Reduction of electrical size of bulk capacitors in mobile power supplies
View Patent ↗A capacitor input circuit for a mobile power supply includes a bulk capacitor and a switch. The switch connects the bulk capacitor to receive a rectified AC voltage from a rectifier when an AC line voltage input to the mobile power supply is lower than a threshold voltage. When the AC line voltage is greater than the threshold voltage, the switch electrically floats the bulk capacitor.
1. A mobile power supply comprising:
a rectifier that is configured to rectify an AC line voltage to generate a rectified AC voltage;
a capacitor input circuit that is connected to an output of the rectifier to receive the rectified AC voltage, the capacitor input circuit comprising a first bulk capacitor, a second bulk capacitor, and a switch that is connected to an end of the first bulk capacitor and to an end of the second bulk capacitor, the switch being configured to connect the first bulk capacitor and the second bulk capacitor to receive the rectified AC voltage when the AC line voltage is lower than a threshold voltage, and to electrically float the first bulk capacitor and the second bulk capacitor and thereby disconnect the first bulk capacitor and the second bulk capacitor from the capacitor input circuit when the AC line voltage is greater than the threshold voltage; and
a converter that is connected to an output of the capacitor input circuit to receive an input voltage and to convert the input voltage to a regulated output voltage.
2. The mobile power supply of claim 1 , wherein the capacitor input circuit further comprises an inductor having a first end that is connected to the first bulk capacitor and a second end that is connected to the second bulk capacitor.
3. The mobile power supply of claim 1 , further comprising a Zener diode that is connected across the second bulk capacitor.
4. The mobile power supply of claim 1 , further comprising a first filter capacitor that is connected across the rectifier.
5. The mobile power supply of claim 4 , further comprising a second filter capacitor that is connected across the converter.
6. The mobile power supply of claim 5 , wherein the first and second filter capacitors are multilayer ceramic chip capacitors.
7. The mobile power supply of claim 1 , wherein the switch comprises a metal oxide semiconductor transistor.
8. The mobile power supply of claim 7 , wherein the capacitor input circuit further comprises a resistor having a first end that is connected to a gate of the transistor and a second end that is connected to ground.
9. The mobile power supply of claim 1 , wherein the converter is a flyback converter.
10. A capacitor input circuit for a mobile power supply, the capacitor input circuit comprising:
a first bulk capacitor;
a switch that is configured to connect the first bulk capacitor to receive a rectified AC voltage from a rectifier when an AC line voltage that is input to the mobile power supply is lower than a threshold voltage and to electrically float the first bulk capacitor when the AC line voltage is greater than the threshold voltage;
an inductor having a first end that is connected to a first end of the first bulk capacitor;
a second bulk capacitor having a first end that is connected to a second end of the inductor and a second end that is connected to a second end of the first bulk capacitor,
wherein a first electrode of the switch is connected to the second end of the first bulk capacitor and to the second end of the second bulk capacitor, a second electrode of the switch is connected to ground, and
wherein the switch is configured to connect the second ends of the first and second bulk capacitors to ground when the AC line voltage is below the threshold voltage, and to disconnect the second ends of the first and second bulk capacitors from ground when the AC line voltage is greater than the threshold voltage.
11. The capacitor input circuit of claim 10 , wherein the switch comprises a MOSFET.
12. A method of operating a mobile power supply, the method comprising:
rectifying an AC line voltage that is input to the mobile power supply to generate a rectified AC voltage;
connecting a first bulk capacitor and a second bulk capacitor to ground to receive the rectified AC voltage when the AC line voltage is lower than a threshold voltage;
disconnecting, by a switch that is connected to an end of the first bulk capacitor and an end of the second bulk capacitor, the first bulk capacitor and the second bulk capacitor from ground when the AC line voltage is greater than the threshold voltage; and
converting, by way of a converter, the rectified AC voltage to a regulated output voltage.
13. The method of claim 12 , further comprising:
filtering the rectified AC voltage with a filter comprising a filter capacitor that is across a rectifier that generates the rectified AC voltage.