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Bldc driver current sensing
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warfull:
Hi.
I'm developping a high power bldc driver and I can't explain what I see on my scope...
I'm using a pre-existing power-board to speed up the process and build only logic and mosfet driver board.  The power board uses copper traces to make shunt resistor and each phase has one of about 50 µohms for current sensing.
I use INA225 with Vcc=5V, G=100 and Vref=0.5V.
In the pictures next I'm trying to get the rotor position using the variable inductance strategy. So phases V and W are driven low  and U is driven high(30V) in the first pulse, then i reverse current : phase U is driven low and V and W are driven high. next phase swapping and so on.
Shunt resistor are on the low side. Yellow is phase U, clear blue is phase V and pink is W.




And here a schematic of the pcb layout:



During the first pulse U is driver high and V and W low, current is only flowing on the low side of V and W but as you see the OP AMP see roughly the same thing on every phases, and i'm pretty sure that no current is flowing on low side of U phase.

So is there any one to explain why the yellow trace is following the blue and pink in the first pulse ?


coromonadalix:
why your r8 r15 r20 r12 r21 resistors aren't equal on each phase ?

you have r9 r13 r17   who are equal on each phase
warfull:
Yes you are right. It's a mistake, consider this one :



Shunt resitors are r7, r14 and r18.
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