Circuit and method for regulating discharge of a capacitor

• US 8,525,487 B1
• Filed: 02/26/2009
• Issued: 09/03/2013
• Est. Priority Date: 03/05/2008
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Stevenson, Paul E.
• Primary Examiner(s): Dunn, Drew A
• Assistant Examiner(s): GRANT, ROBERT J
• Application Number:
  US12/393,639
• Time in Patent Office: 1,650 Days
• Field of Search: 307/109, 307/110, 320/166, 363/59, 363/60
• US Class Current: 320/166
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 2310/48 for electric vehicles [EV] or hybrid vehicles [HEV]
• CPC Class Codes: H02J 7/0063 with circuits adapted for supplying loads from the battery
• CPC Class Codes: H02J 7/007182 in response to battery voltage
• CPC Class Codes: H02J 7/345 using capacitors as storage or buffering devices
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps

Abstract

Embodiments of the present invention include techniques for regulating discharge of a capacitor. In one embodiment, the circuit may be used to store power on a capacitor and regulate the discharge of the capacitor to power a load, such as system electronics, circuitry, or electronic devices. In one embodiment, a first capacitor is charged from a power source and stores energy for powering an electronic device. A second capacitor is coupled to the electronic device for providing power to the electronic device. Switched capacitors are configured to transfer charge from the first capacitor to the second capacitor. A control circuit controls switching of the switched capacitors in response to voltage on the first capacitor. The switching frequency may be increased as the voltage on the first capacitor decreases so that a steady flow of charge is provided across all capacitor voltage levels.

Claims

1. A circuit comprising:

a first capacitor having a terminal for connection to a power source that is external to the circuit, wherein the first capacitor stores a charge from the power source when the terminal of first capacitor is connected to the power source;

a second capacitor having a terminal for connection to an electronic device to provide power to the electronic device;

a plurality of switched capacitors configured to transfer a charge stored by the first capacitor to the second capacitor, wherein the charge transferred to the second capacitor from the first capacitor serves as the power provided to the electronic device via the terminal of the second capacitor; and

a control circuit configured to control switching of the plurality of switched capacitors based on a voltage of the second capacitor,

wherein the plurality of switched capacitors are switched at a frequency that is inversely proportional to a voltage of the first capacitor.

2. The circuit of claim 1, wherein the plurality of switched capacitors comprise a plurality of capacitors and a plurality of switches, wherein in a first configuration a first portion of the plurality of switches is closed to arrange the plurality of capacitors in parallel, and wherein in a second configuration a second portion of the plurality of switches is closed to arrange the plurality of capacitors in series, wherein each switched capacitor of the plurality of switched capacitors is coupled to the first capacitor to receive a charge from the first capacitor in the first configuration, and wherein each switched capacitor of the plurality of switched capacitors is coupled to the second capacitor to deliver the charge received by the switched capacitor to the second capacitor in the second configuration.

3. The circuit of claim 1, wherein the plurality of switched capacitors comprise:

a first switching capacitor having a first terminal coupled to a reference voltage and a second terminal coupled to the first capacitor via a first switch; and

one or more additional switching capacitors each having a first terminal coupled to a first terminal of a preceding capacitor via a second switch and a second terminal coupled to the first terminal of the preceding capacitor via a third switch and further coupled to the reference voltage via a fourth switch,

wherein a terminal of a last capacitor of the one or more additional capacitors is coupled to the second capacitor via a fifth switch.

4. The circuit of claim 1, further comprising:

a comparator configured to receive the voltage of the second capacitor as a first input and a reference voltage as a second input, and initiate switching of the plurality of switched capacitors based on the voltage of the second capacitor,

wherein the plurality of switched capacitors transfer charge from the first capacitor to the second capacitor when the voltage of the second capacitor is determined to be below the reference voltage by a predetermined amount.

5. The circuit of claim 1, wherein the control circuit comprises a voltage-controlled oscillator that is coupled to the first capacitor to receive the voltage of the first capacitor as an input, wherein the voltage-controlled oscillator is configured to output an oscillating signal, wherein the switching of the plurality of switched capacitors is responsive to the oscillating signal, and wherein a frequency of the oscillating signal increases as the voltage on the first capacitor decreases.

6. The circuit of claim 1, wherein the electronic device has a designated operating current, and wherein a maximum frequency of the switching of the plurality of switched capacitors produces a current at a node coupling the second capacitor and the electronic device, such that the produced current is greater than or equal to the designated operating current of the electronic device.

20. The circuit of claim 1, wherein the frequency of the switching increases as the voltage on the first capacitor decreases.

7. An electronic system comprising:

electronic circuitry; and

a capacitive power supply having

a first capacitor Configured for connection to a power source that is external to the capacitive power supply, wherein the first capacitor is configured to store a charge from the power source when the first capacitor is connected to the power source;

a second capacitor coupled to the electronic circuitry for providing power to the electronic circuitry;

a plurality of switched capacitors configured to transfer the charge stored at the first capacitor to the second capacitor, wherein the charged transferred to the second capacitor from the first capacitor serves as the power provided to the electronic circuitry; and

a control circuit configured to control switching of the plurality of switched capacitors based on a voltage of the second capacitor,

wherein the plurality of switched capacitors are switched at an increasing frequency when a voltage of the first capacitor decreases, wherein the voltage of the second capacitor increases as the charge is transferred from the first capacitor to the second capacitor, and wherein the voltage of the first capacitor decreases as the charge is transferred from the first capacitor to the second capacitor.

8. The electronic system of claim 7, wherein the plurality of switched capacitors comprise a plurality of capacitors and a plurality of switches, wherein in a first configuration a first portion of the plurality of switches is closed to arrange the plurality of capacitors in parallel, and wherein in a second configuration a second portion of the plurality of switches is closed to arrange the plurality of capacitors in series, wherein each switched capacitor of the plurality of switched capacitors is coupled to the first capacitor to receive a charge from the first capacitor in the first configuration, and wherein each switched capacitor of the plurality of switched capacitors is coupled to the second capacitor to deliver the charge received by the switched capacitor to the second capacitor in the second configuration.

9. The electronic system of claim 7, wherein the plurality of switched capacitors comprise:

a first switching capacitor having a first terminal and a second terminal, wherein the first terminal of the first switching capacitor is coupled to a reference voltage, and wherein the second terminal of the first switching capacitor is coupled to the first capacitor via a first switch; and

one or more additional switching capacitors, each additional switching capacitor having

a first terminal coupled to a first terminal of a preceding capacitor via a second switch, and

a second terminal coupled to (i) the first terminal of the preceding capacitor via a third switch, and (iii) the reference voltage via a fourth switch,

wherein a terminal of a last capacitor of the one or more additional capacitors is coupled to the second capacitor via a fifth switch.

10. The electronic system of claim 7, further comprising:

a comparator configured to

receive the voltage of the second capacitor as a first input and a reference voltage as a second input, and

initiate switching of the plurality of switched capacitors based on the voltage of the second capacitor,

wherein the plurality of switched capacitors are configured to transfer the charge stored at the first capacitor to the second capacitor when the voltage of the second capacitor is determined to be below the reference voltage by a predetermined amount.

11. The electronic system of claim 7, wherein the control circuit comprises a voltage-controlled oscillator that is coupled to the first capacitor, wherein the voltage-controlled oscillator is configured to i) receive the voltage stored at the first capacitor as an input, ii) output an oscillating signal, wherein the switching of the plurality of switched capacitors is responsive to the oscillating signal output by the voltage-controlled oscillator, and wherein a frequency of the oscillating signal increases as the voltage of the first capacitor decreases.

12. The electronic system of claim 7, wherein the electronic circuitry is a motor.

13. The electronic system of claim 7, wherein the electronic system is an electric vehicle.

14. A method of powering an electronic device, the method comprising:

charging a first capacitor with a charge received from an power source that is external to the electronic device, wherein the first capacitor is charged to achieve a supply voltage;

during a first phase, arranging a plurality of switched capacitors in parallel with the first capacitor, and transferring charge from the first capacitor to the plurality of switched capacitors;

during a second phase, arranging the plurality of switched capacitors in series, wherein one of the plurality of switched capacitors arranged in series is coupled to a second capacitor, and transferring charge from the plurality of switched capacitors arranged in series to the second capacitor; and

transferring a charge stored at the second capacitor to the electronic device,

wherein the plurality of switched capacitors are switched between the first phase and the second phase based on a voltage of the second capacitor, and

wherein a switching frequency of the plurality of switched capacitors increases as the supply voltage of the first capacitor decreases.

15. The method of claim 14, further comprising comparing the voltage of the second capacitor to a reference voltage, wherein the first and second phases are activated when the voltage of the second capacitor is determined to be below the reference voltage by a predetermined amount, and wherein the plurality of switched capacitors are configured to transfer a charge stored at the first capacitor to the second capacitor when the voltage of the second capacitor is determined to be below the reference voltage by the predetermined amount.

16. The method of claim 14, further comprising:

determining the voltage of the first capacitor; and

generating an oscillating signal based on the determined voltage of the first capacitor,

wherein the switching of the plurality of switched capacitors is responsive to the oscillating signal, and wherein a frequency of the oscillating signal increases as the voltage of the first capacitor decreases.

17. The method of claim 14, wherein the first capacitor is coupled to a charge port via a charging circuit.

18. The method of claim 14, wherein the plurality of switched capacitors comprise:

a first switching capacitor having a first terminal and a second terminal, wherein the first terminal of the first switching capacitor is coupled to a reference voltage, and wherein the second terminal of the first switching capacitor is coupled to the first capacitor via a first switch; and

one or more additional switching capacitors, each additional switching capacitor having

a first terminal coupled to a first terminal of a preceding capacitor via a second switch, and

a second terminal coupled to i) the first terminal of the preceding capacitor via a third switch, and ii) the reference voltage via a fourth switch,

wherein a terminal of a last capacitor of the one or more additional capacitors is coupled to the second capacitor via a fifth switch.

19. The method of claim 14, wherein the electronic device has a designated operating current, and wherein a maximum frequency of the switching of the plurality of switched capacitors produces a current at a node coupling the second capacitor and the electronic device, such that the current produced by the maximum frequency of switching is greater than or equal to the designated operating current of the electronic device.