An Introduction to Linear AC-DC Power Supplies

hey guys and girls my name is Tim this is the solid state workshop and today's video is called an introduction to linear AC to DC power supplies so if you have no idea what those are or you want to learn more about what those are this might be a good video for you so sit tight and let's figure this one out so I guess the first thing we should figure out is what exactly an AC to DC power supply is and in general an AC to DC power supply is some kind of device electronic device that converts AC electricity from say your wall outlet into DC electricity that a sensitive piece of electronic equipment or device can use so we're going to define what AC and DC are later but that as the definition is what an AC to DC power supply is so you may ask well where would I find one of these AC to DC power supplies and the answer is a lot of places for example your laptop power adapter that's an example of an AC to DC power supply your phone charger is also an AC to DC power supply and if you have a desktop computer and if you were to open it up and look in the corner in the back corner you'd see this very unsuspecting metal box well that's your AC to DC power supply so as you can see there in a lot of places and there because they're just incredibly vital without them we'd not have power for any of the devices that we use to help illustrate some of the concepts involved in power supply design I'm going to be using some graphics that mimic what you would see if we were to use a piece of test equipment called an oscilloscope and an oscilloscope is an instrument which allows you to view changes in voltage over time and that's what one looks like in actuality we're not going to be using a real oscilloscope today but we'll be using some graphics that look like the screen on an oscilloscope so this box to the right here represents the screen on an oscilloscope now on the x-axis we have time and on the y-axis we have voltage and voltage can be either positive or negative depending on whether or not it's above or below this zero volt line right here and we also have this grid this grid of lines that covers the oscilloscope and this grid is called graticule and each line represents an increment in both the units so both voltage and time it's one increment so for instance between here and here might be one millisecond and between here and here might be one volt so with all this put together we can figure out and we can observe how voltage changes with respect to time which is extraordinarily useful in electronics design and troubleshooting so if that didn't make sense to you right now I would really recommend you pause and try to figure it out because it's going to be really helpful because you're going to visually be able to see what's going on in these circuits especially the power supply circuits that we're going to get into in this video so in all electrical and electronic systems there's two different types of current and the first word we'll look at is direct current or DC and in DC the direction of current is always the same because the voltage is always greater than zero for the overt over time so if we look at the oscilloscope there is what we would see a voltage here that we look at at the point is over this entire stretch greater than the zero line here so just of course to reiterate the point at Delta T equal to zero seconds the voltage we measured 1.5 volts at Delta T equals 3 seconds 1.5 volts and that delta T equals 7 seconds 1.5 volts so exactly what I just said but I had these little animations for you the voltage is consistently greater than zero now direct current can also work in the other direction as long as it's it can also work as consistently a negative voltage so if it was below the zero volt line for the entire time so if it was down here somewhere for the entire time that is still direct current is just flowing in the opposite direction alternating current is a little bit different well it's actually quite a bit different in altering current the direction of current is constantly changing because the voltage is constantly passing through zero volts so it's changing from a positive voltage to a negative voltage and then from a negative voltage to a positive voltage and this causes the current kind of oscillate back and forth so if we look at the oscilloscope that is an AC waveform as you can see part of the AC waveform is above the above that 0 volt line but then another part is below that zero volt line so from here to here our current goes in one direction and then when it gets to this point right here it stops very very briefly and then reverses direction and goes another and goes in the reverse and then it does it over again and does it over until the cows come home so that that's alternating current an all Drinker is good for some things but for a lot of our electronics and for our more sensitive equipment it's really no good for powering it so as I had in the other in the other slide here we are at this point here we're at 2 volts and then we're going to we're going to hit 0 volts and then over time we're going to hit a negative voltage so just to really drive that home so now we're going to try to get into some of the design aspects and the the steps you need to take in order to convert our AC from a wall outlet to that nice straight line DC that we saw two slides ago so the voltage that is available and is provided at a wall outlet is really much too high and it's always changing polarity we're always changing and the current is always changing direction because it's AC and because of that it makes it useless for sensitive electronics so the first thing that we need to do is to reduce that voltage and we're going to do that using a transformer and here's our chance oh how did that get in there oh I'm such a jokester now now alright um but a transformer is a device that allows us to convert an AC voltage note AC voltage to a higher or lower level so as I kind of emphasized before transformer can only be used with alternating current so if you were to provide a direct current to a transformer um it wouldn't work at all as you'd want it to so they operate on the basis of a theory or I guess it's I don't know if it's even a theory anymore it's basically proven but electromagnetic theory called mutual inductance which basically means when you have two coils wrapped around a a common iron or ferrous core the energy is transferred from one coil to another coil that's basically what what that means and you'll see what that means on the next slide so around five or six seconds ago is talking about transformers and how their devices that have a common iron core and two coils wrapped around them so let's see what that would look like right here we have a iron core and what we would do is we will wrap around so while you're on one side and then we could wrap around some wire on the other side and although they're not physically touching and they're electrically isolated meaning that there's no electrical contact between these two sides here the the theory of mutual inductance says that the that the energy will be transferred over to that other coil if you have a voltage applied on this side here and and that's what would happen so let's say that on this blue side here which we're going to call the primary side also known as the input side we have twice as many turns or twice many loops around this core as we have on this green side which is also known as the secondary side or our output side so we have twice as many loops on this side around the core as we have on this side and now if we were to apply a hundred and uh well here here's the ratio two to one and if we were to apply a hundred and twenty volts to our primary input side then what would you guess would be the output voltage if we have a ratio of two to one and you guessed it sixty volts and so on that on that secondary side we'd have half the voltage because we have half as many loops of wire on that secondary side so that's really awesome and it's um extraordinarily useful just like every component in a power supply but it's it really really important that we can be able to do this if we were to use the transformer we just described in the previous slide we'd get something that looks a little bit like this what you see here is on the blue trace you see the 120 volts input and on the yellow trace you see the 60 volts output and this type of transformer is known as a step-down transformer and step-down I guess is an obvious name for because it reduces the voltage another thing we should we should note here is that the frequency is not changed by the transformer that's why all these peaks and all these troughs and every time it passes through zero they all line up with each other each other both on the input and the output the amplitude or the voltage is less but the frequency remains the same so depending on where you live that's between 50 and 60 Hertz so that is probably against the two things that you should know about transformer transformers come in all shapes and sizes the first one were going to look at is the e Corr transformer if you could take a guess as to why it's called an E chord transformer you guessed it yeah it's because its core is shaped like an e Wow mind-blowing but anyway you can't see the middle part of the e here because it is wrapped in wire but if you were to take it apart you you definitely see it and the e core transformer is relatively inexpensive and it has pretty good performance so it's pretty widely used because of that the next type of transformer is the toroidal transformer here in the middle a toroidal transformer looks a little bit like a Dona do I wouldn't bite into it because well you're dead well your dentist would be happy about it after you pay the bill but I wouldn't I wouldn't bite into it but anyway the toroidal transformer has a couple advantages over a standard Ecore transformer a toroidal transformer works in the same way an eclair transformer it does but it does a debatably a little better and the reason is because it produces less stray magnetic fields which is good for more sensitive equipment like audio or maybe medical equipment and in addition it's a little more efficient it can be a little smaller produce it's a little better regulated than the Eco transformer but this is all at the literal expense of price and toroidal transformers require a little more complex machinery took manufacture and that's why they tend to be more expensive but if you need them they are available the final type of transformer which is actually quite similar to an E chord transformer in construction but its use is a little different and that is the high frequency transformer and the high frequency transformer isn't typically used in a linear power supply which is what we're talking about today usually these are used in switch mode power supplies which we'll briefly briefly really talk about at the end of this video but high frequency transformers are generally a little smaller and they can operate at higher frequencies hence the name though we have successfully reduced the voltage we still have the problem of the voltage fluctuating from a positive value to a negative value and then back to a positive value and so forth unless of course causes the current to kind of oscillating and go back and forth inside the conductor's so to force the current to only flow in one direction and to stop reversing we just want to go in one direction we're going to construct a circuit called a bridge rectifier and it uses four semiconductor devices called diodes here's the circuit for a bridge rectifier and a bridge rectifier uses four diodes and a diode remember only allows current to flow in one direction and if you look at the circuit symbol up here it only allows current to go from anode to cathode or in the direction of the arrow that's the only way that current is allowed to flow through a diode and in this circuit over here we have it arranged in a way that it'll force the current to only flow in one direction so let's try to figure out how this works so say we have a current that flows in through here in this direction and it's going to go out in this direction so this is when the voltage is positive the voltage of the AC is above that zero volt line on our oscilloscope in this case what's going to happen is the current is going to go through this diode here it can't go through this diode right here because it's reverse biased so it's going to go through it's going to go through this diode into our load our resistor we're going to call the load back out from the load and it's going to meet up right here and it can't go through this diode because this diode is going to be reverse biased again and instead it's going to go through this diode and then back back out to the source all right so so remember the the current was flowing through the load in this direction clockwise I guess you would say now if we if we have a negative voltage our current flows in the opposite direction so let's see what would happen our current comes in here and it's flowing in this direction and it comes up to here and it can't go here because that's reverse biased so it goes through this diode here and then it can't go here so it goes through the load and it comes back comes back comes back comes back and once again now it's going to go through this diode here and out so what did we just observe what we observe that even though the alternating current was going in the opposite direction it went through the load in the same direction as it did when the voltage was positive so that's really that's really awesome so let's see what that out that'll look like on the oscilloscope so here's what it would look like on an oscilloscope and there we are the yellow trace is our output from our bridge rectifier and our blue trace is the input to the bridge rectifier coming from the transformer so a bridge rectifier in a mathematical sense I guess takes the absolute value of that AC waveform that you provide it with so wherever it went negative the the AC you've now produced a a mirrored positive voltage and now instead of the current constantly reversing and going back and forth and back and forth the current now goes in one direction only so now we're in one step one step in the right direction and if you look on the oscilloscope here you'll notice something a little bit funny and that's that the the output of the bridge rectifier has an amplitude slightly less than that of the input to the red rectifier which doesn't seem to make too much sense but if you think about how a diode works a diode you need about 0.7 volts in order to turn on a diode so you need to provide that dial with some push to get it to work and with that push you lose some of your voltage so if you lose point seven volts across a diode that's what you're seeing there and you're probably going to see two diode losses two diode drops across two diode drops is what you're viewing there because you have a bridge rectifier so usually it's not too big of a deal if you lose a volt or two on a bridge rectifier but if you're working with some really low AC voltages it might it might actually make a difference so always keep that in mind that you are going to lose a little bit of voltage when you use any type of rectifier here are some examples of bridge rectifiers now bridge rectifiers can be made of four discreet diodes as we saw in the in the slide two slides ago and we can arrange them and this is fairly cost effective because these diodes individually are pennies or less probably even less so they can be very it can be very cheap to construct a bridge rectifier using these individual diodes the problem they have the problem that you have with using individual diodes is that usually they can't handle too much current you might be able to pass about one ampere through these discrete diodes so if that's enough for you then then then then that should work but for higher current applications you generally have to go with these integrated packaged diode bridges or bridge rectifiers and this is I guess what you'd call a gbu type bridge these that's what I know it as most of the names of these parts are gbu and then some number and these can usually sink I don't know between three and five amps or something that can pass three and five amps or maybe even more seven amps depending on how big of a package you get so if you have a little higher current need then you'd get something that looks like these like this and this these are pretty common actually you'll see these in a lot of different power supplies and if you even have even higher current passing ability you would get one of these high powered bridges here which are chassis chassis mount and they get bolted right down to the metal on a chassis or or to a heatsink of some sort and you attach quick connect terminals to them because well they pass so much current that they need these low low resistance connections so these are especially useful if you need to pass you know upwards of maybe 20 amps or 30 amps or something like that a very high-powered application but I guess for the most part most people are going to be encountering either discrete diodes or a smaller diode bridge like this and there's many other types as well come in different types of packages but these are I guess some of the most common so woohoo we have direct current or well at least by definition its direct current our current all flows in the same direction now but we have these mountains on our oscilloscope and that's not too great this this fluctuation in voltage can have ill effects on whatever circuit we're trying to power and the reason is because a lot of semiconductor devices like the diode we just talked about but other things too like a processor might have minimum turn-on voltages or or a voltage that they need to work properly so for like a diode you need point seven volts across it and for maybe like a processor you might need five volts or something and we have all this fluctuation in voltage and a lot of times the voltage falls beneath these these different requirements so we might fall beneath five volts for a certain amount of time and that's not good because for the time that it's below five volts that processor is going to be off so it won't work and then you know your circuit is pointless so because it dips is constantly dipping to very low voltages we have a lot of problems so to fix this problem we're going to use something called a filter capacitor or filter capacitors and we're going to see how that works on the next slide here's the circuit now including the filter capacitor on the output of the bridge rectifier and the filter capacitor is really going to help to remove that Ripple it's going to smooth out that ripple that we saw on the oscilloscope in the previous slides and how is it going to do that well if you remember how a capacitor works if you pass a current through a capacitor you charge it up kind of like a battery but a little bit differently you can charge it much more quickly so if you if you pass a current through a capacitor you charge it up and you store charge in its electric field because there's two plates here and because the plates aren't touch you can create a voltage you can you can create a voltage a difference in potential between these two plates here so essentially you have a little voltage source when you charge it up kind of like a battery again but not quite so if you imagine the waveform when it's rising the waveform that we have it's rising it charges up that capacitor to some voltage and then as that waveform as the waveform from the bridge rectifier waveform here and here as that waveform drops in voltage the capacitor still has a certain voltage across it and and the capacitor effectively is kind of like a little buffer as the waveform from the bridge rectifier drops very quickly the capacitor doesn't discharge nearly as quickly and so the effective voltage across the load here is much more constant and we'll see what what I mean by that in the next slide here's the effect of a filter capacitor on the circuit this is if we use a relatively low capacitance so what happens here well the blue waveforms from the bridge rectifier and the yellow waveform or the yellow trace is the output of the filter capacitor across the load so as the as the bridge rectifier produces a voltage that ramps up here we charge up our capacitor and as the blue waveform from the bridge rectifier dips all the way down to zero you notice that the voltage across the capacitor does not go all the way down to zero instead it might go down to a much higher voltage say this might be in on a 1 volt or half a volt here and so as the capacitor discharges as the charge rushes out of that capacitor and through the load its voltage also decreases a little bit and that's what you see here this relatively straight ramp downwards and the reason that happens is because as the charge exits the capacitor less charge in a capacitor means there's less voltage across that capacitor and now say we used a a higher capacitance well if we use a higher capacitance the capacitor can can provide a greater voltage for a longer amount of time and that's useful for us because now you see the voltage doesn't dip down nearly as much and we'll see how that'd be helpful in a second and if there was such thing as an infinite capacitor if one existed we would get a perfectly straight line like that and that would be all fine dandy except infant capacitors don't exist so it's pretty hard to do something that doesn't exist right here are some examples of filter capacitors they're all actually very similar but there are some distinctions to be made the first type over here on the left in the yellow box is the standard electrolytic capacitor an electrolytic capacitor is used very widely for a filter capacitor because it has a very high capacitance density meaning you can get a very large capacitance out of a relatively small package which is why it's very useful it's not the most high-performance capacitor of all time it doesn't respond well to transients very well but for the most part it's is sufficient now how is much alerted capacitor made well you get too long maybe three or four foot strips of aluminum you put a paper soaked in a liquid dielectric in between these two strips and you roll it up and you roll it up real tight and then you stuff it in a can like this and you put two leads coming out of it basically that's what electrolytic capacitors so those two metal aluminum strips are acting as two parallel plates and that's what creates the capacitor and you have a liquid dielectric to separate them now to the right in the green box we have bulk electrolytic capacitors now these are the exact same technology as the standard electrolytic capacitors I'm just making the distinction because they're different and people might call them a different name like a bulk capacitor a bull capacitor is just a bigger version of this electrolytic capacitor over here and a book of passages of course as I said has a higher capacitance and they might be just a little beefier meant for a little beefier applications the way they're attached to the circuit board is also a little different well not really but a little bit they use these snapping terminals here versus just standard through-hole legs really not too much of a difference between those two but yeah thought I'd point it out and the last type over here which isn't used nearly as much but they do have some use is the solid polymer type capacitors and solid polymer are actually constructed very similar to standard electrolytic capacitors except instead of having a liquid dielectric separating the rolled up aluminum strips we have a solid polymer acting as a dielectric and what is this - well improves reliability because the liquid dielectric in electrolytic capacitors all many times will dry up and that actually causes a lot of failure in all bunch all sorts of electronics that when a dielectric dries up the capacitor doesn't work as it once used to so the solid polymer doesn't really dry up because well it's already dry and it's meant to be dry so it'll last longer usually they have better performance than standard electrolytic capacitors but this is of course all at the expense of being more pricey but sometimes you do need them and they are available if you need them the power supply that we have right now consists of a transformer a bridge rectifier and a filter capacitor this type of power supply is called an unregulated power supply the reason is called an unregulated supply is because it's voltage the voltage it produces is highly dependent on other factors so the voltage produces depends on the demand of the load and the capacitance that we provide if the load is very demanding and our capacitance is not very not very much then we're going to see a lot of ripple on the output of our power supply because it's going to be discharging that capacitor very quickly and causing the voltage to drop also something that we didn't touch on before is that the Alpha voltage is highly dependent on the input voltage across the transformer remember the transformer works in a ratio it it works by transforming the voltage in a ratio so if if our voltage say from the wall outlet is a hundred and forty volts instead of 120 volts what happens well the output voltage from that transformer will also increase because the output is not set certain values simply just scaled down so that can be a problem because now if the output of voltage from our transformer is too high for our circuit or if it's too high there's no way of controlling it here you simply get that maximum voltage ideally we want the output voltage of the power supply to remain constant regardless of changes in the load and regardless of fluctuations from the voltage source so we want the output voltage to be completely independent of all other factors so to accomplish this we're going to use this wonderful integrated circuit called a voltage regulator and it does exactly what its name implies it keeps the voltage regulated at a set value here's the voltage regulator placed in circuit as you can see it's a three terminal device you have an input pin here an output pin here and a pin that goes to ground now on the input you of course apply your input voltage on the output you get a regulated constant voltage and ground goes to ground so you can buy voltage regulators in fixed values so you can buy a 5 volt regulator or a 9 volt regulator or a 12 volt regulator or you can buy an adjustable type regulator where you can adjust the output voltage using some external components so a couple design tips for you in order for the voltage regulator to work you need to apply an input voltage that is in general at least 2 volts greater than what you expect on your output so if you have a 5 volt regulator you need to provide at the very least 7 volts at this pin if you don't provide 7 volts while you're not going to get 5 volts on the output so take that one more step and what does this mean for our capacitor well we want to choose a capacitor that will produce a voltage across it that never will dip below seven volts because if it dips below seven volts then at any point where it's below seven volts then our output will be less than five volts and the voltage this difference in voltage this two volts that we're talking about that the voltage regulator needs that difference between here and here that voltage is called the dropout voltage of the voltage regulator now they make low dropout voltage regulators or ldos as they're called and these might have dropout voltages of maybe a volt or a half a volt so you could have a voltage across your capacitor that's much more close to the voltage you expect on the output of your regulator across your load but those are a little more expensive but they're pretty widely used if you're like I am you might be curious as to how exactly this voltage regulator works because we know what it does but we don't really understand how or why it's able to do what it does so I'm going to try to explain what's going on internally in a voltage regulator and so here is a simplified block diagram schematic that kind of highlights what's going on inside a voltage regulator now in reality the real schematic is much more complicated because everything is in terms of discrete transistors and discrete components pet passive components but for now this should do so we're going to look at each component individually and the first one is this red triangle in the middle here and this red triangle is an operational amplifier or an op amp for short an op-amp has two inputs it has this negative sign or minus sign level input and that's called an inverting input and it has this plus sign labeled input and that's called a non-inverting input and it also has one output over here and the op-amp has one goal in life and that is to make its two inputs be the same voltage to have the same voltage on both of these pins here and you may ask well how can you possibly change an input you know it input the nature of an input is that it goes in how do you change what goes in well you change what goes in by connecting a feedback loop to one of those inputs and this feedback loop right here will be able to change the voltage on that inverting input right here alright so now let's look at the next part here in the next part we're going to look at is the voltage reference and the voltage reference or V reference labeled here is in this pink Pentagon and this voltage reference is connected to the non-inverting input or the plus input here so what is the job of a voltage reference well the Javal voltage reference reference is to provide a stable unconditional voltage to that non-inverting input so regardless of all conditions temperature how much current is being passed anything basically the voltage reference will produce a voltage on this pin that does not change so we'll see how that works or how that's helpful in a minute or two and the third part of the circuit that we're going to look at is this part over here on the right consisting of two resistors and this these two resistors form what is called a voltage divider and we know that if we connect two resistors across a voltage from ground I mean from from a voltage to ground and then you look at the voltage on the node in between these resistors you see a voltage here that is proportional to the voltage up here so in the instance that both resistors are the same values and you know their values are not important but they're the same values and the voltage at the middle here will be half alright so the last major element that we're gonna look at is this yellow piece over here and this is our pass element and in this case it's an NPN bipolar transistor and this is working as what is called a voltage controlled current source and this means when you alter the amount of current that flows into this base here into the base of this NPN transistor you alter how much collector emitter current flows so by having a small amount of base current flow into this into this transistor you have a small collector to emitter current and if you put a large current a really large current into this base and you get a large collector emitter current again hopefully we'll see how this works later so let's try to tie all this together let's imagine a situation where say we wanted 5 volts on this output over here well how we gonna get 5 volts on that output regardless of all other conditions let's start off by looking at the resistor Network here let's say we make the value of both resistors to be the same as we talked about before what is that going to do well we know if if this is going to be 5 volts up here and if these two resistor values are the same then it will help to point 5 volts here and let's just say that we also set our voltage reference to be 2 point 5 volts here so if this is at 2.5 volts and this is at 2.5 volts then the op amp is going to be happy because both inputs are the same and when both inputs are the same in this case 2.5 volts and 2.5 volts then we must have 5 volts up here because the voltage dividers dividing it by 2 in this case so 2.5 times 2 is 5 up here so that's kind of in its happy state but now let's just say for instance that the load which we're going to say is a resistor connected on the output here to ground suddenly decreases in resistance or effectively gets more demanding Ohm's law is going to tell us that the voltage across the load will also drop so the voltage up here appearing at the top of this resistor right here we also drop meaning that the voltage here between the two resistors on the voltage divider also drop so this will cause our feedback network to produce a lower voltage and in a matter of microseconds the op amp is going to change its output to match to get the the inverting input here to match this non-inverting I mean yes this non-inverting input so let's just say that this voltage here dropped to 2.3 volts then the output of this op amp is going to force more current into the base of this transistor to allow for a greater collector emitter current and when there's a greater collector emitter current and there will be a greater voltage across the load and a greater voltage will appear at the top of this resistor and thus will stabilize again at 5 volts up here and we'll get 2.5 volts up here and again if it worked in the opposite direction where the load got less demanding or the resistance went up then the output the op-amp will output a a lower current and the lower current will drive a will mean that there's a smaller collector emitter current and a smaller collector emitter current will fix the voltage up here appropriately so it works in all different situations it could be there could be a fluctuation and the input voltage over here and the op-amp again will react accordingly to stabilize that there always be 5 volts up here and I'll do that by using its sensing feedback Network here so hopefully that made some bit of sense I know I'm not the best explainer but hopefully also a good idea how this were needed a 5 volt regulated supply and we talked about in the previous slide and let's say we supply it with a voltage that look like this and the blue voltage is from the filter capacitor and the yellow voltage is the output of the voltage regulator so as you can see the input that we gave to the voltage regulator isn't anything special really it's it's kind of ugly looking but the voltage regulator is able to take care of all those fluctuations provided that the input voltage to the regulator or the output voltage from the filter capacitor same thing is at least and always 2 volts greater than then the output we're expecting which is 5 volts so as you can see on the input or rather the output of the capacitor here this voltage is changing but as long as this these bottoms here these little troughs in the in the voltage as long as those never pass the low 7 volts which is 2 greater than 5 then everything will work just fine and you know voltage regulators have finite response times to to adjusting the output voltage but for this case the the frequency here is was it 120 Hertz or something so it's not anything that the voltage regulator can't take care of rather easily so don't be worried about that here are some examples of the packages that voltage regulators can come in and a package is simply the shape or the form that a particular component takes so the most common is the to-220 package and you'll see these a lot if you open up some electronics or you don't fear about it if you're going to design your own you'll probably use one of these to-220 can pass usually between 1 and 2 and peers that's its thermal limitation can't do much more than that but that's usually enough for most applications that you'll encounter a step up from that is a to3 package these aren't used as much anymore but these are a more traditional package that you might have seen in years past but they are still used not probably as widely but still used and these can pass much higher currents usually in excess of 5 amps or something like that they can do that again they all work all the same they all are three terminal devices but they are used in different applications and over here we have a teo 92 package and teo 92 is the same package that's used on small signal transistors and you'd use a regulator in a teo 92 package if you didn't really have to supply too much current and maybe you didn't have enough space on your board to fit a big to-220 or something like that so teo 92 can usually add its very maximum pass about 500 milliamps or about 1/2 of 1/2 of an amp which isn't too much and I wouldn't even get close to that maximum because these packages are really not designed to to dissipate too much too much heat but for a lot of applications 500 milliamps or even less than that is is uh more than enough to power your circuit on this slide we have some part names of some commonly used voltage regulators and so if you're ever going to go purchase some or you see them in a circuit you might recognize them the most popular line of voltage regulators is the LM 7 8 series and LM 7 8 as you see I've written here X X and where the x axis is where you would insert a certain voltage so if it was a 5 volt regulator it'd be an lm7805 and if it was a 9 volt regulator it would be a 7 8:09 and if it was a 12 volt regulator you got it LM seven eight one two alright so that's how you would identify those regulators the lm317 is also very popular in the lm317 is an adjustable regulator meaning you can choose what your output voltage is using in the feedback resistor network the LM 3 3 8 is a higher powered version of the 317 basically it's I think a bhoot I believe it's a either a 3 or a 5 amp version of the 317 the LM 723 is an older chip that actually has a couple more options and you can work with a little more but it's kind of a it can be a kind of a pain and not worth it but depends on what you're doing the l200 is also an adjustable regulator but it also has two extra pins to provide current current control so you can set a maximum current that you'd like it to pass and that can be good for applications where you need that and the LT 1085 is a linear technologies part and it is some might say it's an improvement on the lm317 but the 317 is still very widely used today thanks for sticking with me for this entire video we're going to recap basically everything we've talked about in this entire presentation so what do we learn well we're going to look at the basic linear power supply topology right here so first we have our mains input from our wall outlet it produces either 120 volts or 240 volts ac we need to reduce this voltage because it's it's really much much too high so we use a transformer which makes the voltage lower but it's still alternating current so to make it into direct current we use a bridge rectifier and the bridge rectifier forces all the current to flow in the same direction but it's still kind of erratic as you can see so to get rid of some of those that ripple on the bridge rectifier we use filter capacitors that helps to smooth it out I want it smooth out enough for us we're going to use a voltage regulator and the voltage regulator ensures that the output voltage of our power supply is constant regardless of the input conditions or the load and that's basically the topology of a basic linear power supply there can be more complicated versions with different and more things in them but for our sake this is basically how we would do it thank you for watching I hope you enjoyed this video and I hope you got something useful from it because I know it's always tough to get on the right foot for any topic and especially in electronics you know you want to learn something it's not always easy to get started with it so hopefully I gave you a decent or good enough introduction for you to go further with your exploration in power supplies and linear power supplies and switch mode power supplies and any type of power supply so I'd love to hear your feedback if you have anything at all say anything that you need or want answered I can do my best I'm I am in college so sometimes I might not get back to you too quickly but um I'll do my best so if you liked the video please thumbs it up and if you want to see more content you can subscribe to my channel and I will do my best thanks so much

Channel: Solid State Workshop

Views: 74,206

Rating: 4.9049616 out of 5

Keywords: Linear Power Supply, Direct Current (Electric Current Type), Alternating Current (Invention), Power Adapter, LM7805, LM317, Linear Regulator, DIY Power Supply, Transformer, Filter Capacitors, SolidStateWorkshop, Do It Yourself (Website Category)

Id: brB1sZyJPls

Length: 50min 32sec (3032 seconds)

Published: Fri Jan 03 2014