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Solution InstaSPIN-BLDC Slide 13
Here is a typical example. The bus voltage is 24 volts that means that the motor will see a 48-volt peak-to-peak voltage across its terminals as the PWM in the motor. That will tend to cause some pretty significant current ripple which may end up overheating the motor if it has very low inductance. So, this actually shows InstaSPIN working with another PWM technique. Now, this is what is called in-channel recirculation or unipolar PWMs. Now, in this case, the neutral point voltage will not remain fixed. In fact, it is moving up and down as the designer is PWM-ing. Now, this makes it a little bit more of a challenge to get the back-EMF signal. When dealing with the processor which has the ability to precisely time the sampling of the A to D converter with the PWM waveform then once again it is not a problem. Make sure that in the interval to take the back-EMF reading, actually time the A to D converter so it is sampling right in the middle of the PWM on time to avoid the switching edges. So, bipolar PWMs or unipolar PWMs, both actually will work with InstaSPIN-BLDC.
PTM Published on: 2013-01-24