Product category:
Power Supply ICs and Controllers
News Release from: Zetex | Subject: ZXBM1016
Edited by the Electronicstalk Editorial
Team on 10 June 2005
Motor drivers banish tail-end spikes
Zetex has developed a novel technique to remove the current spike at the end of the commutation cycle in single- and two-phase brushless DC motors.
For single- and two-phase brushless DC motors, the current spike occurring at the end of the commutation cycle has a distinctly adverse effect on circuit efficiency, cost and audible noise Making use of existing PWM circuitry in half- and full-bridge BLDC controllers, Zetex has developed a novel technique for its complete removal
This article was originally published on Electronicstalk on 24 Jul 2008 at 8.00am (UK)
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Named "tail-end current control", the technique uses voltage controlled PWM to very slowly ramp down the coil current, from a low level at a point 75% through the commutation cycle, to the zero level at the end of the commutation.
With a high voltage control signal stimulating 0% PWM and a low voltage 100% PWM, moving between these voltages produces a variable amount of PWM drive that is directly proportional to the input control voltage.
In order to accurately apply a current reduction signal to the correct portion of the commutation cycle, the motor speed needs to be closely monitored.
An integrator therefore becomes one of the first requirements of the new technique.
A triangular waveform is then generated as a voltage against commutation period signal.
By combining integrated and triangular waveforms, a third signal is produced to modulate the PWM control.
As well as improving overall circuit efficiency, removal of the high current peak through tail-end current control offers other significant advantages.
Enabling the use of lower rated power switching devices and bridge capacitor, the technique helps reduce circuit cost.
The stress on motor core plates is also diminished and audible "clicks" are removed as a result.
Zetex is to integrate tail-end current control into its next generation motor predriver ICs.
The first product to incorporate the technology will be the ZXBM1016.
To be sampled during Q3 2005, the device will suit a wide range of single-phase brushless motor control applications.
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