In electronics, what is the difference between a varistor and a resettable fuse?
In: Technology
Varistor: changes resistance based on voltage. Can help control but not limit current. Is also solid state.
Fuse: specifically used as overcurrent protection. Not solid state. Does not have effect on current when not blown.
A varistor will be used to keep a relatively steady current flow. The current will usually still increase with voltage but not linearly. It prevents overcurrent without interrupting operation. A fuse is either on or off and completely stops operation of what it’s controlling when it detects overcurrent.
They can be used together with the varistor maintaining current and the fuse as the last line of defense. A resettable fuse is just a fuse that can be reset instead of needing to be replaced.
A varistor *shorts* when it sees over*voltage*. A fuse *opens* when it sees over*current*. A varistor is almost always accompanied by a fuse before it, and is used to forcibly trip the fuse in an overvoltage scenario by causing a short circuit across the power rail and ground. A resettable is a fuse that doesn’t melt, but instead quickly increases in resistance when it sees overcurrent, and will stay high resistance until it is unpowered and allowed to cool down for a few seconds. It lets through a small current even in tripped state, which keeps it heated up and in the high resistance state.
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