Given their high efficiency, lower audible noise and long life cycles, brushless DC (BLDC) motors are widely used in household appliance subsystems such as refrigerator, dishwasher and washing machine fans and pumps. These subsystems usually require less than 100W of output power for the motor and are typically driven by high DC voltages (over 150/300V) derived from the 110/230VAC mains. In this blog post, I’ll discuss an alternative solution for driving appliance subsystems using a low-voltage (typically 24V) motor drive.
For high-voltage motors, the AC mains supply is rectified to get the high-voltage DC bus, which drives the inverter stage consisting of discrete insulated-gate bipolar transistors (IGBTs), MOSFETs or integrated power modules (IPMs). The system usually requires a bias power supply to provide 5VDC or 3.3VDC supplies to the controller units and 12V or 15V for the gate driver. Figure 1 shows the typical block diagram of a high-voltage motor-control system.
Figure 1: System block diagram for a high-voltage motor control system
In low-voltage DC motor-drive systems, the AC/DC power-supply unit generates a lower DC bus voltage (such as 24V) with the required output-power capability. The power stage uses this low DC bus voltage to drive the motor. Using voltage regulators enables the AC/DC power-supply unit to derive the required bias power supplies.
Figure 2 shows the typical block diagram of a low-voltage motor-control system.
Figure 2: System block diagram for a low-voltage motor-control system
Here are some benefits of low-voltage motor-control systems:
However, using low-voltage BLDC motors in the system requires a power supply capable of providing a low-voltage DC output to power the motor drive.
To address the challenge of using low-voltage motors, the TI Designs 150W High Efficiency Primary Side Regulated DCM/CCM Flyback Supply Reference Design features a 24V, 12V output, 150W isolated primary-side regulation (PSR) flyback controller-based power supply, with built-in protections for overcurrent, overvoltage, feedback-loop open/short detection, overtemperature, overload timer, AC line undervoltage and brownout. PSR helps eliminate the need for secondary-side feedback and regulation components and an optocoupler, enabling cost optimization and increasing reliability. The additional 12V can power up the gate drivers and generate the bias power supplies.
Figure 3 shows the block diagram of the 150W PSR flyback power supply. The power supply is designed and tested for a universal input AC range from 85-270VAC. The electromagnetic interference (EMI) filter at the front end of the circuit is designed to meet EN55011 Class A conducted emission levels. The design achieves low standby power of 200mW at 230VAC.
Figure 3: 150W PSR flyback power supply block diagram
I hope you now understand the benefits of a low-voltage BLDC drive for low-power applications in terms of safety, integration, size, cost and design-cycle reduction, especially compared to a high-voltage system.
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