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Mini-Breaker Miniature Thermal Cutoff (TCO) Devices

Thermal Cutoff (TCO) devices, such as Bourns® Mini-Breakers, are utilized as safety measures to help prevent heat and fires produced by excess current, most notably in lithium-ion batteries. These products are used to safeguard batteries in electronic devices such as notebooks, PCs, tablets, digital cameras, and smartphones.

The trip temperature of the mini-breaker is a critical parameter for battery packs, and it is designed with the ability to target certain trip temperature values. The component has UL and TÜV safety standard certifications and also uses environmental protection measures all around the globe. Bourns® Mini-Breakers are self-preserving devices that are intended to remain tripped (operated) at abnormal temperatures and then recover when power is turned off and the temperature returns to a safe level. When compared to polymer PTCs and temperature fuses used for the same applications, this enables protection at lower temperatures.

The Bourns® Mini-breaker is a combination of two common circuit protection technologies; a PTC and a bimetal switch, providing several advantages over either technology on its own. The skills developed by Bourns over 70 years in precision metal stamping, plastic injection molding and high-end assembly turn these ubiquitous technologies into a marketleading circuit protection solution. The lighter, smaller and higher capacity advantages provided by Model AC TCO devices help designers extend Li-ion cell usage beyond the traditional laptop, tablet and smart phone applications to power tools, electric vehicles, e-bikes and grid storage applications. The figure below provides a simple schematic of how the Mini-breaker is constructed. The two terminals (arm terminal and base terminal), are connected in a normally closed position to allow current to flow through the device. Naturally, the contact point between both terminals provides a critical function and a testament to the high precision of the Bourns® Mini-breaker is that the contact resistance is as low as 2 mΩ (max.) in some model families.

Thermal Cutoff (TCO) devices - also known as mini-breakers - offer an effective overtemperature protection solution for USB Type-C cables. These TCO devices incorporate existing technology in such a way to enhance their protection capabilities. TCO devices are constructed using both a bimetal disc and ceramic PTC in parallel. The overheating of the USB connector causes the bimetal to open at a very accurate temperature. Once open, the current passes through the PTC which generates sufficient heat to keep the bimetal open and prevents nuisance resetting.
Understanding the need for both temperature sensing capability and the low resistance of the bimetal switch, Bourns designed these additional benefits into a hybrid TCO device that is available in several temperature ranges and has 100 percent in-line inspection of the trip temperature.

Features

Miniature Thermal Cutoff (TCO) device
Surface mount, smallest body size
Overtemperature and overcurrent protection
Controls abnormal, excessive current virtually instantaneously, up to rated limits
Wide range of temperature options
High corrosion resistance

Application

Battery cell protection for:

Notebook PCs
Tablet PCs
Smart phones

Overtemperature protection for:

USB Type C cables (e.g. smart phone cables, notebook AC adapters)
Electronic cigarettes
Medical heaters

Key components

Bourns® SC Series Miniature Resettable Thermal Cutoff (TCO)Device
Bourns® AC Series Miniature ResettableThermal Cutoff (TCO) Device

Benefits

Bourns’ broad line of Mini-breaker TCO products have been usedin more than six billion circuits, providing precise, reliable, long-life overtemperature protection.