Chip Level Drivers FAQs

• Expand All FAQs
• Collapse All FAQs

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 (4 coils/6 lead wires) - The unipolar driver’s output current direction cannot be changed. There are two sets of coils for each phase in a motor. Only one set of the coils can be energized at a time. Each coil represents one phase; therefore, only 50% of the winding is utilized in the unipolar drive. The number of mechanical phases equals the number of electrical phases. Due to the fact unipolar drivers only use 50% of the windings, the performance ranges from low to moderate. The benefit of this is that it doesn’t generate too much heat.

Bipolar (2coils/4 lead wires) - The bipolar driver’s output current direction can be changed. 100% of the winding is utilized in the bipolar drive. That means the two sets of the coils in each phase can be connected either in series or in parallel to become one set of a coil. Current direction changed from the driver creates another mechanical phase. The number of mechanical phases is always twice the number of electrical phases. Bipolar drivers provide 40% more holding torque than unipolar drivers, but typically run at higher temperatures. For this reason, proper heat dissipation is important with bipolar drivers.

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.