high bandwidth automotive power supply for low-cost pwm audio amplifiers mikkel c. w. høyerby...

High Bandwidth Automotive Power Supply for Low-cost PWM Audio

Amplifiers

Mikkel C. W. Høyerby (Ørsted·DTU)

Dennis R. Andersen (Bang & Olufsen ICEpower a/s)

Michael A. E. Andersen (Ørsted·DTU)

Lars Petersen (Bang & Olufsen ICEpower a/s)

High Bandwidth Automotive Power Supply for Low-cost PWM Audio

Amplifiers

• Reduction of switching amplifier output EMI • Reduction of switching amplifier idle losses • Requires high bandwidth and dv/dt• Tracking supply for PWM SE amplifiers is new ground

”Supply pumping”

• Switching SE amplifier transfers power between rails• Tracking converter must have bidirectional outputs in

addition to high bandwidth!• SE amplifier still desirable in multi-channel system

due to low cost

Suitable topology

• No single stage solution found suitable• Energy storage is cheaper than energy transfer when

dealing with ”supply pumping” in the buck topology

Current measurement vs. estimation

• High control bandwidth requires current feedback• Short-circuit protection not essential• Current estimation eliminates noise problems• DC information is not available with current

estimation => Current loop transfer function is altered

Standard current measurement Employed estimation technique

Effect of employing current estimation

• Dominant pole movement caused by load variation is restricted when LF cutoff is introduced in current loop

• Reducing current loop gain at output filter cutoff frequency causes increased influence of filter Q on closed loop transfer function

Low current loop LF cutoff frequency Higher current loop LF cutoff frequency

Control system achievements

• Inductor current signal is practically noiseless

• Closed-loop bandwidth is high• Controller is stable with any resistive load

Estimated inductor current

Actual inductor current

4Ω loadUnloaded

Conclusion

• Tracking PSU for single ended switching amplifiers is technically possible

• Tracking PSU with suitable topology has been prototyped

• Current estimation provides an alternative set of properties when compared to current measurement

The prototype tracking PSU