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issue: August 2008 APPLIANCE Magazine

Motor Technology
Sensorless Control

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A new sensorless motor controller offers high performance in the size of a business card.

A new digital EC sensorless controller from Maxon offers engineers performance and flexibility in a compact package. Features include a wide input range of 10–50 V and 1⁄3-hp output power capability,

With functionality up to 250 W at 10–50 V dc, the DECS 50/5 sensorless controller from Maxon Motor (www.maxonmotorusa.com) of Fall River, MA, U.S. is a high-performance driver for brushless dc motors. Factor in small size, and you have an ideal motor control solution for smart pumps and fans where speed regulation is critical to the application and thermal or overload protection is required, says Kirk Barker, Maxon electronics product manager.

According to Barker, multilayer board and efficient placement of SMT components help keep the controller small, while a creative firmware algorithm and sensorless brushless motor commutation sequence enable the functionality. “We used a sensorless start-up algorithm divided into two parts,” he explains. “First is the alignment phase, which sets the motor shaft to a defined rotor position by supplying a controlled current ramp at a  fixed step configuration (nonrotating stator field). Second is the acceleration phase, where a synchronous rotation is forced on the motor at a fixed acceleration rate until the speed is high enough for EMF sensing.”

Barker says that the device’s 80% duty cycle renders up to 90% efficiency. “A portion of the PWM duty cycle is required to bootstrap the N junction MOSFETs,” he adds. “Depending on the required speed, this is flexible.”

This type of flexibility is one of the key features offered by the controller. In addition to the wide input voltage range, it is available with a pluggable PCB screw connector or a four-lead flex cable connector. An adjustable start-up algorithm is also available via DIP switch settings. The speed value can be set with an integrated potentiometer or an analog set value. The 1-Q amplifier can be operated up to a maximum speed of 80,000 rpm.

Barker says new microprocessor availability and high-performance field-effect transistors (FETs) enable the controller’s flexibility, a feature engineers will find especially beneficial. “Tunable performance range over a variety of brushless motor applications renders longer product life cycles,” he says.

The new component offers control inputs for selecting motor direction, enable, and braking, as well as an operating status LED display and speed monitor output. Applications range from blowers and fans to power tools. Designs can also be tailored to fit custom applications.

Suppliers mentioned in this article:
Maxon Precision Motors

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