Inrush current suppression for AC-DC power supplies
A power supply can include a bulk capacitor that receives a DC bus voltage; one or more DC-DC converters that convert the DC bus voltage to a DC output voltage; an inrush current limiting circuit that includes a resistor coupled in series with the bulk capacitor so as to limit an inrush current to the bulk capacitor; and a solid-state switching device that selectively bypasses the resistor once the bulk capacitor is charged; and control circuitry that operates the solid-state switching device to selectively bypass the resistor once the bulk capacitor is charged. The inrush current limiting circuit can further include a relay responsive to the control circuitry that selectively bypasses the resistor under high load conditions once the bulk capacitor is charged; and the control circuitry can further operate the solid-state switching device to selectively bypass the resistor once the bulk capacitor is charged under low load conditions.
1 . A power supply comprising:
one or more input stages that receive an AC input voltage and produce a DC bus voltage;
a bulk capacitor that receives the DC bus voltage;
a low power DC-DC converter that converts the DC bus voltage to a first DC output voltage;
a high power DC-DC converter that converts the DC bus voltage to a second DC output voltage connected in parallel with the first DC output voltage;
control circuitry that selectively enables and disables the high power DC-DC converter responsive to load conditions; and
an inrush current limiting circuit that includes:
a resistor coupled in series between the one or more input stages and the bulk capacitor so as to limit an inrush current to the bulk capacitor;
a relay responsive to the control circuitry that selectively bypasses the resistor under high load conditions once the bulk capacitor is charged; and
a solid-state switching device responsive to the control circuitry that selectively bypasses the resistor under low load conditions once the bulk capacitor is charged.
2 . The power supply of claim 1 wherein the one or more input stages that receive an AC input voltage and produce a DC bus voltage further comprise:
a rectifier that receives the AC input voltage and produces a rectified AC voltage; and
a power factor correction converter that receives the rectified AC voltage and produces the DC bus voltage.
3 . The power supply of claim 1 wherein the resistor is a negative temperature coefficient thermistor.
4 . The power supply of claim 1 wherein the resistor is a positive temperature coefficient thermistor.
5 . The power supply of claim 1 wherein the resistor is a regular resistor.
6 . The power supply of claim 1 wherein the relay has contacts coupled in parallel with the resistor and a coil driven by the control circuitry.
7 . The power supply of claim 1 wherein the solid-state switching device includes a MOSFET having source and drain terminals coupled in parallel with the resistor and a gate driven by the control circuitry.
8 . The power supply of claim 7 further comprising a gate driver interposed between the control circuitry and the gate of the MOSFET.
9 . The power supply of claim 7 further comprising a gate drive and isolator interposed between the control circuitry and the gate of the MOSFET.
10 . A power supply comprising:
a bulk capacitor that receives a DC bus voltage;
two or more DC-DC converters that convert the DC bus voltage to a DC output voltage, wherein outputs of the two or more DC-DC converters are connected in parallel;
an inrush current limiting circuit that includes a solid-state switching device coupled in series with the bulk capacitor so as to limit an inrush current to the bulk capacitor; and
control circuitry that operates the solid-state switching device responsive to bulk capacitor voltage to limit an inrush current to the bulk capacitor.
11 . The power supply of claim 10 wherein the solid-state switching device is a MOSFET operated in the active region to limit the inrush current to the bulk capacitor and operated in the saturation region to improve operating efficiency once the bulk capacitor is charged.
12 . The power supply of claim 10 further comprising:
a rectifier that receives an AC input voltage and produces a rectified AC voltage; and
a power factor correction converter that receives the rectified AC voltage and produces the DC bus voltage.