Pololu High-Power Stepper Motor Driver 36v4
This discrete MOSFET stepper motor driver enables control of one bipolar stepper motor. It supports a wide 8 V to 50 V operating voltage range and can deliver up to 4 A continuous per phase without a heat sink or forced air flow (6 A max with sufficient additional cooling). The SPI interface allows configuration of the current limiting, step mode (9 step modes from full-step through 1/256-step), decay mode, and stall detection. The driver also provides back-EMF feedback that can be used for more advanced control and stall detection algorithms. Additional features include reverse-voltage, under-voltage, and over-current protection.
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- I want to control a 3.6 V, 2 A per phase bipolar stepper motor like this, but your Pololu High-Power Stepper Motor Driver 36v4 has a minimum operating voltage of 8 V. Can I use this driver without damaging the stepper motor?
Yes. To avoid damaging your stepper motor, you want to avoid exceeding the rated current, which is 2 A in this instance. The Pololu High-Power Stepper Motor Driver 36v4 lets you limit the maximum current, so as long as you set the limit below the rated current, you will be within spec for your motor, even if the voltage exceeds the rated voltage. The voltage rating is just the voltage at which each coil draws the rated current, so the coils of your stepper motor will draw 2 A at 3.6 V. By using a higher voltage along with active current limiting, the current is able to ramp up faster, which lets you achieve higher step rates than you could using the rated voltage.
If you do want to use a lower motor supply voltage (under 6 V) for other reasons, consider using our DRV8834 low-voltage stepper motor driver carrier or the STSPIN220 low-voltage stepper motor driver carrier.
- Do I really need to set the current limit on my stepper motor driver before using it, and if so, how do I do it?
Yes, you do! Setting the current limit on your stepper motor driver carrier is essential to making sure that it runs properly. An appropriate current limit also ensures that your motor is not allowed to draw more current than it or your driver can handle, since that is likely to damage one or both of them.
Setting the current limit on the Pololu High-Power Stepper Motor Driver 36v4 is done through its SPI interface (this is very different from most of our other stepper motor driver carriers, which have their current limits set through their on-board potentiometers). The Pololu High-Power Stepper Motor Driver 36v4 defaults to its maximum possible current limit setting on start-up, which is much more current than the board can safely deliver, so you will need to set the current limit to an appropriate value for your stepper motor before enabling the driver outputs to prevent damage to the board. This is done by adjusting the TORQUE and ISGAIN bits in the TORQUE and CTRL registers, respectively. The DRV8711 datasheet (3MB pdf) has more information on how to set the current limit through the SPI interface, and our Arduino library for the Pololu High-Power Stepper Motor Driver includes example sketches showing how to implement this in software.
- How do I connect my stepper motor to the Pololu High-Power Stepper Motor Driver 36v4?
The answer to this question depends on the type of stepper motor you have. When working with stepper motors, you will typically encounter two types: unipolar stepper motors and bipolar stepper motors. Unipolar motors have two windings per phase, allowing the magnetic field to be reversed without having to reverse the direction of current in a coil, which makes unipolar motors easier to control than bipolar stepper motors. The drawback is that only half of the phase is carrying current at any given time, which decreases the torque you can get out of the stepper motor. However, if you have the appropriate control circuitry, you can increase the stepper motor torque by using the unipolar stepper motor as a bipolar stepper motor (note: this is only possible with 6- or 8-lead unipolar stepper motors, not with 5-lead unipolar stepper motors). Unipolar stepper motors typically have five, six, or eight leads.
Bipolar steppers have a single coil per phase and require more complicated control circuitry (typically an H-bridge for each phase). Pololu High-Power Stepper Motor Driver has the circuitry necessary to control a bipolar stepper motor. Bipolar stepper motors typically have four leads, two for each coil.
Two-phase bipolar stepper motor with four leads.
The above diagram shows a standard bipolar stepper motor. To control this with the high-power stepper motor driver, connect stepper leads A and C to board outputs AOUT1 and AOUT2, respectively, and stepper leads B and D to board outputs BOUT1 and BOUT2, respectively. Note that if you happen to swap which way the wires are connected for any coil, the stepper motor will turn in the opposite direction, and if you happen to pair up wires from different coils, the motor should be noticeably erratic when you try to step it, if it even moves at all. See the DRV8711 datasheet (3MB pdf) for more information.
If you have a six-lead unipolar stepper motor as shown in the diagram below:
Two-phase unipolar stepper motor with six leads.
you can connect it to the high-power stepper motor driver as a bipolar stepper motor by making the bipolar connections described in the section above and leaving stepper leads A’ and B’ disconnected. These leads are center taps to the two coils and are not used for bipolar operation.
If you have an eight-lead unipolar stepper motor as shown in the diagram below:
Two-phase unipolar stepper motor with eight leads.
you have several connection options. An eight-lead unipolar stepper motor has two coils per phase, and it gives you access to all of the coil leads (in a six-lead unipolar motor, lead A’ is internally connected to C’ and lead B’ is internally connected to D’). When operating this as a bipolar stepper, you have the option of using the two coils for each phase in parallel or in series. When using them in parallel, you decrease coil inductance, which can lead to increased performance if you have the ability to deliver more current. However, since the high-power stepper driver actively limits the output current per phase, you will only get half the phase current flowing through each of the two parallel coils. When using them in series, it’s like having a single coil per phase (like in four-lead bipolar steppers or six-lead unipolar steppers used as bipolar steppers). We recommend you use a series connection.
To connect the phase coils in parallel, connect stepper leads A and C’ to board output AOUT1, stepper leads A’ and C to board output AOUT2, stepper leads B and D’ to board output BOUT1, and stepper leads B’ and D to board output BOUT2.
To connect the phase coils in series, connect stepper lead A’ to C’ and stepper lead B’ to D’. Stepper leads A, C, B, and D should be connected to the stepper motor driver as normal for a bipolar stepper motor (see the bipolar stepper connections above).