Journal of Power Electronics

The Korean Institute of Power Electronics (전력전자학회)
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Design of a TRIAC Dimmable LED Driver Chip with a Wide Tuning Range and Two-Stage Uniform Dimming

  • Chang, Changyuan (School of Integrated Circuits, Southeast University) ;
  • Li, Zhen (School of Integrated Circuits, Southeast University) ;
  • Li, Yuanye (School of Integrated Circuits, Southeast University) ;
  • Hong, Chao (School of Integrated Circuits, Southeast University)
  • Received : 2017.02.15
  • Accepted : 2017.07.15
  • Published : 2018.03.20
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Abstract

A TRIAC dimmable LED driver with a wide tuning range and a two-stage uniform dimming scheme is proposed in this paper. To solve the restricted dimming range problem caused by the limited conduction ratio of TRIAC dimmers, a conduction ratio compensation technique is introduced, which can increase the output current up to the rated output current when the TRIAC dimmer turns to the maximum conduction ratio. For further optimization, a two-stage uniform dimming diagram with a rapid dimming curve and a slow dimming curve is designed to make the LED driver regulated visually uniform in the whole adjustable range of the TRIAC dimmer. The proposed control chip is fabricated in a TSMC $0.35{\mu}m$ 5V/650V CMOS/LDMOS process, and verified on a 21V/500mA circuit prototype. The test results show that, in the 90V/60Hz~132V/60Hz ac input range, the voltage linear regulation is 2.6%, the power factor is 99.5% and the efficiency is 83%. Moreover, in the dimming mode, the dimming rate is less than 1% when the maximum dimming current is 516mA and the minimum dimming current is only about 5mA.

Keywords

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Fig. 1. System diagram of the proposed circuit.

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Fig. 2. Key operation principle waveforms of the proposed circuit.

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Fig. 3. Constant current control circuit.

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Fig. 4. Dimming control circuits with a wide tuning range.

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Fig. 5. Theoretical dimmer outline of a wide tuning range design.

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Fig. 6. Wide tuning range and a two-stage uniform dimming control circuit.

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Fig. 7. Theoretical output outline of the wide tuning range andtwo-stage uniform dimming design.

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Fig. 8. Design implementation of the conduction ratio compensation circuit.

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Fig. 9. Key operation waveforms of the conduction ratiocompensation circuit.

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Fig. 10. Design implementation of the switch circuit.

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Fig. 11. Key operation waveforms of the switch circuit.

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Fig. 12. Design implementation of the pull-down current controlcircuit.

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Fig. 13. Micrograph of the fabricated chip.

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Fig. 14. Prototype of the proposed LED driver.

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Fig. 15. Diagrams of: (a) measured steady-state waveforms under90Vac; (b) measured steady-state waveforms under 110Vac; (c)measured output current IOUT versus the ac input voltage VIN.

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Fig. 16. Diagrams of: (a) measured power factor under 110Vacand 60Hz-input; (b) measured PF versus the ac input voltage.

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Fig. 17. Measured efficiency versus the ac input voltage.

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Fig. 18. Measured steady waveforms under 110Vac and 60Hz at:(a) D=75%; (b) 50%; (c) D=30%.

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Fig. 19. Measured output current waveforms under 110Vac and60Hz at: (a) D=75%; (b) D=50%; (c) D=30%.

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Fig. 20. Measured output current versus the conduction ratio.

TABLE I KEY COMPONENTS AND PARAMETERS

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TABLE II COMPARISON BETWEEN THE PROPOSED METHOD AND PRIOR STUDIES

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