Electronics notes/Inductors and transformers

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This is for beginners and very much by a beginner / hobbyist.

It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.

Some basics and reference: Volts, amps, energy, power · batteries · resistors · transistors · fuses · diodes · capacitors · inductors and transformers · ground

Slightly less basic: amplifier notes · varistors · changing voltage · baluns · frequency generation · Transmission lines · skin effect

And some more applied stuff:

IO: Input and output pins · wired local IO · wired local-ish IO · ·  Various wireless · 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 · Solenoids

Noise stuff: Stray signals and noise · sound-related noise names · electronic non-coupled noise names · electronic coupled noise · ground loop · strategies to avoid coupled noise · Sampling, reproduction, and transmission distortions

Audio notes: See avnotes

Platform specific

Arduino and AVR notes · (Ethernet)
Microcontroller and computer platforms ··· ESP series notes · STM32 series notes

Less sorted: Ground · device voltage and impedance (+ audio-specific) · electricity and humans · power supply considerations · Common terms, useful basics, soldering · landline phones · pulse modulation · signal reflection · Project boxes · resource metering · SDR · PLL · vacuum tubes · Unsorted stuff

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer ·

See also Category:Electronics.


Inductor intro

Core inductor (design)

Stick inductor (design)

Toroidal inductor (design)

On magnets

See also



Filters (application)

(compared to RC filters)

(Note: The L seems to refer to Lenz)

RL filter (application)

LC filter (application)

Choke (application)

This article/section is a stub — probably a pile of half-sorted notes and is probably a first version, is not well-checked, somay have incorrect bits. (Feel free to ignore, or tell me)

Ferrite beads

Ferrite beads, also known as ferrite chokers, are designed to eat a certain range of frequencies, and turn it into (a negligible amount of) heat.

They work as inductors, and act as a passive low-pass filter.

One thing they address are that oscillators such as clock generators (and modern power supplies, since they're typically switch-mode) act as little radio-frequency transmitters, particularly when there is something around to act like an antenna, such as wires.

So high frequencies easily get around. While most things are fine with a little high frequency EM around, not always. So there's regulations about this.

You pass these tests by suppressing things. Ferrite beads can do this.

Note that often it's easier to suppress earlier (near the source) rather than later (on an external wire), meaning that ferrite beads are sometimes a sign of laziness.

And in some cases they're not particularly necessary for your case, but e.g. qualifying for worldwide RF emission tests made it easier to slap one onto the cable and be done with a single variant that passes worldwide.

Note that since they're inductors, mis-applied ferrite beads could cause resonance. So don't just slap on one you found somewhere because you think it will Magically Make Things Better.

See also:


Named purposes / designs

This article/section is a stub — probably a pile of half-sorted notes and is probably a first version, is not well-checked, somay have incorrect bits. (Feel free to ignore, or tell me)

Bootstrap, feedback, and other windings

Audio transformers

On cores, on windings, on taps

Going from transformer to DC - design considerations

Rectifying AC

Could I reverse primary and secondary?

Can I series-connect for higher voltages?

Can I add more transformers in parallel later for more current?