The days of the simple alternating current, single-speed appliance motors are gone. To wring the most work out of our limited power grid, device manufacturers are turning to advanced digital electronic control circuitry and highly efficient motor systems.
Toshiba TP416XK in through-hole package. Image used courtesy of Toshiba
Motor drives lie in a murky fringe of digital electronics. In general, frequencies are low—usually in the tens of kilohertz, where timing and tolerances are typically not an issue. However, the drivers connect to a high-current whirling source of irregular EMI, EMF, and noise of all sorts. This makes motor drive electronics a combination of digital, analog, and magic. With too-low frequencies, audio noise is introduced and motor wiring overheats. Too high a frequency and switching losses become a first-order factor, leading to inefficient power use and excess heat in the electronics. In all cases, timing is a balance between current shoot-through, turn-off time, and turn-on time.
The following three offerings illustrate ways the industry is working to tame motor control.
ST Launches Series of Integrated Motor Drivers
STMicroelectronics has released its new high-current motor drive series, the STSPIN9 line. The first two offerings in this series integrate a high-current, 58-V power stage; PWM control logic; and current-sensing electronics. The drivers target high-end appliances for industrial, home, and professional applications.
STSPIN line of motor controllers. Image used courtesy of STMicroelectronics
The 4.5-A STSPIN948 has dual-power, full-bridge (H-bridge) motor drives allowing for use with brushed DC motors or bipolar stepper motors. The two bridges can be configured for five different full-bridge and half-bridge drive modes. The 5-A STSPIN958 has a single full-bridge with seven different operating modes, including dual independent half-bridges, dual parallel half-bridges for extra current capability, or a single H-bridge.
Both drives come with a low standby current consumption, low and under-volt protection, over-current protection, and a thermal shutdown. The two chips have RDS(on) values of .36 and .33 Ω, respectively. They have integrated current sense amplifiers, adjustable power MOS slew rate, and adjustable off-time with slow or mixed decay.
These devices can reconfigure the high current output stage, allowing them to deliver great flexibility and counter one of the common complaints with fully integrated systems. With such reconfigurable output options, the vendor can get by with fewer individual product variations, and the motor control design engineer has more options to choose from before turning to a discrete solution.
Toshiba Replaces Induction Motors With BLDC
The Toshiba TP416XK are self-contained sensorless brushless DC (BLDC) motor drive chips. They include integrated bipolar transistors (IGBTs), drive transistors, gate drives, internal 5V-regulators, current sense and over-current protection, and input logic in one package. They take microcontroller logic level signals and drive BLDC motors at up to 600 V with minimal external componentry. The TPD4163K delivers DC current rated to 1 A, and the TPD4164K delivers 2 A.
Block diagram of the TPD4163K. Image used courtesy of Toshiba
The BLDC is replacing AC motors in most appliances. Past installations put inexpensive single-phase AC induction motors into most appliances. With the need to manage EMI and power usage, OEMs use more efficient systems, such as multi-phase brushless DC motors, more often. This series of drivers from Toshiba targets the installation of BLDC motors in air conditioners, air handlers, and pumps.
EPC Takes the GaN Route for Smaller Motor Drivers
Gallium nitride (GaN) has been in the news a lot lately for its ability to deliver the same or better performance as silicon in a smaller package. EPC has just announced a three-phase brushless DC (BLDC) motor driver evaluation board, the EPC9194, that demonstrates more than 2x power-to-weight improvement with their parts compared to silicon MOSFETs.
At the heart of the EPC reference design are six (two per phase) EPC2302 enhancement-mode, gallium nitride field-effect transistors (eGaN FETs). It sports a 1.8 mΩ maximum RDS(on), allowing it to deliver a 100-V drain-to-source rating at 101 A continuously. GaN allows for higher voltages, higher current, and faster switching speeds than silicon MOSFETs and is often simpler to drive. This allows EPC to address motor drive efficiencies with a lower overall system cost.
A motor driver is generally paired with a microcontroller when being tested or implemented. The new eval board comes in several versions optimized for different microcontrollers. Most engineering departments, and most individual engineers, have a set of microcontrollers that they are comfortable with and experienced in. While the basic motor control concepts don’t change with the drive electronics, the specific mechanisms and software code will vary based on the selected microcontroller family.
EPC9147A development board tailored for Microchip MCUs. Image used courtesy of EPC
EPC hopes to speed the adoption of its eGaN devices by reducing as many obstacles for design engineers as possible, and having development boards optimized for popular MCU families is a good step in that direction.
Motor Controls and Power Savings
Motor controls are one of the unsung heroes of the modern world. We hear about power requirements for server farms, electric vehicles, and air conditioning as major opportunities for power savings, but motors are in just about everything these days. We just don’t tend to think much about them. Implemented poorly, motors contribute to electromagnetic noise and power consumption. The ability to drive motors more efficiently, as these three announcements address, allows engineers to get more out of their motors with a smaller overall footprint.
