# how to control brushless dc servo motor?

I have one of this motor and would like to make a controller for it ( just a speed controller with regulator that change speed from zero to maximum. ). I know micro controller and embedded system, but have no idea about power electronics part.

The technical literature does not say much about it. any help regarding how to run it will be good.

I have model no: QB01700 A00. ( 24 Volt , Peak Current 36 A )

Allegro A3595 controller IC seems like it would work OK. Would need to study datasheets in more detail. Also needs external MOSFETS.

That's an exceptionally nice motor. Unless you have specific needs for the very high performance high power capabilities of that motor you may be better off starting with something smaller and cheaper to control. The issue is that the smallest of the motor on the page you reference is rated at 16A peak and others are in the 20 - 30 - 40 Amp range. These are no toys!

You can buy both made up controllers and ICs for controlling BLDCMs. Your motor has built in hall sensors so should be a good fit to a wide range of controllers. The "real" controller for your motor is probably "rather expensive" but simpler and cheaper alternatives would probably suit you well enough.

The page you reference has a range of motors on it with a wide range of ratings. Can you provide a specific model number?

Anything on that page is of such high current that most standard controller ICs would not manage it directly and any that did would be extremely expensive. The best choice will be a controller IC with external transistors (usually MOSFETS) .

If you search Digikey for

bldc controller


you will find 100's of possibilities. You may want to subset down to eliminate fan speed controllers.

As samples only:

The Allegro A3935 IC in stock Digikey at \$8.37/1 appears to be a good fit to your need.

• A3935 datasheet

• [A3935 pricing page(http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=620-1292-6-ND)

The device is aimed at automotive applications so some features relate to that area. xternal drive of N Channel MOSFETS as drivers allows as cheap as possible control of a motor of this sort. This IC assumes microcontroller control. This is not a necessity but even something like an Arduino or similar would make 'housekeeping' much simpler.

• They say

The A3935 is designed specifically for automotive applications that require high-power motors. Each provides six high-current gate drive outputs capable of driving a wide range of N-channel power MOSFETs.

A requirement of automotive systems is steady operation over a varying battery input range. The A3935 integrates a pulsefrequency modulated boost converter to create a constant supply voltage for driving the external MOSFETs. Bootstrap capacitors are utilized to provide the above battery supply voltage required for N-channel FETs.

Direct control of each gate output is possible via six TTLcompatible inputs. A differential amplifier is integrated to allow accurate measurement of the current in the three-phase bridge.

Diagnostic outputs can be continuously monitored to protect the driver from short-to-battery, short-to-supply, bridge-open, and battery under/overvoltage conditions. Additional protection features include dead-time, VDD undervoltage, and thermal shutdown.

The A3935 is supplied in a 36-lead 0.8 mm pitch QSOP (package LQ, similar to SOICW). The lead (Pb) free variants (suffix –T ) have 100% matte tin leadframe plating

Here are some other idea starters if the above is less suitable than it appears:

• Edited question for Motor Model No. – iamgopal Aug 9 '11 at 13:27
• Added comment at top - allegro IC looks to be worth a look. Many others exist. – Russell McMahon Aug 9 '11 at 14:00