The high capacitance values of supercapacitors (Ultracapacitors) make them a useful circuit element for serving as a temporary power source. Today, the use of supercapacitors, which can have capacitance values of up to 6 kF, is increasingly common. Supercapacitors are favored in applications that require numerous rapid charge/discharge cycles rather than long-term compact energy storage. They are utilized in automobiles, buses, trains, cranes, and elevators for tasks like regenerative braking, short-term energy storage, and burst-mode power delivery. Another application is in the protection of memory operations. In scenarios where the integrity of memory operations is crucial, a secondary energy source is required to activate immediately if the primary source fails or to provide enough time for the circuit board to execute shutdown functions safely. In such cases, supercapacitors can offer the necessary current and voltage to maintain memory operations during power interruptions.
Supercapacitors, also known as ultracapacitors, are sometimes referred to as double-layer capacitors because of their unique structure. Their capacitance can range from as low as 3 µF to as high as 6000 F. Typically, they have a rated voltage between 1.4V and 12V, but some can be rated up to 320V. In addition to being available in THT (Through-Hole Technology) package types, they can also be found in SMD (Surface Mount Device) packages. The capacity tolerances for supercapacitors are relatively high, typically around ±20%. They tend to have greater internal losses compared to other capacitor types, but they boast exceptionally high instantaneous current capacities. Due to their large capacitance values and impressive instantaneous current capabilities, they are predominantly used in power applications.
Application Examples of Supercapacitors (Ultracapacitors)
The high capacitance values of supercapacitors make them perfect for a myriad of applications, particularly those related to power supplies. For instance, they can be used to protect data during power interruptions in memory applications or to bridge the brief gap between a device's main power supply cut-off and the activation of its backup power supply in UPS systems. In these scenarios, supercapacitors act by storing energy over extended periods.
Applications that require continuous charge and discharge of supercapacitors are widespread. The combination of high capacity and superior peak current capability makes supercapacitors especially important in electric vehicles or in other applications with variable battery loads, where these two attributes are vital. For battery-driven systems controlling variable loads, such as electric or hybrid vehicles, it's crucial that they don't induce fluctuations on the power line. These battery-induced variable load systems, which can be exemplified by the aforementioned vehicles (and the list can indeed expand), contain numerous non-linear loads. This presence can lead to current-voltage fluctuations and harmonics during battery charging. Power oscillations can not only reduce the system's efficiency but also produce parasitic effects on other connected systems. To combat this, the high peak current capability of supercapacitors can be harnessed. They can satisfy the peak current demand on the power line, effectively acting as a buffer.
Table 1: Summary table to facilitate comparison of supercapacitors with other capacitor types.
3 µF – 6000 F
Rated Voltage Range
(Can be found: 1,4 V – 320V) (Widespread: 2,4V – 2,8V)
High capacitance value, High peak current capability.
High tolerance, High losses.