Single phase BLDC doesnt exist?

[treez]

**broken link removed**

...on this page is a "single phase BLDC motor driver IC", -surely there is no such thing, ?. I mean, there needs to be at least three phases so that you can rotate the motor by pulsing from one phase to the next round the circumference of the stator?

 

[jpanhalt]

Here is one explanation: https://www.onsemi.com/pub_link/Collateral/TND6041-D.PDF

John

 

[treez]

thanks, I see it is possible, but it strikes me that it could just come to a stop with both halves of the coils pulling it the opposite way.
Anyway, my other query is how does one change the speed of a dc 'brushed motor.....and your article confirms that its done by changing the voltage....so I cannot understand why we are being told to vary the speed by varying the current.
Do you know why one might feed a dc brushed motor with a controlled current source...I thought it would just mean more commutator sparking?

 

[jpanhalt]

Either voltage or current controllers can be used. In my limited experience, most the the chips I saw for brushed motors were current controlled. It was a few years ago when I did any of that, though. Here is a presentation by Microchip that summarizes the differences:

https://www.microchip.com/stellent/groups/SiteComm_sg/documents/Training_Tutorials/en527885.pdf

The speed of control and cycle-by-cycle response seem to be the major advantages of current control that were mentioned in datasheets.

John

 

[treez]

Sorry bit I didn't explain myself properly. I am not talking about whether the smps that supplies the dc motor is in voltage mode or current mode. I am speaking about actually regulating the current flowing to the dc motor, or regulating the voltage applied to the dc motor......you first article states that one controls a dc motor by varying the votage applied to it...not the current.
Has anyone ever heard of controlling a brushed dc motor by varying the current supplied to it?.....I am sure it never occurs, and is a bogus method which our company has told us to do just to proove that we are muppets?

 

[FvM]

In Gieras/Wing, Permanent Magnet Motor Technology - Design and Applications, I find a paragraph about single phase BLDC motor design. They are made e.g. with non-uniform air gap to generate a starting torque. They are basically suited as a replacement for single phase AC motors (e.g. shadow pole type) with considerable better efficiency. Similar to the AC motors, they can only serve for applications without much static friction.

 

[jpanhalt]

I recognized the title was SMPS, but the advantage of fast response is not limited to SMPS. One of the chips I used was the LT1158 in a half-bridge, brushed motor controller:

http://cds.linear.com/docs/en/datasheet/1158fb.pdf

Note, the same point is made for that chip. I guess that datasheet doesn't say cycle-by-cycle per se. If that phrase is important, I am sure I can find a datasheet for another chip that uses it.

John

 

[treez]

thanks, and with the top fet on all the time, i presume that gives maximum speed to the brushed dc motor?