power supply dynamics

John Larkin · 2023-06-30T17:39:31+00:00

I want to build a cheap-ish 8-channel DC power supply.Each channel can be a half-bridge, which is easy.If I filter with an inductor and a low-ESR cap, I get good ripple butif I take feedback from the output the loop dynamics, the phasemargin, sucks.So why not take the voltage feedback from the switch node? No phaselag! If we know the load current and the circuit losses, we can tweakthe output regulation pretty well. ADCs can even be synchronized to the PWM drive, so we can do FPGAtricks to synchronously filter the maybe-ripply voltage feedback, orjust apply an arbitrarily complex lowpass filter ahead of theclosed-loop math.Digitizing the current allows even fancier loop dynamics.

Jun 30, 2023 Last reply: 2 years ago 21 Replies

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tridac 3 years ago

Why not Sense the output voltage with a separate diode and smaller cap just to sense the voltage alone ?. Depends on what regulation you need. but why add complexity and cost with an fpga. Overthinking ?

Chris

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John Larkin 3 years ago

I posted the almost-final circuit below, repeated here

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It does combine fast feedback from the switch node and slow feedback from the final output. That gives good dynamics and good regulation.

The board plugs into a mainframe and needs the FPGA to handshake with the main controller, a MicroZed board. The FPGA allows a lot of features too, like programmable slew rate, cc/cv/cr modes, data logging, things like that. The Efinix part is just $10.

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