Chip Level Drivers FAQs

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A six-lead stepper motor, which is a unipolar stepper motor, can be used when a bipolar drive is being used to run the motor. Since bipolar motors only need four wires to run, there are options in connecting a six-lead wire to a bipolar drive. Typically, we refer to the six wires as A, /A, A Common, B, /B, B Common. Half-coil connection would be to use A, A Common, and B, B Common (or /A, A Common, and /B, B Common). To use full-coil, also known as series connection, you would use A, /A and B, /B. For full-coil the two common wires are ignored. The full-coil connection (or series) is ideal for lower speeds requiring more torque. The half-coil connection will give an overall amount of torque across a wider range of speeds.

The rated current is what the motor is rated at. The peak current refers to the amount of current the driver outputs.

Non-microstepping drivers
Peak Current = Rated Current

When using a driver that only does full stepping, the rated current is the same as the peak current. (Rated current = Peak Current).

Microstepping Drivers
Peak Current = 1.4 x Rated Current

When using a driver that is capable of doing microstepping (microstepping = 1/2, 1/4 stepping or more), the definition of peak current becomes 1.4 times the rated current. Microstepping drivers are made differently in order to maximize their ability to drive the stepper motor. Therefore, step motors can handle up to their rated current multiplied by 1.4. (Peak Current = 1.4 x Rated Current). This will not damage the motor because the power output is more or less the same.

Unipolar motors are so named because each of their coils only has one polarity.  Unipolar motors have two windings per coil and employ only one winding at a time.  Current flows through these windings such that each winding only ever acts as a north or south electromagnet.  These windings are switched on and off to create movement.  In contrast, bipolar motors have only one winding per coil which switches polarity to create movement.

Because current only flows in one direction in each coil of a unipolar motor, unipolar windings are preferred in high speed applications.  Unipolar windings, unlike bipolar windings, do not need the current to decay in one winding before the opposite polarity coil can be energized.

Bipolar motors are preferred for high torque applications because the entire coil is energized.  Unipolar motors are at a disadvantage here because each winding is half of the coil whereas bipolar windings use the whole coil.

When using a hybrid motor, NPA does not recommend using either a L/R or voltage drive. These drives, which provide constant voltage, create heat during operation and as a result will increase the motor’s resistance. Any change to the motor’s resistance will change the current supplied. NPA recommends using a constant current drive, such as PWM/chopper drive, for all applications with hybrid motors. When using tin-can motors, these limits do not apply.