What Is Capacitor Loss?

When measuring a capacitor, you may often notice a parameter labeled DF (Dissipation Factor) below the capacitance value. This is an important but sometimes overlooked parameter that reflects the loss of a capacitor.

Understanding Capacitor Loss

Capacitor loss refers to the portion of energy that is consumed as heat during the capacitor’s operation, rather than being effectively stored or transferred. This loss is mainly caused by the internal resistance of the capacitor, known as Equivalent Series Resistance (ESR).

High losses not only reduce efficiency but can also lead to overheating, which shortens the capacitor’s service life. Therefore, understanding and controlling capacitor loss is essential for ensuring the reliability and efficiency of electronic systems.

The Role of Dissipation Factor (DF)

The dissipation factor can be expressed as:

where:

• ESR is the equivalent series resistance

• Xc is the capacitive reactance

DF is a measure of how much energy is dissipated in the capacitor relative to how much energy is stored. In other words, when a capacitor operates, internal resistance generates heat—this heat represents energy loss. The larger the DF, the higher the losses and the lower the efficiency.

Another way to understand DF is in terms of power:

• P: Active power (the energy consumed by the capacitor)

• Pd: Reactive power (the energy stored by the capacitor)

A smaller DF means that the active power consumed is small compared to the reactive power stored, resulting in lower loss and higher efficiency.

High-Q Capacitors

In practice, you may also come across the term High-Q capacitors. The Q factor (Quality Factor) is simply the reciprocal of DF:

A higher Q value indicates a lower DF, meaning the capacitor has lower losses and higher efficiency. In circuit applications, high-Q capacitors help minimize losses and improve overall system performance.

✅ In summary:

• Capacitor loss = energy dissipated as heat instead of stored.

• DF is the key parameter to evaluate capacitor loss.

• Lower DF → lower loss → higher efficiency.

• High-Q capacitors are essentially low-loss capacitors.