Electronics notes/Inductors and transformers: Difference between revisions
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====Current sense transformers==== | |||
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"So a power transformer / voltage transformer outputs voltage, and a current transformer outputs current?" | |||
No, the basic principle is the same - a current sets up a magnetic field, a core couples it, a field can become flowing current again. | |||
The coil part will generate an output current in the secondary proportional to the current in the primary, | |||
but due to the resistor that is essentially part of it, that can be sensed as a voltage. | |||
Due to the thing it is optimized for, it also consumes minimal power in that resistor or anywhere | |||
Without that resistor or other burden, it may go pretty high voltage, which shouldn't kill you but might kill the CT itself. | |||
So '''don't ''assume'' that resistor is part of a CT you buy'''. | |||
Yet the thing as a whole has been optimized for a different case, | |||
''particularly'' if you are used to looking at power transformers (which, even if barely familiar with them, are ''usually'' what you are looking at). | |||
In a current sense transformer | |||
* the primary has low impedance, so that it has less effect on the thing you are measuring it | |||
* the secondary has low impedance | |||
it is often sampled almost as a short circuit -- transferring almost no power (which also means that secondary can be small). | |||
In fact that power is basically ''always'' used and wasted in the secondary, whether you are measuring it or not. | |||
* the primary can be non-continuous and still work. | |||
Say, current clamps and such are often a split ring made of ferrite or iron or such. | |||
Ring core is a little more accurate, but may not be practical or even ''legal'' to put around the wire you want. | |||
https://docs.openenergymonitor.org/electricity-monitoring/ct-sensors/interface-with-arduino.html | |||
There are currently e.g. the YHDC with a TRS plug, where Tip and sleeve; ring is not conneced. | |||
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====Audio transformers==== | ====Audio transformers==== | ||
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Audio transformers | Audio transformers should deal well with the audio range., but on top of that they may have some less-usual demands/properties. | ||
Unlike power distribution transformers, | |||
they don't care much about moving the most current, | |||
and in many uses power loss isn't important either. | |||
Unlike transformers in classical phone networks, | |||
they don't care about [[transmission line]] properties of what they're feeding into. | |||
They care more than most things about equally passing at least 20Hz..15kHz. | |||
: Phones did ''somewhat'', but classically accepted low-frequency frequency loss (Actually even cheap audio transformers tend to attenuate content below 50Hz or so) and never tried to carry higher frequencies. | |||
It turns out higher impedance means more equal response in more frequencies{{verify}}, | |||
and higher impedance comes from | |||
: a more permeable core material | |||
: more windings | |||
They tend to be ''at least'' 600 ohms (AC impedance) on both sides | |||
Specific designs are often one of: | |||
* ground loop isolation transformers | * ground loop isolation transformers | ||
:: avoid having a conductive ground (also a side effect of others), otherwise just 1:1 transformers | :: avoid having a conductive ground (also a side effect of others), otherwise just 1:1 transformers | ||
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* mic transformer | * mic transformer | ||
:: center-tapped | :: center-tapped | ||
:: unbalanced to balanced (doesn't reduce hum) | :: unbalanced to balanced (doesn't reduce hum by itself, though) | ||
* baluns | * baluns | ||
* DI box | * DI box | ||
:: adapting impedance from pro line to pro mic, so | :: adapting impedance from pro line to pro mic, so a ratio around 12:1 | ||
* amplifier stages | * amplifier stages | ||
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Latest revision as of 23:02, 21 April 2024
Inductors
Inductor intro
Core inductor (design)
Stick inductor (design)
Toroidal inductor (design)
On magnets
See also
http://electronics.stackexchange.com/questions/12930/capacitors-or-inductors
http://www.avrfreaks.net/forum/inductor-current-smoothing
Filters (application)
(compared to RC filters)
(Note: The L seems to refer to Lenz)
RL filter (application)
LC filter (application)
Choke (application)
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:
- http://computer.howstuffworks.com/question352.htm
- http://images.google.com/images?q=ferrite+beads
- http://www.analog.com/en/analog-dialogue/articles/ferrite-beads-demystified.html