AN1627 Freescale Semiconductor / Motorola, AN1627 Datasheet - Page 25

• Manufacturer Part Number: AN1627
• Description: Low Cost High Efficiency Sensorless Drive for Brushless dc Motor Using MC68HC (7)05MC4
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
detected (see 2.2 Back-EMF Sensing). The alignment of the Back-EMF with the commutation events
is good and the motor runs with high efficiency. The cursors define the time interval where the
measurement of mean, RMS and peak values of the phase current are done. See results on the right
side of the oscillogram.
A.1.1 Motor Load
The start-up capability of the drive was tested at more than 150% of the nominal load. The drive
successfully reached the working speed (2400rpm) within 5s, as required. Figure 2. shows the obtained
waveforms at the steady state condition.
Figure 2.
t,
Ch1 is the motor phase curren
Ch2 is one half of the DC-Bus voltage and CH3 is the branch voltage
Ch2 and Ch3 are divided by the resistor network down-to 0-15V level). The DC-Bus voltage is created
by rectifying the mains and therefore channel 2 varies according to charging/discharging of the DC-Bus
capacitor (10ms period). This variation has no impact on the Back-EMF zero crossing detection.
Figure 3.
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AN1627
MOTOROLA
REV 0.2
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