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Capacitance multiplier to further reduce noise

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  • Capacitance multiplier to further reduce noise

    I have to design a USB powered 5V boost to 24V ~50mA IEPE power supply and have seen it suggested in other audio circuits to use a 'capacitance multiplier' to reduce power supply noise. In the mixed signal course, I have taken lots of notes on separating and filtering sensitive analog power supply rails, but have not noticed him referring to this kind of filtering. I expect any of the standard RLC or CLC Pi filters would be required (possibly both pre and post boost regulator), but I'm thinking that I'll need some heavy filtering, based on my requirements. Effectively I have a max +/- 10V AC signal sitting biased around 12V on a current limited 24V rail and thus need the supply to be as 'quiet' (<2mV) as possible.

    I wonder if Phil or others who may have experience in this area would mind weighing in on whether this additional filtering is recommended?

    If you're wondering what this is all about, some references:
    I've had it suggested to specifically use the Sziklai pair for my application and would be interested to get any further feedback.

  • #2
    Another article from Analog Devices (formerly Linear Technology) showing the effect of adding a capacitance multiplier to reduce noise:

    Ultralow Noise, 48 V, Phantom Microphone Power Supply Using a Tiny DC-to-DC Boost Converter