AN4339 Datasheet, PDF (1/27 Pages) STMicroelectronics – BLDC motor based ceiling fan solution proposal

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
design of single stage high power factor flyback topology using the STMicroelectronics^®
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
DMOS, a centralized logic circuit to decode Hall effect sensors and a constant t_OFF PWM
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.
November 2013
DocID025039 Rev 1
1/27
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