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A low pass filter (LPF) is a type of electrical circuit that removes (attenuates) high frequencies and allows lower frequencies to pass through. In this piece, we’ll explore what a low pass filter is, how it works, and common uses.

What Does a Low Pass Filter Do?

Low pass filters remove unwanted frequencies from a signal above a determined “cutoff” frequency. LPFs are used in various applications across industries to block high frequencies and let low frequencies pass through the circuit. 


Here are a few examples:


  • Certain digital telecommunication systems
  • Control system filters
  • Audio amplifiers, equalizers, and speakers
  • Semiconductors
  • Distribution systems
  • Power supply and equipment
  • Speech signal processing
  • Image processing
  • Radar systems

How Does a Low Pass Filter Work?

Low pass filters work by using resistors with either inductors (low pass RL filters) or capacitors (low pass RC filters).  

Low Pass RL Filter 

A low pass RL filter has a very high resistance to high-frequency signals and low resistance to low-frequency signals. High-frequency signals are blocked from entering the circuit, and low-frequency signals pass through unimpeded.


With a low pass RL filter, the inductor is placed in series with the input signal. The resistor is aligned with the input signal.  

Low Pass RC Filter

A low pass RC filter has a high resistance to DC signals, so it blocks DC from entering by passing them off to an alternative section of the circuit. High-frequency signals go through the very low resistance path through the capacitor.


With a low pass RC filter, the resistor is placed in series to the input signal. The capacitor is placed parallel to the input signal. 

Contract Manufacturing

Now that you know the basics of what a low pass filter is, what it does, and how it works, contact Schott Magnetics to get custom magnetics development, prototyping, and manufacturing in the United States, Mexico, and China.

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