if we go back to our circuit over here
you know we have this current coming in
here and if I look at the current let me
let me just switch over to my to my
ammeter really quickly here and I see
the current is either zero when it's off
but then when it's on it's 0.3 milliamps
so 0.3 milliamps and so you can imagine
I could I could use if I could send
point three zero point three milliamps
from my base to my to my emitter then
this little guy inside the transistor
he's going to say 0.3 milliamps I want
to multiply that by a hundred and I want
to make sure that you know the collector
to emitter current is going to be a
hundred times that so he's going to try
and make that 30 mil 30 milliamps 100
times point three and 30 milliamps is
enough to turn on an LED and so by using
a transistor we can take that point 3
milli amp current and essentially
amplify it to this 30 milliamps now in
reality an LED is not going to draw 30
milliamps particularly if we have a
resistor in line and everything you know
the LED wants to draw 20 milliamps but
this guy's going to try and get it as
close as he can so he's going to turn
this resistance down he's going to he's
going to basically kind of move he's
going to move this this little this
little variable resistor up to reduce
the resistance to try to get as close to
30 milliamps as possible but if the LED
only wants to draw 20 milliamps then
he's going to have this turned up all
the way and so he's actually not going
to be able to get it to 30 milliamps
he's only going to get it to 2 maybe 20
to 20 milliamps and when that happens
there's there's kind of a word for this
that you might see it's called the
transit the transistor is is saturated
or or sometimes we'll say it's in
saturation and so in saturation is when
basically there's a short between the
collector and the emitter so as much
current as possible will flow through
there because the current that is
flowing through in this case maybe it's
only 20 is is less than what this guy is
trying to make he's trying to get 100
times 0.3 so he's trying to get third
to flow but just because of what's hoped
up to this if it's just an LED and a
resistor it's only going to draw 20
milliamps so he's going to he's going to
turn this resistor down as much as
possible and basically make this a short
and we call that saturation now on the
other hand if this current if the base
current shuts off which it's doing
remember remember in our circuit if we
look back at our circuit
it's either 0.3 or it's where it's
basically 0 because this signal is
turning on and off on and off so when
it's 0.3 like this then it's on when
it's 0 it's off so if this base current
coming back here if the base current is
zero then this guy is going to want to
make the the collector current over here
zero as well and so he's going to end up
turning this down he's going to end up
moving this down and trying to create as
much resistance as possible and when
that happens the transistor we have we
have a word for that as well that you
might see it and that's called the
transistor being in cutoff not caught
off cutoff so the transistor is in
cutoff so down here the trend he's the
transistor is basically not passing any
current from the collector to the
emitter so cut off basically means that
the collector the current of the
collector is equal to 0 and in
saturation it means that the current
from the collector is as much as as much
as it can be it's basically maximum it's
passing it's passing as much current as
the circuit wants in that case and so in
this sense this is why you see
transistors some time or you hear
transistors sometimes referred to as
switches because with with a current
situation like this and actually this is
going to be the case in our circuit the
transistor will either be saturated or
cut off and when it's saturated it's
just passing current through and when
it's cut off it's not passing current
through at all and so this is why you
sometimes hear transistors referred to
not only as current amplifiers but also
as switches so in the next video we'll
we'll take everything we've we've sort
of looked at here and see if we can
build
the circuit