BLDC / Brushless DC Motor Symbol
Definition: The BLDC / Brushless DC Motor symbol represents a three-phase permanent-magnet synchronous motor that is electronically commutated via an inverter or ESC, shown in circuit diagrams as a circle with three phase-winding terminals (U, V, W) per IEC 60617-07 rotating-machine symbol conventions.
Also known as: brushless DC motor, BLDC motor, PMSM, permanent-magnet synchronous motor, brushless motor, EC motor, electronically commutated motor.
What the BLDC / Brushless DC Motor symbol means
The BLDC Motor symbol denotes an electric motor whose rotor carries permanent magnets and whose stator carries three-phase AC windings that are energised in sequence by an electronic controller rather than by mechanical brushes and a commutator. The symbol identifies the motor as requiring a dedicated brushless ESC (Electronic Speed Controller) or BLDC driver IC that switches the three phase windings (U, V, W) in the correct sequence based on rotor-position feedback from Hall-effect sensors or back-EMF sensing.
BLDC motors offer higher efficiency, longer service life, and better power density than brushed DC motors. They are standard in robotics, drones, electric vehicles, HVAC compressors, and precision servo drives. The circuit symbol reminds the engineer that three separate phase conductors (not two) must be routed from the inverter to the motor.
How to identify the BLDC / Brushless DC Motor symbol
The BLDC Motor symbol is drawn as a circle (the motor body) with three connection lines exiting from the left side or distributed around the circumference, labelled Phase U, Phase V, and Phase W. The letter 'M' or the designation 'BLDC' is printed inside the circle. In three-phase power diagrams the three phase wires are often shown as a triple-line or bus notation; in block-level schematics the motor is a rectangle with U, V, W pins. Some symbols include a Hall-sensor feedback line or encoder output pin.
Function in a circuit
A BLDC motor operates by energising successive pairs of stator windings to create a rotating magnetic field that pulls the permanent-magnet rotor into alignment. The electronic controller (ESC or BLDC driver) determines the firing sequence by reading rotor position from Hall-effect sensors or by sensing back-EMF on the undriven winding. Speed is controlled by varying the PWM duty cycle of the inverter switches; torque is proportional to current. Unlike brushed motors, BLDC motors require no brush maintenance, produce less electrical noise, and achieve efficiencies of 85–95%.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-07 (rotating electrical machines) defines the motor symbol as a circle; a brushless DC motor is identified by the letter combination 'M' inside the circle plus an annotation or additional qualifier. IEC 60034-30 classifies efficiency ratings of motors including BLDC types (IE4, IE5 super-premium). |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 uses the same circle symbol with 'M' for a motor. A BLDC motor is distinguished by showing three phase terminal leads and a label 'BLDC' or 'EC MOTOR' adjacent to the symbol. No unique glyph exists in ANSI Y32.2 specifically for brushless motors. |
| Key difference | Both IEC 60617-07 and ANSI Y32.2 / IEEE 315 use a circle with 'M' for any motor. BLDC motors are identified by labelling and the presence of three phase leads (U, V, W) rather than the two leads of a brushed DC motor; the core glyph is identical in both standards. |
Terminals / pins
| Pin | Name |
|---|---|
| u | Phase U |
| v | Phase V |
| w | Phase W |
Typical values
Voltage: 3–48 V DC (hobby/robotics) to 400–800 V DC bus (industrial/EV). Power: 5 W (fan motors) to 250 kW+ (EV traction). Speed: 100–100,000 RPM depending on pole count. Efficiency: 85–95%. Torque constant Kt (N·m/A) and back-EMF constant Ke (V/rad/s) are key datasheet parameters.
Where the BLDC / Brushless DC Motor symbol is used
- Drone and UAV propulsion systems where three-phase ESC-driven BLDC motors provide the high RPM required for multi-rotor lift
- Electric vehicle traction drives and e-bike hub motors requiring high torque density and variable-speed control
- HVAC compressors and variable-speed fan drives in heat pumps and air conditioners (inverter-driven compressors)
- CNC machine spindles, servo axes, and robotic joint actuators requiring precise speed and position control
- Computer hard-disk drive spindle motors and cooling fans (ultra-low vibration, long life)
- Power tools, electric scooters, and cordless appliances where high efficiency and compact size are critical
Example
In a drone motor wiring schematic, four BLDC Motor symbols (each showing Phase U, Phase V, Phase W leads) connect to four individual 30 A ESCs; each ESC's three PWM output lines drive one motor's windings. The ESC signal inputs (PWM control lines) connect to the flight-controller output pins, and the ESC power inputs connect to the LiPo battery bus, forming the complete propulsion circuit.
Key facts
- A BLDC motor has three stator phase windings (Phase U, Phase V, Phase W) and a permanent-magnet rotor; it requires an electronic inverter or ESC to commutate the windings in sequence.
- The IEC 60617-07 symbol is a circle with 'M' inside; BLDC is distinguished from brushed motors by showing three phase leads (U, V, W) rather than two DC leads.
- Efficiency of BLDC motors typically ranges from 85% to 95%, significantly higher than comparable brushed DC motors (60–75%).
- Speed control is achieved by varying the PWM duty cycle of the inverter switches; torque is proportional to phase current.
- Rotor position sensing uses Hall-effect sensors (3 sensors at 120° spacing) or sensorless back-EMF detection on the undriven winding.
- BLDC motors are classified under IEC 60034-30 efficiency tiers; premium-efficiency BLDC motors reach IE4 or IE5 ratings.
- The designation PMSM (Permanent Magnet Synchronous Motor) is used interchangeably with BLDC in industrial documentation, though PMSM typically implies sinusoidal drive whereas BLDC implies trapezoidal commutation.
- Pins in circuit diagrams: Phase U (left), Phase V (left), Phase W (left); some symbols add Hall A, Hall B, Hall C sensor outputs and a 5 V/GND for sensor supply.
Diagrams that use this symbol
- bldc motor controller circuit diagram
- 48v brushless motor controller wiring diagram
- bldc motor winding diagram
- brushless motor controller wiring diagram
- 36v brushless motor controller diagram
Frequently asked questions
What does the BLDC motor symbol look like in a circuit diagram?
The BLDC motor symbol is a circle with the letter 'M' or 'BLDC' inside, and three connection lines labelled Phase U, Phase V, and Phase W exiting from the left or distributed around the circle. It follows the IEC 60617-07 rotating-machine convention where any motor is shown as a circle with an internal designator.
What does the BLDC motor symbol mean?
The symbol indicates a three-phase brushless DC motor requiring an electronic speed controller or inverter to operate. It tells the engineer that three separate phase conductors must connect the driver IC or ESC to the motor, and that the motor cannot be run directly from a DC supply without a commutation controller.
What is the difference between a BLDC motor and a brushed DC motor in a circuit diagram?
A brushed DC motor symbol shows only two terminals (+ and −) and can be connected directly to a DC supply. A BLDC motor symbol shows three phase terminals (U, V, W) and requires an inverter or ESC between the DC power supply and the motor. Both use the IEC/ANSI circle symbol, but the number of leads and the label distinguish them.
What are the pin names on a BLDC motor symbol?
The three main pins are Phase U, Phase V, and Phase W — the three stator winding terminals. Sensorless BLDC motors have only these three terminals. Sensored BLDC motors add Hall A, Hall B, Hall C (position sensor outputs), and a 5 V and GND pin for sensor power, bringing the total to eight terminals.
What standard defines the BLDC motor symbol?
IEC 60617-07 (rotating electrical machines) defines the base motor circle symbol with 'M' inside. ANSI Y32.2 / IEEE 315 uses the same circle convention. Neither standard provides a unique glyph specifically for BLDC motors; the three-phase labelling (U, V, W) and the 'BLDC' or 'EC' annotation on the symbol distinguish it from other motor types.
What is the efficiency of a BLDC motor compared to brushed motors?
BLDC motors typically achieve 85–95% electrical-to-mechanical efficiency because they eliminate brush friction and arcing losses. Comparable brushed DC motors achieve 60–75% efficiency. Under IEC 60034-30, premium BLDC motors qualify for IE4 (Super Premium Efficiency) or IE5 (Ultra Premium Efficiency) classification.
Can a BLDC motor run directly from a battery?
No. A BLDC motor cannot run directly from a DC battery because it requires electronically sequenced three-phase AC waveforms to create rotor rotation. An ESC (Electronic Speed Controller) or BLDC inverter converts the DC battery voltage into the three-phase PWM signals that drive Phase U, V, and W in the correct commutation sequence.
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