Electronic ballast with load-independent and self-oscillating inverter topology

• US 8,699,244 B1
• Filed: 10/29/2010
• Issued: 04/15/2014
• Est. Priority Date: 10/29/2010
• Status: Expired due to Fees

• Current Assignee: Universal Lighting Technologies Incorporated (Panasonic Holdings Corporation)
• Original Assignee: Universal Lighting Technologies Incorporated (Panasonic Holdings Corporation)
• Inventors: Xiong, Wei
• Primary Examiner(s): PATEL, RAJNIKANT B
• Application Number:
  US12/915,317
• Time in Patent Office: 1,264 Days
• Field of Search: 363 17- 20, 363/25, 363/26, 363 71- 76, 363 95- 98, 363/79, 363/132, 323/222, 323/223, 323/224, 323/266, 323/271, 323/289, 315/224, 315/226, 315/244, 315/291, 315/247, 315/307, 315/219
• US Class Current: 363/37
• CPC Class Codes: H02M 7/53832 in a push-pull arrangement
• CPC Class Codes: H05B 41/2827 using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations
• 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 self-oscillating inverter provides an output voltage with fixed operating frequency and amplitude independently of a load. First and second switching elements are arranged in a half-bridge configuration. A resonant circuit having a primary winding of a resonant inductor and a resonant capacitor is coupled between the switching elements. A clamping circuit limits the voltage across the resonant capacitor to a predetermined maximum value, and along with the resonant capacitor defines a capacitance compensation circuit having an equivalent capacitance greater than that of the resonant capacitor alone, wherein the actual resonant frequency of the inverter is less than the natural frequency of the resonant circuit such that soft-switching is assured. An output voltage across the resonant inductor during steady-state operation is a quasi-square waveform with a fixed amplitude, wherein a load voltage across a secondary winding of the inductor is also a quasi-square waveform with a fixed amplitude.

Claims

1. An inverter comprising:

first and second switching elements arranged in a half-bridge configuration;

a resonant circuit having a primary winding of a resonant inductor coupled on a first end to a node between the first and second switching elements and a resonant capacitor coupled between a second end of the resonant inductor and a negative terminal for the inverter;

a load circuit comprising a secondary winding of the resonant inductor effective to drive a load when an output voltage is generated across the primary winding of the resonant inductor;

a diode having its anode coupled to a node between the resonant capacitor and the primary winding of the resonant inductor and its cathode coupled to a positive terminal of the inverter, the diode effective to clamp the voltage across the resonant capacitor to a predetermined maximum value wherein an output voltage during a steady-state operation across the primary winding and thereby the secondary winding of the resonant inductor is a quasi-square waveform with a fixed amplitude; and

a starting circuit having at least a second secondary winding of the resonant inductor and effective to cause self-oscillation of the first and second switching elements, the starting circuit further effective to fix the operating frequency of self-oscillation in the first and second switching elements equal to the natural resonant frequency of the resonant circuit regardless of a load condition.

2. The inverter of claim 1, the starting circuit further effective to interrupt self-oscillation in response to a short load condition in the load circuit.

3. The inverter of claim 1, the diode and the resonant capacitor collectively defining a capacitance compensation circuit having an equivalent capacitance greater than the capacitance of the resonant capacitor alone, wherein the actual resonant frequency of the inverter circuit is less than the natural frequency of the resonant circuit.

4. The inverter of claim 1, the first and second switching elements further comprising N-channel MOSFETs, and the starting circuit further comprising second and third secondary windings of the resonant inductor coupled to the gates of the first and second switching elements, respectively.

5. The inverter of claim 1, the first switching element further comprising an N-channel MOSFET and the second switching element further comprising a P-channel MOSFET, and the starting circuit further comprising a second secondary winding of the resonant inductor having a first end coupled to the node between the first and second switching elements and a second end coupled to the gates of the first and second switching elements.

6. An inverter comprising:

first and second switching elements arranged in a half-bridge configuration between positive and negative inverter terminals;

a resonant circuit having a primary winding of a resonant inductor coupled on a first end to a node between the first and second switching elements and a resonant capacitor coupled between a second end of the resonant inductor and the negative inverter terminal;

a load circuit comprising a secondary winding of the resonant inductor effective to drive a load when an output voltage is generated across the primary winding of the resonant inductor;

a clamping circuit further comprising a first diode having its anode coupled to a node between the resonant capacitor and the primary winding of the resonant inductor and its cathode coupled to the positive inverter terminal, and a second diode having its cathode coupled to said node and its anode coupled to the negative terminal; and

a starting circuit having at least a second secondary winding of the resonant inductor and effective to cause self-oscillation of the first and second switching elements.

7. The inverter of claim 6, the clamping circuit effective to clamp the voltage across the resonant capacitor to a predetermined maximum value wherein an output voltage during a steady-state operation across the primary winding and thereby the secondary winding of the resonant inductor is a quasi-square waveform with a fixed amplitude.

8. The inverter of claim 6, the clamping circuit and the resonant capacitor collectively defining a capacitance compensation circuit having an equivalent capacitance greater than the capacitance of the resonant capacitor alone, wherein the actual resonant frequency of the inverter circuit is less than the natural frequency of the resonant circuit.

9. The inverter of claim 6, the starting circuit effective to fix an operating frequency of self-oscillation in the first and second switching elements equal to the natural resonant frequency of the resonant circuit regardless of a load condition, and further effective to interrupt self-oscillation in response to a short load condition representative of a missing load in the load circuit.

10. The inverter of claim 6, the first and second switching elements further comprising N-channel MOSFETs, and the starting circuit further comprising second and third secondary windings of the resonant inductor coupled to the gates of the first and second switching elements, respectively.

11. The inverter of claim 7, the first switching element further comprising an N-channel MOSFET and the second switching element further comprising a P-channel MOSFET, and the starting circuit further comprising a second secondary winding of the resonant inductor having a first end coupled to the node between the first and second switching elements and a second end coupled to the gates of the first and second switching elements.