By alternately exciting the stator coils with unidirectional "pulsed DC", a stepping rotating magnetic field is generated to continuously attract the rotor to rotate. Visual diagram and control of the brushless motor working principle.
Any magnet has two ends, called the N pole (North/Red) and the S pole (South/Blue).
When two magnetic poles are close to each other:
• Like poles repel: N meets N, or S meets S, they repel and push each other away.
• Opposite poles attract: N and S meet, they attract and stick together tightly like best friends.
A regular copper coil instantly becomes an electromagnet when current passes through it. By controlling the switch, we can make its magnetic force appear and disappear at any time. The motor relies on these switchable electromagnets to continuously attract and pull the center magnet to rotate!
In this model, the three stator coils (A, B, C) are each connected to a switch (MOSFET). The external input is a pure DC power source (VCC). By alternately turning on the switches according to a specific timing sequence using a microcontroller (MCU), the DC electricity flows through each phase coil in a unidirectional pulsed manner. When each coil is energized, it becomes an electromagnet with a fixed N polarity, attracting the S pole of the rotor to align sequentially, achieving continuous rotation.
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| Step | Rotor Angle | MOS A (Coil A) | MOS B (Coil B) | MOS C (Coil C) | Field Dir | Current Type |
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Traditional AC brushless motors alternate the coil current direction to switch the poles between N and S. In a unipolar brushless motor, the polarity of each coil is fixed (only producing N pole). We don't need to switch positive and negative poles; we only need to follow the sequence of "A ON -> A OFF / B ON -> B OFF / C ON", which is like lighting up magnetic field indicator lights at different physical locations in turn. Due to opposite poles attracting, the S pole of the rotor is pulled to rotate in a specific direction by the stator magnetic fields that are turned on sequentially.
In the 3-step full-step mode, every time the coil is switched, the rotor magnetic field must jump 120°. A step angle that is too large causes severe vibration. The half-step mode introduces a "dual-phase energized" state: when coils A and B are energized simultaneously, their magnetic fields superimpose to produce a combined magnetic field in the middle (60°). As a result, the jump angle is cut in half, from 120° to 60°, totaling 6 steps. The rotation will be significantly smoother and finer than in the full-step mode.
Although the unipolar pulsed DC drive circuit is extremely simple, at any given moment, 2/3 of the motor's windings are completely idle, and the copper windings are not utilized bidirectionally, leading to extremely low power density and material utilization. Modern mainstream brushless motors flow real bidirectional AC (three-phase sine wave AC) in the coils, utilizing 100% of the stator coils at all times, achieving extremely high efficiency and very smooth torque.
The stator coil is a highly inductive load. When the MOSFET is suddenly turned off, the current flowing in the coil cannot disappear instantly, generating a very high transient back EMF (even up to hundreds of volts), which can easily break down the MOSFET chip. The freewheeling diode connected in parallel with each coil provides a discharge path for this residual energy, allowing the current to circulate and decay within the diode and coil, ensuring the safety of the driver circuit.
This demo tool is perfect as an auxiliary teaching material for electrical engineering, automation, mechatronics, and other related majors. Teachers can use this interactive model to vividly demonstrate stator coil excitation, MOSFET switch toggling, unipolar pulsed DC flow, and how the permanent magnet rotor rotates in the stepping magnetic field, skipping dry formula derivations and helping students quickly build intuitive understanding.
The page features an easy-to-understand "Secrets of Magnets" basic knowledge card. Through vivid polarity comparisons, K-12 students and science enthusiasts without a physics background can quickly and intuitively grasp the scientific mysteries of "opposite poles attract, like poles repel" and "current-carrying wires become magnets", making it an excellent interactive experiment tool for electromagnetism.
The real-time synchronized "Unipolar Pulsed DC Driver Circuit Diagram" visually displays MCU control signals to MOSFETs, voltage damping paths of freewheeling diodes, and marching-ants dynamic current flow inside the coil inductors, helping hardware engineers quickly understand the core logic of simple pulsed DC motors.
Developers can learn the IO timing logic of microcontrollers driving brushless motors by observing the timing switching between 3-step full-step and 6-step half-step modes. Through high/low levels in the truth table, they can deeply understand the basic workflow of motor control algorithms.
Supports 30 major languages including Chinese, English, and Japanese. All UI text can be switched seamlessly on the current page, making it convenient for global learners.
Provides one-click switching between "Single-phase Full-step Mode (3 steps)" and "Single-dual Phase Half-step Mode (6 steps)", visually showing how refining the step angle from 120° to 60° improves the smoothness of motor rotation.
Supports auto run and manual single-step operation (prev/next/reset), with stepless adjustment of play speed (0.3s - 2.5s/step), making it easy to analyze the electrode and magnetic field status of each step in detail.
The rotor deflection, stator coil magnetic glow, corresponding MOSFET switch indicators in the circuit diagram, and current flow direction in the three-phase coils are fully synchronized in real time. What you see is what you get.
The truth table is highlighted in synchronization with the current step. Users can directly click any node on the timeline to instantly jump to the corresponding state for static analysis.
Supports one-click toggling of dark/light minimalist visual themes, and uses localStorage to automatically remember the user's theme preference, enhancing visual comfort for repeated learning.