Inductor basics - What is an inductor?
Welcome to my first video about
inductors.
So, what is an inductor?
Generally speaking an inductor is a device
that temporarily stores energy in the form of a magnetic field. Inductors are usually just coils of wire
and one of the basic properties of electromagnetism is that when you
have current flowing through a wire, you will create a small magnetic field around it. So if you coil up a lot of wire you'll get
a stronger magnetic field.
When current first starts to flow through
the coil, the magnetic field starts to expand... then stabilizes...and then you've got some energy stored
in the magnetic field. When current stops flowing, the magnetic
field starts to collapse and the magnetic energy gets turned back into
electrical energy.
So they're kind of like a temporary
storage area for energy.
Capacitors store energy in the form of a
static charge and resist sudden changes in voltage. well, Inductors are very similar... they
store energy in the form of a magnetic field and resist sudden changes in
current.And if you only learn one thing from
this video remember, "the current in an inductor cannot instantly change."
It always lags by certain amount of time.
Now let me give you an example.
Normally when you connect a voltage
source to a load resistor the current will be given by ohms law. In this case 10 volts divided by 20 ohms
gives you 0.5 amperes. And for this demo I'm going to be using a
50% duty cycle square wave.
So half the time you'll get 0.5 amperes
flowing and half the time
there will be no current flowing.
Okay so here's the 1kHz input square wave.
And here's the current waveform... also
perfectly square.
Now watch what happens when I add a 5 milli henry
inductor in series with
the circuit.
All of a sudden the square wave isn't so
square anymore. There's a little bit of lag in the
current.This is because it takes a certain
amount of time to
store and release the energy in an inductor.Now let's try that again with a higher
input frequency of 10kHz.Now it's even more obvious that the
inductor is impeding the sudden changes in current.
This happens more and more as I raise the
frequency of the input wave.
At 100kHz there is no square wave anymore.
It takes a longer time to
store and release the energy in the
inductor than the time it takes for the
input wave to switch from high to low. So in this situation the inductor is
starting to average out the current over time.
This is very useful. It forms the
basis of LC low-pass filters which
I will cover in another video. A quick example: If I add a 1000 microfarad capacitor after the inductor here I get a very
clean D.C. output from a square wave input. And this is what good power supplies
use to smooth out voltage.
To prove to you that all this
happens because of expanding and collapsing magnetic fields I'm going to feed a square wave into this unshielded inductor.And I'm going to use another inductor as
a magnetic probe.So I can view any magnetic field changes on the oscilloscope.On top I have the input wave and on
the bottom you can see the magnetic field that I'm picking up as I get
closer to the inductor.
Finally, inductors have almost no effect
on D.C. They're basically just pieces of wire with a resistance of a few Milli ohms.Alright that's the basics of how an
inductor works. Now I've got a few more videos with more information on them
and some practical examples.
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