Fuses are an essential electronic component in most circuits, and act as a safety feature to keep the other components within the circuit safe. Billions are used today to safeguard against circuit failures.
If a circuit is overloaded, or there is a voltage surge, the fuse essentially self-destructs to protect the rest of the circuit. A traditional fuse contains a central fusible element that, when heated to excessive temperatures, melts and stops the flow of current through the circuit.
The speed that the thermal fuse melts depends on the how much heat is being caused by the current, and what temperature the fuse is designed to react to. The fuse can be designed with different melting elements that have varying melting points and resistance, so the currents they can cope with can differ.
The new kid on the block is the newer electronic fuse, or eFuse. This component is an updated, re-usable version of the more traditional thermal, one-use fuse.
This component comprises of a field-effect transistor (FET) and a sense resistor. The resistor measures the voltage across it, and when it exceeds a certain limit, the current is cut off by the FET. Usually, the eFuse is placed in series with a thermal fuse rather than replacing it, giving the circuit a second layer of more localised protection for components.
Often eFuses are used as a protection when components are plugged into a computer while the power is still on, also called hot-swapping. In automotive applications, programmable logic controllers (PLCs) and battery management eFuses are a great tool to protect the circuits.
As thermal fuses have been around for so long, it’s unsurprising that there are certain things the more recent eFuse can do slightly better.
The first and most straightforward advantage is the lifespan: once a thermal fuse is activated and the element inside it fuses, it will have to be replaced. The eFuse, however, can be reset and used multiple times without requiring replacement.
The eFuse is also able to respond to a circuit overload more quickly and works in circuits with a lower current and voltage. For some eFuses the current level it reacts at is set, but for some types it can be altered by an external resistor.
It’s possible to create a homemade eFuse too, just by putting together a few FETs, a resistor and an inductor, which filters the output and acts as your sense resistor.
Both fuses have their uses, and utilised together are even more effective as a circuit failsafe. However, each designer must consider their requirements and what will best suit their clients. There are scenarios where the thermal fuse just won’t do the job, and it’s better to be safe than sorry, right?
