What is a Filter Capacitor : Working and Its Applications

The capacitor is a reactive component, used in analog electronic filters because the capacitor impedance is a function of frequency. The capacitor that affects a signal can be frequency-dependent. So this property is widely used in designing the filter. Analog electronic filters like LPF can be used to execute a function of predefined signal processing. The main function of this filter is to allow low frequencies and block high frequencies. Similarly, an HPF allows high frequencies and blocks low frequencies. The electronic filter can be made with the help of analog components like resistors, capacitors, transistors, op-amps, and inductors. This article discusses an overview of the filter capacitor and it’s working.

What is a Filter Capacitor?

A capacitor that is used to filter out a certain frequency otherwise series of frequencies from an electronic circuit is known as the filter capacitor. Generally, a capacitor filters out the signals which have a low frequency. The frequency value of these signals is near to 0Hz, these are also known as DC signals. So this capacitor is used to filter unwanted frequencies. These are very common in different types of equipment like electronics as well as electrical and applicable in different applications.

Filter Capacitor
Filter Capacitor

Working of Filter Capacitor

The working of this capacitor mainly depends on the capacitive reactance principle. It is nothing but how the impedance of a capacitor alters with a signal frequency that is flowing through it. A nonreactive component like a resistor offers similar resistance to a signal apart from the frequency of the signal. This means 1Hz & 100KHZ signals flow throughout a resistor with equal resistance.

But, a capacitor is different because its impedance or resistance will change based on the signal frequency which is flowing through. These are reactive devices that offer high resistance to low-frequency signals and low-resistance to high-frequency signals using the formula like XC= 1/2πfc. A capacitor gives dissimilar impedance values for dissimilar frequency signal. In a circuit, it can operate as a resistor.

Filter Capacitor Formula

In power supply circuits, this capacitor can be calculated to ensure the least ripple at the output. The formula is C = I / 2f Vpp

From the equation above, ‘I’ is load current, ‘f’ is i/p frequency of AC and ‘Vpp’ is the minimum ripple that may be acceptable because almost it’s never possible to make this ‘0’

Filter Capacitor Circuit

The circuit diagram of the filter capacitor is shown below. In this circuit, the capacitor works like a high pass filter that allows high frequencies and blocks direct current. Similarly, they can also work as a low pass filter to allow DC and block AC.

Here the capacitor is connected in parallel with the component instead of connecting in series. This circuit is a high-frequency capacitive filter. Here, the flow of current will be in the least resistance direction.

Filter Capacitor Circuit
Filter Capacitor Circuit

Because a capacitor gives extremely low resistance for high-frequency signals, so these signals will supply through the capacitor. Like this, the circuit in this arrangement, it is a high-frequency filter. The signals like low-frequency current will not supply throughout the capacitor, as it gives high resistance for low-frequency signals.

Filter Capacitor Circuit to Block DC and Pass AC

For low-frequency signals, the capacitor offers extremely high resistance and for high-frequency signals, it proves less resistance. So it acts as a high pass filter to allow high-frequency signals and block low-frequency signals.

Circuit to Block DC and Pass AC
Circuit to Block DC and Pass AC

In a circuit, both AC and DC signals can be used several times. But, in some cases, we need only AC signals & the DC signals will be taken out. The best example of this is a microphone circuit. In this, as an input, DC is given to the microphone. We need DC as input to the microphone to power on & we require AC as input to represent the music, voice signals, etc

Filter Out the DC Component from the Signal

A capacitor is used to filter out the DC signal. This can be done by connecting the capacitor in series in the circuit. The following circuit is the capacitive high-pass filter. In this, signals like DC or low frequency will be blocked.

Generally, a ceramic capacitor with 0.1µF value can be placed following the signal that includes both the AC and DC signals. This capacitor allows AC and filters out the Dc component.

Filter Capacitor Applications

The applications of this include the following.

  • The line filter capacitor is applicable in several industrial loads as well as appliances in order to defend the appliance from the noise of line voltage noise and to defend other devices on a similar line from the generated noise within the circuit.
  • These capacitors can be used in all types of filters which are used in signal processing. The best example of this application is like an audio equalizer. It uses different frequency bands to permit amplification for low, high, and midrange frequency tones.
  • It is used for glitch removal on DC power rails
  • It is used for RFI removal (radio frequency interference) for power or signal lines to come in or exit equipment.
  • This capacitor can be connected after the voltage regulator to get a smooth DC power supply.
  • This capacitor is used in audio, IF or RF filters


1). What is the function of a filter capacitor?

It is used to filters out a range of frequencies from a circuit.

2) How the capacitor is used as a filter?

In a power supply, a capacitor is used to filter the pulsating DC o/p once rectification so that an almost stable DC voltage can be supplied to the load.

3). What are the limitations of the capacitor filter?

Both voltage regulation & filtering are poor.

4). What is the difference between bypass and decoupling capacitor?

The bypass capacitor is used to push the noise signals whereas the decoupling capacitor is used to smoothen the signal through stabilizing the distorted signal.

Thus, this is all about an overview of filter capacitor, working, formula, circuits, and its applications. Here is a question for you, what is the main function of a filter capacitor?