# 50 Hz frequency Low Pass Filter Design

Discussion in 'The Projects Forum' started by Ahmed Nadeem, Feb 12, 2014.

Jan 14, 2014
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Hey Everyone

I have to design a Low pass RC filter of 50Hz output frequency for 150 Watt sine wave inverter. Input peak Voltage of PWM is signal is 12 V. The carrier frequency of PWM is 8 kHz.

P
the picture of 50Hz sine PWM

Last edited: Feb 12, 2014
2. ### crutschow Expert

Mar 14, 2008
13,013
3,233
Is this a low power signal or a high power signal that you want to filter? What degree of filtering do you need (how much 8kHz ripple is allowed)?

Jan 14, 2014
4
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Hello Crutschow.. It is a high power signal with 12 V peak. The output power depends on load. I need maximum filtering.. i.e Pure 50Hz sine output with minimum ripples of 8kHz.

4. ### crutschow Expert

Mar 14, 2008
13,013
3,233
You don't want to filter a high power signal with an RC filter since it will dissipate power, reduce the efficiency, and give poor voltage regulation with a change in output load. You need an LC filter.

"Maximum filtering" is not a numerical value. What value is "pure" and "minimum ripples"?

Last edited: Feb 13, 2014

Jan 14, 2014
4
0
Then how can I design the LC filter? Actually problem is that in my city Inductors of fixed value are not available Please provide me any solution..

6. ### crutschow Expert

Mar 14, 2008
13,013
3,233
The value of the inductor depends upon how much you need the 8kHz suppressed. You need to assign a number to the amount of attenuation you need (the amount of 8kHz ripple you can tolerate (1mV, 10mV, 100mV, etc.). Without that value you can't do a design. Of course, the lower the allowed ripple, the higher the inductance required, and the larger and more expensive is the inductor. One of the difficult parts in doing a design is often in determining what the acceptable performance parameters are so that the system performs the job adequately without unnecessarily tight (and perhaps expensive) design requirements. This is such a situation.

If you can't buy inductors (that sees odd), then can you buy ferrite magnetic cores and make you own inductors?