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Sensorless VS Sensored BLDC motors

Lord_grezington

May 3, 2013
124
Joined
May 3, 2013
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Hello All

Got an issue where I have a PCB that uses the Allegro A4963 IC. I am trying to displace another cheap Chinese JRC per-driver that runs sensored motor, please fin th link here http://www.njr.com/semicon/products/NJM2626.html.

Now, running the same motor (and load) at the same supply voltage the JRC achieves around 52% more speed. (the A4963 schematic is very similar to the demo one as the PDF attached).

I took a trace of the motor phase voltages and note that the JRC sensored driver produces a square wave where the A4963 produces a trapezoidal one. I am guessing that the voltage losses due to being trapezoidal may be the reason for my decrease in speed.

I spoke to the Applications engineers at Allegro and all they can say is that I need to increase the supply voltage or adjust the phase advance (which I tried every value going with no luck).

So, I was hoping one of you had seen a similar issue in the passed and willing to share their knowledge, all traces and schematics are attached (I cant find one for the Chinese driver unfortunately).

Thanks

PS - Before you mention that the JRC driver uses high side N-channel mosfets that are more efficient, no it doesn't, both drivers use P-channel high side fets...

I cant seem to attached any files, anyone help me with a format? not even PDF goes through without an error...
 
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