November 2013

DocID025039 Rev 1

1/27

AN4339

Application note

BLDC motor based ceiling fan solution proposal

Harjeet Singh

Introduction

Due to recent directives by the “Bureau of Energy Efficiency” (BEE) to reduce power

consumption of consumer loads, it is necessary to analyze energy consumption by each of

the house hold loads and implement how the energy can be saved in running such

equipment. Some of the major loads that fall under this category are like lighting loads,

refrigerators, air-conditioners, fans, televisions, audio equipment and so on. There are

developments going on in different segments meet the desired energy saving norms. The

fan is one of the major contribution in house hold as well as industrial usages. Currently fans

build up with an AC induction motor which is approximately 60 - 70 W power rated. These

motors are heavier and less efficient, not more than 50% of overall efficiency.

In the near future these motors will be phased out and instead a BLDC (brushless DC

motor) is going to be introduced in fan application. In a practical scenario it is seen that

a 40 - 50% lesser power rated motor can provide the same amount of air flow output. That

means that the approximately 30 W BLDC based fan system will replace existing 60 - 70 W

power consumption with the AC induction motor. This is a huge power saving. Moreover the

BLDC motor are much lighter as compared to the heavy AC induction motor.

In this application note the proposed scheme to drive a BLDC fan motor is described.

Usually the low voltage DC motor is well suited for this application, mainly a 24 V BLDC

motor. The system requires mainly 2 sections: a front-end AC/DC power supply for the

universal range followed by a 3-phase bridge inverter to drive a motor. The power supply

has to be galvanic isolated having high efficiency, high PF and low THD. For the same the

innovative PFC L6564 controller is considered. The L6564 device is a current mode PFC

controller operating in transition mode (TM). The highly linear multiplier, along with a special

correction circuit that reduces crossover distortion of the mains current, allows wide range

mains operation with an extremely low THD even over a large load range. This topology

gives high power factor but on the other hand when operated in high PF configuration

significant magnitude of twice of mains frequency ripple at output DC voltage because of no

electrolytic capacitor after bridge rectification. But in our application, this will not impact the

performance of the second stage driving motor.

Coming to the BLDC driver section i. e. second stage of this scheme (see Figure 1), we

propose the ST's 3-phase brushless DC motor driver - L6235. The L6235 device is a highly

integrated, mixed-signal power IC that allows to easily design a complete motor control

system for a BLDC motor, specially for low power small motors. The IC integrates six power

current control technique (synchronous mode) plus other added features for safe operation

and flexibility.

The typical BLDC motor power requirement is 24 V/1 A maximum including losses inside

the driver stage and motor. This requires 24 W power supply to run the motor driving stage.

Assuming efficiency of power supply as 85% over an universal voltage range, the power

supply requires maximum input power somewhere around 28 W.

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