Sunday 11 January 2015

power supply - Driving LM3886 at 100 KHZ in Bridge Tied Load (BTL) configuration?


Would someone have experience with driving a pair of LM3886 Overture Power Amplifiers in BTL with up to 100 KHz sine wave?


My parameters:




  • Frequency band of interest: 20KHz to 100 KHz, sine wave

  • Load is pure capacitive, 10-20 Ohm, 5000 pF

  • Power delivery to load: Up to 50 watts RMS

  • Amplifier Configuration: Bridge Tied Load

  • THD / noise, even up to 5%, not a concern

  • Power: Unregulated +/-35 Volts 5+5 Amperes, 10000 uF reservoir capacitor on each rail


Found a useful whitepaper on BTL with LM3886. However, the operating band for this paper is 20Hz-20KHz.


Starting with the schematic from here: enter image description here


Of course, input / output / feedback part values shown would need to change for my frequency band of interest, but my analog-fu is a bit rusty circa 1988, so some brushing up to be done.





My questions:



  • Will this work at all? (I don't see why not, but found no useful information found)

  • Any suggestion on a different single-chip power amp to use instead?

  • What is the gain I should design for?

    • More immediate interest: What input Vpp range is needed?




  • What do I need to take care of in terms of feedback / compensation and stability management

    • Info found so far is for audio frequency range, little mention of high frequencies

    • Found a discussion about oscillation at high frequencies (50KHz+) due to electrolytic caps.

    • No info found about driving capacitive load, as audio = inductive loads, typically.

    • How do I get an essentially flat response for 20-100 KHz?



  • For the power supply:


    • Recommendations between single and dual bridge

    • Is the 5 + 5 ampere calculation good, with reasonable headroom?

    • Is there a switching power supply alternative that might save cost / reduce heat?



  • Anything else critical to address even at experimental stage (One-off DIY, isn't going to production)




Any other inputs / help / advice gratefully accepted!




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