Hi. In a previous video, we took a look at how to redesign the current measurement functionality of a typical multimeter and how to make it better in terms of lowering the burdened voltage across the not only the shunt resistor, but the fuse as well. So click here if you haven't seen that video because this is a follow-on from that, so it probably may not make much sense where we're starting from here. so definitely check that out first.

Now last time we looked at this, what we did is we optimized the rangers here from 500 micro amps up to 5 or 10 amps here, and we got basically a maximum of 50 millivolt shunt burdened voltage plus the fuse burden voltage of 5 or 50 millivolts. And that was pretty good. And we came up with solution with just a couple of muxes here and a times 10 low offset chopper amp here, but this is not necessarily how you'd implement this in practice. It showed that we went through and got all these ranges and sort of, you know, here's our maximum burden voltage, But as far as practically implementing this goes, we can actually do better than this.

We haven't done any optimization yet, we just figured out this is the concept of what we needed, but there's a way to actually optimize this circuit so that we can actually get rid of these maxes. and I want to show you an additional way that which I hinted at in the last video where we can actually get rid of the times 10 chopper Ab as well. And this sort of circuit optimization is a very common technique. You come up with the concept first of what you actually need and then you go through and optimize it from either a component count point of view.

usually less components, the better you can make it on a smaller sized board. usually cost less and we might be able to reuse components for example or other stuff. Bomb Optimization Bill of Materials optimization All that sort of jazz so you know this is not necessarily how would implement it now I did this in my microcurrent gold and I've probably done this in a video. not specifically, but maybe in as part of a video or somewhere I'm sure and if you have a look at my microcurrent circuit, you can see it's a little bit complicated.

the switching arrangement used in terms of the microwave, the milliamp, and the amps range there. Now in this particular case, I came up with a clever switching arrangement for using the type of switch that I had available for the particular current. There was actually limited choices in this I thought I had to come up with a solution here to match the switch in solution that I had found and that I wanted to use. Now in the nano amp range, it's pretty easy.

Here's the switch configuration for that. You can see that there's basically a 10k shunt resistor hooked directly onto the X 10 a amplify the other two shunt resistors in. there aren't used very simple, but if we switch to the micro amp range here, then you can see that we're actually switching the 10 Ohm resistor in series with the 10 milli ohm shunt there. it's actually in series.

we've got both from there, but because the 10 milli ohms is 3 orders of magnitude less than the 10 Ohms it, it's still within spec. and you can ignore the 10 milli ohms there. And you might notice as well that the 10k is still in parallel with that. So once again, it's three orders of magnitude larger, so it's still within all the specs we wanted, so you don't have to worry about the 10k in parallel.

Now, in both these cases, we've been reading the voltage directly across the particular shunt resistor, the 10k or the 10 ohm resistor used just like we did in this year, we're reading directly across any particular shunt resistor every in this range, this range, or this range up here, But something interesting happens if we switch it to the Amps range. here. You can see that actually the current is switched just through the 10 milli ohm shunt resistance, but we're actually tapping off via the additional tion that 10 Ohms shunt resistor were actually tapping the voltage off. That, and the reason that we can do that is because the input impedance of our amplifier is extremely high.

Essentially infinite. There's no input current, so there's no voltage drop across that tone Ohm Shanthi resistor. So we're actually using one of the shunt resistors as a tap to measure the voltage. So that's actually not an uncommon technique.

And you guessed it, we can apply it here as well. So let's take a look at how we're tapping this off. As we said before, we just implement in a MUX because that just explained it real easy. So in the amps range down here, or the amps and 500 milliamps, we measure directly off the 10 milli ohm shunt resistor.

Then, when our multimeter switches to 50 or 500 milli as we read off this shut resistor, well, it's actually across both of them. but it's still directly off the top of the shunt resistor there. And likewise, for this one, we measure directly across that shunt resistor. But what if we can stack them in series like this and actually optimize and even get rid of our maxes? So what we're going to do is rub out that we don't need that tap.

We don't need that tap. And let's see if we can just get away with a single tap from the top while cascading these resistors. Kind of like we did on the micro current. So what we did is the hundred Ohm resistor here.

Okay, we can. Well, let's put that in there. Let's tap that over to there. So now we've got all three in series and we're only now.

what. we've only now got this single tap off the top. Now if we do that, if we take the case of the micro amp range up here, our range switches up here. so we use our we plug our probe into the mic ramps jack.

we short out this and we've actually got these three resistors now in series like this. So of course you might have nineteen. not sorry, this might be a 909 for example, Nine Point Nine, Ohms. And then we've got our one Ohm and our 10 Milli Ohms down.

here. it could be 10 Ohms, but you know we mentioned that in the last video. Anyway, if you just wanted to make it a nice even value across there, you would actually have to take into account that you had all three in series like that. so you can see how in this case it works.

Easy. We've basically got our 100 ohm shunt resistor still or slightly higher if you didn't bother changing the values and we just tap off that like that. Bingo - easy. Now, if we take the case of the Milliamp range, our probe is still plugged into here.

our milliamp position switch switches down to here. So it actually this now becomes open circuit here. Okay, but we're shorting onto this range. so our shunt resistor is the 1 Ohm plus the 10 milli Ohms series like this.

But we're still tapping off this top bit here because our hundred Ohm resister. There's no voltage drop across that because it's disconnected here. Actually, there we go. And the input impedance of our Marx Oil amplifier or whatever you want ADC or whatever you want to plug this thing into is extremely high.

Consider it infinite, especially considering we're down in the hundreds of Ohms region here. Then there's no voltage drop across this, and you're just using that as a sense line to sense directly off this 1 Ohm resistor here. Beauty. And likewise, for the Amps range, we now move our probe over to here so effectively there.

it doesn't matter which position we select here, my cramps or milliamps doesn't matter, that's now become open circuit and we're now got our 1 Ohm in series with the hundred Ohm. but it's still high impedance over here, so there's no voltage drop. So we're now sensing directly across the 10 amp 10 milli ohm current shunt resistor. But aha, trap for young players.

Remember how in the previous video I said that? Because this is 10 milli Ohms, it's a very significant fraction of the PCB trace resistance. It's important to do the four terminal measurement technique. What you do is instead of having your 1 Ohm like, well, let's just get rid of the whole thing. then our 1 Ohm resistor.

You would actually put that into the tap on the 10 milli Ohm shunt resistors. So when you're in the Amps range, you're actually tapping that off. But when if you switch to Milliamps for example, you can still use those sense channels, they're still. you know, really beefy.

Quite tournament. You know, beefy terminals on them are usually on the current shut resistors. Then you can actually use that and feed the current back in Because remember, these, these are just basically just a join in there. It's just a solder joint or two tracers coming off or whatever that you know.

So you can still feed current through the sense line. And that's exactly how I do it on the micro car. so you can see how. Now we've actually eliminated our MUX here.

Beautiful. and that can be fed directly into our app here. And of course, we don't necessarily have to have a MUX here. We could put a a switch in here that actually switch the two ranges.

so actually take a quick look at that because there's a little trap in there. So it comes down to whether or not you want to use a MUX chip. you might have a spare MUX chip somewhere else in the design. In that case, Beauty You'd probably do it like that.

You'd either tap off the input or you tap off the output of your times ten ampere. But if you wanted to do it with, say, a single fit or something like that, a single FETs going to be cheaper than a MUX chip? maybe? it depends I Don't know like a MUX chip can be a simple 405 one. For example, you know 4000 series CMOS or the 7400 series equivalent. They're very common in multimeters.

If you open up multimeters, you'll find lots of seven 4hc 405 ones. For example, doing a lot of the switching in there because they cost like cents each. But if you wanted to get rid of the MUX you can do that and you can just have it as an amplifier like this. For example, straight into your amp.

positive negative in you can have your resistor and then that could go into a MOSFET I've drawn a Japheth there. but whatever, you know that can go into a switching MOSFET and then you can go like that and bingo Bob's your uncle. You can actually switch in whether or not you want your times 10. So if this is on equals times ten gain because if you actually break this circuit then this resistor is just flapping around in the breeze.

It's doing nothing. So you've just effectively created a voltage follow. You should be familiar with your Op Amp basics and just becomes a times 1 voltage follow. So you can switch in either x 1 or X 10.

But sometimes there's a trap for young players using this switching in your feedback path here. Not in this particular case, because these resistor values here can be. you know quite high. they can be you know 90 K and 10 K or you know something like that And in which case the on resistance of the MOSFET does not matter.

It doesn't actually affect. It's a pretty insignificant compared to say a 10 K there. But if you were happy, but if you had a say a high speed or Pampa something that use low value resistance then you might not want to actually switch this thing with a MOSFET. So in this particular case, what you do is you move your mosfet out of the feedback path and into the path of the input of your Op amp which is of course high impedance.

Now I've drawn the MOSFET as a switch. Here it could be a MUX a mosfet, a physical switch. whatever it is. anyway.

So we've moving it out of the path. so it's it. doesn't matter what the on resistance of this switch is, there's no current flowing through it because it's into the high impedance input of the Op amp. Here, it's outside that path.

So now the gain is purely determined by those two resistors, the MOSFET or switch or MUX or whatever. The resistance of that plays no part. And of course you would have to have two of them in here like that so that then you could just turn this one off and then turn that one on to get your voltage follower. Although you could technically have a high value resistor in there if that wasn't an issue and you wouldn't need your second switch there so you can switch it off and on.

So anyway, that's nothing really to do with this multimeter. You wouldn't implement it in a multimeter like this, but in some sort of other situation that can be real handy. And of course, as I said in the previous video there, it's important that this actually goes down to the top point on that 10-million resistor. So it's sensing directly across there.

So when we're in the Amps mode, that really matters because our 10 milli ohm shunt resistor where it's happening. our voltage on for their high impedance, so there's no drop across these. But you could introduce an error due to your ground configuration here, so it's important to tap it right off that. that's why these current shunt resistors come with four terminals, so there you go.

That's kind of groovy. That's how we'd probably implement that in practice if we wanted to go with exactly the same switching and range configuration that we had before, and that is quite a reasonable solution. Either way would work. There's other, maybe a couple of other configurations.

You can also do switching configurations to do it. If you had the range switches available, you could use those for switching and stuff like that. but that's is a neat solution I used in the Mike It works quite well, and you'll find this in a few multimeters as well. But as I briefly mentioned in the previous video, there's another method to doing this rather than use your X 10 amp.

let's say cuz these are expensive. These max 42:39 that are using my microcurrent. these are a couple of bucks a pop so they're actually even like in high volume in thousands our volume. so they're pretty expensive little beasts.

And also these fuses are expensive. What if there was a solution where we could get rid of the MUX amp because these have limited bandwidth as well. and of course chopper amps have like a little pole in them at the switching frequency and stuff like that. and we won't get into the details, but you know they might be a little bit troublesome.

So what if we could get away, get rid of the cost of that, get rid of the cost of this extra 600 milliamp or 1 amp fuse up here as well? because these Hrc fuses are a couple of bucks a pop as well even in volume, and just get away with the single 11 amp fuse here. and I mentioned MOSFET switching in the previous video. So that's what we'll take a quick look at now. and there are actually a couple at just a couple of meters on the market that actually do this particular technique that only use the one 10 or 11 app or 50 nephew's and then do all the switching with MOSFETs and once again, if you had the ranges on your rein switch, you'd go back to the old days before nullus newfangled auto-ranging rubbish.

If you had a manual range multimeter, you could actually switch to the various ranges on the multimeter and switch in. You wouldn't need MOSFET switch and you do it physically on the switch. You couldn't do it for the enter for the 10 amp range because you can't put 10 amps through one of those our PCB wafer switches. It's not going to work, but you could certainly do it in terms of all the other ranges they can easily handle.

In fact, almost every multimeter on the market has the milliamps up to 500 milliamps or whatever the count a particular count of the meter is going through those wafer PCB range switches and a few hundred milliamps like that is fine. Now, one of the problems with MOSFET switching is that as I said before, you have to switch this 10 milli ohm shunt resistor and it's like you've got 10 or 2 any amps momentarily on some multimeters and you've got to switch that. you can't do it with the wafer rain switch. So you've got to do it with a big beefy MOSFET you know, won't like in a big to-220 Dsquared pack.

You know, a decent package rated for 20 or 50 amps or something like that. A big MOSFET and they're a dime a dozen, right? Again, there's a million on the market that can actually do this. So an N-channel Big beefy N-channel MOSFET like this is required to switch our 10 milli ohms shan't resistance. And of course we don't want to increase our burden voltage.

So what you want to do is pick a particular MOSFET that has quite a low RDS on RDS Honor is just the drain source resistance. The drain and the source here is just the effective resistance. when you switch on that MOSFET hard and you know a decent one is any jellybean 1 is going to be less than 10 milliamps. And of course you want it to be less than 10 million ohms because you know, don't And if it's higher than that, then you're more than double in your shunt resistance here.

so you don't want to do that. you might pick a couple of millions. 5 milli ohms might be fine. And remember, you've also still got the resistance of your HRC fuse up here, so your MOSFET has to be as low as possible.

Now just using a single mosfet like this end channel works just fine. If you put a voltage on here, let's say you put 5 volts or you might ne 3 volts or something like that your multimeters only working from couple of batteries. it switches this MOSFET I won't explain how MOSFETs work but it switches on. It acts like a switch.

It's got like 5 or 10 million ideas on it's on resistance so effectively it's just works just like a resistor. and if the input goes negative because you might want to be measuring AC current for example, you might have put the probes in backwards. Then it works as a switch. It doesn't matter if this voltage on the gate is positive with respect to the source down here then, or Vgs is positive, Then it's going to switch it on and act like a switch.

and it works in both directions. Everything's hunky-dory Now it could actually put shunt resistors in parallel and then switch them like that. But hey, then we get into the same MUX problem that we did before. You'd have to switch all the different taps.

So we use our trick before. we've actually stating them in series like this. So we'll add our next shunt resistor. and the goal here is to have a different shunt resistor value for each and every range and we'll switch in the particular shunt resistance.

The reason that you want to do that is then we can eliminate the amplifier as we'll see later. So yes, we're going to need a different shunt resistor for each one. But MOSFETs A pretty treat. Shunt resistors are pretty cheap and we might have the space available because we've gotten rid of the extra few years.

We've only got the 111 air pipe here, which is shared between the ads, the milliamps, and the micro amps here, so stick with me. so we've added in the extra. Now we'll go up a decade because we're going from five amps to 500 milliamps. So if we have were happy with the 50 millivolt drop that we had before, then we'll stick with our 10 milli ohm shunt resistor here and our next one will have 50 millivolts drop as well.

Because then we're using a hundred milli ohms so A But we're using an order of magnitude less current order maybe two greater resistance, same voltage drop Ohm's law. So we put that off the tap once again to eliminate any issues there in terms of sensing. and then we had another MOSFET in up here. But because it's only 500 milliamps doesn't need to be nearly as beefy as this one over here, so you know it's still.

it still has to be reasonably beefy, but not as and not as good as this one. In fact, the unresisting scan be once again 10 times higher. But yeah, you could use any jellybean and channel MOSFET in their beauty. So now if we set this to zero volts, it'll switch off this MOSFET so that this shunt resistor is disconnected.

and if we put our voltage on there, then once again, the gate and the source here, the voltage or the gate normal actually here and here. Plus the voltage drop across that and that is gonna switch on this MOSFET And bingo we're using that one. No worries, and you guessed it, we just continue that ad nauseam. And there you have it.

I Almost ran out of whiteboard space here. but then you just cascade these in series. These shunt resistors right up to a hundred ohm so ten milli ohms, hundred milli ohms, one ohm, 10 ohms, and a hundred ohms. and they.

It's what you would use for all your different ranges. So we'd have to redo this table. But the good thing about this is that the the burden voltage is exactly the same on each particular range depending on the resistor you choose because we're going up by a decade 10 times an order of magnitude each time. So if you want to switch on your 500 milliamp range, well, this becomes zero volts your than zero volts on here.

their zero volts on here and you'd have your 5 volts or whatever switching on that MOSFET up there. And once, as I said, these ones down here, these three MOSFETs down here carrying 50 milliamps or less or five or hundreds of micro amps, they can be just nothing. MOSFETs You know they don't need any power handling capability at all. Really so.

and the RDS on it practically doesn't matter anymore, it's going to do the job provided Of course that the Vgs on is suitable here and you have to choose a particular mosfet. and I won't go into the details because that's a whole separate video of how to choose a mosfet for something like this that has a particular Vgs on voltage that you want and ensures that zero volts on here can genuinely switch all these other ones off. And you might think a hard day. There's a trap for young players here because we've cascaded them.

The Vgs here is going to be dependent upon the shunt resistor value because it's not between here and here. it's between here and here. and it's between here and here. And it's between here and here down here because you're going to get that drop across the shunt resistor.

But as we said, the maximum shunt resistor in the maximum burden voltage on each range is only 50 millivolts regardless of which range. Iran full-scale for a five thousand count multimeter, a fifty thousand count multimeter, then 50 millivolts. It doesn't really add much to the Vgs, so you might put this to zero. And yeah, this one here is 50 millivolts higher, but that's the mosfet is going to be off.

it's gonna be hard off. so that's pretty clever. By simple logic level drive On each one of these. MOSFETs you might want to get a logic level drive mosfet.

You can actually get those. There is just a particular characteristic that works nicely with, you know, typical 3.3 or 5 vote logic levels. Then you can just turn on each FET Like that and switch in the current shunt resistor beauty. And as before, the cascading nature of these resistors works as a voltage tap.

so you would actually have this going off. One single tap into our amplifier. our ADC or whatever it is. But because our burden voltage is slowed low, we don't need that times ten amplifier anymore.

We've actually gotten rid of it. If you're happy with the 50 millivolts plus the fuse a plus a tiny bit for the MOSFET as well burden voltage. And yeah, you know that's pretty good. So you just have this one tap point.

and even if you had this one here turned on and this one here, all the others turned off and you were measure and you're on your apps range here. it's the the voltage tap is on that four terminal things. So we've got no loss on our no errors introduced by a piece of B it goes through this resistor. can't go anywhere else.

This MOSFETs off, it's going to be super ridiculously high impedance, so it's effectively open circuit. Same with this one. Boom, and you've just got basically a hundred ohm in just over a hundred and ten hundred and eleven point One ohms going into your amplifier, which is high impedance so there's no drop across there. So you're tapping off that voltage.

You don't need any switching for the tax beauty. Alright, so if you redo our table down here like we had in the previous video for our new switching MOSFET configuration, we've got 50 millivolts burden voltage Just due to the shunt resistance on each range, you'd do the same as before. he says multiply the current by the range resistor. but because it's dropping by order mate changing by an order about the 2ds time, the 50 millivolts remains constant except for the 10 amp range.

But now let's not worry about that. Then and then we have our particular burden voltage specified in volts perhaps. And then we have the actual burden voltage because that was theoretical Over here is just theoretical due to the shunt resistor. But of course we have the MOSFET the RDS on of the MOSFET plus the 10 or 11 amps or whatever HIC fuse up here.

So it's going to be our 50 milli volt burden voltage. We have to add on another, the millivolts due to our HRC fuse up. here, it's going to be in the order of 10 million something like that cold resistance. It will actually increase when it heats up, but let's not get into those sort of details.

were just, you know. ballparks are the back of the envelope stuff here. 50 millivolts there plus 25 millivolts for the RDS on. this might be 5 milli ohms for example.

So 5 milli ohms times your 5 amp. 25 millivolts say a total burden voltage your true burden voltage across your terminals here on that 5 amp range. Yeah, at low ish, currents are until it heats up. Of course, the fuse heats up talking 125 millivolts something like that.

Still pretty decent. Not a problem on the apps range. Now it starts to get better and better as you go up the ranges, say the 500 milliamp range Here We still got our 50 millivolts to do our 100 milliohms shunt resistor here, but then because we've dropped our current by an order of magnitude. Ow.

But our fuse up here is still same fuse on all these ranges where as 50 millivolts before, it's now 5 millivolts and then let's just assume that we use the same MOSFET in here with the same RDS on. Then it's dropped from 25 millivolts to 2.5 So it starts to become much less significant. And of course, when you go up a range again, it starts to be less than an order of magnitude difference. So we just call it me 50 millivolts plus me best Spec Ever.

And that's the same for all these three ranges up here. So you can see how this configuration is actually better than the previous one we came up with because it was sweet. Only had one range here, which was met now with a three. or maybe even full with net beauty.

And of course we don't need the amplifier. we've just got times. One amplifier in there can go straight into the ADC the morning meter chipset. whatever.

So you don't need anything, but you've just got. You know, you know you've got five MOSFET switching configuration here, but you know MOSFETs are reasonably cheap as long as you the space for the layout and you were happy to buy the shunt resistors and everything else. it's actually a pretty good solution. I Like now, of course, if you wanted to actually improve what happens the 50 millivolts burden voltage, you could say decrease all these range resistors by an order of magnitude.

So this instead of 10 millions could become 1 milli ohm or maybe 5 milli ohms. You know, choose your value. doesn't matter. Drop them all by the same order and then you could use your times tener.

But if you drop this to 1 milli ohm 110 millions hun hundred milli ohms 1 ohm 10 ohms. then you use it just whack in a times 10 Yeah, but fixed times 10 amp. You don't have to change any of the gain on it, so that's an advantage from the previous circuit as well. But I know you're saying Dave You've forgotten all about the protection.

Where's the protection? You're gonna blow the ass out of this thing if you apply a voltage directly across it. Well, let's have a look at protection if you remember the circuit from the previous video, we actually had the a diode bridge across. the input for the milliamp ranges. only the apps' range kinda takes care of itself.

The apps' range is usually a big beefy sort of micro ohm resistance wire shunt in there so it's it's not gonna melt away anytime soon. And the MOSFETs got to be able to handle itself. It's big and beefy, you've chosen well, and the HRC fuse is going to blow. If you put any voltage across there which exceeds that 10 amp current, it'll just it'll blow so that's no worries.

But what happens when you've got this MOSFET disconnected? You've got zero volts here and then you apply it. so this MOSFETs switched off actively switched off and then you apply a voltage on. here. you can blow the arse out of this range resistor or this one or this one or this one if you apply voltage.

So we definitely need our back-to-back diode protection, just like we did last time. And I have a diode bridge across here to protect these lower ranges. Now we could just use the diode bridge again or back to back shot keys or whatever. right? You know, whatever you wanted to do.

But aha, we can reduce our bill of materials cost and by reusing the same component and using a property of our Big Fat Beefy MOSFET here, we've probably paid quite a few cents for this fed. here. we want to get our money's worth out of here. If you know your MOSFETs which you should, It has a diode in here.

caught a body diode because there's in the body of the construction of the MOSFET won't go into details. I've probably done that in my how our transistor Works video perhaps anyway, which I'm like linking down below. If you haven't, check that out. there's a reverse, effectively a reverse body diode in there, and these are usually pretty beefy in these big MOSFETs like this.

So we've already got diode protection in there if we put a positive here and a negative in there. Even if this MOSFET is switched off, the body diode doesn't switch off. it's always there. Its inherent, usually unwanted, often unwanted characteristic of this particular Dyer.

But in this case, it's actually really good. It's also good for some other configurations as well, but that diode. if you've got a positive one on here, we've still got. Remember our ten milli ohm Chakras is deeds of being beefy bit of wire practically short-circuit it's never going to blow, it's always going to be there so effectively.

We have diode protection across all these other resistors here. Beauty assuming that you put a negative voltage onto your input here. But what happens if you put positive? We want another diode on there. Yeah, we could just wake another suitable diet in there in terms of leakage and everything else on there.

But hey, we've already got this MOSFET in our Bill of Materials Uh-huh So what we do is we use our same MOSFET that were chosen here and we put it in the reverse direction. So now we've got the source here. the drain here. Whereas before the drain was here and the source was down like this.

Put it backwards, swap those two, and then we just join these two gates together like this and Bingo! We have another body diode in there like that back to back using the same Bill of Materials item so there's one less real. We put on our pick-and-place machine and everything else that comes down into. you know, just practical considerations for designing stuff like this. so you will use the same mosque.

Just put it back to back and it doesn't matter if you tie these two gates together, it'll still work exactly the same. You can go simulate this or build it up and try it out for yourself. Just put these back to back the the gate. This still operates the same as you put zero volts here.

The mosfet switches off. if you put five volts or 3.3 or whatever voltage you want on there, then it should switch on. And it works for both positive and negative currents. And now all of these range resistors here are entirely protected due to these body diodes and this big beefy 10 amp current.

Shut. Winner winner chicken dinner. So there you go. There's another look at how to reduce burden voltage in a typical multimeter.

and there's a couple of meters on the market that actually use MOSFET switching like this a Gossamer one in particular, and an old Tektronix R-tx 3a one as well, which was sold as the Fluke One Eight Nine for a brief 180 series for a brief period of time there and a MOSFET switching can actually work quite well, and you've reduced your cost. Maybe you'd have to do a whole bomb cost analysis, but you've only got one HRC fuse now we had two before, but now you've got some beefy MOSFETs in there. But you save the cost of your amplifier unless you wanted to decrease all these resistors and use a Times 10 amp. But you've gotten rid of the amplifier, you've gotten rid of any muxing considerations and stuff like that, and it's still protected.

And the good thing is, it's good for the user because you're less likely to blow a fuse on this. How many times have you blowing your Mili Amp range fuse on your body meter? Come on, put your hand up. Yeah, everyone's done it. It's much harder though to blow your amps range.

so we're using the big Beefy 11 air fuse to actually protect all these other, even the piddly little 50 of 500 micro @ range as well. And by the way, you can have a 50 micro amp range easily without any really any major noise issues. Apart from the usual are stuff, you'd stay a 50 millivolt full scale you know, another MOSFET and use a 1k resistor up there. We know it's a pretty nice configuration.

I Kind of like this. There's lots of advantages to it. Not a huge number of disadvantage, but you know this might be maybe a more expensive all up option, which is why a lot of manufacturers very few actually implement this except on real high-end expensive meters. So there you go: I Hope you learned something interesting here.

In terms of you know, it's amazing what you can do with such a simple thing. I Just want to reduce the burden voltage of a multimeter and you can go into all sorts of stuff and then you can get in the MOSFET selection and here you know you're getting the body diode and and pulse print, impulse response of your MOSFETs in your body diodes and everything else and how they withstand any pulse currents coming in and it can. You know you can really go down the design a rabbit hole there, but that's really interesting. We've got several interesting configurations there over these two videos.

To you know, reduce the burden voltage in multimeters and a lot of manufacturers. They just really don't bother. You can probably implement it with little or no additional cost. So as always, if you like that video, please give it a big thumbs up because that always helps a lot.

If you want to discuss it, links down below to the Eevblog forum and all that sort of stuff. and thank you to all my Patreon supporters, you want to support me. there's a patreon link at the end of the video usually and follow me on Twitter and all that sort of jazz social media stuff. you know.

Anyway, catch you next time you.