Active pre-charge circuit

A power converter, comprising:

• an AC/DC converter configured to receive power from an AC source, and to supply DC power to a load during normal operation;
• a charge storage device configured to store power during a pre-charge phase and to supply power to the load during a start-up phase prior to normal operation;
• and
• an active pre-charge circuit configured to provide power to the charge storage device during the pre-charge phase and to be inactive during normal operation, the pre-charge circuit comprising:
• a transistor configured to control current to the charge storage device during the pre-charge phase;
• a diode having an anode coupled with a source of the transistor, and a cathode coupled with a drain of the transistor;
• a shunt resistor coupled between the source of the transistor and a positive end of the charge storage device;
• an inductor coupled between the shunt resistor and the positive end of the charge storage device;
• a circulating diode having an anode coupled with a negative end of the charge storage device and a cathode coupled with the source of the transistor and the shunt resistor, configured to circulate current through the inductor, the charge storage device, and the shunt resistor when the transistor is turned off;
• a current controller coupled to a gate of the transistor and configured to:
• receive a current measurement indicating an amount of current flowing through the transistor;
• process the current measurement to determine a switching duty cycle for the transistor;
• configure a pulse width modulator within the current controller with the switching duty cycle;
• and
• provide an output of the pulse width modulator to the gate of the transistor;
• and
• a pre-charge power supply coupled with the source of the transistor and the drain of the transistor and configured to supply power to the current controller during the pre-charge phase, wherein the power supply is powered by a voltage difference between the source of the transistor and the drain of the transistor such that the current controller is off when the charge storage device is charged.

A method for pre-charging a charge storage device, the method comprising:

• measuring a current flowing through a switching transistor, the switching transistor configured to control current charging the charge storage device during a pre-charge phase;
• providing the current measurement to a current controller;
• the current controller processing the current measurement to determine a switching duty cycle for the switching transistor;
• the current controller configuring a pulse width modulator to produce a switching signal oscillating at the switching duty cycle;
• the current controller providing the switching signal to a gate of the switching transistor;
• and
• supplying power to the current controller with a power supply during the pre-charge phase, wherein the power supply is powered by a voltage difference between a source of the switching transistor and a drain of the switching transistor such that the current controller is off when the charge storage device is charged.