Bypass Capacitors – Why and How to Use Them?

You may have heard about the phenomenon of bypassing in circuits, however, we may not have sufficient knowledge of how to apply this technique in real circuits. In this tutorial, we will discuss about the bypass capacitors, why we need to use and how to use these capacitors in circuits.

What is a Bypass Capacitor?

A capacitor that filters out the AC signal removing the noise and provides a DC signal is known as a bypass capacitor. The capacitor connected in the figure below is a bypass capacitor bypassing AC noise and allowing pure DC signal to pass through the component.

Bypass Capacitors

Why Use Bypass Capacitors?

In electronics, most of the circuits are digital in nature using direct current (DC). It has been observed that variations in voltage can cause problems to the circuit operation. A circuit may operate incorrectly due to voltage swing. In practical circuits, the voltage fluctuation is usually caused by the AC component that may ride over DC signal causing noise. Therefore, a bypass capacitor is needed to dampen the AC or noise present at all frequencies. Also, it prevents the unwanted communication between devices sharing the same power source.

When do you Need Bypass Capacitors?

Firstly, the low frequency circuits may not require bypass capacitors. However, many low frequency active devices comprise of high frequency units. For example, a microcontroller is a low frequency device using a clock making a low frequency system, but the rising and falling glitches can occur due to internal gate transitions without proper filtering of power supply that will traverse the circuit. Therefore, you may need a bypass capacitor with an appropriate value to achieve proper filtering of power supply.


Secondly, you may have this misconception that only digital devices need bypass capacitors. However, bypass capacitors also benefit the analog circuits and devices in a different way. In digital systems, bypass capacitors control the fast timing of rising and falling glitches. Conversely, bypass capacitors help in reducing noise of power supply in analog systems. Generally, analog devices have built in capability of filtering power supply that is effective for reducing low frequency power supply noise, but it is not useful at higher frequencies.


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