Current-mode direct-drive inverter

• US 7,265,499 B2
• Filed: 12/14/2004
• Issued: 09/04/2007
• Est. Priority Date: 12/16/2003
• Status: Expired due to Fees

• Current Assignee: Polaris PowerLED Technologies, LLC (Microchip Technology Incorporated)
• Original Assignee: Microsemi Corporation (Microchip Technology Incorporated)
• Inventors: Ball, Newton E.
• Primary Examiner(s): Philogene; Haissa
• Application Number:
  US11/011,760
• Publication Number:
  US 20050162098A1
• Time in Patent Office: 994 Days
• Field of Search: 315/209.R, 315/291, 315/307, 315/219, 315/225, 315/247, 315/276, 315/279, 315/224, 315/206, 315/DIG.5, 315/DIG.7, 315/177, 315/178, 315/282, 363 16- 19, 363/41, 363/60, 363/124, 323/222, 323/224, 323/277
• US Class Current: 315/282
• CPC Class Codes: H05B 41/2828 using control circuits for the switching elements H05B41/2827 takes precedence
• CPC Class Codes: H05B 45/382 with galvanic isolation between input and output
• CPC Class Codes: H05B 45/39 Circuits containing inverter bridges
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
• CPC Class Codes: Y10S 315/04 Dimming circuit for fluorescent lamps

Abstract

An efficient and flexible current-mode driver delivers power to one or more light sources in a backlight system. In one application, the current-mode driver is configured as an inverter with an input current regulator, a non-resonant polarity-switching network, and a closely-coupled output transformer. The input current regulator can output a regulated current source in a variety of programmable wave shapes. The current-mode driver may further include a rectifier circuit and a second polarity-switching network between the closely-coupled output transformer and a lamp load. In another application, the current-mode driver delivers power to a plurality of light sources in substantially one polarity by providing a regulated current to a network of time-sharing semiconductor switches coupled in series with different light sources coupled across each semiconductor switch.

Claims

1. A current-mode inverter comprising:

a current regulator configured to accept a DC voltage and to output a regulated current;

a non-resonant switching network configured to produce an AC driving current by periodically alternating conduction paths for the regulated current; and

a closely-coupled output transformer configured to conduct the AC driving current in a primary winding and a corresponding load current in a secondary winding, wherein the closely-coupled output transformer has a magnetization inductance to leakage inductance ratio that is greater than 30;

1.

2. The current-mode inverter of claim 1, wherein the load current has a substantially identical wave shape as the AC driving current.

3. The current-mode inverter of claim 2, wherein the amplitude of the load current is proportional to the amplitude of the AC driving current.

4. The current-mode inverter of claim 1, further comprising a feedback circuit coupled to the non-resonant switching network on the primary side of the closely-coupled output transformer to sense the AC driving current and to generate a feedback signal for the current regulator.

5. The current-mode inverter of claim 1, wherein the current regulator is a switching current regulator using hysteretic pulse width modulation, a switching current regulator using clocked pulsed width modulation or a linear current regulator.

6. The current-mode inverter of claim 1, wherein the non-resonant switching network uses a push-pull topology with semiconductor switches coupled to respective opposite ends of the primary winding and the regulated current applied to a center tap of the primary winding.

7. The current-mode inverter of claim 2, wherein the non-resonant switching network uses a full-bridge topology.

8. The current-mode inverter of claim 7, wherein the full-bridge topology comprises a pair of p-type semiconductor switches coupled between an output of the regulated current and respective opposite terminals of the primary winding and a pair of n-type semiconductor switches coupled between the respective opposite terminals of the primary winding and the feedback circuit.

9. The current-mode inverter of claim 1, wherein semiconductor switches in the non-resonant switching network are closed to conduct a predetermined idle current when the load current is substantially zero.

10. The current-mode inverter of claim 1, wherein a fluorescent lamp is coupled across the secondary winding, and the voltage across the secondary winding automatically increases to ignite the fluorescent lamp.

11. A method to operate an inverter in current mode, the method comprising the steps of:

converting an input power source into a regulated current;

periodically alternating conduction paths for the regulated current using a non-resonant switching structure to generate an AC current source; and

coupling the AC current source to a lamp load with an output transformer, wherein the output transformer is a tightly-coupled transformer with a magnetization inductance to leakage inductance ratio that is greater than 30;

1.

12. The method of claim 11, wherein semiconductor switches in the non-resonant switching structure are closed to stop generating the AC current source if the lamp load is off, missing or faulty.

13. The method of claim 11, further comprising sensing the AC current source to generate a feedback signal for controlling brightness of the lamp load.

14. The method of claim 11, wherein the lamp load comprises a plurality of cold cathode fluorescent lamps coupled in series across a secondary winding of the output transformer.

15. The method of claim 11, wherein the inverter operates in a single continuous mode for striking and regulating power to the lamp load.

16. The method of claim 11, wherein the lamp load comprises one or more light sources for backlighting a liquid crystal display.

17. A current-mode inverter comprising:

means for generating a regulated current source;

means for periodically alternating conduction paths for the regulated current source with non-resonant switching to generate an AC driving current; and

output transformer means for coupling the AC driving current to a lamp structure, wherein the lamp structure conducts a lamp current with a substantially identical wave shape and proportional amplitude as the AC driving current, and wherein the output transformer means comprises a tightly-coupled transformer with a magnetization inductance to leakage inductance ratio that is greater than 30;

1.

18. The current-mode inverter of claim 17, wherein light intensity of the lamp structure is controlled by a combination of adjusting duty cycles or burst mode durations of the regulated current source and duty cycles or burst mode durations of the AC driving current.

19. The current-mode inverter of claim 17, further comprising means for sensing the AC driving current to control brightness of the lamp structure by adjusting the regulated current source.

20. The current-mode inverter of claim 17, wherein the lamp structure includes one or more fluorescent lamps used for backlighting a liquid crystal television, a desk top monitor, an automotive display, a notebook computer or a tablet computer.

21. The current-mode inverter of claim 17, wherein the non-resonant switching is implemented by metal-oxide-semiconductor field-effect-transistors.