Abstract: This paper introduces the design of a brushless DC motor controller based on the high-voltage monolithic integrated chip ECN3067, focusing on its hardware composition and implementation. Keywords: Brushless DC motor; ECN3067; Control 1 Introduction Brushless DC motors, with their advantages of simple structure, reliable operation, high efficiency, and good speed regulation performance, have become a hot topic in motor development recently. By eliminating brushes, spark-free operation is achieved, greatly improving the motor's lifespan and safety. Electronic commutation replaces mechanical commutation, eliminating motor friction losses and changing the motor's structure, reducing electrical losses in various aspects and making the motor more energy-efficient. In practical applications, low-voltage brushless motors are relatively mature, but the application of high-voltage brushless motors is still relatively rare. This design is an application example of a high-voltage brushless motor and has been successfully tested. 2 Motor Control Circuit Brushless motors use electronic commutators instead of mechanical commutators, and in many applications, power MOS-FETs or IGBTs are used as electronic switches. In this application, the motor is directly rectified and powered by AC mains, with a DC voltage exceeding 300V. Controlling a three-phase six-step brushless motor requires six IGBTs. Given the large number of electronic switches and the high voltage, designing the drive circuit using discrete components would be extremely complex and detrimental to system stability. Therefore, this application uses Hitachi's ECN3067 instead of the six IGBTs, and the MC33035, widely used in low-voltage brushless motor drives, controls the ECN3067. 2.1 Working Principle of ECN3067 The ECN3067 is a new type of high-voltage drive chip specifically designed for brushless DC motor control, manufactured by Hitachi. It is suitable for three-phase brushless DC motors powered by AC 200-230V rectified power. Its internal block diagram is shown in Figure 1. The most significant feature of this IC is its integrated six IGBTs. The motor power supply is directly connected to the IC to drive the motor; only a 5V-CMOS or LSTTL level is needed to control the opening and closing of the corresponding phases of the motor via the ECN3067. The ECN3067 has six input terminals: three upper arm inputs (UT, VT, WT) and three lower arm inputs (UB, VB, WB), controlling six IGBTs in the upper and lower arms respectively. A low input level turns the corresponding IGBT on, and a high input level turns it off. Combined with the motor position signal obtained from the motor's Hall effect sensors, the motor can be driven when these six input terminals are input with high and low levels in a specific timing sequence. Furthermore, by changing the low-level signal controlling the IGBT's on-time to PWM, the IGBT's conduction time can be controlled by the PWM duty cycle, thereby controlling the motor's speed. The internal structure of the ECN3067 is shown in Figure 1. As shown in Figure 1, each phase has two built-in totem-pole IGBTs. To enable the IGBTs to turn on, the gate voltage should be higher than the threshold voltage (approximately 5V). For the lower arm, the IGBT's emitter is fixed at ground potential; therefore, the IGBT's gate can be driven by the power supply voltage Vcc. However, for the upper arm, the IGBT's emitter potential rises to Vs, so the IGBT's gate drive voltage should be higher than Vs. The simplest way to achieve this drive is to connect a controllable ungrounded power supply to the emitter and gate of the IGBT. When the IGBT needs to be turned on, the ungrounded power supply is applied to the emitter and gate; when the IGBT needs to be turned off, the ungrounded power supply is disconnected. While this design is simple, it increases cost. Another method can be achieved using a bootstrap capacitor. The specific circuit is shown in Figure 1. A capacitor Cb is connected between the emitter and gate input of the IGBT. When the IGBT in the lower bridge arm is turned on, Vcc charges capacitor Cb through Db to obtain a voltage higher than Vs. In addition, the ECN3067 also has overcurrent protection. The magnitude of the protection current can be adjusted by changing the resistance value of Rs. The ECN3067 has an internal logic protection circuit. When the input voltage at the RS terminal exceeds a certain value (standard value is 0.5V), the protection circuit shuts down all six IGBTs in the upper and lower arms. As shown in Figure 1, the current flowing through the motor all flows through resistor Rs. The overcurrent protection circuit setting current value (Io) can be determined by the following equation: Io = Vref / Rs (Vref is the overcurrent protection value at the RS terminal, standard is 0.5V) [align=center] Figure 1 Internal structure diagram of ECN3067[/align] 2.2 Controlling ECN3067 with MC33035 The MC33035 is a widely used brushless DC motor controller, generally used for controlling low-voltage brushless motors. It cannot directly drive brushless DC motors operating under AC200~230V rectified power supply through electronic switches, but this can be done through the high-voltage driver chip ECN3067. The MC33035 has quite good performance in controlling low-voltage brushless motors. Its most outstanding feature is that it can directly decode the position signal detected by the Hall sensor, and the peripheral circuit of the system is also very simple. In driving low-voltage brushless motors, a common practice is to input the position signal detected by a Hall sensor into an MC33035 for decoding. The drive output pins of the upper and lower arms of the MC33035 then directly drive electronic switches to control the on/off state of the corresponding phases of the brushless motor. In high-voltage applications (driving brushless DC motors powered by AC 200-230V rectified electricity), the MC33035 is inadequate. However, using the control signal obtained after decoding the position signal with the MC33035 to control an ECN3067 to drive the brushless DC motor can achieve quite good control results. In fact, the ECN3067 can also be directly controlled by a microcontroller with PWM functionality. However, the biggest potential problem in controlling a three-phase six-step brushless motor is that, under unexpected circumstances, the electronic switches of the upper and lower arms in the same phase may mistakenly turn on simultaneously. In this unexpected situation, current does not flow through the motor, and the voltage is entirely applied to the two turned-on electronic switches, causing the chip to burn out due to a short circuit. Because microcontrollers may experience program malfunctions due to interference, this could cause the electronic switches of the upper and lower arms in the same phase to erroneously turn on simultaneously. Since the MC33035's internal logic circuitry has error correction capabilities, preventing the upper and lower arms from simultaneously providing turn-on signals, using the MC33035 to provide control signals to the ECN3067 can prevent this fault. 2.3 Connection between MC33035 and ECN3067 To reduce the cost of peripheral circuits, the MC33035's upper bridge arm outputs a low level to turn on the electronic switch and a high level to turn it off. The lower bridge arm does the opposite: a high level turns the electronic switch on, and a low level turns it off. For the ECN3067's upper and lower bridge arms, a low level triggers the corresponding IGBT to turn on, and a high level turns it off. Therefore, the output of the MC33035's lower bridge arm has the opposite input rules to the ECN3067's lower bridge arm, requiring a logical "NOT". On the other hand, the ECN3067 has overcurrent protection, undervoltage protection, and error correction functions. In the following situations: 1) Motor current exceeds the rated value; 2) Chip supply voltage is insufficient; 3) Input signals simultaneously activate the upper and lower arms of the same phase; 4) Charge pump capacitor undervoltage. The ECN3067 will then shut down all IGBTs. Therefore, when starting the motor or restarting it after the above faults, a start action must first be applied to the ECN3067, ensuring all six input pins of the upper and lower bridge arms are at a high level and remain high for the required start time before the motor can start running. Considering that the MC33035 does not have this start action (all six output pins of the upper and lower bridge arms output a high level simultaneously), and that the lower bridge arm output of the MC33035 needs to be inverted, according to the logical relationship, the connection between the MC33035 and ECN3067 requires an OR operation on the upper bridge arm and a NAND operation on the lower bridge arm. (See Figure 2) Then, the microcontroller controls two logic gates to start the motor: when PA.1 outputs "1" and PA.0 inputs "0", all six inputs of the ECN3067 are simultaneously "1", meeting the start-up requirements. After a start-up delay, PA.1 outputs "0" and PA.0 outputs "1", ending the start-up action. Additionally, the MC33035 is designed so that the upper and lower bridge arm outputs can directly drive electronic switches. Therefore, when the lower bridge arm output is "1", the voltage to ground is relatively high, requiring a resistor divider to obtain a 5V output level (see Figure 2). Due to the different internal circuits of the upper and lower bridge arms, the upper bridge arm output only needs an external pull-up resistor to reach the 5V power supply. [align=center] Figure 2 Connection circuit of MC33035 and ECN3067[/align] 3 Motor Speed ​​Control The MC33035 adjusts the motor speed by changing the duty cycle of the PWM output from the lower bridge arm drive output pin. Changing the input voltage of pin 11 of the MC33035 changes the PWM duty cycle. Therefore, a microcontroller with D/A converter can be used to control the motor speed. Alternatively, considering the slow motor speed response, a microcontroller with PWM can also be used, with the analog signal obtained through RC filtering. For cost considerations, this design uses the HOLTEK 46R47, which has PWM and A/D converters, meeting the control requirements. 4. Application The motor controlled in this design is used for the air outlet of a central air conditioning system. The motor control requirements are to ensure stable airflow, adjustable air speed, and no change with mains voltage fluctuations. Mains voltage generally has a certain fluctuation range; if the setpoint remains unchanged, voltage changes will alter the motor speed, thus changing the airflow. Therefore, the setpoint for the motor is corrected by detecting the mains voltage to achieve constant airflow. 5. Conclusion Using the MC33035 to control a high-voltage drive chip to achieve control of a high-voltage brushless motor has proven through experiments to be not only safe and reliable with good stability but also convenient to control, and has certain application value. References [1] Hitachi ECN3067 application note, http://www.hitachi.com.jp/pse [2] Hitachi ECN3067 data sheet, http://www.hitachi.com.jp/pse [3] Motor MC33035 data sheet, http://onsemi.com