Low Pass Filter Design: Choosing L & C for Cut-off Frequency of 50Hz

In summary, the conversation discusses designing an LC low pass filter for a single phase sinusoidal pwm inverter with a cut off frequency of 50 Hz. The speaker is trying to determine the values for L and C in order to achieve this frequency and wonders how to choose these values with consideration for the load and its effect on the filter's performance. They also suggest using maths and frequency response graphs to analyze the behavior of the filter.
  • #1
hisham.i
176
2
Hello,

I am designing LC low pass filter for single phase sinusoidal pwm inverter, where the cut off frequency is f = 50 Hz.

And i have to chosse L, C such that: f = 1/2π√(LC)
but there is many combinations of L and c that result in this cut off frequency.

So my question is, how to choose these values?
 
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  • #2
A load is going to appear across C? This may have a major effect on the filtering ability of your L-C arrangement. You need to design it as an LCR circuit from the start, assuming you can represent your load as R.

Apply some maths, and sketch frequency response graphs, you'll see how it behaves.
 
  • #3
hisham.i said:
Hello,

I am designing LC low pass filter for single phase sinusoidal pwm inverter, where the cut off frequency is f = 50 Hz.

And i have to chosse L, C such that: f = 1/2π√(LC)
but there is many combinations of L and c that result in this cut off frequency.

So my question is, how to choose these values?

Do you need to select real parts, or is it just values that you need to select?
 

1. What is a Low Pass Filter?

A low pass filter is an electrical circuit that allows low frequency signals to pass through while attenuating high frequency signals. It is commonly used in electronic devices to remove unwanted noise from a signal.

2. How do I choose the values of L and C for a cut-off frequency of 50Hz?

To choose the values of L (inductance) and C (capacitance) for a low pass filter with a cut-off frequency of 50Hz, you can use the formula: fc = 1/(2π√LC). Rearrange the formula to solve for L or C, and then choose values that satisfy the equation.

3. What is the significance of a cut-off frequency of 50Hz?

A cut-off frequency of 50Hz means that any signals with frequencies below 50Hz will pass through the filter with minimal attenuation, while signals with frequencies above 50Hz will be significantly attenuated. This is useful for removing high frequency noise from a signal.

4. Can I use any values for L and C in a low pass filter?

No, the values of L and C must be carefully chosen to achieve the desired cut-off frequency. If the values are too small, the filter will not effectively attenuate high frequency signals. If the values are too large, the filter may attenuate low frequency signals as well. It is important to calculate the values using the formula and choose appropriate components.

5. How can I test the effectiveness of a low pass filter with a cut-off frequency of 50Hz?

You can test the effectiveness of the filter by measuring the output signal with and without the filter in place. A signal generator can be used to generate various frequencies and the output can be observed on an oscilloscope. The filter will be most effective at reducing the amplitude of high frequency signals near the cut-off frequency of 50Hz.

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