Sensorless BLDC Motor Driver Circuit Part 1

In this post we investigate what's a BLDC motor and subsequently we learn regarding the design of a sensorless BLDC motor driver circuit.

Seen those fast moving fans in CPUs, voltage stabilizers, DVD players, and other similar equipment, which work with utmost efficiency, consuming minimum space, current and yet are able to deliver the important operations as stipulated for the particular equipment?

Yes, these are all the modern versions of BLDC fans or the brushless DC motors which are much superior than the old traditional brushed motors.

Image Courtesy: https://en.wikipedia.org/wiki/Computer_fan#/media/File:Geh%C3%A4usel%C3%BCfter.jpg

However a BLDC motor will require a sophisticated driver circuit, and yes all these CPU fans contain these driver modules in-built, although these appear easily operable using an ordinary DC, internally the system is already fitted with a smart circuit.

Here we will learn about one such smart BLDC motor driver circuit, using a single chip DRV10963 for driving any small BLDC motor with incredible efficiency, and later on in one of the upcoming articles we will see how this IC circuit may be upgraded for driving even the powerful high current BLDCs such as the ones which are used in quadcopters.

But before this it would be interesting to learn a bit about BLDC motors

The difference between a brushed motor and a brushless motor and the efficiency rate is rather obvious.

Since brushed motors have the wound armature itself moving between magnets, has to employ "brushes" (rubbing contacts) so that the moving coil terminals are able to receive the supply voltage consistently without having to reach the supply source themselves, which would otherwise make the working impossible and jeopardize the operations.

In a brushless motor, the coil or the winding is never moving and is constant, here the rotor carries a set of permanent magnets and rotates in the influence of surrounding winding's magnetic fluxes.

Since the magnet is free from all the hassles, and is able to work without involving terminals to manage or to receive power, it can go about effortlessly, spinning at a rapid speed and virtually at a noiseless level.

But there's a catch here. In order to make an electromagnet respond to a permanent magnet's fluxes, there needs to be a constant shift of magnetic phase or poles, so that the two counterparts are able to constantly react and go through an opposing force thereby releasing the required torsional force over the rotor and execute the rotation with the resultant torque.

In a brushed motor, this becomes easier due to the self adjusting nature of the armature coil which is able to rotate and create a self sustaining opposing magnetic force and keep rotating without the need of any external pulses or processing.

However in a BLDC this becomes a problem since the magnet rotor remains "clueless" and requires a calculated magnetic command from the winding in  order to rotate in a meaningful way and not in a haphazard manner.

That's exactly why all BLDC motors mandatorily require a motor driver circuit for commanding the three distinct sets of winding inside the motor. Thus all BLDC are essentially 3-phase motors and compulsorily require three phases for producing the rotational torque on the rotor.

The sensor less BLDC driver circuit simply electrifies the 3 sets of winding in a sequential manner such that the magnetic rotor is able to go through a consistent opposing force enabling the motor to accomplish a sustained torque and rotational force.

But this sequential powering of the BLDC winding by the circuit cannot be just randomly set, it has to be in tandem or in response to the rotational position of the rotor magnet, otherwise the implementation could go haywire and we may witness the motor shaft (rotor) rotating haphazardly, that is jerking in between a clockwise and an anticlockwise with no sensible rotation.

Therefore, we introduce sensors positioned inside many BLDC motor variants, these sensors (typically Hall effect sensors) "understand" the changing position of the magnetic poles of the rotor magnet,  instruct the attached processor circuit to electrify the corresponding winding and execute a rotational movement with an optimal torque.

Hall effect sensors are effectively employed in most BLDC motors which are relatively larger in size, but for smaller motors such as in CPU fans, CPU drives, DVD players, in small exhaust fans, for motors used in quadcopters, hall effect sensors can become inappropriate and therefore an alternative sensor less approach is implemented.

This involves the exploitation of the winding's inherent back EMF electricity which is taken as the reference source for processing and electrifying the relevant sets of winding and executing the rotational torque.

In the above crude simulation we can visualize how the released back EMF is taken as the reference and used for producing the sequencing pulses for the subsequent sets of winding, imposing a rotating torque on the central permanent magnet rotor. The simulation might not be the exact replication, nevertheless it gives a rough idea of the working principle.

It is interesting to note that the pulse is switched when the N/S of the magnet is exactly at the center of the winding core, which enables the winding to either energize as N or S depending on the pulse polarity and produce an attracting and repelling force on the N/S magnets, thereby generating the required torque at the maximum possible level.

And this in turn becomes possible due to the back EMF released through the switching of of the previous winding.

The above discussion clarifies the working of a sensor less BLDC motor, now let's learn how a specified circuit handles the above complex execution of a 3 phase switching

After some Googling I found this sensorless BLDC driver circuit using a single chip DRV10963 which employs negligible amount of parts in the configuration and yet is able to implement a sophisticated processing for the intended actions.

The DRV10963 is a state-of-the-art chip which is specifically designed to operate sensor less BLDC motors by merely anticipating the back EMF from the motor winding and delivering a precise command over the winding and accomplishing an optimal rotational torque over the rotor.

The above image shows the simple layout of the circuit which apparently includes nothing but the IC itself.

The various pinouts are allocated for carrying out the specified functions such as PWM speed control of the motor, direction control, etc by simply feeding the relevant pinouts with the specified datas from an external source.

The sensorless BLDC driver circuit and the device details are discussed in the next article.



9 thoughts on “Sensorless BLDC Motor Driver Circuit Part 1

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Hi bro, can we use the above circuit for cd-rom motor. it was brushless with more than 3 wires. please give some info about how to drive those motors without expensive gadgets.

  3. Hola buenas tardes. Voyiniciandome en esto de los motores y quisiera saber si pidieras desir donde en berdad puedo encontrar un diagrama de circuito para un motor brushless.
    De antemano gtasias

  4. "later on in one of the upcoming articles we will see how this IC circuit may be upgraded for driving even the powerful high current BLDCs such as the ones which are used in quadcopters."

    Thanks so much Mr. Majumdar. Very helpful. Have you written this follow up article that you are speaking of?

    Regards,
    Amit

  5. later on in one of the upcoming articles we will see how this IC circuit may be upgraded for driving even the powerful high current BLDCs such as the ones which are used in quadcopters.

    Thanks so much Mr. Majumdar. Very helpful. Have you written the follow up article that you speak of?

    Regards,
    Amit

    • thank you Amit, No I have not yet written it, my idea was to run a small dummy BLDC motor with the above explained IC, and then feed the back EMF signals from its wires to the input of any powerful BLDC driver IC.
      Actually t is not necessary to receive feedback signals for driving a sensorless BLDc, it can also implemented by creating an external sequencing 3phase signal and apply it to any standard high power BLDC driver IC.



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