In control terms, design A can easily achieve stability, stability of design B is uncertain and depends on the load impedance. Design B can under circumstances react faster on load changes.
In control terms, design A can easily achieve stability, stability of design B is uncertain and depends on the load impedance. Design B can under circumstances react faster on load changes.
Thanks, I am relieved to hear you both saying this, since “A” is how I did the first prototype PCB.
However, I then modified “A” to be like “B” and the current as seen in the sensor has less disturbance in it. Do you know why?
I wonder if I should also have the sensor upstream of the 220uF electrolytic (C70 in “A”)?
If you mean "upstream" as "after the inductor but before
the filter" as opposed to "after the filter but before the
load" I don't see anything but a wire-length's worth of
difference.
Thanks, The Hall sensor has to be downstream of the 150nH inductor ("L6" or "L2" respectively) otherwise the current seen in the sensor has a 80kHz oscillation in it.
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Upstream means the sensor sees all the high freq current info into the capacitor - this will always be more stable ...
Thanks....I am just wondering if it would be even better to have just a 10uF film capacitor at the DCDC module output, then the 150nH inductor, and then the Hall Sensor, and then all the electrolytic capacitance (approx 2mF's worth)?
I initially declined to do it like this because the DCDC module needs 220uF at its output for stability......and so i put this 220uF right at the module's output.
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Taking circuit A, there is an LC output filter there with a resonant frequency of 10273Hz (150nH and 1.6mF). The crossover frequency of the DCDC module is said to be 20kHz…….
so isn’t this a recipe for instability?.....having said that….i would expect the added external output capacitance to reduce the crossover frequency of the overall power supply……so this stability fear could be wide of the mark…….with Vicor modules, there is no way of measuring the crossover of the overall thing, so we’re stuffed?
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I have implemented the external current clamp, because there will be forty of these DCDC modules all operating together….kind of all in parallel with each other….the modules have a droop sharing algorithm (vout reduces by 5% from no load to full load)….however, due to the sheer size of our system, the volt drops from each module to the load will be widely different, and so droop sharing along won’t be enough…and we believe we need the current clamp as shown…(to stop any individual module over-hogging current)