Power supply unit with re-rush current limiting

1. A method comprising:

detecting, by an alternating current (AC) input monitoring circuit, an AC voltage dropout;

placing, by the AC input monitoring circuit, a first transistor in an OFF state in response to detecting the AC voltage dropout, wherein the first transistor is connected in series with a first bulk capacitor of a power supply unit;

detecting that the AC voltage is re-applied;

adopting, by a current source, an adaptive gate voltage to control the first transistor in response to the re-applied AC voltage, wherein the adaptive gate voltage includes diversion of a gate current when the first transistor reaches a plateau region;

providing the diverted gate current to a virtual miller capacitor to set a re-rush current through the first transistor at a constant value; and

turning on the first transistor based on the adaptive gate voltage to keep the first transistor operating in the plateau region.

2. The method of claim 1 , wherein placing the first transistor in the OFF state comprises:

providing an OFF signal to a second transistor;

activating the second transistor in response to the OFF signal; and

pulling a voltage level of a gate electrode of the first transistor to a ground voltage level in response to the second transistor being activated.

3. The method of claim 1 , further comprising:

placing, by the AC input monitoring circuit, a second transistor in the OFF state in response to detected the AC voltage dropout, wherein the second transistor is connected in series with a second bulk capacitor of the power supply unit;

detecting that the AC voltage is re-applied;

adopting the adaptive gate voltage to control the second transistor in response to the AC voltage being re-applied; and

turning on the second transistor based on the adaptive gate voltage to limit a re-rush current within the power supply unit after the AC voltage is re-applied.

4. The method of claim 1 , wherein the AC voltage dropout is a brown-out event in the power supply unit.

5. The method of claim 1 , wherein the gate current is diverted to a virtual miller capacitance circuit that is coupled to the first transistor.

6. The method of claim 1 , wherein turning on the first transistor further comprises:

delaying the turn on of the first transistor based on a delay time of a delay circuit.

7. A power supply unit comprising:

a rectifying module to rectify an alternating current (AC) voltage;

a first bulk capacitor to receive the rectified AC voltage from the rectifying module;

a first transistor coupled in series with the first bulk capacitor;

an AC input monitoring circuit coupled to the first transistor, the AC input monitoring circuit to hold the first transistor in an OFF state when the AC voltage is in a dropout state;

a current source coupled to the first transistor, the current source to adopt an adaptive gate voltage to control the first transistor in response to a detection of the AC voltage being re-applied, wherein the adaptive gate voltage includes diversion of a gate current when the first transistor reaches a plateau region to limit a re-rush current; and

a virtual miller capacitance circuit coupled to the first transistor, the virtual miller capacitance circuit to set the re-rush current through the first transistor at a constant value.

8. The power supply unit of claim 7 , wherein no current flows through the first bulk capacitor and the first transistor in response to the first transistor being held in the OFF state.

9. The power supply unit of claim 7 , further comprising:

a second transistor coupled to the first transistor, wherein the AC input monitoring circuit holds the first transistors in the OFF state in response to activating the second transistor.

10. The power supply unit of claim 9 , wherein when the second transistor is activated, a voltage level on a gate electrode of the first transistor is pulled to a ground level.

11. The power supply unit of claim 7 , wherein the gate current is diverted to a virtual miller capacitance circuit that is coupled to the first transistor.

12. The power supply unit of claim 7 , further comprising:

a delay circuit coupled to the first transistor, wherein the delay circuit delays the turn on of the first transistor based on a delay time of the delay circuit.

13. The power supply unit of claim 7 , further comprising:

a second bulk capacitor; and

a second transistor coupled in series with the second bulk capacitor, wherein the AC input monitoring circuit to hold the second transistor in the OFF state in response to the detection of the AC voltage dropout, the current source to adopt the adaptive gate voltage to control the second bulk transistor in response to the detection of the AC voltage being re-applied, and to turn on the second transistor based on the adaptive gate voltage to limit the re-rush current within the power supply unit after the AC voltage is re-applied.

14. A power supply unit comprising:

a first bulk capacitor to receive a rectified alternating current (AC) voltage from a rectifying module;

a first transistor coupled in series with the first bulk capacitor;

an AC input monitoring circuit coupled to the first transistor, the AC input monitoring circuit to hold the first transistor in an OFF state in response to a detection of an AC voltage dropout;

a current source coupled to the first transistor, the current source to adopt an adaptive gate voltage to control the first transistor in response to a detection of the AC voltage being re-applied, and to turn on the first transistor based on the adaptive gate voltage to limit a re-rush current within the power supply unit after the AC voltage is re-applied; and

a virtual miller capacitance circuit coupled to the first transistor, the virtual miller capacitance circuit to set the re-rush current through the first transistor at a constant value.

15. The power supply unit of claim 14 wherein no current flows through the first bulk capacitor and the first transistor in response to the first transistor being held in the OFF state.

16. The power supply unit of claim 14 , further comprising:

a second transistor coupled to the first transistor, wherein the AC input monitoring circuit holds the first transistors in the OFF state in response to activating the second transistor.

17. The power supply unit of claim 16 , wherein when the second transistor is activated, a voltage level on a gate electrode of the first transistor is pulled to a ground voltage level.

18. The power supply unit of claim 14 , wherein the AC voltage dropout is a complete power loss to the power supply unit.

19. The power supply unit of claim 14 , further comprising:

a delay circuit coupled to the first transistor, wherein the delay circuit delays the turn on of the first transistor based on a delay time of the delay circuit.

20. The power supply unit of claim 14 , further comprising:

a second bulk capacitor; and

a second transistor coupled in series with the second bulk capacitor, wherein the AC input monitoring circuit to hold the second transistor in the OFF state in response to detecting the AC voltage dropout, the current source to adopt the adaptive gate voltage to control the second bulk transistor in response to the detection of the AC voltage being re-applied, and to turn on the second transistor based on the adaptive gate voltage to limit the re-rush current within the power supply unit after the AC voltage is re-applied.