4 Main Varieties of Polymer Capacitors, their Characteristics
Capacitors find their applications in almost all kinds of electrical appliances, although their sizes, capacities, materials of construction etc., vary depending on the application, the basic functionality is the same.
According to a White Paper from Panasonic, “Advanced capacitors based on conductive polymers maximize performance and reliability.” The Paper communicates that capacitors may seem simple enough, but specifying them has actually grown more complex in recent years. The reason why comes down to freedom of choice. The universe of capacitors has expanded greatly over the past few years, in large part because of capacitor designs that take advantage of advances in conductive polymers. These advanced capacitors sometimes use conductive polymers to form the entire electrolyte. Or the conductive polymers can be used in conjunction with a liquid electrolyte in a design known as a hybrid capacitor. Either way, these polymer-based capacitors offer a performance edge over conventional electrolytic and ceramic capacitors when it comes to:
• Electrical characteristics.
• Life cycle cost.
The various polymer and hybrid capacitors have distinct sweet spots in terms of their ideal voltages, frequency characteristics, environmental conditions and other application requirements.
Polymer capacitors come in 4 main varieties, including the hybrid. Each type has different electrolytic and electrode materials, packaging and application targets:
• Layered polymer aluminium capacitors use conductive polymer as the electrolyte and have an aluminium cathode. Depending on the specific model, these capacitors cover a voltage range from 2-25V and offer capacitances between 2.2-560µF. The distinguishing electrical characteristic of these polymer capacitors is their extremely low Equivalent Series Resistance (ESR). For example, as per Panasonic, some of their SP-Cap polymer capacitors have ESR values as low as 3mΩ, which is among the lowest in the industry. Packaged in a molded resin as compact surface mount devices, these layered polymer capacitors have a low profile. As a result of the electrical and form factor characteristics, they have applications in a variety of handheld electronic devices or other applications that require a low-profile capacitor that will not interfere with a nearby heat sink.
• Wound polymer aluminium capacitors are also based on conductive polymers and aluminium, but they have a wound foil structure. The wound polymer capacitors cover a wider range of voltages and capacitance values than other types of polymer capacitors. Voltages extend from 2.5 to 100V, while capacitances run from 3.3 to 2700µF. Like the layered polymer capacitors, the wound style has extremely low ESR values. Some of our OS-CON capacitors, for instance, have ESR values below 5mΩ. The wound style can also be surface mounted, though they are not quite as compact as the layered capacitors.
• Polymer tantalum capacitors employ a conductive polymer as the electrolyte and have a tantalum cathode. They span voltages from 1.8 to 35V and capacitances from 2.7 to 680µF. They too have low ESR, with some of Panasonic’s POSCAP capacitors exhibiting ESR values as low as 5mΩ. Packaged in a molded resin case, the tantalum polymer capacitors are among the most compact on the market. Their POSCAP M size, for example, measures just 2.0 by 1.25 mm. Though compact, a wide range of sizes is available for this capacitor type.
• Polymer hybrid aluminum capacitors, as their name suggests, these capacitors use a combination of a liquid and conductive polymer to serve as the electrolyte and aluminium as the cathode. Think of this technical approach as the best of both worlds: The polymer offers high conductivity – and a correspondingly low ESR. The liquid portion of the electrolyte, meanwhile, can withstand high voltages and provide higher capacitance ratings due to its large effective surface area. The hybrid capacitors offer a voltage range from 25 to 80V and capacitances between 10 and 330µF. At 20 to 120mΩ, ESR values for hybrids are higher than other types of polymer capacitors, but still very low considering the higher power applications they address.
(Adopted from the Panasonic’s White Paper, ‘Understanding Polymer and Hybrid Capacitors’)