In modern industrial, automotive, and robotics applications, controlling the speed of a sensorless Brushless DC (BLDC) motor accurately and efficiently is critical. Among various speed regulation methods—such as analog voltage, pulse signals, and PWM—Pulse Width Modulation (PWM) is the industry standard due to its high efficiency, minimal thermal loss, and precise control capabilities.

This guide outlines how engineers can easily implement PWM speed control using JUYI Tech’s sensorless BLDC motor driver boards and core controller ICs (such as the JYQD-V9.3E and JY03B IC).

PWM regulates the average power delivered to the motor by rapidly switching the power transistors (MOSFETs) on and off.

• Duty Cycle (0–100%): Changing the duty cycle adjusts the effective voltage supplied to the motor windings, directly controlling the rotational speed.

• Frequency Range: JUYI Tech drivers typically support a PWM frequency range of 1–20 kHz, compatible with standard microcontroller PWM outputs.

To enable PWM speed control, the MCU's PWM signal must be connected to the VR (Speed Control Terminal) of the JUYI Tech driver board. The connection method depends on your controller's logic voltage level (5V vs. 3.3V):

1)Power & Motor Phase Lines:

•  Connect the DC power supply to V+ and GND.

• Connect the motor phases (U, V, W) to the output terminals.

2)5V PWM Control System (e.g., 5V Arduino/MCU):

Direct Connection: Connect the 5V PWM signal through a 10K resistor and filtering capacitor directly to the driver board's VR terminal.

3)3.3V PWM Control System (e.g., STM32, ESP32):

• Level Shifting Connection: 3.3V logic cannot drive the 5V VR input directly. An NPN transistor (e.g., S8050) circuit must be used. Pass the 3.3V PWM signal through the transistor base, using the driver's onboard 5V pull-up to feed the VR terminal.
• Forward/Reverse (F/R) Control: Similarly, 3.3V F/R signals should be connected via a transistor isolation circuit to the driver's F/R terminal.

4)Common Ground: Ensure the MCU GND is securely connected to the driver board GND.

• Frequency Matching: Ensure your MCU’s PWM frequency is configured within the optimal range of 1–20 kHz. Too high may increase MOSFET switching losses; too low may cause audible motor noise.

• Leveraging Soft Start: JUYI Tech controllers (built around the JY03B IC) feature a built-in Soft Start mechanism. When applying PWM at startup, the controller gradually ramps up the duty cycle to prevent instantaneous high current surges, protecting both the driver and the motor.

• Issue 1: No response or limited speed range when using a 3.3V MCU (e.g., STM32).

  • Solution: JUYI Tech's VR input is designed for 5V logic. Direct 3.3V PWM input will not reach maximum speed. Always use the recommended NPN transistor level-shifting circuit as shown in the schematic.

• Issue 2: Motor speed decreases as the PWM duty cycle increases.

  • Solution: The single-transistor circuit for 3.3V level shifting introduces signal inversion. Engineers should invert the duty cycle in their MCU firmware (e.g., set Output Duty = 100% - Target Duty).

• Driver Board: JUYI JYQD-V9.3E (10V-36V 20A Sensorless BLDC Motor Driver Board with PWM & Analog Control)

• Core Driver IC: JUYI Tech JY03B (Highly Integrated Sensorless BLDC Motor Control IC in SSOP-28)