Hello everyone, how are you?
on today's lesson we'll learn about diodes, what they do, how to measure them and their physical appearance
so, let's get started
Welcome once again, here we are on another lesson, another day, so we can learn a bit more about board repairing
we're making this basic mini course for everyone who just started on this job
On this lesson we'll talk about diodes. who's the diode? how we'll measure it? how to know if it is failing? and all of that, ok
So we can start talking about diode first we need to know it's symbol
the diode's symbol it's something like this
the letter that represents it is "D"
and the diode splits in two parts
the positive it's called Anode
and the negative it's called Cathode
if we go to the schematic
let's go to the schematic
we'll see we have a diode here
this would be it's symbol
we have the letter D
and we have two parts
one would be the Anode and the other one would be the Cathode
Usually
the cathode side of the diodes always have this stripe
so by now we know the symbol, it's letter and their parts
But what does the diode do? What is a diode for?
Diode theory says that it only allows current pass in one direction
so, if we take a look on it's symbol, the diode only allows the current pass
from Anode to Cathode
the diode only allows the current pass in one direction
now, if we want to reverse polarity
and pass current from Cathode to Anode
the diode has a barrier here, so there's no way the current passes from Cathode to Anode
I mean, from negative to positive there's no pass
it only passes from positive to negative
But why do I need a diode? What use I can give it?
Here I'll make a simple drawing
let's imagine I have a diode over here
and here's the entrance to some circuit
this is the circuit, this is the entrance and here's the exit
on the exit I have this resistance and this LED
for now I'll just write LED
over here we have GND, that means ground
So what does the diode do? As we said before, it only allows the current pass from one direction
over here I have + positive and - negative
so what this do is, the current flows freely from here to here
make work the LED
and the current keeps it's way
until it closes the circuit
That's a functional diode, here everything is fine, but
if for some reason there is a polarity reversal
and connect the positive on the negative, what the diode does?
if I do that, then the diode will...
if I connect the positive here, all the current that comes from here
will protect my diode
my diode will protect here
the circuit, so
we'll always see diodes
they're there for protect the circuit in case there are some reversal or power surge
the diode protects itself and it sacrifices itself so the circuit doesn't get damaged
so, that's why they're there, to protect the circuit
since it only allows the current pass in one direction, and in case there are some polarity reversal, the diode blocks it and everything is fine
Now that we know what the diode and all its parts do, let's take a look at it's physical appearance.
Let's go to the microscope and look here, there we have a diode
we're going to see it from Apple devices, ok?
so if we pay attention, the diode has this stripe, that would be out cathode, and this side would be the anode
But, the diode will let pass all that current, but nothing here is free, the diode will charge a fee
it will let it pass, but it will say "Hey I require this much so you have to pay me if you want me to let that current pass", so
if we go back to this drawing
if I had, for example, a battery over here
positive and negative, and this battery is 3 volts
and my LED over here needs 3 volts to turn on
and I have a diode here
depending in which kind of diode we have, because we could have rectifier diodes, LED diodes
Schottky diode and Zener diode, that's something we'll see in some future video
so, depending which one it is, it will charge toll
Now, let's imagine here we have a rectifier diode
it will charge 0.7 millivolts, okay?
So that means, here on the entrance, I have 3 volts
but on the exit I'll have 2.3 volts
therefore, 2.3 volts will feed my LED
and the LED will not turn on because it need 3 volts for that, so
the engineers already did this math
I'm just explaining to you, because if we have to check some circuit, we must know
which kind of diode we need to use, so we can know how much consumption it will have
and that way know which kind of power it needs, in this case if we know
the LED needs 3 volts to turn on
and we have this rectifier diode that consumes 0.7 volts, that means I need to put a power supply of 3.7 volts
so once it consumes that voltage, on the exit only leaves 3 volts
I hope you're understanding
But now, how do we measure a diode? What we shall do to measure a diode?
Let's go over here
and we'll do some practices
let's put the multimeter on diode, and put the tips
the positive, would be anode
the positive is anode and negative is cathode
if we see here, my diode here has a consumption of 215 millivolts
a consumption of 215 millivolts
on diode function
on iPhone devices we'll be using the Schottky diode
Why Schottky diode? It can be blocked at high frequencies
What does this means? the Schottky diode
if the current wants to go back, let's say it's because some coil is switching it, that's something we'll see later
what the diode does is protect itself
the diode protects itself, it doesn't allow the current to pass to the other side
but the Schottky diode has the ability to do it faster
it can block it at an insanely fast speed
The consumption of the Schottky diode is 215 millivolts
that's the fee it will charge
here's very important to know the consumption of every diode
because, in some cases I've measure them
and the diode has a consumption of 1.50, for example
if I know the normal consumption is 215
then that means the diode opened
meaning it is letting pass more current than we need, it could damage the circuit
So it's very important know how much it consumes so we can test the anode and cathode
Remember, when we're using diode scale, what we're doing is inject voltage
approximately of 3 volts with my positive tip
and because the diode allows the current to pass in one direction, if I draw this
I'm injecting voltage from my positive
3 volts
and here with the negative, I'm finding a voltage drop of 215 millivolts
Now, if I find 1.50 or more, that means my diode is open
How else are we going to measure it?
we'll reverse our tips
now I'll put the negative on Anode
and the positive will go to Cathode
What I'm going to do is check if my diode allows the current to pass in the opposite direction
Now let's go to the microscope
and I'll put the positive on cathode
here
and negative on anode
I'm sending with the positive to the other side, so I see
if I have OL or I don't have any voltage drop, that means the diode it's blocking
my diode is making it's job, and that's how we know it is not reversing
Ok, now we're going to the last example, here we have a circuit
we'll not see the values or the resistances or anything
here I have a circuit with a 7.9 volts battery
if I close the circuit what happens? My LED starts working
the electrons are flowing freely
Now, if I reverse the diode here
in this case, flip the diode
What happens here?
if I close the circuit, it doesn't flow
the circuit is closed but nothing is flowing
unlike what happens if we flip the diode
and close the circuit again, there's flowing again
but from cathode to anode doesn't works
it only works from anode to cathode
Now, the diodes behave differently on DC and AC current
On AC current
we will have a Diode Bridge, it is a group of diodes that will help us to not waste
the negative part of the AC current
Everything about the diode bridge, the AC current, the diode behavior on AC current we'll see them in a future video
That's everything on today's lesson, guys
Take care, keep practicing, start measuring diodes
so you can learn these measures
so once we get to diagnose, you'll know what we're talking about
Hugs to everyone and see you later, bye!