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Sensorless BLDC motor ESC

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Martynas Jankūnas

Newbie level 6
Aug 9, 2015
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I want to make the electronic speed controller for sensorless BLDC motor. I came across driver chip for this aplication from Microchip: **broken link removed**. Max current for this chip is 1A and I want to drive a motor with max 10A current. So I made a schematic in which MTD6505 outputs is fed to **broken link removed** MOSFET driver, which drives **broken link removed** NMOS transistors.
So problem is I don't know how to make a feedback to MTD6505 outputs for zero crrosing detection. I suppose direct connection, which I made in the schematic, isn't a good idea :D
Also what value should be MOSFET's gate resistors?


There's essentially no information in the datasheet about the implemented locking and out-of-sync detection. I don't see how you would use the device with an external power stage and still keep this feature. At worst case, the BLDC driver doesn't work at all with an external driver.

You probably need to chose a more versatile BLDC driver IC.

Well I searched a lot for similar chips, but all I could find was similar chips in small packages for computer fan like aplications, nothing with large currents, I chose MTD6505 because it was cheapest in my local electronics store. Yes in datasheet its not information for phase detection, but from my researches about BLDC motors I think that one phase is driven high, one is driven low and third phase gives BEMF signal.

I believe your assumptions may have some merit.

But the ultimate test is to actually build a prototype and validate those assumptions.

Don't believe it would work.
Why not use an of the shelf controller like this one?

**broken link removed**
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I don't know about the details of driving a BLDC, but perhaps this will help...

A magnet passing close to a coil induces a spikey waveform. Amplitude depends on several factors (including distance, speed, magnet strength, coil impedance).

Perhaps you can detect this spike in your non-energized coil.

The peak of the waveform would be the trigger telling you to start a new cycle of coil energizing.

Thank you aminpix for that thesis, at this point I'm too considering use MCU for zero-crossing detection. I came around this application note from Microchip: Sensorless BLDC Motor Control with PIC16. It has a schematic and code for PIC16F690 in C. So I think I will try to alter the code for my application.

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