High-efficiency adaptive DC/AC converter

• US 20060077700A1
• Filed: 11/17/2005
• Published: 04/13/2006
• Est. Priority Date: 04/24/2002
• Status: Active Grant

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 International Limited
• Inventors: Lin, Yung-Lin
• Granted Patent: US 7,515,446 B2
• Time in Patent Office: Days
• US Class Current: 363/98
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 7/4815 Resonant converters H02M7/4811 and H02M7/4826 take precedence
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current
• CPC Class Codes: H05B 41/2828 using control circuits for the switching elements H05B41/2827 takes precedence
• CPC Class Codes: H05B 41/2855 against abnormal lamp operating conditions
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A CCFL power converter circuit is provided using a high-efficiency zero-voltage-switching technique that eliminates switching losses associated with the power MOSFETs. An optimal sweeping-frequency technique is used in the CCFL ignition by accounting for the parasitic capacitance in the resonant tank circuit. Additionally, the circuit is self-learning and is adapted to determine the optimum operating frequency for the circuit with a given load. An over-voltage protection circuit can also be provided to ensure that the circuit components are protected in the case of open-lamp condition.

Claims

1-60. -60. (canceled)

61. A DC to AC inverter circuit, comprising:

an input voltage source;

a plurality of switches being selectively coupled to said voltage source;

a transformer having a primary side and a secondary side, said primary side being selectively coupled to said voltage source in an alternating fashion through said switches;

a load coupled to said secondary side of said transformer; and

a feedback control loop circuit receiving a feedback signal indicative of power being supplied to the load and adapted to control the conduction state of at least one of said switches so that said switches have a plurality of conduction states comprising a first state in which said switches deliver an amount of power to said load determined by said feedback signal, and a second state in which said switches deliver a predetermined minimum power to the load.

62. An inverter circuit as claimed in claim 61, wherein said feedback control loop circuit comprises:

an error amplifier comparing said feedback signal to a predetermined reference signal and generating an error signal indicative of the difference between said feedback signal and said predetermined reference signal; and

a flow-through switch coupled to said error amplifier and having a first conduction state wherein the output of said flow-through switch comprises a DC signal indicative of said first state of said switches, and a second conduction state wherein the output of said flow-through switch comprises a DC signal indicative of said second state of said switches.

63. An inverter circuit as claimed in claim 62, further comprising protection circuitry comprising a current sense comparator, said current sense comparator comparing said feedback signal to a second reference signal;

wherein if the compared value of said feedback signal and said second reference signal is within a predetermined range said current sense comparator generates a first control signal to control the conduction state of said switch corresponding to said first conduction state; and

wherein if the compared value of said feedback signal is outside a predetermined range said current sense comparator generates a second control signal to control the conduction state of said switch corresponding to said second conduction state.

64. An inverter circuit as claimed in claim 61, further comprising a sense resistor coupled between said load and said secondary side of said transformer, said sense resistor generating said feedback signal.

65. An inverter circuit as claimed in claim 63, wherein said protection circuitry further comprising an overvoltage protection circuit comprising a voltage comparator comparing a predetermined voltage reference to a voltage signal indicative of load voltage conditions and generating a voltage control signal.

66. An inverter circuit as claimed in claim 62, wherein said reference signal represents desired load conditions.

67. An inverter circuit as claimed in claim 63, wherein said second reference signal represents the minimum or maximum current permitted by said switches and/or said load.

68. An inverter circuit as claimed in claim 65, wherein said voltage control signal represents the maximum voltage at said secondary side of said transformer.

69. An inverter circuit for converting a DC voltage source to an AC voltage source to power a load, comprising:

a plurality of switches being selectively coupled to said DC voltage source; and

a feedback control loop circuit receiving a feedback signal indicative of power being supplied to said load and adapted to control the conduction state of at least one of said switches so that said switches have a conduction state in which said switches deliver an amount of power to said load determined by said feedback signal when said feedback signal is greater than a predetermined threshold.

70. An inverter circuit as claimed in claim 69, wherein said conduction state of said switches further comprises a second state in which said switches are controlled to deliver a predetermined minimum power to the load.

71. An inverter circuit as claimed in claim 70, wherein said second state occurs if said feedback signal is below said predetermined threshold.

72. A DC to AC inverter circuit comprising:

a plurality of switches being controlled in an alternating fashion; and

a feedback control loop circuit receiving a feedback signal indicative of power being supplied to a load and adapted to control the conduction state of at least one of said switches so that said switches have a conduction state to deliver a predetermined minimum power to the load.

73. An inverter circuit comprising:

a plurality of switches being controlled in an alternating fashion; and

a feedback control loop circuit receiving a feedback signal indicative of power being supplied to a load and adapted to control the conduction state of at least one of said switches so that said switches have overlapping conduction states, said overlapping conduction states comprise a first state in which said switches deliver an amount of power to said load determined by said feedback signal when said feed back signal is greater than a predetermined threshold; and

a second state in which said switches deliver a predetermined minimum power to the load.