MOSFET boards balance supercapacitors

Supercapacitor auto-balancing (SAB) MOSFET arrays used in each ABM810028 board to provide a scalable, low-power stack. The ALD810028SCLI SAB MOSFETs balance 2.8, 3.0 and 3.3V supercapacitors arranged in a series stack by equalising the leakage current of each cell. The MOSFETs also balance each cell through low levels of leakage current without exposure to supercapacitor charge/discharge voltage levels for cells of 3000F or more.

According to the company's president and founder, Robert Chao: "New, higher voltage supercapacitors are being introduced to address the energy storage needs of data centres and industrial automation which require high reliability to meet very demanding standards for back-up power systems." He adds: "These boards provide the ideal platform for balancing high voltage supercapacitors through a low-voltage, low leakage and low current controlling method in a small and scalable form factor."

The boards are rated for operation from -40 to +85°C. There are three voltage ratings available: 2.8V, with 1µA operating current, 3.0V with 100µA operating current and 3.3V with 1,000µA operating current. In many cases, says the company, the operating current is equivalent in magnitude to the leakage current of the supercapacitors.

Another challenge is over-voltage conditions, which are a leading cause of failures for supercapacitors. Design engineers need to balance all supercapacitor cells in a stack of two or more. The SAB MOSFET(s) installed on the board preventing over-voltage, and the boards enable system engineers to test, evaluate, prototype products or enter production volume. The SAB MOSFET technology also offers an improved circuit design compared to other passive or active balancing schemes  and provides design space options. 

The boards are scalable to meet the growing application of multiple supercapacitor cells in modules for higher voltage systems. For example, engineers needing to meet the demands of new 700V systems, can arrange 64 ALD SABMB810028 boards together to ensure safe voltage balancing, advises the company.

The SAB MOSFET boards allow supercapacitor cell charging and discharging currents to pass through the cells themselves directly, bypassing the SAB MOSFETs mounted on the board with near-zero additional leakage current. This gives them an advantage over other methods where additional power dissipation used by the circuitry far exceeds the supercapacitor energy burn caused by leakage currents.

The boards are designed for ease of use as a plug-and-play PCB for supercapacitors of 0.1 to 3000F and beyond. The average additional power dissipation due to DC leakage of the supercapacitor is zero, which makes this method of supercapacitor balancing energy efficient and well suited for low-loss energy harvesting and long-life battery operated applications. 

Products can be ordered directly from the manufacturer or ordered from online distributors DigiKey or Mouser.