An electric motor is the most efficient energy converter invented in human history, with a record efficiency of up to 99.05%. It is used in many applications to convert electrical energy into mechanical. However, not all electric motors are created equal: the most commonly used variants are the three-phase and the single-phase AC Induction Motors (AC IMs). While three-phase AC IMs are widely used in demanding industrial applications, single-phase AC IMs are limited to home appliances, white goods, small pumps, and similar non-critical applications due to their low efficiency, speed control complexity, and low torque.
However, with the advent of Brushless DC (BLDC) motors, this situation has changed in favor of single-phase solutions. Relying on a magnetic field generated using permanent magnets instead of induction, the BLDC design overcame many inherent disadvantages of single-phase IMs. As a result, single-phase HV BLDC motors became a very tempting solution for many different applications in which traditional IMs could not meet the requirements. They offer much simpler and lighter design, easier control over a much wider RPM range, greater efficiency, and ultimately – reduced costs.
HV BLDC motors and drivers
Unlike AC IMs, BLDCs cannot be powered directly from the grid. Instead, they must use specialized inverter-driver circuits that control current direction through their windings, according to the rotor’s angle. This allows for very efficient and accurate speed control. However, the choice of the optimal inverter-driver solution is a critical step in the system design process.
The drive circuit typically utilizes a full-bridge topology, with the motor windings connected between two half-bridges (also known as H-bridges) for single-phase BLDCs or multiple half-bridges for multi-phase BLDCs, allowing control over current flow direction. However, this topology requires very accurate timing, which considers delays caused by the MOSFET gate charges, signal propagation, inductive loads, and other factors that could affect switching timings. As a result, a design with discrete components can become considerably complex to ensure reliable system operation and prevent current shoot-through events. This is where specialized integrated solutions such as BridgeSwitch™ from Power Integrations can help: besides taking up much less space than the equivalent discrete design, these integrated devices may include various protection and fault reporting features, ensuring very reliable operation while significantly reducing the design complexity and time to market.
Power Integrations (PI) is a renowned semiconductor supplier, specialized in high-performance semiconductors used in HV applications. Their BridgeSwitch™ family of integrated H-bridges incorporates ‘smart’ control logic with numerous protection features, combined with two N-channel power FREDFETs ideally suited for highly-efficient hard-switched inverter-based motor drivers up to 400 W without heatsink, thanks to their ultra-soft and ultra-fast intrinsic diode structure. The BridgeSwitch family provides high robustness, comprehensive fault reporting, and excellent efficiency, making it the perfect choice for the broadest range of applications where space is an issue, such as HV fans, compressors, and pumps in various applications (vacuum cleaners, dishwashers, fume-hoods, washing machines, air conditioners, fridges, etc.)
EBV BridgeSwitch MB: a success story of an efficient single-phase BLDC motor control implementation
In collaboration with Power Integrations, EBV Elektronik developed EBV BridgeSwitch MB – the complete single-phase BLDC motor control solution based on BridgeSwitch reference design. EBV BridgeSwitch MB demonstrates the design simplicity with BridgeSwitch integrated H-bridges, allowing easy evaluation and exploration of their fault reporting and protection features in a real-world application.
The EBV BridgeSwitch MB demonstrator is very simple to use and requires only an external 220 V AC power supply as it features an on-board AC/DC converter. The PCB design follows a modular concept in a break-away format, allowing each submodule to be physically separated and placed behind a barrier, away from the HV components and the motor itself. An isolated SWD programming/debugging interface further reduces the risk of equipment damage and electric shock, even while the demonstrator board is powered directly from the mains, in cases where an isolating transformer is not available.
The HV section
The HV section includes the AC supply input stage and the switched output stage with two BRD1160C BridgeSwitch integrated H-bridges. The HV section also contains an external current sensing circuitry (optional) and an NTC header for remote thermal sensing. The size of the entire PCB area that contains the complete switching circuitry (both BridgeSwitch devices with the supporting components) is 30 x 38 mm only, which is a good testimony about space savings when integrated BridgeSwitch devices are used. This is primarily because of their compact size of only 9.4 x 10.8 mm (InSOP-24C package), but also because these devices do not require an additional heatsink. A further contribution to space reduction is provided by the fact that BridgeSwitch ICs do not require a separate power supply for their logic section, which reduces the number of external components to a minimum.
HV voltage section also includes Power Integrations LinkSwitch-TN2, an off-line switcher IC with an integrated MOSFET and system-level protection, connected in buck mode, which is used to provide power supply for the Microcontroller Unit (MCU).
The Microcontroller Section
The EBV’s BridgeSwith MB design is based on the NXP LPC804 Arm® Cortex®-M0+ 32-bit MCU, which includes a touch interface, Programmable Logic Unit (PLU), and safety-ready libraries compliant with the IEC60730 Class B standard for household safety requirements, among many other features. Although even an 8-bit MCU would suffice in combination with BridgeSwitch ICs, the LPC804 ensures plenty of headroom for running additional software, while reducing the risk of becoming obsolete. PLU is the most remarkable feature of the LPC804 MCU, allowing it to execute all control-related PWM operations in a single clock cycle, thus providing almost autonomous commutation. This leaves the MCU core free to execute other instructions allowing debugging during runtime, even as the motor spins. Programming and debugging can be performed via the insulated SWD interface.
This section of the PCB also houses three fault reporting LED indicators (Thermal, Voltage, and Current), which are used to signalize overcurrent, overvoltage, undervoltage, and thermal faults. The fault events are reported to the MCU by the BridgeSwitch devices over a single-wire bi-directional interface.
Although EBV BridgeSwitch MB is designed to extract 5 V from the HV DC bus, a two-pole screw terminal allows MCU power to be supplied externally once the MCU section is detached. This is very useful when performing live tests, measurements, and evaluation, reducing the risk of electric shock.
The User Interface Section
EBV BridgeSwitch MB provides a dual user interface for the motor control: it allows speed control using either an isolated shaft potentiometer or a capacitive touch slider. The insulated potentiometer shaft prevents users from coming into direct contact with the powered board. When a touch slider is used, the user interface can be detached and placed under protective glass, preventing direct contact with the board and reducing the risk of electric shock.
EBV BridgeSwitch MB clearly demonstrates the benefits of using BridgeSwitch compact and efficient H-bridges in a realistic example, showcasing the resulting simplicity and reliability in one such design. With its competitive pricing and many benefits, BridgeSwitch is the perfect solution for single- and multi-phase BLDC motor driving in a wide range of applications in consumer, but also in industrial markets. For the full list of features, please visit the official BridgeSwitch landing page.
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