| This is for beginners and very much by a beginner. It's meant to try to cover hobbyist needs, and as a starting point to find out which may be the relevant details for you, not for definitive information.
Some basics and reference:
Volts, amps, energy, power · Ground · batteries · resistors · changing voltage · transistors · fuses · diodes · varistors · capacitors · inductors · transformers · baluns · amplifier notes · frequency generation · skin effect
And some more applied stuff:
IO: wired local IO wired local-ish IO · · · · Shorter-range wireless (IR, ISM RF, RFID) · bluetooth · 802.15 (including zigbee) · 802.11 (WiFi) · cell phone
Sensors: General sensor notes, voltage and current sensing ·
Knobs and dials ·
Pressure sensing ·
Temperature sensing ·
humidity sensing ·
Light sensing ·
Movement sensing ·
Capacitive sensing ·
Touch screen notes
Actuators: General actuator notes, circuit protection ·
Motors and servos ·
Some stuff I've messed with: Avrusb500v2 ·
Hilo GPRS ·
basic audio hacks ·
amps and speakers ·
device voltage and impedance, audio and otherwise ·
Less sorted: Common terms, useful basics, soldering ·
Microcontroller and computer platforms ·
Arduino and AVR notes ·
ESP series notes ·
Electronics notes/Phase Locked Loop notes ·
mounts, chip carriers, packages, connectors ·
signal reflection ·
pulse modulation ·
electricity and humans ·
See also Category:Electronics.
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits.
A varistor is a short name for a Voltage Dependent Resistor (VDR)
Often specifically a metal-oxide varistor (MOV), to the point MOV and varistor are near-synonyms to most people.
A MOV responds to voltage: high resistance at low voltages, lowering resistance at high voltages.
But not linearly - find an I-V curve for one,
and you'll note they present a steepish curve over a specific threshold
, the MOV's rated voltage is basically that curve's knee where it starts conducting noticeable current.
This characteristic makes them useful in parallel with a sensitive load, to protect that load against high transient voltages / small surges, effectively shunting them away and wasting them as a heat.
Which is also why they cannot deal with sustained over-voltages; they would basically become the load, heat up, and probably burn. MOVs used as protection are often combined with other protective elements .