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Søren Poulsen Ph.D. Student Ørsted ·DTU Technical University of Denmark spo@oersted.dtu.dk

Integrating switch mode audio power amplifiers and electro dynamic loudspeakers for a higher power efficiency. Michael A. E. Andersen Professor Ørsted ·DTU Technical University of Denmark ma@oersted.dtu.dk. Søren Poulsen Ph.D. Student Ørsted ·DTU Technical University of Denmark

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Søren Poulsen Ph.D. Student Ørsted ·DTU Technical University of Denmark spo@oersted.dtu.dk

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  1. Integrating switch mode audio power amplifiers and electro dynamic loudspeakers for a higher power efficiency Michael A. E. Andersen Professor Ørsted·DTU Technical University of Denmark ma@oersted.dtu.dk Søren Poulsen Ph.D. Student Ørsted·DTU Technical University of Denmark spo@oersted.dtu.dk

  2. Using the voice coil inductance as output filter Integrating switch mode audio amplifier and loudspeaker

  3. Maximum phase shift ~ 65° Real part caused by eddy current losses in the magnetic system Resonances at high frequencies Voice coil inductance Voice coil capacitance Loudspeaker impedance

  4. 2-level modulation 3-level modulation PWM modulation schemes

  5. 2-level modulation 3-level modulation PWM HF output spectra M=0.01 M=1

  6. Layer to layer capacity Pushing up ressonance frequency

  7. Minimizing L·C L  N2 C  1/number of winding layers Fewer turns More winding layers Pushing up voice coil resonance frequency

  8. Voice coil fill factor

  9. Efficiency constant for same fill-factor Higher fill factor benefits efficiency Efficiency improvement with low impedance voice coils

  10. Output stage losses Using same DIE area and voice coil fill factor for different supply voltages Ripple current included Power stage losses, 2-level modulation Single ended and full bridge output stage 5V, 10V, 20V, 40V supply

  11. Modifying magnetic system with other materials near the voice coil Ferrite Exellent HF properties Bmax0,5T Powder iron Exellent HF properties Bmax 1-1,4T Improving the magnetic system

  12. Prototype magnetic system, FEM simulation-26 iron powder material used

  13. Blue: Above gap Green: In gap Red: Below gap Short voice coil Standard magnetic system

  14. Blue: Above gap Green: In gap Red: Below gap Short voice coil Prototype magnetic system

  15. Blue: Prototype system Green: Std. system Full length voice coil Standard and prototype magnetic system

  16. Magnetic system power loss vs. fs, 2-level modulation Standard magnetic system Prototype magnetic system Blue: M=0Green: M=0.25 Red: M=0.5 Magenta: M=0.75Orange: M=1

  17. Magnetic system power loss vs. fs, 3-level modulation Standard magnetic system Prototype magnetic system Green: M=0.25 Red: M=0.5 Magenta: M=0.75Orange: M=1

  18. Listening tests carried out ABC blind test No prove of sound degradation Audio quality

  19. Using the voice coil inductance as output filter for the amplifier possible Eddy current losses in the magnetic system can be reduced significantly Higher voice coil fill factor possible Dedication favours low impedance interface Significant improvement of power efficiency achievable Conclusion

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