AN414 Datasheet, PDF (1/14 Pages) STMicroelectronics – Variable speed drives have become widespread in the home appliance field

AN414
Application note
Controlling a brushed DC motor
with an ST6265C or ST6260C MCU
Introduction
Variable speed drives have become widespread in the home appliance field. The most
classical way to achieve it is to use an AC universal motor with TRIAC and a specific circuit
which controls the TRIAC firing angle. We chose rather to use a permanent magnet DC
motor driven by a chopper. The chopper is driven by a high frequency PWM signal.
Controlling the PWM duty cycle is equivalent to controlling the motor voltage, which in turn
adjusts directly the motor speed.
Why did we make such a choice?
■ The main reason is the need of a speed sensor and a closed loop regulation for the
universal motor. For the permanent magnet DC motor, the speed is almost proportional
to the motor supply voltage. Therefore it is sufficient to control the motor voltage (through
duty cycle adjustment) if a 10% speed accuracy is sufficient. This saves the expensive
speed sensor.
■ The DC motor with chopper has higher efficiency, as there are no 50 Hz copper and iron
losses, due to lower current ripple.
■ The DC operation allows to reduce the acoustic noise, especially at 100 Hz.
Figure 1. Block diagram
DC Motor
M
ST6265C
IGBT
Table 1 lists the microcontroller products concerned by this application note.
.
Table 1.
Applicable products
Type
Microcontroller
Part number
ST6265C, ST6260C
MS19688V1
February 2013
Doc ID 1876 Rev 2
1/14
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