Let's build a voltage multiplier!

got a nine volt battery here and if I hook it up to my multimeter here to measure the voltage you can see it's about 9.6 volts but let's say that I need a higher voltage of the net for some reason well I could hook up a second nine volt battery in series and that would give me a higher voltage let's say I want a higher voltage but I don't want to use a second battery is there some way to do that well here's a one microfarad capacitor and if I put the capacitor across the battery like this it'll charge up the capacitor and so now this capacitor is charged with 9 volts if I put this in series just like I put the other nine volt battery in series with the first nine volt battery I get a higher voltage almost 18 volts of course as the capacitor discharges the voltage is going to drop and I can move the capacitor back charge it up again then put it in series and the voltage will jump up again but of course again it's going to drop and when I take the capacitor out of the circuit to recharge it the voltage also drops because I'm breaking the circuit when I take the capacitor out so what I want is a way to somehow keep recharging the capacitor and putting it in series with the battery but also keep the output from dropping to zero well what I can do is add another capacitor across the output here like this that way when I take the first capacitor and I put it in series not only does it produce an output voltage here but it also charges the second capacitor so now when I remove the first capacitor you can see the voltage doesn't actually drop to zero and that gives me some time to charge the capacitor put it back in series the voltage will jump up I can go ahead and then charge the capacitor again the voltage doesn't drop to zero put it back in the voltage jumps up again and so now what I need is just to find a way to move the capacitor back and forth faster well here's something I came up with that will help make that easier I've got a capacitor connected to a switch like this and when the switch is in one position the capacitor both legs of the capacitor are connected to the blue wires and if I flip the switch to the other position both legs of the capacitor are connected to the green wires and so if I put this in the circuit here I can connect the blue wires across the battery and I can connect the green wires in series with the circuit that way when the switch is flipped in One Direction the capacitor is charging through the blue wires and if I flip the switch to the other position the capacitor is now in series with the circuit and the voltage jumps up I switch it out of the circuit it charges switch it back in the voltage jumps up switch it out charge it put it in the circuit charge it put it in the circuit and you see as I switch this faster and faster I can get the output voltage to remain relatively stable and so this sort of circuit is called a charge pump and I get a better picture of how this charge pump circuit works I've hooked it up to an oscilloscope here and right now this second capacitor here is completely discharged and we're measuring zero volts across it the first capacitor though is connected up and is currently charging and if I go ahead and switch it into the circuit you see the voltage jumps up to about 9 volts if I switch it out to recharge it and then switch it back into the circuit here you'll see it jumps up again charge it switch it in search it switch it in and as I switch back and forth you can see I can keep it charged and keep it switching back and forth in and out of the circuit and the voltage stays more or less around you know what is this 5 10 15 around 18 volts or so if I'm continually flipping this switch and of course the faster I flip the switch the smoother if it doesn't come come out here the faster I flip that switch the smoother it stays the smoother that voltage level will be and you can even imagine if I were flipping this switch hundreds of times per second which I'm not physically able to do the output voltage would be even smoother so how could we do that well this is an a stable 555 timer circuit and as you can see it's turning this led on and off rapidly and for more details on how this circuit works you can check out my video on 555 timers but if we hook a oscilloscope up to this you can see it's fluctuating between zero volts and about 9 volts on and off and of course the nice thing about this is that we can adjust the the frequency you can either make it faster or slower and in fact we can make it as arbitrarily fast as we like how do we take a signal that's fluctuating between zero volts and nine volts and turn that into something that looks like charging a capacitor across a nine volt source and then putting that capacitor that's charged to 9 volts in series with 9 volts well there's a clever way to do it so imagine there consider the scenario first where we've got nine volts here and that nine volt signal is connected to a capacitor that we've somehow already charged to nine volts so this capacitor already has a nine volt charge on it somehow well if we have 9 volts here in series with the nine volt charged capacitor then we're going to have 18 volts right here but of course that assumes that we've somehow figured out a way to charge that capacitor so now let's look at the other half of the signal where we're at zero volts so if we have zero volts here and we connect that to the capacitor then we can charge this capacitor as long as we feed in 9 volts from from our power source somewhere so if we've got nine volts coming in here we've got zero volts connected here at the bottom of the capacitor then the capacitor is going to charge up to 9 volts then when we get back into this scenario our capacitor is charged with 9 volts we put it in series with 9 volts and we get 18 volts here the problem though is if this is still connected to our 9 volt Source then current is going to want to flow from high voltage to low voltage and this capacitor is basically just going to discharge right into our battery but the clever thing we can do to prevent that is put a diode in here and the diode will prevent current from flowing from high voltage to low voltage so that when we have our 9 volt signal coming in here and we put it in series with our nine volt charged capacitor we get 18 volts here and that 18 volts isn't going to cause a current to flow into the battery and cause the capacitor to discharge immediately and over here if we have that same diode in our circuit then when we bring this to zero volts down here as long as this capacitor is charged at some value below 9 volts then current is going to want to flow through this diode and charge the capacitor up back up to 9 volts then when we switch it back over to this scenario we've got a nicely charged nine volt capacitor we put it in series with nine volts from our fluctuating signal and that gives us 18 volts and of course I'm using round numbers here 9 volt batteries aren't exactly 9 volts the diode is going to introduce a drop nothing's 100 efficient but you get the idea and so this scenario allows us to take a 0 and 9 volt fluctuating signal and turn it into an 18 volt and 9 volt fluctuating signal flux rating between 9 volts and 18 volts it's not exactly what we want if we want a steady 18 volts but it's a step along the way so let's go ahead and try this out so I'll connect the output of the 555 timer to a capacitor and then the other side of that capacitor will go to our positive voltage through a diode then I'll hook the oscilloscope up again to look at the output of the 555 timer and then compare that to this node here between the capacitor and the diode so that's this point here that's going to switch between 9 volts and 18 volts so now if I connect a battery I've got channel one here connected to the output of the 555 timer and you can see that switching between zero volts and 9 volts just like we expect but if I turn on Channel 2 I've got that connected to this node here between the capacitor and the diode and so that should be switching between 9 volts and 18 volts and if you look here this little green icon indicates where zero volts is for channel two so if I can move that around so if I set that you know right to the the middle there you can see this is five volts per division so the bottom here is about 9 volts and then the top here is actually looks like closer to 15 volts but you know close enough so this is switching sort of nominally between 9 volts and 18 volts so we're getting that higher voltage at least intermittently at that point so now that we've got 18 volts at least some of the time and I'm going to keep saying 18 volts even though as we saw this is really closer to 15 volts because you know yeah the diode's going to drop some voltage and the 555 timer isn't putting out exactly 9 volts here and so on but you know ignoring real world inefficiencies this will be roughly double the supply voltage so uh yeah I'm more interested in talking about the theory um so anyway we've got 18 volts at least some of the time so how do we turn this into a steady 18 volts well you know when I say 18 volts that's 18 volts relative to ground so if we connect this to a capacitor to ground this capacitor is going to get charged to 18 volts but of course then when this node switches to 9 volts this capacitor which is charged 18 volts here is going to want to discharge it'll want to discharge back down to 9 volts through this node effectively moving the charge from this capacitor into this capacitor or we can stop that with another diode right here into this diode we'll let this second capacitor here charge up to 18 volts you know again assuming some theoretical perfect diode but then when it switches to 9 volts it won't let the capacitor discharge so this node here will remain relatively steady at that higher voltage level so let's give it a try we'll connect this diode and then the capacitor and the capacitor goes to ground like that so I'll reconnect this oscilloscope probe here that's looking at this node that's switching between 18 volts and 9 volts then I'll connect a third probe to this new node here that's either going to be at 18 volts or at 18 volts so if we connect the battery we've got our 555 timer output here switching between you know nominally zero volts and nine volts looks more like 8 volts and then our other node here that's switching between 9 volts and 18 volts looks like it's actually getting up to about 15 volts and if we turn on Channel 3 which is our output we see it's a steady you know about 15 volts maybe a little bit less than the peak there because of that other diode drop and so we've got our steady voltage here at this node here and we've approximately doubled our our battery voltage and I say it's a fairly steady voltage because if we actually zoom in we switch this to AC coupling and change our scale you can see the capacitor charging and discharging charging and discharging but this is maybe you know a quarter of a volt fluctuation which is is probably good enough for a lot of applications so that's cool that we can almost double a voltage source but what if we want even more voltage well I've redrawn what we've got so far and we've got this signal that's switching between zero volts and nine volts and when it's zero volts this capacitor charges up to 9 volts and then when we switch here we put that 9 volt charge capacitor in series with another 9 volts and get 18 volts that 18 volts then charges the second capacitor then when we switch back to zero volts here to recharge the first capacitor this second capacitor stays charged at 18 volts but what if at the same time we switch this down here to be at 9 volts so now we've got an 18 volt charge capacitor in series with 9 volts that would give us 27 volts right here and then when this switches back to 18 volts here we'd have to switch this back down here to zero volts so that this capacitor could be you know continue to be charged to 18 volts but you know we can do this but you know for it to work we just need two zero to nine volt clock signals that are opposite of each other so we've got the one from the 505 timer that's switching between 0 and 9 volts we just need a second one that's switching between 0 and 9 volts that's uh just the opposite and then of course you know once we've got this we could easily add another diode here going to another capacitor that goes to ground just like we did before and this would stay at 27 volts and just like we saw in the last iteration this will keep this third capacitor charged to a relatively constant 27 volts and of course you can imagine we can keep going with this but let's build this for now we've already got the output of the 505 timer for this first clock but we need a second clock that's inverted and for that I'm going to make a pretty simple inverter uh just with a mosfet now mosfets are voltage switched so when this gate voltage here goes up to 9 volts the mosfet will switch on and the output here will be connected to ground here through the mosfet so that output will go to ground and then when the gate voltage here drops to to zero volts then the mosfet will switch off and this output will be connected through this resistor to 9 volts and so the output here will be the inverse of the input it's not perfect but it'll work so I have the mosfet here and then connect the output of the 555 timer to the gate of the mosfet and the source the mosfet goes to ground and then the drain we've got connected to a 1K resistor to 5 volts and so here we should have our inverted clock and with our new circuit here what we want is our inverted clock going into the second capacitor here so instead of tying this capacitor to ground we'll tie our inverted clock into that second capacitor so that's here so when our clock is high this will be low when our clock is low this will be high then we'll connect from our second capacitor to our third capacitor through a diode and here's our third capacitor connected to ground let's give this a try so we'll connect the battery here and again we've got channel one is hooked up to the 555 timer so that's looking at the output of that channel two I've got hooked up to the output of this little uh you know simple inverter circuit and so there we see you know what is effectively an inverted copy of the five five timer so we've got our two timer circuits there for these two inputs now we can kind of just explore what else we've got here so if we go to this first node right here we're seeing that switching between you know 9 volts and 18 volts like we expect if we go to this next note past this diode we're going to see a higher switching voltage this time between you know normally 18 volts and 27 volts and then finally on the other side of this diode we should see our final output which is the high voltage and you can see that's relatively stable at what is it 5 10 15 20 20 something volts so you know not quite 27 but close enough so of course you're probably wondering how far we can take this well we're going to need a bigger breadboard so here I made a charge pump with a ridiculous number of stages because uh why not and as you can see it's pretty straightforward you know we just need to invert the clock between each stage yeah but we already inverted the clock here with this mosfet so to invert it again would just get us back to the original clock so I'm just alternating between those two clock signals for each stage of the charge pump so let's see what it can do I've got a volt meter hooked up we'll turn that on and we'll hook up a nine volt battery here and we've got uh 110 volts so I can see the voltmeter is also showing this little lightning bolt symbol which suggests that there's a potentially dangerous voltage level here and I guess this is the point in the video where the thumbnail promised I'd attempt to electrocute myself so I suppose I have to attempt to electrocute myself well okay I guess I'll just touch my finger across these two terminals and I don't feel anything you can see the voltage drops when I touch it because the capacitors are in fact discharging through my skin but you know these are tiny capacitors so despite the relatively high voltage there's actually very little energy in here so you know high voltage represents the potential to move a lot of energy but if there just isn't much energy to move I'm not going to feel it do any real work so you know sorry this is kind of anticlimactic but I guess that's you know how video thumbnails work but anyhow the reason the voltage drops when I touch it is that the capacitors are charging relatively slowly you know because there's just not that much energy moving into them per unit time and so you know there's discharging through me faster than they can recharge so if you're looking to build yourself a breadboard taser this is not the way to do it so what is a charge pump circuit like this useful for well maybe you need to send a signal using a particular voltage level and you know with the signal you're not trying to deliver a lot of energy you're just trying to transmit information so for example hypothetically maybe you want to transmit information using the standard rs-232 protocol you know in that case ones and zeros are signaled using plus and minus 10 to 15 volts so if your circuit that's transmitting rs232 happens to only have a 5 volt power supply you know maybe a charge pump like what we built in this video could be a good way to get those other voltages you know if you hypothetically wanted to do that for some reason but anyway hopefully you found that interesting and as always thanks to my patrons for helping make these videos possible I'll see you in the next one

Channel: Ben Eater

Views: 1,940,023

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Id: 4alV5LzHLE4

Length: 16min 31sec (991 seconds)

Published: Sat Feb 04 2023