gate of the synchronous rectifier FET and further coupled to the first pull-up element; and

a first pull-down element coupled to the first pull-up element, the second pull-up element, and the gate of the synchronous rectifier FET, and further coupled to a second node at a second voltage level.

16. The AC-DC power adapter device of claim 13 , wherein the phase and slew rate controller circuit comprises a drive strength and slew rate controller, an adaptive bias controller, and a phase and drive strength controller, and wherein the phase and slew rate controller circuit is to provide a control signal to control the voltage generator circuit and the gate driver circuit.

17. The AC-DC power adapter device of claim 13 , wherein the phase and slew rate controller circuit is a control block coupled to the voltage generator circuit and coupled to the gate driver circuit, and is configured to generate a control signal to enable one of a first phase, a second phase, a third phase, or a fourth phase of operation of the SRGD and wherein the phase and slew rate controller is to:

in the first phase:

maintain the second plate of the capacitor at a first voltage level;

maintain the first plate of the capacitor at a second voltage level, higher than the first level; and

charge the gate of the secondary-side FET to the second voltage level;

in the second phase:

charge the second plate of the capacitor to the second voltage level;

charge the first plate of the capacitor to a third voltage level, higher than the second voltage level; and

charge the gate of the secondary-side FET to the third voltage level;

in the third phase:

discharge the second plate of the capacitor to the first voltage level;

discharge the first plate of the capacitor to the second voltage level; and

discharge the gate of the secondary-side FET to the second voltage level; and

in the fourth phase:

maintain the second plate of the capacitor at the first voltage level;

maintain the first plate of the capacitor at the second voltage level; and

discharge the gate of the secondary-side FET to the first voltage level.