i am currently in the process of playing with a brushless dc motor, i have had great fun with sensored commutation and am fine with that and would now like to have a go at sensorless commutation using the pic's comparator inputs for zero cross detect.
most of the up to date datasheets in my collection mention using a voltage divider/low pass filter circuit to help eliminate commutation noise, the attached datasheet has a calculation formula on page 9 that i have been trying to work with inputting the values used to try and come up with the same cutoff frequency to verify that i have done it correctly but after trying many ways and googling for the last couple of hours i seem to not have made any progress.
the part i cant get a good understanding on is: (R1R2)/(R1+R2) R1 = 2.2k and R2 = 10k, could someone help explain how i calculate this for the correct value to put in the remainder of the full calculation on page 9 to get the same result for the cutoff frequency just to get an understanding for when i use it later for my own circuit.
i am currently in the process of playing with a brushless dc motor, i have had great fun with sensored commutation and am fine with that and would now like to have a go at sensorless commutation using the pic's comparator inputs for zero cross detect.
most of the up to date datasheets in my collection mention using a voltage divider/low pass filter circuit to help eliminate commutation noise, the attached datasheet has a calculation formula on page 9 that i have been trying to work with inputting the values used to try and come up with the same cutoff frequency to verify that i have done it correctly but after trying many ways and googling for the last couple of hours i seem to not have made any progress.
the part i cant get a good understanding on is: (R1R2)/(R1+R2) R1 = 2.2k and R2 = 10k, could someone help explain how i calculate this for the correct value to put in the remainder of the full calculation on page 9 to get the same result for the cutoff frequency just to get an understanding for when i use it later for my own circuit.
thanks
tony
Last edit: tony golding 2017-03-24
ok never mind, think ive got it or at least must do now as doing calc matches end result of 4.01 khz