DRV8701EVM: Drive a Single Phase Brushless DC (BLDC) with a Brushed Motor Driver Reference Design

Hey Bella,

I read through the TIDA-00875 guide and it doesn't appear they have issues starting in certain positions. I feel like it would be mentioned somewhere in the guide if that was the case. 

Do you have a smaller motor you could test with?  I'm wondering if starting at certain positions is too much current for the DRV8870. Or does the motor "wiggle" at all when trying to start at certain positions?  Maybe there is some software control you could add in during starting like to turn on/off/on/off/on with decreasing delays between each change to help it wiggle out of the problematic starting positions.  

You could try replacing the ISEN resistor (R8) with a 0-ohm to disable current regulation and seeing if the behavior changes.  

Regards, 

Jacob

Hi Bella,

Bella (GZ) Li said:

But I had a problem with the motor starting itself in certain positions and not in certain positions 。

Can you elaborate more? 

The circuit has been proven to work. 

regards,

Pablo Armet

hi Jacob,

I have replaced the ISEN resistor (R8) with a 0-ohm. The starting current is up to 1.5A, but in some specific positions the motor still does not start, so I ruled out the fact that the starting current is not large enough to prevent the self-starting。

I have not a smaller motor I could test with. Because this is the motor that the customer has specified to use. 

In some starting positions, the motor starts smoothly.

But in some starting positions, the motor has a small swing, but it seems to be stuck at the starting point by a force. I can take a video tomorrow.

Can I find the author for TIDA-00875? I want to ask him what kind of experiments he did.

hi Pablo,

Single-phase permanent magnet synchronous motors have a "dead point", as shown in the following figure, the motor torque consists of two components, electromagnetic torque and reluctor torque, to a single-phase permanent magnet motor with a uniform air gap structure. There is a periodic "dead point" of its electromagnetic torque, that is, when the winding is energized, the angle of the stationary rotor magnetic field is 0° or 180°, the electromagnetic torque is 0, so when the motor is stationary, the rotor cannot be stopped at the dead point. In order to eliminate the "dead point", in the motor design need to change the symmetry of the rotor magnetic circuit, use asymmetric air gap structure design, use the magneto resistive torque and electromagnetic torque synthesis, This allows the rotor to obtain starting torque at all electrical angles, solving the motor "dead point" problem.

KP82201SG built-in intelligent startup algorithm, in different air gap design structure and different load conditions, the motor can start smoothly.