Jianwen Shao

Improved direct back EMF detection for sensorless brushless DC (BLDC) motor drives

A novel back EMF detection method for sensorless BLDC motor drives without the motor neutral point voltage information is presented in this paper. The true phase back EMF signal can be directly obtained from the motor terminal voltage by properly choosing the PWM and sensing strategy. As a result, the method proposed is not sensitive to switching noise, no filtering is required, and good motor performance is achieved over a wide speed range. The detailed circuit model is analyzed and experimental results verify the analysis and demonstrate advantages of the new technique.Improved back EMF detection circuits for low voltage/low speed and high voltage sensorless BLDC motor drives are presented in this paper. The improvements are based on the direct back EMF sensing method from our previous research work described in reference, which describes a technique for directly extracting phase back EMF information without the need to sense or re-construct the motor neutral. The reference method is not sensitive to switching noise and requires no filtering, achieving much better performance than traditional back EMF sensing scheme. A complementary PWM (synchronous rectification) is proposed to reduce the power dissipation in power devices for low voltage applications. In order to further extend the sensorless BLDC system to lower speed, a pre-conditioning circuit is proposed to amplify the back EMFs at very low speed. As a result, the brushless DC motor can run at lower speed with the improved back EMF sensing scheme. On the other hand, another improved detection circuit is presented for high voltage applications to overcome the delaying problem caused by large sensing resistors. The detailed circuit models are analyzed and experimental results verify the analysis.

A novel microcontroller-based sensorless brushless DC (BLDC) motor drive for automotive fuel pumps

This paper presents a novel back EMF detection method for sensorless BLDC motor drive systems. By this method, a true back EMF signal can be directly extracted for each phase without sensing the neutral point of the motor. The method proposed is not sensitive to switching noise and requires no filtering. Good motor performance is achieved over a wide speed range as well. This novel sensing scheme is implemented into a hardware macro cell inside a mixed-signal microcontroller. The proposed microcontroller-based sensorless BLDC drive system has been successfully applied to automotive fuel pump applications, which require high reliability and intelligence at a low cost.

Single Stage Offline LED Driver

A non-isolated soft-switched high power factor offline LED driver is introduced in the paper. The Buck-Boost converter is chosen for this application due to its simplicity and low cost. The converter operates with constant peak current for constant power control, and in transition mode (boundary mode between CCM and DCM) to achieve soft switching. High power factor is achieved by reshaping the peak current nearby the zero crossing of input AC line.

Improving current regulation for offline LED driver

A buck converter is a very common choice for non-isolated offline LED applications, using peak current regulation. The problem for peak current regulation is that the average current of the LED string will vary with different numbers of LEDs. This paper presents two simple and cost effective ways to compensate the average current variation without losing the simplicity of peak current regulation.

Smart Home Appliance Control

Around the world, performance and cost efficiency have always been the challenges facing home appliance manufacturers. Advances in semiconductor technology have enabled the appliance industry to meet these challenges by increasing machine performance, efficiency and user-friendliness, while lowering overall control costs. This paper presents 3 technological advancements addressing key trends in Smart Appliance control, in the context of semiconductors.

A novel sensorless brushless DC (BLDC) motor drive for automotive fuel pumps

This paper presents a novel back EMF detection method for sensorless BLDC motor drive systems. By this method, a true back EMF signal can be directly extracted for each phase without sensing the neutral point of the motor. The method proposed is not sensitive to switching noise and requires no filtering. Good motor performance is achieved over a wide speedxange as well. This novel sensing scheme is implemented into a hardware macro cell inside a mixed-signal microcontroller. The proposed microcontroller-based sensorless BLDC drive system has been successfully applied to automotive fuel pump applications, which require high reliability and intelligence at a low cost.

A cost effective high performance LED driver powered by electronic ballasts

Many T8 LED tubes are currently available in the market; however, the majority of commercial products are passive converters, so the lamp current is not well controlled. This paper presents a low voltage, current-fed Buck converter for a T8 LED tube application. A very simple control method with zero-crossing synchronization is proposed; the operation of the circuit is described, and the performance of prototype proves the concept. The current-fed Buck converter is compatible with most commercial electronic ballasts.