# RC Filter calculations

1. ## RC Filter calculations

Hi,

I am giving controllers PWM to the IPM Power modules.

My controller pwm will be 8 KHZ now i want to add an filter which can passes frequency upto 10KHZ

When i was calculating value of RC

FL=1/(2*PI*R*C)

FL=10KHZ

Now the two components are unknown here..

Are R or C Takes randomly or are there any criteria to select the Proper R and C...

I assumed C=10nF (assuming is ok or not) and i got R value=1.59K

is this right approch..??

2. ## Re: RC Filter calculations

You have correctly calculated the cut-off (3dB attenuation) frequency of a first order low pass filter.

To understand if it serves the intended purpose, we should know more about the problem and involved waveforms.

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3. ## Re: RC Filter calculations

Yes..
i will start for the PCB Works.

Will let you know..

Thanks FVM..!!

Marx

4. ## Re: RC Filter calculations

If you have an 8kHz PWM signal, running it through a 10kHz filter will have only a small effect on the waveform.
What is the purpose of this filter?
Normally you want to make the low-pass filter corner frequency low enough to recover the PWM modulation signal.

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5. ## Re: RC Filter calculations

My controller will give a 8 mhz frequency to the IPM Modules.

To avaoid the high frequency to get read by IPM AND TO WORK IN A SAFER RANGE

6. ## Re: RC Filter calculations

Originally Posted by Bjtpower
My controller will give a 8 mhz frequency to the IPM Modules.

To avaoid the high frequency to get read by IPM AND TO WORK IN A SAFER RANGE
Sorry but I don't understand what you are talking about.
Are you saying the IPM modules operate at 8MHz (not 8 millihertz) and you want to operate at 8 kHz??

7. ## Re: RC Filter calculations

Sorry Typing mistake,,

Its 8 khz of pwm from controller to directly IPM..

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8. ## Re: RC Filter calculations

I couldn't understand what this filter will serve to ...
IPM works with time domain signals so either ONE or ZERO in PWM mode, what is your intention by using this filter ??
If your intention is to reduce the harmonics, they will be regenerated in the IPM module again..
PWM signals are already harmonically variable and rich signals, cutting-off at the input I think will not bring any advantage at all.

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9. ## Re: RC Filter calculations

I just want to limit the Hogh frequency noise to the IPM Pins so that nuisance behavior will not happen.

I am going to give pwm to IPM From ucontroller.

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