Overcoming Circuit Protection Challenges in Lithium Battery Cell Operated Electronics

Komatsulite™ Mini-Breakers Application Note

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LC Series

HC Series

KCA Series

NR-C Series

NR-A Series

During normal operation, the disc is curved downward such that a direct path is available

for current to flow through from one terminal to the other. If the arm is exposed to rising

temperatures or excessive current, the temperature of the bi-metal disc rises. Once the

temperature of the bi-metal disc is heated to the trip temperature, the disc reverses such that

its ends point upward and lift the arm to the open position. In this tripped position, the path

between terminals is physically removed and the current is shunted to the PTC. The heat in

the PTC keeps the bi-metal disc open and latched. Once the overtemperature or overcurrent

condition is removed, the bi-metal disc returns to its original shape and restores the path for

current between the terminals. This operation occurs instantaneously, and the mini-breaker is

stable with impedance as low as 1.5 mΩ and no more than 15 mΩ.

The Komatsulite™ mini-breaker also offers resettable activation enabling normal operation

to resume immediately once the overcurrent or overtemperature condition is removed. Its

design is resistant to false trips that can occur with typical thermal fuses. Furthermore, the

mini-breaker does not require a reset circuit or power cycling, nor does it have to be replaced

following tripping unlike standard fuses. Mini-breakers feature a very small footprint; they

are compact enough to be placed directly across battery terminals to provide temperature and

current protection instantaneously.

Komatsulite has specifically developed its mini-breaker portfolio through its several-decade

history to meet the overtemperature and overcurrent protection needs of battery-powered

applications. The LC series was the first mini-breaker available with a trip temperature range

of 72 - 85 ˚C. The low profile LC Series offers a reduced height option measuring 0.1 mm. The

new HC series introduced mini-breakers with higher current capacity of 7 A to 12 A at 60 ˚C.

The low profile design extended to the 2014 release of the NR-C low capacity series and NR-A

high capacity series. In 2015, another application characteristic was addressed with the release

of the corrosion-free KCA series.

Currently, mini-breakers are manufactured where the thermal cut off subassembly and nickel

tabs are attached by welding. Future mini-breakers will feature welding of the nickel tabs only,

which allows for automated inspection. The roadmap also includes a heat resistant surface

mount package that provides the ability to handle reflow soldering three times. Komatsulite

continues to increase the protection options for developers. The existing series of Komatsulite™

mini-breakers are shown in Table 1.

MINI-BREAKER TECHNOLOGY OVERVIEW (Continued)

HISTORY OF MINI-BREAKER INNOVATION