Open Collector Gates Video Lecture | Digital Electronics - Electrical Engineering (EE)

hello everyone in this video I'm going
to let you know why exactly we need a
resistor whenever we have an open
collector not yet okay let me first draw
an open collector circuit okay whatever
we have whatever with you we have a 1 at
the output because that's not gate okay
and remember we have one we have as you
at the out okay but how can you Lee is
this you will turn out to be a one world
will be enriched itself to be a one
inside the not gate and how is the one
going to be inverted to be as you at
inside the not gate well actually there
is there exists a transistor inside and
let's assume that it is bipolar Junction
transistor the CC okay and here this is
the ground okay so you know that the
whatever you have a not gate you need to
connect the chip the chips VCC and the
ground to both the 5 volts and to the
ground which is you holes however you do
not see these internal connections and
generally we just draw this not gate
using this structure but we do not know
you might not be aware that inside the
transistor there exists this scienter
not getting exist this transistor okay
and the output is really taken from you
okay so this is goodbye
okay directly to this album okay so
whenever we put here is you this
transistor is designed that when you put
a 0 volt at the input this becomes fine
bones for some reason of course it is
close to 5 it's not exact if I but it is
close to 5 volts and this why you read
here a logic 1 and when this one when
this transistor has a logic 1 which is
equal to 5 volts so if it here 5 volts
which is what we represent we say that
this is a logic one then you expect that
this will become would somehow be
connected to the ground this this would
be a short circuit and this would be the
zero will show up at the output okay
but perhaps you do not know why this
exactly is happening inside the
transistor but at least let's assume
that take it for granted immunity study
and advanced electronic class you might
know how this is exactly operating but
remember that the main reason why it is
operating is because we have a VCC
connected to the transistor or connected
to the nor gate and we have a ground
connected to the nor gate so whenever
you put five zero volts the logic the an
output of logic one comes out at the
output and this logic one corresponds to
roughly speaking five volts which comes
from the VCC which is internally
connected inside the non-kill and
whenever we have a logic one and then at
the output we have a logic 0 and this
logic 0 comes from the ground which is
the zero volt okay so when we have an
open collector not gate actually this is
how it looks like this is how it looks
like right and this is why we should not
keep him we should not have whatever we
have assumed you want to have a one how
would the one who come out if no VCC is
connected you do not really expect to
have an a logic a logic one here which
is the 5 volts how would how would it
come out to thee yes if you have a logic
one then you expect to have logic 0 at
the output why because the series is
going to come from the ground but when
it has a lot when we have any bit of
logic 0 how would the circuit output a
logic 1 how would it get version should
it get the 5 volts from it would not
okay and this is why whatever we have an
open collector not gate we have to
connect from external side from the
external side we have to connect
this to a resistor and then connected to
the VCC this resistor could be around 1k
ohm
okay because internally the resistor in
the open collector in the non open
collector not gate was around 1 kilo and
this is why whenever we have an open
collector not gate which means that it
does not have the resistor and the VCC
connected internally then we have to
connect it externally
okay and this is why whenever you have
an open collector and you do this kind
of external connection if you have an
input of 0 then the output would be
logic 1 and the logic 1 would be equal
to complain to the 5 volts which comes
from the VCC okay of course you might be
asking yeah ok so why do we need to do
an open collector although we design
open collector transistor an open
collector not gate although we have the
privilege of having an odd gate which is
not an open collector
why do we need to emit the resistor and
the BCC from the internal connection of
the not gate although we could keep them
inside
I mean why what's the benefit of this do
not really focus on what the value then
of course it has a lot of benefits and
perhaps when you take microprocessor
class you might know this this benefit
but at least you know that whenever you
have an open collector buffer you would
be do not ask yourself why are we
connecting this why do we have to
connect the resistor and the BCC at
least take it for granted right now that
this resistor and the BCC are required
ok and this is how it operates why are
they required because they are not
implemented internally inside the market
okay if you have any questions please
let me know