Get the Noise Out! Introduction to Power Supply Filtering

[Music] okay welcome back and if you take a look at the screen here we're doing the next lecture we stopped on the last one it was a kind of a good stopping point we had our transformer so we had kind of the standalone or open frame transformer that we had plugged into our system and then we decided we're going to switch that to a PCB transformer that could solder into a PCB and one of those look like this right here hopefully you can see that there we go so we're going to use that Tamura part which is already in the circuit alright so now what we're gonna do is we're gonna look at that and we are now going to experiment around with inductive loads a motor and so what - what this lecture is gonna be about which is a lot of fun is so say you design something and you've got a digital power supply you got a couple of them like the 7805 and this MC three three two six nine so you got five volts you got 3.3 volts and you decide to hook a motor up to one of these supplies alright so seems reasonable but then all of a sudden you hook it up to the supply and maybe you've got the motor hooked up to the five volts supply or the three three volts supply and then maybe you've got your digital electronics to the five or the three three either way the motor turns on and then over a period of time the processor keeps locking up or the digit electronics fail and the reason why is because you're inducing noise that inductive load that motor as that motor is turning around it's generating all kinds of noise and back EMF which then gets pumped back into the the voltage supply mains and dirties up everything and those spikes can cause the processor to fail or the electronics to do something wrong so what we're gonna look at is how to clean that up so we're gonna analyze it on the oscilloscope this is a lot of fun and what our goal is is when we're done is when we turn that motor on and power it up power down really really quick rapidly the power supplies stay nice and clean or as clean as they can be all right so that's kind of what we're gonna experiment on okay so let's go directly to the bench and just get right into it and and go from there and we're just gonna in real time kind of play with these different components and see we can do to create noise and then get rid of noise and we'll go back to the blackboard here and kind of show where we would add these components and so forth right so I'll meet you at the bench all right and so as you can see I've already plugged in this Tamura transformer so because it's a little bit tricky to connect and push in there I already didn't kind of made sure everything was good so just to reiterate what we're doing here so we've got AC is coming in here off this line right here which this let me let me show you this so this is basically connected to our AC lines and everything is often unplugged that's why I don't have gloves on right now uh so this is our AC line coming in and then I've made this cable this is 14 gauge stranded wire very very good wire and then brought that in and then those AC lines go directly into the primary of this tomorrow right and then I've got the primaries in parallel and we're we've got it in the 115 voltage mode 115 volts then the output I've got the outputs in parallel as well and I've got them connected under the transformer so you can't really see them and then the AC output which is in this case going to be six point three volts is then going to our bridge rectifier and everything else is the same from there all right now some other stuff that I want you to look at is this so I've kind of fabricated this cable here that you see and and this plugs in our AC lines here now if this wire pops out while I'm doing something I could possibly get touched here and hit my wrist or something like that so what I wanted to show you and again you know building things is all about fabrication and you got to fabricate things cleanly and all that so I want to show you some stuff here so these little cable management clips little cable management clips they come in all kinds of different sizes and so what these do is basically they hold cables in place so this one right here is a little it too small to hold this cable but this one will do so the whole thing is I could just use a piece of tape and I could just tape this down here like that I could do that right but you know the the tape is you know not not very reliable so maybe I'll do some cable management this is an AC line I don't want to get shocked so what I'm gonna do is I'm just gonna pull this a double-sided tape off the back here throw that away and then I'm going to kind of place this where I think would be a good position maybe right about here all right push it down and then I'm gonna put this cable in here and I'm going to pinch it down in there so now what's nice is this cable is nicely and cleanly tucked away here it's managed you know this is not going to come up into me and then these hot AC lines which over here in the corner of the camera are gonna stay where they're gonna stay which is what we want all right so just a little trick there don't be afraid to put some cable management when you're doing these experiments to keep your wires away and all that you can tape them or do these now obviously this is gonna be really hard to get off of here but you know I'll probably use that again so that's fine I'll leave that there all right so let me get rid of these okay so we've got our transformer here and again what I've done here is I put our probe leads for our oscilloscope here's the 3.3 volts supply and here's the five volt supply on channel 1 and channel 2 so we can look at those voltages so I got that and then what else do we have here anything else interesting oh yeah so here's the the really cool thing that we're going to play with is you know I showed you some motors and so these are a couple pump motors and let's zoom in a little bit and let's take a look at these so I don't have to bring them up to the camera can bring the camera down so that we can see things okay so here's one of these pump motors right here and hopefully you can see it I think you can and so this is a micro air pump a p2p oh one from smart pumps seeing three volts DC at 480 milli amperes alright 480 or is it four sixty four sixty milli amperes three volts so we only need three volts to drive this but it's gonna pull a lot of current I mean 460 milliamps that's half an amp but if you recall our 3.3 supply can go up to 800 milli amperes but our five volt supply I believe goes up to 500 milli amperes all right now so and then I've got another motor and this one right here is I believe this is not from the same company and this one does not say what the voltage is on here but it's it's roughly the same it's a three volt supply and this one probably pulls about to 300 milli amperes alright so but it'll run faster because it's smaller right so okay so the whole thing is is these motors is they run are gonna create a cyclic noise alright because they're an inductive load you're powering up an inductor you're creating a magnetic field the magnetic fields collapsing that's what a motor does right and so we're gonna have this noise generator right so the first thing that I want to do is I want to turn on the system and I want to make sure the thing works okay so I'm gonna go ahead I'm gonna plug this in and because I'm gonna be working and trying to get these components in here I'm not gonna put the gloves on but the AC is over there pretty safe and it's out of the way so I'm not going to touch that I'm not going to get near these hot leads alright so I'm just gonna be careful but it would be better to wear the gloves but it's just too hard to get parts in here alright so I'm gonna go ahead and turn this on and I turn it on and we see we've got both of our supplies 23.3 and the 5 volt supply are good to go alright and so now we've got our system here and so let's let's start doing a couple things so let's just let's confirm stuff so the first thing that I want to do is why don't we get one of our little probes and I'm going to get our multimeter and the first thing we're gonna do is we're going to measure our voltages here and we're gonna see if everything is what we think it is and we already know it is but so I've got the multimeter here and this and this gets really really tough because you got cables everywhere you got parts everywhere and things just get smushed and crunched and slid off and and it's tough so just bear with me here but I like to I'd like you to see things in real time so I'm just going to go right here and we're put this up here and we're gonna look at the 3.3 volt line alright so I plug that into the 3.3 volt line and let's see if you can see that meter there it is three point three okay good let's do the five volt line it's right under here put that in there okay push that in looks good let me show it to you five volts okay and then over here on the Left I've got this line right here and this is looking at the DC that's coming directly in from our wall transformer here our bridge rectifier and our smoothing capacitor because I want to monitor that voltage there and that's the only voltage we're going to monitor right now with the multimeter so I'm gonna kind of try and get this out of the way here so I can see it and the reason why we want to see that is as we pull current from that transformer that voltage is going to keep dropping and dropping and dropping now remember that the 7805 requires a two volt voltage above the regulation voltage so it requires seven volts to maintain regulation remember that at at you know high current or whatever so as we drop voltage by pulling current from the transformer here to power this 3.3 volt supply we're gonna start messing up the five volts alright so it is gonna start having trouble regulating so that's one little thing to note there okay so so here we go let's have some fun so what we're going to do is we are just going to connect a motor to this little switch right here so I've got I've got two plus three point three coming into this switch and then right from the switch I'm going to take that three point three and then I'm gonna connect another wire here to ground so now this motor is basically gonna get powered when I press this button okay so let's see if it is and it's a pump so it pushes or it pulls its pushing alright so that's a pump and it's very high frequency very high rpm all right now let me put the other one in so you can see the difference here's the other one same thing but these are color coded for polarity so red is plus and there's - okay here we go here's this one much slower right okay all right so let's go back to the fast one because it's more noisy okay so we got this noisy motor all right so that's great you hook that up and you're making some piece of hardware and you got a motor in there and everything's great the three point three is also powering some digital electronics and the five is alright and so you got the motor in there between the motor on and nothing and something goes wrong what goes wrong so let's go take a look at the oscilloscope alright so over here on the oscilloscope we've got channel 1 and let's turn on channel 2 alright and the first thing I want to do is let's make sure both of these are on DC DC coupling so we want to see DC on both of these and then we got to change the we'll change the vertical vertical gain here so that we're 2 volts on the 2 volts on the 5 volts supply so it's 2 volts per division on the 5 volts supply so you can see here's ground and then one two and a half divisions so there's our 5 volts and let's get rid of that display and but our 3.3 is off the screen so let's drop this down there it is so there's our 3.3 and it's 1 volt per vertical division so 1 2 3 and about 3 and a half so so that looks good so we're seeing the DC signals what you're saying there and then you see this little noise on here this is little AC noise writing on top of the DC signal ok so now the question is what happens if I turn that motor on so so I want you to think about it for a second what do we think is gonna happen here so this motor is going to generate a lot of inductive noise on that 3 3 line alright so let's turn it on see what happens you see those little spikes on the yellow line that's the 3.3 volt and then look at the five volt line say oh it's wavering we're not getting noise too much on the five volt line right it's a we're not seeing that noise alright and and this is the noise I'm talking about these spikes alright we're not getting noise on the five volt but we're seeing some wavering so something's happening there so let's speed this up and again it's gonna be noisy so what I'm going to do is maybe I'll cover this a little bit in something right alright so now I'm going to change his frequency and okay so now look at that five volt line see that noise getting induced on there so that's a waveform that waveform is the motor waveform so that is the the motorcycling and if we were to look at that frequency there right if we were to look at that it would be the RPM rate of the motor now here's another thing right when I power this thing up the moment I power it up I want you to watch both the signals watch how they dip innate and they gyrate alright look did you see that look at the blue signal see it dropping all right let me let me speed this up a little bit more there we go or slow it down so you can see the event there look at that so right when I power it up boom see that spike boom alright so the five volt for a second there really drops drops like a whole two volts doesn't it and then we just get constant noise on the 3.3 volt whine okay which we do not like alright so first what's going on with the five volt line we're gonna deal with that a little bit later alright but what I'm gonna do now is I'm going to put the both traces in AC mode so we're gonna get rid of the DC offset alright there we go so now all we're seeing is the AC signal so the DC component is now gone alright and so now we'll just look at the noise on both of these signals here okay so now let's turn the motor on again all right so the five volt line has that sinusoidal no noise on there which you can't see because the scale so now what I'm going to do is I'm going to turn the scale way down to 200 millivolts and 200 millivolts okay so now we're gonna really start to see this noise and you're gonna be quite surprised okay alright so here we go there we go alright so again the five volt line is 200 millivolts per division so I'm seeing about 400 millivolts of sinusoidal noise getting put on that and I can let me let me slow this down a little bit more now you can see look at that Wow alright and then we're getting noise just pure random noise and spikes on the three point three all right now let's well there we go and I want you to see this there so the five volt line has got about 400 millivolts of sinusoidal noise and that sounds like it's the motor itself right so that looks like that's the motor frequency that the RPM is going at giving us that noise that's something's happening there we're and we're causing something to happen there and but we're getting all kinds of spiky inductive noise onto the 3.3 rail now let's get rid of the second channel okay so that's the 5 volt channel let's just turn that off we don't need to look at that right now okay let's focus on the 3.3 all right so the 3.3 here we go okay Wow scary now let's change the scale here so we can see what's going on alright so now let's look what kind of noise are we talking about so we got 500 millivolts per division here 500 millivolts so every division is a volt so if we go up and down that's a whole volt if we go up and down two of them that's two volts alright so look at this noise alright now I'm gonna stop this someplace in here and we're just gonna look at some of these so look at some of these pulses alright so there's a pulse that went up a bolt and a half that went down you know 7.75 volts so we're talking about you know two volts maybe three volts up and down here of noise is getting modulated on that signal and this is only a 3.3 volt supply so we're spiking noise up and down in the noise going below ground so the noise can go below ground so this is really really really really bad alright so again let's turn the oscilloscope on let's look at this noise alright so the question is can we get rid of this noise and there's more noise this is continuous running and then then this is even worse when we only fire this thing up alright so let's try and see we can't really see it there so let's we're gonna speed this up and give me a second here I will put it about that now watch boom boom alright so that's not too bad actually but let's look at the DC so let's also look at the DC here I want to see this there's the DC and we're gonna there we go okay so now let's let's turn the motor on let's see what happens so the AC noise is on top of it little we got it at 1 volt so we're not gonna see it that well but I want to see throws DC reducing here not too bad so it looks like we're just getting AC noise on top of the line alright so let's go back to AC let's put this back so we can see it here okay and alright so there's our signal alright and there's our noise and let's change the scan rate here and let's change the scale so we can really see the noise there's 200 millivolts scale and you can see the noise just horrible alright so can we get rid of this noise let's go back to the bench and let's see if we can add a couple parts here and fix this thing up okay so school excuse me let's go back to the blackboard and and try and see if we can answer what we really have here is is this this is what we have so and I'm just gonna draw it right here so we've got three point three volts here coming in and we got that 3.3 volts and then we've got a switch a momentary switch right so those what are the how do those look like they look like this and then that momentary switch is coming down here and it's going into this motor here right and that's a horrible motor let me make that motor better make it a little bit bigger so you can see it so here's this motor right here that this is going into whatever symbol there's different symbols for motors and this is going directly to ground all right we we flip the switch current flows right the motor runs and then what's happening is as this motor which is generating the currents generating a magnetic field that's switching doing all this its inducing noise back on the 3.3 volt rail and pushing this back into the system okay so what we want to do is can we smooth this out alright so let's try a couple things so first let's do this so right now one thing the moment we turn this motor on it pulls a lot of current to start up so motors have what's called their initial startup current and then after that the current decreases because it's already running right so there's a nurse show already so but when there's when the motors at rest right it wants to stay at rest so it needs more current to get going so that's kind of the starting current and then there's the running current alright and where is it going to get that current from well it's got to go all the way back to the regulator so first thing we're gonna do is we're gonna think about putting a big capacitor here a storage capacitor so this thing is is charged so when we turn this motor on it pulls it from this capacitor so maybe we make this so 2200 microfarad then let's do another thing right over the motor right here to ground let's put a small capacitor let's say point 1 micro farad alright and that's gonna get rid of some of the noise also that's being generated so let's we're gonna put this big capacitor here we'll put this little capacitor right here then let's turn the motor on let's see what kind of noise we get all right so let's go actually put those parts in and see what happens alright so we're back here on the bench and what we're gonna do is we're just gonna do exactly what we just said that we were going to kind of model here alright so here's the motor where the motor leads are right so what I'm gonna do first I'm going to put that point 1 microfarad right across those motor leads alright so here is a point 1 microfarad and another thing I did I've turned off the power here because as I'm moving my arm around I don't want to touch the AC line so here's a point 1 microfarad I'm gonna put that right across our little power lead here and this is all gonna get a little bit small there's not a whole lot of room here all right so me I'll move the switch here like this for a second and I'm gonna put this right across here okay good okay and then here's the the three point three feeder line that feeds the switch so what I'm saying is let's put a capacitor right here to ground so that when we feed we don't have to go back through the rail all the way back to the regulator we'll have a big 2200 microfarad to give us that initial startup current okay so let's look here and I think yep so this one is a 2200 microfarad 10 volt 10 volts okay we're running at 3.3 volt but those spikes are pretty high I got to be careful but they're smaller than 10 all right this is polarized so we're gonna put ground 2 here and let's see we're gonna have to bend this down a little bit bend this down a little bit so we kind of get this in here so we're gonna go ground to here all right there we go I don't know if you just saw that LED flash for a second because there was some charging on there because I was experimenting obviously okay so now we've added our two things in here so we got a big capacitor for our startup current to get this thing going then once it's rolling we're gonna basically have a noise filter this little point 1 micro farad which is gonna filter the noise hopefully and we're gonna get some better results okay so let's go ahead let's turn this thing on all right okay good it's on all right let's uh go ahead and let's press this power button make sure it works okay it's working okay great now I want you to look at the oscilloscope all right and check this out okay so we're at the oscilloscope here and we're at 200 millivolts per division okay let's go ahead and let's put that down to 100 millivolts so let's really look at that noise so there's nothing happening and we can see there's a little bit of little teeny tiny bit of noise but we got at 100 so we're really gonna scale and see any noise that we're generating all right so I'm gonna turn the motor on and let it run in continuous mode all right now look look how small our noise went down to all right so basically we're getting 25 a millivolt spikes if that so now if I put it back down to 200 millivolts that we're looking at it before we're not getting those big spikes anymore they're gone all right now let's up let's pulse this thing on and off and let's see if we can get some big spikes that way but now that big storage capacitor is gonna save us so here we go all right so look at that we're still getting nice performance there and you see that little dip a second every time we turn it on right it's dipping just a couple hundred millivolts but it's getting that current from it's getting that charge in that capacitor and then we got almost no noise all right very very little so we could go and let's let's look at this let's go to 50 millivolts now just sitting here just the ambient noise now here's that one little thing electronics in general they generate just picking stuff up like 20 to 50 millivolts of noise it's like you can't get rid of noise so the noise that you're seeing right here is just a function of there's wires hanging out everywhere these cables this and out it's almost impossible to get rid of that so just keep that in mind now here we go I'm going to turn it on and let it continuous mode and the amplitude I'm seeing some spikes right now probably 25 millivolts up and down and now we'll hold that on and now we can see the envelope we're staying within a good plus and minus 50 millivolts no more volts remember before we're like at a vote volt and a half so we're at 50 millivolts now and again if I hit it and spike it all right we get that little spike there that was 50 millivolts and again everything looks bad zoomed in but we'll zoom out of this just a little bit all right there there's like one volt scale and now you can't even see it right so as we zoom in 200 millivolts scale you see a teeny tiny bit of noise let's let's get that noise so that we can see it a little bit better we'll put it at 50 millivolts all right there we go let's go ahead let's switch motors so does our solution we decide hey let's switch motors to this bigger motor it's a little bit slow and how does that look so let's do that and I'm gonna switch this motor and get it in here there we go alright here we go look at that barely anything out of that motor so there's motor not on there's motor on nothing looks looks great okay so let's go back to the other motor because it's more noisy and we want a noisy source okay alright so let's go back to the southern motor let's plug it in here okay alright okay so it looks like we've got the noise down to 50 millivolts plus and minus and a couple times there it gets a little bit higher alright can we do better is there anything else we can do alright so again we can keep working with capacitors and doing this and do it now there's other things you can do but let's go back to the blackboard on the computer here and I'll show you something else we can add okay so we're back here on the computer and so there's something else we can do so let's remember let's remember let's let's just erase some stuff up here so give it give yourself some room we don't need all this anymore do we alright and a matter of fact we don't need this let's get rid of all this just give ourself a little bit of room here I'll keep all the circuitry so we can refer to it okay so here's an inductor L right now what was what was the inductive reactance remember that so what was the inductive reactance so X sub L what was that do you remember it was 2pi FL and remember what X sub C was if we had that it would be 1 over 2 pi FC okay but we don't need that we just need this one so this says that it's impedance goes up proportional to the frequency so remember an inductor is basically a frequency dependent resistor so the higher the frequency the more resistance or impedance right so we are trying to get rid of high frequency noise that noise is very high frequency so what if we put an inductor in line with the power so let's take a look over here so our powers coming in through the 3.3 rail right here right so what why don't we try this so right where it's coming in let's uh so here's the power coming in right here let's put an inductor right here alright and then this point right here will be 3.3 volts so we're gonna put an inductor L here and so now what's gonna happen is this inductor for DC it's just gonna pass it but for AC it's going to impede it all right so what's nice is is that as this motor generates noise and it puts that noise let's draw that noise here so here comes this noise and it's all noisy coming through the system right and it gets that inductor and in a matter of fact let's draw it let's draw it bigger here's this noise and it's happy it's happy and it's that inductor uh-oh impedance and that noise gets smaller alright so this right here we could we could use like a 1 micro Henry or 2 micro Henry we could do math and we could model this and we we know how to do this we know how to do complex impedance and compute for various frequencies what the impedance is and so forth and all that we could do a bunch of calculations but when you do real electronics that is extremely time consuming now you can model it in the computer with simulation but instead what you do is you use intuition a lot and that's what you want to get here you want to get some intuition right just like when you fix a car you're gonna bolt something on right you take off that the tires take off the lug nuts right and you kind of have this feel for how much torque you need to apply those lug nuts to put that tire back on and keep that tire from falling off right you don't go get a torque wrench I don't think anyone is ever out of torque wrench other than Indy pit crews to check how much torque they're putting on things and they just use a a tool that when it hits the right torque it stops turning it alright those impact wrenches all right impact drivers so same thing here let's use intuition so what we want is we're going to use what's called a ferrite bead and I told you about these before and ferrite beads are inductors all right they've got a little piece of ferrite and they've got wire and they've got some coils through it and they're an inductor and they have different sizes and and they're spected like maybe at 1 megahertz they're a 1 kilo ohm of resistance or and we know that noise that noise is pretty fast right so it's up there in kilohertz and megahertz range that noise that we're inducing and so we're just gonna put off-the-shelf little ferrite bead that I have a couple of right where we're looking at it right here right into the feeder of this whole system and we're gonna see if that helps so that's the first thing that we're gonna do and then there's one more idea we can try to get even less noise out all right but first let's try this so let's go put a ferrite bead in here and see how that helps alright we're back here on the bench and I've got a couple of ferrite beads and here they are here here's what they look like so that's ferrite which is it's basically you know powdered iron right and then there's some wires so you can get the camera to cooperate there's some wires okay and that's it it's and they're and they're coiled in let's look at this on the zoom camera all right and let me see if it'll focus for us I'm so we can get it to focus and it's not gonna cooperate it just likes that image in the back too much oh there we go so you can see so see that so it's coiled through there looks like three times all right so that's a ferrite B that's a big one then I got another one right here and that's a real simple one so it just has that ferric going right around it so obviously the other one's got more inductance okay all right so let's go ahead and let's put this ferrite bead into the power laying there alright so I'm gonna turn this off to systems off now look at that what's happening there oh we had a bunch of charge inside that capacitor that's why you saw that slow decrease all right so we want to put this right in front of everything so I want everything to go in through that two ferrite bead so we got to be careful here so I'm gonna pull this now so we can see it a little bit better alright so I'm just gonna kind of undo this a little bit and see what I'm doing here all right so let's do let's do this so what we're gonna do is we're gonna pull this out and we are going to put the ferrite bead right here like this alright and then that's that's gonna give us trouble so I'm gonna try what I'm gonna try and do is I'm gonna put the ferrite bead right here and I don't want to bend it or break it okay so there's a ferrite bead right there now what I'm going to do is I'm going to connect power to the ferrite bead right here so there's our three three going through the ferrite bead because the ferrite bead is just too flimsy okay all right and so here's power going to the ferrite bead now I want to put the capacitor I don't want to put it upstream I could I could put it upstream but we're not trying that let's put it downstream here all right so we're gonna put it here so here's ground and then the other end of this is right here okay make sure everything is good okay so power goes into the ferrite bead and then the cap and the capacitor as well capacitor charges to ground and then we flip the switch we turn the system on all right let's couldn't connect our motor again let's get our small motor alright tricky tricky and get our small motor here and make sure it's correct polarity and I'm gonna put the motor right here alright and we still got a capacitor there and remember that's only one capacitor that point one microfarad and that's one big frequency band of noise it's taken care of we could try a point no one will you try a point 0:01 we could try one microfarad right we could play around and you know you do if you're gonna do this professionally you're gonna sit here a couple hours try things out model it on the computer and all that but these are some good tricks to try that should work right and they already did okay so I just turned the system on you can see the lights are on alright so again take a look at the oscilloscope so we're did this is just standard noise on that line we're not even doing anything and we're getting you know 25 millivolts of noise in each direction okay so we're already getting that noise now here we go so I'm gonna try turning this on we're going to see if this helps a little bit now we don't have anything to compare to right now unfortunately we just have to remember kind of what it was but I remember so I'll let you know alright so here we go Wow so look at that so almost nothing every now and then I see a little spike every now and then I see a little spike a couple big ones but that's pretty good pretty good alright and then we could try switching the position of the ferrite bead and putting the capacitor you know upstream we could put the capacitor upstream here so the capacitor is at the beginning of the ferrite bead all right instead of at the end of it so let's give that a try right so again what I'm going to do is I'm going to power down because the capacitor is gonna be charged I want to let it discharge okay so it's discharged so now we're gonna do is we're gonna put the capacitor right here so we don't have room here so what I'm gonna do is I'm going to move a couple things around being very careful here I don't want to break this this is just asking to be broken all right okay and then we're gonna put our capacitor here right there okay now capacitor and the ferrite beats the capacitors upstream okay so let's turn it on okay everything didn't didn't explode so we're good alright so I'm going to turn on again and we're gonna look at our oscilloscope so we look at the oscilloscope and nothing's on you see the amount of noise and now we turn on it's almost the same maybe a little spike once in a blue moon so not much difference there right and again if we lower the the vertical division back down to 200 millivolts you turn this on it is clean as a whistle clean as a whistle all right now let's let's let's finish off right now I'm gonna disconnect all this so there it is you can see it's very very clean all right and then we get that little quick jump when it turns on sometimes very very very little noise okay very happy with that okay so remember what that looks like now I'm going to turn it off and we're gonna really quick we're gonna pull this thing all apart okay we're going to pull it apart we're going to take this off we're going to pull this capacitor out of here all right and then we're going to connect this thing up we're gonna put this like this and because I just want you to see I want you to remember all right and then here's plus and here's ground alright ready so now we got no filtering let's do it looks like and what did we do what did we do what we got to turn it on okay here we go whoa so we did indeed make a really nice filter system and we cleaned that up and you know that's that's great that's that's what we want to do all right so now the problem with the five volt is we weren't pulling so much current what we're doing is we're taking that regulator out of regulation so we're just drawing too much current now if we had a L do a low dropout regulator for the FI Vil then we could look and see are we inducing noise enough where the five volt supply is singing noise then we could address that the same way we did this we would put filtrate filters on it we would put capacitor we put an inductor and so forth right now I want to go back to the computer and I want to I think we've got everything we wanted to do here I think we did you know a lot of cool stuff so I think we're done here let's go to the computer and I want to draw a couple things for you a couple ideas that I want you to try when you're building power supplies and to give them a try to reduce noise and just make good power supplies all right oh and one last thing that I want to talk about we bring the power in let's get this on the screen here so you can see so we bring the power in and we'll draw this on the computer when we talk in a moment but we've got the power coming in you know through the AC line all right so if you make a real power supply and it's an AC power supply off line that plugs in you are going to have a fuse here and I'm gonna this is hot right huh let's do this I'm gonna zoom out a little bit more here all right I'm gonna zoom out so here's the hot line right there right there in the corner so these hot lines are going to come in here we're going to have a fuse on this some kind of fuse right there's different kinds of is there what I call a PTC positive thermal coefficient and when they break they they that basically they get hot and then they melt and then they resell it if I so they're really nice then there's little glass fuses normal glass fuses you probably seen I don't think I have any here but you're one gonna want to fuse that AC line now if you're going to build AC power supplies that are offline with transformers and all that there's a lot more you need to do it's beyond the scope of this course right now maybe we'll do a scope on AC power supply is one of these days but we'd want to put a protection we'd want to put those XY capacitors on there for filtering we'd want to put a fuse and a bunch of other stuff now let's assume that all this is from a wall adapter something like that so we don't mess with it we just get a DC unregulated voltage which we plug in to our regulators alright even still in those places we can put fuses we can put these what are called PTC fuses to protect things also hey what if there's a lightning strike or something and we get a big voltage spike coming through the transformer and all that well we can put clamping diodes and what are called transient transient voltage suppressors CVS's t v--'s and Victor s is in Sam T is in Terry T V s we can put those in front of those regulators as well and I'll show you that when we go on the board but what those do is clamp the voltage so if we ever get a really high spike voltage because of a transient due to lightning strike or something that won't damage our power supply and of course damage our computer downstream than our power supply is powering all right so anyway let's go back to the to the blackboard on the computer there and let's look at some of these other things and we're gonna kind of wrap it up with that so anyway so that was a lot of fun so I will meet you back at the computer okay so we're back here on the computer and the first thing is alright let's just we got this let's just erase this and let's kind of summarize what we're talking about here so so let's let's do this alright so we've got a three pin regulator we've been talking about here here's our three pin regulator all right and let's we can draw that let's just draw that a little bit of a different color here for fun here is our regulator and we don't know what voltage this is regulating right it could be anything but but we'll just say it's like a five volt regulator all right and it could be just the standard linear regulator or it could be an L do and I'm going to tell you I want you to use L Dios okay they're just better more efficient less heat all that and only a little bit more expensive so you're gonna use an L do and that means that we can probably maintain regulation if this thing is like five point two volts or five point three volts but it surely doesn't need to be seven or eight volts or something like that so the whole point is we can have that low dropout okay all right so this is kind of what we're talking about and we over here we've got our VN and if this is a five volt maybe this is you know anywhere from 6 to 12 volts typically right and that's a wall wart I don't know where that's coming from it's coming from someplace and it's DC it's unregulated unregulated all right it's just DC it's maybe a smoothing capacitor or a bridge rectifier all that but it's DC unregulated out here we've got V out and we've got 5 volts regulated right it's Riggi that's the whole point that's what this is regulated okay okay so that's kind of what we have and then bare minimum we want to have a couple capacitors here all right that's what the bare minimum is and many of these designs and they say whatever they are but what I'm telling you is I want to see in general I want to see like a ten to forty seven micro farad big one I want to see a ten to forty seven micro farad big capacitor then I want to see also a smaller one for noise like this and I want to see this is going to be 0.01 two point one microfarad you can play with that and again over here for noise again 0.01 2.1 micro farad alright so we got these four capacitors alright between V N and V out alright now what else do we want to put in here so let's add some other stuff okay so the other thing that we're gonna add here is this we are gonna add some ferrite beads all right and all kinds of analysis has been done and and this really helps so we're gonna put a ferrite bead there and we're gonna put a ferrite bead right there so these are ferrite beads and ferrite bead okay and here's our V out again so well now what these are gonna do is these are gonna reduce noise coming into the system coming into the regulator and then also so whatever noise comes in is is now gonna get dampened by this ferrite bead so that the output is gonna be real clean we're gonna hit it again with another one and moreover if noise comes in this direction right this will dampen it right and then if it tries to get back through the regulator and back out here because maybe here this is also going to another supply so I want to make sure any noise getting injected into this is getting dampened alright so we'll pour ferrite beads on both of them alright and so that's what we want to do there now what are these other things that I was talking about so I was talking about transient voltage suppressors and whatnot right okay so let's talk about what that is so at EVs transient voltage suppressor so what what that is and what will draw that in another color to just be colorful today so right here on the input we're gonna put a t vs and there are many many of these alright and they basically are diodes that are put in this opposite direction here and these diodes are very similar to Zener diodes so they'll have this kind of symbol and this is a t vs all right and and so what does that stand for it stands for transient voltage suppressor all right t vs and so what this does is say so normally we're expecting six to twelve volts in here we're all happy right we got our six to 12 volts yada-yada-yada here it is then all of a sudden is lightning strike lightning strike finds its way through everything the Transformers the power strips and all that and then goes boom goes crazy right and you got this big you know transient voltage spike this T V s is like a Zener diode except this thing works in like or picoseconds so it works super super fast and shunts that voltage and and Clips it and clamps it so that your system doesn't see that so it works super super super fast this thing an enormous amount of energy it can shunt for nanoseconds or picoseconds so you put these TBS's on this input here to these DC lines and that protects your entire system so now it's kind of protected against voltage strikes and so forth and and transient voltage right now this isn't gonna help you against shorts and over current situations so now say down at this end here's our V out right let's say that you know this thing is rated at a say it's rated at 1 amp ok and you start you put a resistance on here that's so low that we pull an amp out then maybe try and pull 1.25 amps out something like that right and so what's gonna happen is very quickly this thing is gonna overheat right and it's gonna shut down now a lot of these will have automatic shutdowns and that kind of thing right but if if it doesn't react fast enough or it doesn't have that feature and you were too short this you could potentially very quickly pull you know like 5 to 10 amps through this or more 20 amps something like that who knows and so in that case what we might want is we might want to have a some protection on the input right so that we don't pull all that current through here alright and so basically if whatever is connected over here I don't want to drag so much current through it that I cause damage to that as well so then what we can put over here is something else right we can put a little fuse and let me do this here so now we can put and go here and we can put a little fuse and these these things have different symbols these these little things here these little fuses but PTC fuse positive thermal coefficient and so what this means is is as current more and more current runs through here and this thing gets hotter and hotter and hotter and when a certain amount of current surges through it gets so hot it melts and opens up and then no more current flows then it Risa Lydda Phi's and allows circuit or so if the circuit pulls too much current for too long it basically shuts the thing down all right and opens up and that that event might be a hundred milliseconds to ten seconds so you can get these in different currents in different time constants so basically you can say hey you can pull five amps but you better not full pull it for more than a couple seconds you pull it for five or ten seconds and then that this PTC is shutting you down and it'll shut it off right so here's kind of you know one version of a you know a pretty full-featured power supply so assuming this was an LD L regulator we've got nice filtering on the input we got nice filtering on the output we've got some ferrite beads on the input and output we got high noise we got noise protection we got a TV s for transient voltage and we got a PTC fuse so that we don't pull too much current now you build this on a board you put a switch on it put an indicator LED you got yourself a decent power supply and and when you look at other people's power supplies you'll see hey they won't have let's let's use a different color here they won't have these other capacitors for noise and these capacitors will be very small like one micro farad right they won't have these these ferrite beads right they won't have this transient voltage suppression they surely won't have this fuse they'll basically have the bare minimum just a couple cops a regulator and then you know throw caution to the wind that's not what you want to do you want to build a little bit better stuff and so here is how you want to do your linear and L do regulators and now of course these parts you have to play with them and stuff and experiment and get some intuition again we know how to model all this if we want to we know the math now right but we don't really want to do all that and you can also get on the bench and experiment I took a motor and maybe that's the exact motor I'm gonna use in a product right so I set there and I I turn the thing on boom boom boom boom boom and I look at the noise and I put a couple of parts in I don't got don't have any noise anymore so I'm happy about that so I'm done then I could go back and I could simulate it also find one or two but anyway so that's it so that hopefully you had a lot of fun and the power supply's is it interest of mine and it's always nice because if you know how to make a good power supply then your your hardware will work very well and when transient events happen motors high-current etc you know gonna mess everything else up because it's really hard to debug because if something happens from your power supply you're like you don't really know that it happens because it's a little transient event and if you don't look and see those transient events you might go look in the wrong direction and think your software is not working or firmware is not working right but really what's happening is your power supply is spiking all over the place and creating negative voltages which tripped out your microcontroller and it went nuts right so anyway so that's it in the I think we're done with all this voltage regulation stuff I'm pretty sure we are so in the next lecture we're gonna swing back to transistors again we're gonna talk a little bit more about them we already did a lot of material on at the semiconductor level and we did some experiments we're just going to do a little bit more just kind of go back to it again and then and then after that that'll wrap that up right so anyway I will see you in the next lecture and that's it bye

Channel: HardwareGuruHacks

Views: 3,366

Rating: 4.9436622 out of 5

Keywords: Electronics, PCB design, embedded engineering, analog electronics, digital electronics, amplifiers, microcontrollers, arduino, passive filters, AC analysis, Circuit Design, Circuitmaker, Labcenter Proteus, circuit analysis, PCB manufacturing, ohms law, phasors, Complex Impedance, filters, noise, power supply

Id: 49dfOQbmKvY

Length: 51min 13sec (3073 seconds)

Published: Fri Aug 09 2019