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the following program is brought to you
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by element 14 the electronic design
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[Music]
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hi and welcome back to the learning
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circuit where we learn about basic
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Electronics today we're going to talk
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about dodes diodes are semiconductor
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components that allow electric current
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to flow in One Direction but not the
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other in a previous episode we discussed
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how p Junctions work let's review Pon
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Junction diodes and talk about how they
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differ from other common
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[Music]
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diodes these are considered your typical
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diodes they have a p injunction with a
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threshold voltage that has to be reached
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before current will flow through them in
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Silicon diodes this is 0.7 volts once
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this is reached the current will flow
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flow flow when hooked out backwards in
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Reverse bias these diodes do not allow
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current to flow they're like Gandalf you
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shall not
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pass however like Gandalf against the
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Bell rug they can be defeated when
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connected in Reverse bias if supplied
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with too much voltage more than their
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breakdown voltage the dials will break
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down and allow current to flow in the
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wrong direction and while Gandalf came
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out looking pretty cool we're not so
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lucky with diode the white which got
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that way because it overheated sad
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broken diode well we'll talk more about
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breakdown voltages again a little bit
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later shocky diodes often look like
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typical diodes but unlike PN Junction
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diodes shocky diodes have a metal
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semiconductor Junction in a previous
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episode we talked about how PN junctions
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have a depletion Zone it shrinks when
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connected in forward bias and grows when
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connected in Reverse bias in some
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circuits the direction of current is
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intentionally switched between forward
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and backward rapidly
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silicon diodes require time for their
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depletion Zone to grow and shrink when
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switching from allowing forward current
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to blocking reverse current there's a
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recovery time shot key junctions have no
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depletion Zone because of their metal
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semiconductor Junction shot key diodes
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have virtually no recovery time and
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therefore have much faster switching
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speeds this means they can handle
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switching current better and faster
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which makes them useful in highfrequency
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applications they also have a lower
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forward voltage drop diodes have a
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voltage drop of around 0.7 volts but the
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voltage drop of shocky diodes is between
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0.15 volts and 0.46 volts this means
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they lose less energy to heat making
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them more efficient shaki diodes are not
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useful in all applications though while
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silicon diodes allow little to no
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current to flow backwards through them
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shock key diodes can leak a small amount
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of current backwards this can cause
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problems in certain circuits
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[Music]
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let's talk about xener diodes xener
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diodes unfortunately also look like
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typical and shoty diodes they're really
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not making it easy for us while shocky
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diodes can let some voltage leak through
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backwards xener diodes are actually
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designed to allow current to flow in
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both directions kind of seems like
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they're missing the point of being a
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diode but let's see how current flows
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through them to see why that could be
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useful in forward bias xener diodes
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function just like any other diode we
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talked about how typical diodes have a
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breakdown voltage in Reverse bias if the
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breakdown voltage is exceeded the diode
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is damaged but xenor have a special
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heavily doped PN Junction that allows
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only a certain voltage through and
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without damaging the diode this happens
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at a specific voltage the xener voltage
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in Reverse bias current will not flow
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through until the xener voltage is
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reached but also the voltage will be
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limited to the xener voltage for example
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a 3.3 volt xener diode will not allow
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current to flow until the supply voltage
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reaches 3.3 volts so if it's supplied
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with 2 volts no current flows however
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this diode could be supplied with 5 6 9
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12 volts and it will regulate the
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voltage output to 3.3 volts so it's kind
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of like having two diodes in one package
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but one faces one way and the other
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faces the other way xener can have xener
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breakdown voltages of anywhere from 1.8
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volts all the way up to 200 volts
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the next and probably most recognizable
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diodes are LEDs light emitting diodes
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LEDs use the energy from the particles
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moving through the PN Junction to create
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light they can do this because they are
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made with gallium arsenide unlike
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silicon diodes diodes made with gallium
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arsenide release energy in the form of
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light or photons like other diodes they
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typically have two leads though these
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can vary in length depending on the
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manufacturer I've got stuck with shortle
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LEDs which can make some projects tricky
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so beware LEDs come in a wide variety of
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packages through hole LEDs can be 3 mm 5
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mm 10 mm they can have round and square
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lenses lenses can be clear or colored if
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you're looking for the most common
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through hole LEDs it would probably be
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these 5mm round ones they're pretty
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popular with hobbyists surface mount
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LEDs come in a variety of sizes as well
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here are some examples when choosing an
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LED one of the first things you'll look
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for is color or wavelength here's a
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chart of the color spectrum at the
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bottom you can see the wavelength that
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correspond with each color 400 nanm to
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700 NM looking for just a blue LED might
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not be enough you can often find a range
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of each color to choose from Blue could
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be 445 nanm or 480 nanm or anything in
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that area of the spectrum another Choice
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you'll have is beam angle or viewing
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angle
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beam angle is the amount of degrees
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where the light is visible depending on
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your application you may want a narrow
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beam angle like 10° or a wide beam angle
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like
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120° where common light bulbs are
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measured in watts or lumens the
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brightness of LEDs can be found as
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luminous intensity and is measured in
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mandelas or MCD the higher the number
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the brighter the light a standard LED
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could have a luminous intensity of 7
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mandelas whereas a super bright LED
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could be 120 mandelas LEDs can have a
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range of voltage and current ratings
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they have both a minimum voltage and
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current required to function properly or
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even at all as well as a maximum voltage
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in current that if surpassed could
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shorten the life of the LED or burn it
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out completely it's important to get
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this information off of the component
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data sheet so you know how much
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resistance you'll need to add depending
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on what voltage you are using in your
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circuit while LEDs emit incoherent light
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laser diodes emit high-intensity
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coherent light they do this by having a
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pin or pin Junction rather than the
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standard PN Junction the pin Junction
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has the standard ptype and N type
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regions we're familiar with but between
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them there is an area of undoped or
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intrinsic semiconductor at The Junction
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in that intrinsic layer is where all the
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magic happens when current flows through
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the diode energy is released in the form
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of photons or light into that intrinsic
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layer but it doesn't stop there in a
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laser diode the p and N type regions
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have polished reflective ends which
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causes the photons to reflect back and
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forth hundreds of times in that
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intrinsic layer the photons eventually
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Escape in the form of a laser beam you
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can frequently see where a laser hits a
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surface but you can't always see the
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laser beam itself if you can see the
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laser beam be extra careful that's a
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high-powered laser and it has the
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potential for causing permanent eye
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damage
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[Music]
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while LEDs and lasers emit light photo
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diodes sense light light has these
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energy particles called photons when
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light hits the PN Junction of a photo
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diode energy from the photons is
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transferred to the diode and creates
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free electron and whole pairs remember
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what happens when a diode is in Reverse
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bias mode the changes in the junction
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repel the holes towards the anode and
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the electrons towards the cathode
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this usually restricts the flow of
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current in this case energy is being
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introduced by way of the photons so a
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current is created in Reverse bias mode
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this is called the photoelectric effect
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and the photo diode is considered to be
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in photoconductive mode photo diodes can
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also be used in zero bias or photo
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voltaic mode this is where the current
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is restricted and so the electron hole
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Pairs and therefore the voltage builds
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up that kind of sounds like a solar cell
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doesn't it well they are very similar
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except photo diodes are designed to be
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sensors or receivers and convert light
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into signal whereas solar cells are
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designed to convert light into Power one
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last thing to note is that a photo
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diode's response time gets slower the
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larger the photo diode
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gets there are a ton of uses for diodes
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diodes can be used as rectifiers meaning
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they can convert AC voltages into DC
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voltages so rather than running off of
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batteries you can plug right into the
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wall they can be used to regulate
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current for voltage protection
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controlling signals if you remember the
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HEC mangi game we made on the Ben heck
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show diodes can be used to create logic
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gates LEDs are becoming more popular and
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cost- effective quickly replacing most
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old forms of light bulbs and lighting
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applications lasers aren't just for
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pointing at the wall and teasing your
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cat they're used to read and record CDs
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DVDs and Blu-ray discs they're what make
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barcode readers work they're used in
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printing and scanning fiber optic
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Communications rangefinders technology
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has come so far that lasers can be used
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in surgery and be more accurate than a
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surgical knife I've covered the more
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common types of dodes but there are
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still other types and endless uses I
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haven't covered if you have more
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information you'd like to share on this
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topic or if you have a question about
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diodes please post those on the element4
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community on element14.com thee learning
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circuit get happy learning
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