Power supply system with reduced bulk capacitance

1. A system comprising:

a rectifier coupled to an input power source having a sinusoidal output waveform;

a boost converter coupled between the rectifier and a bulk capacitor, the boost converter increases a voltage across the bulk capacitor in each cycle of the sinusoidal output waveform in response to the voltage across the bulk capacitor decreasing to a predetermined threshold, wherein the voltage across the capacitor is of a curved waveform in phase with the sinusoidal output waveform when the boost converter is disabled; and

an isolated power converter coupled to the bulk capacitor.

2. The system of claim 1 , wherein the rectifier is a full-wave rectifier that is coupled in cascade with the boost converter between the input power source and the bulk capacitor.

3. The system of claim 1 , wherein the boost converter is a charge pump converter.

4. The system of claim 1 , further comprising:

a controller configured to detect at least one voltage of the voltage across the bulk capacitor or an output voltage of the rectifier, and generate at least one signal to control the boost converter.

5. A method comprising:

detecting a voltage across a bulk capacitor of a power supply system, the power supply system comprising a rectifier configured to be coupled to a power source having a sinusoidal output waveform, a boost converter coupled to the rectifier, a power converter and the bulk capacitor coupled between the boost converter and the power converter;

in each cycle of the power source, activating the boost converter after the voltage across the bulk capacitor decreases and reaches a first voltage threshold, wherein prior to activating the boost converter, the voltage across the bulk capacitor is of a curved waveform in phase with the sinusoidal output waveform from the power source; and

in each cycle of the power source, disabling the boost converter after the voltage across the bulk capacitor increases and reaches a second voltage threshold, the second voltage threshold being greater than the first voltage threshold.

6. The method of claim 5 , wherein the rectifier is a full-wave rectifier, and the boost converter is a boost converter including a switch that is configured to adjust the voltage across the bulk capacitor.

7. The method of claim 6 , further comprising:

during activating the boost converter, turning on and off the switch until the voltage across the bulk capacitor is equal to the second voltage threshold; and

during disabling the boost converter, turning off the switch.

8. The method of claim 5 , further comprising:

after disabling the boost converter, activating the boost converter after the voltage across the bulk capacitor decreases and reaches a third voltage threshold between the first voltage threshold and the second voltage threshold; and

disabling the boost converter after the voltage across the bulk capacitor increases and reaches a fourth voltage threshold between the first voltage threshold and the second voltage threshold, wherein the fourth voltage threshold is greater than the third voltage threshold, wherein the third voltage threshold and the fourth voltage threshold are thresholds for adjusting the voltage across the bulk capacitor.

9. The method of claim 8 , further comprising:

after disabling the boost converter, activating the boost converter after the voltage across the bulk capacitor decreases and reaches the third voltage threshold; and

disabling the boost converter after the voltage across the bulk capacitor increases and reaches the second voltage threshold.

10. The method of claim 5 , wherein the first voltage threshold is a minimum input voltage of the power converter, and the second voltage threshold is a maximum input voltage of the power converter.

11. The method of claim 5 , further comprising:

detecting, by a controller, the voltage across the bulk capacitor and a voltage at an output of the rectifier; and

generating, by the controller, a control signal for controlling the boost converter based upon the voltage across the bulk capacitor and the voltage at the output of the rectifier.

12. A method comprising:

detecting a voltage across a bulk capacitor of a power supply system configured to be coupled to an ac power source having a sinusoidal output waveform, the power supply system comprising a boost converter coupled to the bulk capacitor;

in each cycle of the ac power source, applying a first pulse width modulation (PWM) mode to at least one switch of the boost converter after the voltage across the bulk capacitor reaches a first voltage threshold, wherein prior to applying the first PWM mode to the at least one switch of the boost converter, the voltage across the bulk capacitor is of a curved waveform in phase with the sinusoidal output waveform from the ac power source; and

applying an always-off mode to at least one switch of the boost converter after the voltage across the bulk capacitor reaches a second voltage threshold, the second voltage threshold being greater than the first voltage threshold.

13. The method of claim 12 , wherein the boost converter is a boost converter configured to adjust the voltage across the bulk capacitor.

14. The method of claim 12 , wherein the boost converter comprises a first boost converter and a second boost converter coupled in parallel between an input power source and the bulk capacitor, the first boost converter configured to be activated during a first half cycle of the input power source, and the second boost converter configured to be activated during a second half cycle of the input power source.

15. The method of claim 12 , further comprising:

after applying the always-off mode to the at least one switch of the boost converter after the voltage across the bulk capacitor reaches the second voltage threshold, applying a second PWM mode to the at least one switch of the boost converter after the voltage across the bulk capacitor reaches a third voltage threshold between the first voltage threshold and the second voltage threshold;

applying the always-off mode to the at least one switch of the boost converter after the voltage across the bulk capacitor reaches the second voltage threshold;

applying a third PWM mode to the at least one switch of the boost converter after the voltage across the bulk capacitor reaches a fourth voltage threshold between the first voltage threshold and the second voltage threshold, wherein the third voltage threshold is greater than the fourth voltage threshold; and

applying the always-off mode to the at least one switch of the boost converter after the voltage across the bulk capacitor reaches a fifth voltage threshold between the first voltage threshold and the second voltage threshold, wherein the fifth voltage threshold is greater than the third voltage threshold, wherein the third voltage threshold, the fourth voltage threshold and the fifth voltage threshold are thresholds for adjusting the voltage across the bulk capacitor.