MD24 / MD28
– Hardware Description
9
8.3.2
Parallel Connections
An 8 lead motor in a parallel configuration offers a more stable, but lower torque at lower
speeds. But because of the lower inductance, there will be higher torque at higher
speeds. Multiply the per phase (or unipolar) current rating by 1.96, or the bipolar current
rating by 1.4, to determine the peak output current.
8-lead motor parallel connections
9 Power Supply Selection
The MD24 / MD28 can match medium and small size stepping motors (from Nema size
17 to 34) made by any motor manufactures around the world. To achieve good driving
performances, it is important to select supply voltage and output current properly.
Generally speaking, supply voltage determines the high speed performance of the motor,
while output current determines the output torque of the driven motor (particularly at lower
speed). Higher supply voltage will allow higher motor speed to be achieved, at the price of
more noise and heating. If the motion speed requirement is
low, it’s better to use lower
supply voltage to decrease noise, heating and improve reliability.
9.1 Regulated or Unregulated Power Supply
Both regulated and unregulated power supplies can be used to supply the driver.
However, unregulated power supplies are preferred due to their ability to withstand
current surge. If regulated power supplies (such as most switching supplies.) are indeed
used, it is important to have large current output rating to avoid problems like current
clamp, for example using 4A supply for 3A motor-driver operation. On the other hand, if
unregulated supply is used, one may use a power supply of lower current rating than that
of motor (typically 50% - 70% of motor current). The reason is that the driver draws
current from the power supply capacitor of the unregulated supply only during the ON
duration of the PWM cycle, but not during the OFF duration. Therefore, the average
current withdrawn from power supply is considerably less than motor current. For
example, two 3A motors can be well supplied by one power supply of 4A rating.
