Design Of Electrical Machines By Nagoor Kani Pdf. Being a novice regarding stepper drives, I am confused regarding the specification of max step frequency and PWM frequency for the stepper drivers,,, and: • Max step frequency 250kHz is that the microstep frequency? That leads to a max speed of 250,000(200*32)*60 = 2,344 RPM at 1/32 microstepping and 75,000 RPM at full step. Is that correct?

Stepper motor controllers are more complex than DC motor controllers. Driving a bipolar motor with microstepping requires 2 complete H-bridges and 2 channels of PWM. The LV8741V is a 2-channel H-bridge driver IC that can switch a stepper motor driver, which is capable of micro-step drive and supports Quarter-step excitatio. PWM Stepper Motor Driver PART NO. 2183816 Control a stepper motor using this circuit and a servo PWM signal from an R/C controller, arduino, or microcontroller.

• How can 50 kHz PWM frequency work with a step frequency of 250 kHz? My understanding was that the PWM frequency has to be much higher than the step frequency. • For I did not find a specification of the PWM frequency.

• can, according to Application report SLVA416 be modulated with the VREF inputs for the A and B channels. What is the limitation of the timing of the step increments for that input, considering the fixed PWM frequency of 50 kHz?

Looking forward to explanations regarding above questions. Hi Ingvar, This is actually quite a deep question so I will try to answer without confusing you further.

First of all, we must not confuse STEP input frequency with conventional motor operation. When we say the pin can tolerate a 250 KHz signal this is pretty much what it means.

If you were to apply said pulse trail, the internal logic would behave as specified by the datasheet. Now, the motor, on the other hand. Would such a high rate stepping signal be useful at all? There are a few reasons for this to be the case. First, like you point out, the internal chopping frequency is considerably lower.

However, anybody could argue that if we were able to step the motor at those superbly high rates, there would be no current chopping at all, since the motor would be going so fast, the BACK EMF would take the current to such tiny levels, there would be no current regulation at all, in which case the 50 KHz frequency is of no importance. I realize I may be speaking in alien language here, but this is actuall quite easy to see if you have a current probe at any motor wire.

As you increase the motor speed, the current starts to decrease due to the BACK EMF being generated by the motor's rotation. Eventually you will see there is no current chopping at all. The second point follows shortly after, as you keep on increasing the speed. What you will see is the motor will stall and will not be able to move any faster. Stepper motors are not designed to move superbly fast. And as fast as you can make them rotate, you can feel certain 75,000 RPM is not it. That is the field for Brushless DC motors (specialized ones, by the way) and although the stepper is a brushless dc motor, the fact that is operated under open loop conditions makes it basically impossible to reach such high speeds.

On, the matter is completely different. The current chopping engine has programable values through an external pair of a resistor and a capacitor. The capacitor sets the TBLANK and both the resistor and the capacitor set the TIME OFF. The application voltage, motor inductance and motor speed will determine the TIME ON. Do note that the chopping frequency will then be a factor of all of these. It is hard to say what it will be as it is highly application dependent, but it is often anywhere in between 20 KHz to 75 KHz. We do not recommend too high switching frequency as this increases the switching losses and that is not going to help with the maximum current due to power dissipation.

On we again go back to fixed parameters. Again, the limits on the pins will be way much higher than the actual limit the motor will impose. This is both because of the fact that the motor will most likely not be able to move very fast and the fact that if indeed it can move very fast, the laws of physics will then kick in and the BACK EMF will take the current to levels in which there will be no current regulation.