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 measurementEmployed 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 frequencyHigher 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