DRV8424: drive a unipolar or bipolar stepper

Dear Akshay,

1. For a 5-wire unipolar stepper motor, the center taps of each winding are connected together. Can we ignore the center tap and directly use a bipolar driver such as DRV8424?

2. If I want to be compatible with unipolar(5-wire) and bipolar stepper, do I need to use four-channel half-bridge drivers, such as the DRV8932, DRV8935, DRV8955, DRV8844, DRV8847, and DRV8412?
3. I've seen other controllers that use the DRV8825 to drive unipolar(5-wire) or bipolar steppers. Is it possible?

Thanks.

Dear Akshay,

1. When the 5-wire unipolar stepper motor is driven by a bipolar driver, can we use slow decay or fast decay mode? 

2. Although we ignore the center taps, the two windings are connected in fact. Will there be current flowing in the center tap line? Will it cause a problem?

3. As I asked a few days ago, if the center tap is connected to the VM, I think only the lower 4 MOSFETs are effective. This bipolar driver is equivalent to a unipolar drive mode. Is this method feasible?

Thanks for your reply.

Dear Akshay,

1. I read the datasheet of the half-bridge drivers, such as DRV8935. When the LS FETs of two channels turn ON, the HS FETs of the other two channels turn ON. This is very similar to the status of the full step when using a bipolar driver(such as DRV8825) and connecting the center tap of the unipolar stepper to VM. The only difference is that DRV8935 can only turn ON the LS FET of the anyone channel. Are we correct?

2. In the future I would like to test the following two circuits and observe whether there is a difference. Do you think it's feasible?

Thanks for your support.

Dear Akshay,

1. I modify Circuit 2 as follows, Do you think it is not feasible? I guess there may be problems in the current decay mode.

2.  I confirm again. When we ignore the center taps, even in fact the two windings are connected, you think Circuit 1 can work and can use the fast or slow decay mode. Is it right?

Thanks for your support. 

Hey Kevin,

If using bipolar driver then you cannot do the method shown in circuit 2.

Sorry for the confusion, I had a discussion with my team and Circuit 1 will not work on 5-wire unipolar because the two center taps will be shorted together and brought out as the 5th wire. With 6-wire unipolar both center taps are isolated and brought out separately hence can be ignored and rest of the four wire serves as a bipolar connection.

Best,

Akshay

Dear Akshay,

From our discussion, we cannot use a bipolar driver, such as DRV8825 or DRV8424, to drive a 5-wire unipolar stepper.  But we can see some examples of using bipolar drivers to drive 5-wire unipolar steppers. These cases confuse us. We want to design a driver that can drive a 5-wire unipolar stepper or a bipolar stepper. Do you think a Quad Half-Bridge Driver such as DRV8935 is suitable?

Thanks.

Hey Kevin,

Can you send me you example of the bipolar driver driving a 5 wire unipolar motor? I will bring this up with my team.

But a half bridge driver can be used to drive a bipolar stepper and a unipolar (with the center taps connected to VM).

Best,
Akshay

Dear Akshay,

The examples are commercially available products. May not be appropriate for public discussion here. Can I provide your information by email?

Thanks.

Dear Akshay,

We just need to use the full-step or half-step mode. Is there a proper decay mode available?

Thanks.