Capacitor start-up apparatus and method with fail safe short circuit protection
View Patent ↗Electronic circuits couple energy storage devices, such as double layer capacitors or rechargeable battery cells, to a power supply output, thereby improving noise suppression and extending ride-through capability of the power supply. In a typical circuit, an energy storage device is coupled in series with a switch that controls the charging current into the energy storage device. The switch is controlled by a comparator that receives a signal related to the voltage level of the power supply. In some embodiments, the comparator also receives a feedback signal related to a charging current flowing into the energy storage device. The circuit is configured so that the switch limits the charging current to a predetermined current level, or does not allow the charging current to flow until the output voltage of the power supply reaches a predetermined voltage level.
1. A circuit for coupling an energy storage device to an output of a first power supply, the circuit comprising:
a current-sensing resistor;
a switch comprising a pair of outputs coupled in series with the energy storage device and with the current-sensing resistor, and an input receiving a switching signal, the switch assuming a conducting state when the switching signal is at a first level, the switch assuming a non-conducting state when the switching signal is at a second level;
a differential high-gain device comprising an output coupled to the input of the switch, a first input biased by a control voltage, and a second input receiving feedback voltage generated by a charging current flowing through the current-sensing resistor;
wherein:
the output of the differential high-gain device drives the input of the switch with the switching signal at the first level when the control voltage exceeds the feedback voltage by an input offset voltage of the differential high-gain device, and the differential high-gain device drives the input of the switch with the switching signal at the second level when the feedback voltage exceeds the control voltage by the input offset voltage; and
the current-sensing resistor, the switch, and the energy storage device are coupled across the output of the first power supply.
2. A circuit according to claim 1 , further comprising a mechanism generating the control voltage as a function of a voltage appearing at the output of the first power supply, wherein the control voltage increases monotonically with the voltage appearing at the output of the first power supply.
3. A circuit according to claim 1 , wherein the differential high-gain device comprises an operational amplifier.
4. A circuit according to claim 1 , wherein the differential high-gain device comprises CMOS circuitry.
5. A circuit according to claim 1 , wherein the differential high-gain device comprises a low-offset device.
6. A circuit according to claim 1 , wherein the differential high-gain device comprises a comparator.
7. A circuit according to claim 1 , wherein the switch comprises a discrete transistor.
8. A circuit according to claim 1 , wherein the switch comprises a discrete power transistor.
9. A circuit according to claim 1 , wherein the switch comprises a MOSFET.
10. A circuit according to claim 1 , wherein the switch comprises an analog semiconductor switch.
11. A circuit according to claim 1 , further comprising a current-limiting resistor coupled between the output of the differential high-gain device and the input of the switch.
12. A circuit according to claim 1 , further comprising a first resistor and a second resistor coupled in series to form a voltage divider, the voltage divider being coupled across the output of the first power supply, the voltage divider generating the control voltage at a junction of the first and second resistors.
13. A circuit according to claim 12 , wherein the differential high-gain device comprises a low-offset device.
14. A circuit according to claim 13 , wherein the first and second resistors are precision, temperature-stable resistors.
15. A circuit according to claim 14 , wherein the differential high-gain device comprises CMOS circuitry.
16. A circuit according to claim 1 further comprising the energy storage device.
17. A circuit according to claim 16 , wherein the energy storage device comprises a capacitor.
18. A circuit according to claim 16 , wherein the energy storage device comprises a double layer capacitor.
19. A circuit according to claim 16 , wherein the energy storage device comprises at least two capacitors and a voltage balancer.
20. A circuit according to claim 16 , wherein the energy storage device comprises a secondary battery cell.
21. A circuit according to any one of claims 1 , further comprising a second power supply, the second power supply comprising input connections coupled across the output of the first power supply to receive power from the first power supply at a first nominal voltage, and an output providing electrical power at a second nominal voltage to a load.
22. A circuit according to claim 21 , wherein the second power supply comprises a regulator.
23. A circuit according to claim 21 , wherein the second power supply comprises a DC-to-DC power converter.
24. A circuit according to claim 21 , wherein the second nominal voltage exceeds the first nominal voltage by about 7 volts.
25. A circuit according to claim 21 , wherein the first nominal voltage is about 5 volts, and the second nominal voltage is about 12 volts.
26. A circuit for coupling an energy storage device to an output of a first power supply, the circuit comprising:
a switch comprising a pair of outputs coupled in series with the energy storage device to form a series combination, the series combination being coupled across the output of the first power supply, and an input receiving a switching signal, the switch assuming a conducting state when the switching signal is at a first level, the switch assuming a non-conducting state when the switching signal is at a second level;
a connection receiving a voltage reference signal; and
a differential high-gain device comprising an output coupled to the input of the switch, a first input biased by a control voltage, and a second input receiving the voltage reference signal;
wherein:
the control voltage is monotonically related to a voltage appearing at the output of the first power supply so that the differential high-gain device drives the input of the switch with the switching signal at the first level when the control voltage exceeds the voltage reference signal by an input offset voltage of the differential high-gain device, and the differential high-gain device drives the input of the switch with the switching signal at the second level when the voltage reference signal exceeds the control voltage signal by the input offset voltage.
27. A circuit according to claim 26 , further comprising a voltage reference source generating the voltage reference signal.
28. A circuit according to claim 27 , further comprising a first resistor and a second resistor coupled in series with the first resistor to form a voltage divider, the voltage divider being coupled across the output of the first power supply, the voltage divider generating the control voltage at a junction of the first and second resistors.
29. A circuit according to claim 28 , wherein the differential high-gain device comprises a low-offset device.
30. A circuit according to claim 28 , wherein the first and second resistors are precision, temperature-stable resistors.
31. A circuit according to claim 30 , wherein the differential high-gain device comprises CMOS circuitry.
32. A circuit according to claim 28 , further comprising the energy storage device.
33. A circuit according to claim 32 , wherein the energy storage device comprises a capacitor.
34. A circuit according to claim 32 , wherein the energy storage device comprises a double layer capacitor.
35. A circuit according to claim 32 , wherein the energy storage device comprises at least two capacitors and a voltage balancer.
36. A circuit according to claim 32 , wherein the energy storage device comprises a rechargeable battery cell.
37. A circuit according to claim 28 , wherein the differential high-gain device comprises an operational amplifier.
38. A circuit according to claim 28 , wherein the differential high-gain device comprises CMOS circuitry.
39. A circuit according to claim 28 , wherein the differential high-gain device comprises a comparator.
40. A circuit according to claim 28 , wherein the switch comprises a discrete transistor.
41. A circuit according to claim 28 , wherein the switch comprises a discrete power transistor.
42. A circuit according to claim 28 , wherein the switch comprises a MOSFET.
43. A circuit according to claim 28 , wherein the switch comprises an analog semiconductor switch.
44. A circuit for coupling an energy storage device to an output of a first power supply, the circuit comprising:
a switch comprising a pair of outputs coupled in series with the energy storage device to form a first series combination, the first series combination being coupled across the output of the first power supply, and an input receiving a switching signal, the switch assuming a conducting state when the switching signal is at a first level, the switch assuming a non-conducting state when the switching signal is at a second level;
a connection receiving a voltage reference signal;
a first resistor and a second resistor coupled in series to form a second series combination comprising a junction of the first and second resistors, the second series combination being coupled across the output of the first power supply;
a differential high-gain device comprising an output coupled to the input of the switch, a non-inverting input coupled to the junction of the first and second resistors, and an inverting input receiving the voltage reference signal; and
a positive feedback resistor coupled between the output of the differential high-gain device and the non-inverting input of the differential high-gain device.
45. A circuit according to claim 44 , further comprising a voltage reference source generating the voltage reference signal.
46. A circuit according to claim 45 , wherein the differential high-gain device comprises a low-offset device.
47. A circuit according to claim 46 , wherein the first, second, and positive feedback resistors are precision, temperature-stable resistors.
48. A circuit according to claim 47 , wherein the differential high-gain device comprises CMOS circuitry.
49. A circuit according to claim 47 , further comprising the energy storage device.
50. A circuit according to claim 46 , wherein the energy storage device comprises a capacitor.
51. A circuit according to claim 47 , wherein the energy storage device comprises a double layer capacitor.
52. A circuit according to claim 47 , wherein the energy storage device comprises at least two capacitors and a voltage balancer.
53. A circuit according to claim 45 , wherein the differential high-gain device comprises an operational amplifier.
54. A circuit according to claim 45 , wherein the differential high-gain device comprises CMOS circuitry.
55. A circuit according to claim 45 , wherein the differential high-gain device comprises a comparator.
56. A circuit according to claim 45 , wherein the switch comprises a discrete transistor.
57. A circuit according to claim 45 , wherein the switch comprises a discrete power transistor.
58. A circuit according to claim 45 , wherein the switch comprises a MOSFET.
59. A circuit according to claim 45 , wherein the switch comprises an analog semiconductor switch.