| 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: IO and wired communication · localish communication ·
wireless (ISM RF, GSM, RFID, more) · 802.11 (WiFi) · 802.15 (including zigbee)
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 ·
Bluetooth serial ·
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)
Componentwise often specifically a metal-oxide varistor (MOV), and MOV and varistor are near-synonyms to most people.
A MOV responds to voltage (not temperature, like a NTC thermistor):
- high resistance at 'normal' voltages according to its spec,
- with lowering resistance at high voltages
Find a I-V curve for one, and you'll note they present a steepish curve over a specific threshold
(much like a diode's, because its workings are like a diode's, though bidirectional so can be used in AC),
the MOV's rated voltage is basically that curve's knee where it starts conducting noticeably current.
This characteristic makes them useful in parallel with a sensitive load, to protect that load against transient voltages and small surges, effectively shunting said transients away, and wasting them as a heat (which is also why they cannot deal with sustained over-voltages; they would basically become the load, and fry).