Supercapacitors, also known as ultracapacitors, are raising the bar on energy density to better serve robotics, utility boxes, mission-critical data protection, and battery-backup applications. However, excessive voltage surpassing the rated voltage for a prolonged time can reduce supercapacitor's operating life and can even damage it permanently.
Then there is leakage current that can cause voltage imbalance and power dissipation; so leakage current from individual cells must be compensated. Power system designers use MOSFETs to control leakage current and balance voltage in each supercapacitor cell as a deterrence against the over-voltage damages.
Now a new PCB solution from Advanced Linear Devices (ALD) claims to have simplified the use of MOSFETs for automatically balancing each individual supercapacitor cell in the stack. The two-channel SABMB2 board carries out supercapacitor automatic balancing (SAB) for each individual supercapacitor cell—and each SABMB2 board can balance two supercapacitors in a series stack.
The mechanical drawing of the two-channel SABMB2 board for supercapacitor balancing. Image courtesy of ALD.
According to Robert Chao, president and founder of ALD, the SABMB2 boards can be used for both prototyping and manufacturing of designs built around the supercapacitors for industrial controls, remote monitoring, and battery backup applications. The plug-and-play PCB comes in a small package of 0.6 inch by 1 inch.
The SABMB2 PCB. Image courtesy of Digi-Key.
These auto balancing PCBs are available as blank boards, or they come populated with the company's ALD9100XX SAB MOSFETs. It's worth mentioning that the ALD9100XX SAB family of MOSFETs offers a selection of different threshold voltages for various supercapacitors.
Supercapacitors in Energy Harvesting
Supercapacitors are designed to provide high power charging and discharging, peak power shaving, and backup power. So they are a popular choice for many applications, especially the ones where the power need doesn't exceed 30 seconds. That includes automotive systems, data center flash servers, and industrial automation.
Now, with a gradual increase in power density, supercapacitors are eying new frontiers such as energy harvesting applications using a low-energy source. Supercapacitors buffer and store the harvested energy to maximize energy-gathering efforts.
However, the energy harvesting source provides only a few µA of current and the challenge is not to waste any of this current from capacitor leakage and power dissipation of resistors. After all, energy harvesting charging is quite low and usually takes a few days.
And here MOSFETs for supercapacitor come to the rescue by lowering the operating bias voltage of the leaker supercapacitor and balancing the circuit power burn. ALD claims that its SAB MOSFETs are highly suitable for charge balancing because of their high input threshold value.
The schematic diagram of the SABMB2 board for the active cell balancing of supercapacitors. Image courtesy of ALD.
The company adds that its SAB MOSFETs also work well during the trickle charging of supercapacitors because they are less likely to have high transient energy spurts caused by the excessive voltage. And that will ensure a longer lifespan and higher reliability for supercapacitors compared to the energy harvesting systems that rely exclusively on batteries for energy storage.
Do you have experience with the SABMB2 board or one of the other members of the SABMB family? Let us know your thoughts on these PCBs in the comments below.