I'm really sorry about your heart condition ! And wish you a long life , love the way you are fighting it back with living the moments and sharing your knowledge with others 🌷🌷
I connect my mosfets differently: Source = from (P-chanel goes directly to VCC, N-chanel goes to GND), Drain = to (load) works the same way and makes more sense. Also it makes it easier to accomplish Vgs with less effort, avoiding voltage drops across source and load - since you usually need a resistor from G to S for fast switching, if you have a load connected to source it will create a voltage drop across the gate, making it enter the linear zone, heating up the mosfet and limiting the current - this is how i see it, correct me if i'm wrong.
If you use this for low voltage cutoff on a battery pack there is the issue that once cutoff is achieved, the circuit itself will continue to discharge the battery. What is the quiescent current of the circuit with the input source at your programmed cutoff level?
:D yha :D you just need a transistor, once the the (low) level is achieved then it cuts. To find correct transistor and the resistance is the only funny part of such exercise.
I just ran across this video and haven't seen the first, but if you use the voltage source to establish your reference voltage, will this circuit work for low battery cut-off? When the battery voltage lowers, doesn't the reference voltage do so also?
You can use a zener diode to make a simple voltage regulator as a reference voltage, because the ideal opamp input impendence is very high, it woun't suck big current, so a zener diode will to the trick very well. Maybe pick a 3.2V one(for Li-ion single cell cutoff voltage is pretty good I guess), series with the current limit resistance. That can provide you a fix voltage precise enough, even if the battery voltage below 3.2V, the zener diode just like open circuit, so the voltage is pulled high as supply voltage. The only one question is the opamp or comparator can work in very low voltage or not. The circuit is like VCC-(current limit resistance)-*-(3.2V break down zener diode)-GND If your VCC is higher than 3.2V, the * point will alway show 3.2V. If VCC is below, the * point will show you the VCC. Hope this will help.
You are correct. This is just an example though for basic understanding and simplicity. The reference voltage and the battery voltage should be seen as two separate and or independent variables. This way just means that he didn't have to use two power supplies or use a more complex circuit. There are ways to make a steady reference voltage from a battery but that would go beyond the purpose of this video. A simple off the top of my head one would be to use low drop out voltage regulator that outputs a voltage lower than your actual cutoff for the reference and use a divider for the input that would meet the reference at you desired actual battery voltage to cut off. Basically scale the voltage down at the comparator so it works at lower than cutoff voltage.
Yes, you're right. I'd look at something like a LT6703 which has a reference and some hysteresis built in. They have a spice model. I've hand soldered the tsot-23 version to breakout boards and directly to wires for prototyping. It's a bit fiddly but doable. You can make a simple reference voltage with a zener. IME, particularly around 3 volts, they are not great for that but they can be made to work.
393's also come in dual or quad versions and quads were widely used in circuits with led bar-graph type meters like older commercial PA equipment like mixer panels and wireless mic receivers., cheap battery chargers and some RVs also have them in the system monitors that read battery and liquids tank levels The LM3914, 15 and 16 are actually led bar drivers that are virtually plug and play. They wrap all the 393 circuitry into one IC that can support like 15 LEDs? or something. Old Telex wireless mic receivers used them in socketed form so I have a pile of them in my IC bin.
I have one or two questions and suggestions for this circuit. First, would it not have been better to use a p channel enhancement mode MOSFET? This would have had its source connected to the positive supply, with the drain supplying the load, and the gate only requiring a grounding connection to switch it on. This arrangement is compatible with the output of the comparator, which is open collector. As it is, using an N channel MOSFET with the source connected to the load, the voltage on the gate must be Vth (threshold voltage) above the load voltage to turn on the MOSFET, something difficult to achieve if the comparator circuit is powered by the battery it is monitoring. There are significant advantages using the +input as the voltage reference pin and using the -input as the voltage monitor, since when the battery voltage exceeds the +input reference, the comparator output goes low, providing the required drive for the P channel MOSFET to switch it on. It also makes it easier to apply added hysteresis to the circuit, by applying feedback to the +input. In a battery application, the resistor divider voltage will change with the battery voltage, as the comparator is powered from the battery. The solution might be to use a zener diode as the reference or the circuit on LED. Admittedly the zener takes more power to provide the reference, but it is not influenced by the comparator supply voltage until it falls below the zener voltage. With a little thought, it should be possible to convert the circuit to a boot strap arrangement, where the comparator and reference are powered from the switched side of the MOSFET, making the MOSFET effectively the switch for the product (the load). In any comparator circuit it is worth considering if additional hysteresis needs to be added to stop the circuit chattering around the switching point. This can be achieved by adding one more resistor to the existing circuit or maybe two, if a zener or LED is used as the voltage reference. It is good design practice to connect unused inputs to the voltage rails, unless the data sheet say this is unnecessary. This is to stop unused parts of the comparator drawing unnecessary power or going into oscillation. This also assumes the inputs are specified to include both rails in their input range. In testing this circuit, the battery rail should be adjusted to show correct switching operation across the full range of the battery voltage, remembering that for a practical circuit, the comparator is likely to be powered from the battery it is testing. In the configuration shown in the video, the battery voltage is emulated by a potentiometer, not by adjusting the supply voltage to the whole circuit. This is valid approach only if a separate supply is used to power the monitor circuit, as might be the case in monitoring a battery charger with mains supply or a bank of batteries in a telecom or IT installation. Particular attention needs to be paid to the switching point, where the circuit might burst into oscillation for a number of reasons associated with supply rail smoothing/0regulation or lack of adequate hysteresis in the comparator. It is also necessary to consider what happens if the unit is not switched off when the low battery voltage is reached. If the comparator remains powered by the battery, two undesirable events may occurs: 1) the small, but not insignificant, current drain of the monitor circuit may drain the battery beyond the point of recharge. 2) if the monitor is used to switch off the products supply using the power MOSFET, the monitors operation may become unpredictable below the normal operating range of the active elements in the circuit, unless this condition is considered as part of the design. This is all the more reason to design the circuit as a boot strap, so that it turns its self off below a critical battery voltage. Making the circuit do exactly what is required is not as trivial as the simple voltage monitor circuit might suggest. There are a number of design tricks needed to implement the boot strap and make it fail safe under all circumstances. In a real product design, it would also be necessary to consider where to place capacitors to ensure that the circuit would not be susceptible to RF interference. As a demonstration of the principles, the video is very good, but a practical design requires a slightly more complicated circuit.
@@geoepi321975 I did not cover the on/Off switching. With the suggested circuit, turning it on is easy, just pull the MOSFET gate low for a moment. This allows the monitor circuit to take over and hold the circuit on. Turning off is a bit more tricky. It is relatively easy if there is a momentary push button for on and another for off. It is then only necessary to make the battery voltage appear to be low, by pushing the off button to short the monitor point to ground at the input to the comparator. The circuit will then switch off. It is still necessary to check that pushing both on and off at the same time does not produce any undesired switching action. With a little consideration, either the last button released will win or off will win. Making the on/off switch toggle is a little more complicated. A momentary switch can be used to produce a toggle action. The trick here is to use the current state of the circuit (on or off) to select the next state. Given there is one comparator still unused in the comparator psckage, this gives the scope to engineer an on/off toggle. Though I would not be surprised that with a little thought, and understanding of the switching principle, that the suggested circuit can not be made to toggle just using steering diodes and a debounce capacitor. As I said, the trick is to use the current state to trigger the next required state. In this case, pressing the on/off button conditions the circuit for the next state, which is activated upon the button's release. This has the advantage that debounce is inherent to the design. Consider the following possible solution out of many: We know turning the circuit on is simple, just use a switch wired or in parallel with the first ( monitor) compatible output on the MOSFET gate input (forming a wired OR). This is used to force the MOSFET on while the button is pressed. Once on, the comparator is powered, the voltage monitor output takes over driving the MOSFET gate, provided the battery voltage is detected to be sufficiently high. To turn the circuit off: while in the on state, the button is pressed and held down for a sufficient time to allow a capacitor connected between the second comparator +input and the switched positive rail to be charged via a series resistor and diode connected to the button.. Once this +input voltage falls below the -input reference, the second comparator output will switch low, pulling down the voltage monitor input of the first comparator to which it is connected. This fools the monitor circuit into detecting the battery voltage is low. The first comparator then removes the drive to the MOSFET gate, turning it off, switching off the circuit. Once off, the capacitor on the second comparator is discharged either by a high value resistor across it, or a reverse biased diode to the switched supply rail. The latter has the advantage that the circuit is ready to switched back on as soon as the switched supply rail is truly off. This is because in the off state the switched supply rail is at ground potential, providing a discharge path for the capacitor. The switching action is as follows: press the button momentarily while in the off state, and the circuit turns on. Hold the button down for a short delay in the on state, and when its released the circuit will turn off. The circuit does not need lots of additional components, as the same reference voltage can be used for both comparators. Notes: it is necessary to connect a high value resistor between the MOSFET gate and the unswitched positive rail to ensure the MOSFET is held off when neither the button or the first comparator are driving it to the on state. As a consequence of the pull up resistor on the MOSFET gate, it is necessary to use a diode to isolate the +input of the second comparator from the unswitched supply voltage on the MOSFET gate..
My apologies to anyone who has watched me repeatedly edit the above postings. My excuse is that I am using a small android tablet to write these posts and edit on line, rather than compose them off line before posting.
Way cool! I'm using solar panels and a buck converter to charge a 50AH LiFePO4 power pack, but it has no under voltage protection to avoid thermal runaway. With this circuit, I could also add a thermal sensor to the other half of the LM393 to avoid charging below freezing. Thanks!😎
there is a problem. when I use a LIPO with full charge the voltage is 4.2 Volt. the refence voltage will be 2.1 Volt. then I adjust the potentiometer, so the ligth will be on. if the LIPO is empty, the voltage will be 3 volt. the reference voltage will be 1.5 Volt. But the voltage on the potentiometer will be 2 Volt. than I drain the LIPo more. with 2.6 Volt the reference voltage will be 1.3 Volt, but the voltage on the pot will be 1,8 Volt. Every drop on the Lipo takes a drop at the reference Voltage and the potentiometer Volt !
Thanks Paul! I´ve never considered using an n-channel mosfet on the positive side... Hmm... Great Christmas day projekt... Have a great X-mas paul! ...And a happy newyear too. :)
What if you used a zener diode on the comparitor power pin so once it shuts the circuit off the comparitor would bleed the voltage down a tiny amount more and the zener would stop flowing current ?
Now use a Zener Diode or other V Ref device to provide a Accurate Voltage Reference. A 3 volt zener would be handy working on li Ion Cells for the Low Cut Off . Handy Circuits these are. Did you know you can use various color LED to provide a Voltage Reference ?
And if the solar panel that puts out 10 amps of current..? How are you supposed to connect that to a lm324n..? Capacitor in parallel with the panel? Seeing how capacitors don't allow DC current through...
And now expert level: use multiple of those comperators to show high, medium and low level of the battery and then a 4th stage to cut off. Would make an interesting follow up video I think?
Merry Xmas to you and your family too Paul and thanks for all videos created and shared again this year. Always fun to watch and learn something new. Cheers!
Ok question here..i dont think the LED should be in the source line?, because N channel works by voltage difference between gate to source. Since the LED will create some voltage (granted its only .7V), this forces you to have to make the gate an even higher voltage to stay on correctly. The LED should be in the drain I believe, that way you avoid any gate voltage offset like you are going to get with how you have it here. I just dont want people to see this video and put thier loads into the source and then not be able to turn the mosfet fully on because now there is a gate to source offset, that resistor will add even more voltage offset, i am wondering if you are even turning on the mosfet fully beause of this Measure the voltage at the source pin to ground and see what it is, then subtract that from the gate voltage. For this mosfet it has to be 4 to volts to turn on fully for min rds (on) otherwise if its lower than that its on partial and you waste energy in the switch.
what if we don't have 10 volt supply voltage but we only have the battery itself? lets say a 12 volt battery with a led indicator for a voltage below 11 volts?
I know it is a bit more work for you, but a schematic being shown somewhere in the video here is very helpful for me and it stops me from looking elsewhere in others videos for the answer.
Great practical use for the circuit. It might be helpful to link a couple circuits together to show that they can be parts of a larger circuit. Merry Christmas Paul and happy new year. You are my favorite UA-camr and a great friend.
hi, this circuit will not work in practice, you need to add a Schmitt trigger to the circuit, once you disconnect the power of the circuit the voltage rises and it connects again
Merry Christmas to you Paul! And thanks for telling us the secret how to protect our batteries. However I am still wondering how to use this is if the total circuit (for instance a 9 Volt power supply for a DSO-150) is powered by 4p lion cells. How can the power supply shut off the 18650 cells when it sees only 3 volts?
I have this question for you... say my supply voltage is dropping as in trying to monitor a battery voltage as supply then what happens is the voltage divider is also following this drop thus the reference voltage and then the battery just keeps running the load (in this case a small 100mA fan)... so I'm guessing here is that I need to put in a zener diode and current limiting resister to hold that reference voltage at 10.5vdc so this circuit can cut off the fan load and thus save the supply battery from over discharging !! Can you please help on this one.
@ Steve Surick I came to the same conclusion. If we are going to monitor the battery, the trimpot should be regulating the whole circuit simulating voltage drop from the battery. Otherwise the voltage divider does not give a valid reading. Admittedly, I have not tried the circuit.
Love it. Tell me. How would you use this circuit in an actual project you need to put this circuit in, can you give me/us an EXAMPLE. If this make any sense too you. Or can you do another video which shows how this circuit would actually function in a project device... Keep these's great electronic circuits coming. THUMBS UP.
nice!! that was cool the way you showed what it could be used for.. i think it wount'nt be a bad idea to do the same with some(not necessarily all) of your "classic circuits you should know"
I wonder how to go about having things cut off entirely at under voltage. Presumably the battery is still draining a little bit even after the load circuit is "off". Happy Christmas!
I don't understand how this can work as a battery cutoff. I assume you are using the pot to simulate the battery getting lower over time by lowering the voltage into the opamp. However the voltage divider is still based on the full 10v input to create a constant 5v reference. In a true battery scenario wouldn't this reference voltage also drop as the battery voltage decreases? I am a hobbyist so perhaps I'm missing something.
@DJ Mick: Excellent point. If you want cutoff at a specified voltage, you'll need a reference. I'm used to seeing Zener diodes used for this, or sometimes a series stack of several diodes (adding up their forward drops). LM393 spec sheet from TI does not show a voltage reference within the chip.
That is correct, you would need some kind of reference like zener or 431 reference which is very commonly used in all kinds of power supplies for output regulation
It is very difficult to see because Paul's hand is in the way. Two things that sound plausible to me: 1. The jumper wire from the gate shorted to the V+ side of the circuit while moving it around. - or - 2. The jumper wire from the gate of the MOSFET touched Paul's finger and in turn Paul touched the V+ side of the circuit. In both cases this would be enough to charge the gate of the MOSFET and turn it on.
2:37 Lit as Paul made finger contact with the bare end of the wire. Either providing a path to earth through his body, or hand brushing against another component. Worth analysing for sake of beginners, and just out of curiosity.
yes Dustin I think no.2 is what might of happened coz I looked at it over a good few times to see if the jumper its self touched a +V but couldn't see right. I think maybe his finger touched and it was very close or even contacting his finger too. I knew I wasn't seeing things!! thanks for answering!!
Khakoo is right. Inductive coupling through mu body opened the channel. If you want to see a very explanation of this effect watch Julian Ilet's MOSFET experiments.
I will do Paul thank you, ya know iv never played with mosfets!! I must get some the next time I online buying stuff. and some Jfets. actually now I remember you were playing with a Jfet one time showing how sensitive the gate was by connecting an antenna(piece of wire) to the gate and using touch to activate. il check out Julian's page, nice one.
I'm really sorry about your heart condition ! And wish you a long life , love the way you are fighting it back with living the moments and sharing your knowledge with others 🌷🌷
I connect my mosfets differently: Source = from (P-chanel goes directly to VCC, N-chanel goes to GND), Drain = to (load) works the same way and makes more sense.
Also it makes it easier to accomplish Vgs with less effort, avoiding voltage drops across source and load - since you usually need a resistor from G to S for fast switching, if you have a load connected to source it will create a voltage drop across the gate, making it enter the linear zone, heating up the mosfet and limiting the current - this is how i see it, correct me if i'm wrong.
If you use this for low voltage cutoff on a battery pack there is the issue that once cutoff is achieved, the circuit itself will continue to discharge the battery. What is the quiescent current of the circuit with the input source at your programmed cutoff level?
:D yha :D
you just need a transistor, once the the (low) level is achieved then it cuts. To find correct transistor and the resistance is the only funny part of such exercise.
I pray and hope you have a Merry Christmas, and a "blessed" Happy New Year 😎😇 😎
I just ran across this video and haven't seen the first, but if you use the voltage source to establish your reference voltage, will this circuit work for low battery cut-off? When the battery voltage lowers, doesn't the reference voltage do so also?
Yes it does but that drop can be taken into account at the divider.
You can use a zener diode to make a simple voltage regulator as a reference voltage, because the ideal opamp input impendence is very high, it woun't suck big current, so a zener diode will to the trick very well.
Maybe pick a 3.2V one(for Li-ion single cell cutoff voltage is pretty good I guess), series with the current limit resistance. That can provide you a fix voltage precise enough, even if the battery voltage below 3.2V, the zener diode just like open circuit, so the voltage is pulled high as supply voltage.
The only one question is the opamp or comparator can work in very low voltage or not.
The circuit is like
VCC-(current limit resistance)-*-(3.2V break down zener diode)-GND
If your VCC is higher than 3.2V, the * point will alway show 3.2V.
If VCC is below, the * point will show you the VCC.
Hope this will help.
You are correct. This is just an example though for basic understanding and simplicity. The reference voltage and the battery voltage should be seen as two separate and or independent variables. This way just means that he didn't have to use two power supplies or use a more complex circuit. There are ways to make a steady reference voltage from a battery but that would go beyond the purpose of this video.
A simple off the top of my head one would be to use low drop out voltage regulator that outputs a voltage lower than your actual cutoff for the reference and use a divider for the input that would meet the reference at you desired actual battery voltage to cut off. Basically scale the voltage down at the comparator so it works at lower than cutoff voltage.
Yes, you're right. I'd look at something like a LT6703 which has a reference and some hysteresis built in. They have a spice model. I've hand soldered the tsot-23 version to breakout boards and directly to wires for prototyping. It's a bit fiddly but doable.
You can make a simple reference voltage with a zener. IME, particularly around 3 volts, they are not great for that but they can be made to work.
Wonderful explanation dear sir. Great feeling when you said you all are my family and friends. Awesome. ❤️
393's also come in dual or quad versions and quads were widely used in circuits with led bar-graph type meters like older commercial PA equipment like mixer panels and wireless mic receivers., cheap battery chargers and some RVs also have them in the system monitors that read battery and liquids tank levels
The LM3914, 15 and 16 are actually led bar drivers that are virtually plug and play. They wrap all the 393 circuitry into one IC that can support like 15 LEDs? or something. Old Telex wireless mic receivers used them in socketed form so I have a pile of them in my IC bin.
I have one or two questions and suggestions for this circuit.
First, would it not have been better to use a p channel enhancement mode MOSFET? This would have had its source connected to the positive supply, with the drain supplying the load, and the gate only requiring a grounding connection to switch it on. This arrangement is compatible with the output of the comparator, which is open collector. As it is, using an N channel MOSFET with the source connected to the load, the voltage on the gate must be Vth (threshold voltage) above the load voltage to turn on the MOSFET, something difficult to achieve if the comparator circuit is powered by the battery it is monitoring.
There are significant advantages using the +input as the voltage reference pin and using the -input as the voltage monitor, since when the battery voltage exceeds the +input reference, the comparator output goes low, providing the required drive for the P channel MOSFET to switch it on. It also makes it easier to apply added hysteresis to the circuit, by applying feedback to the +input.
In a battery application, the resistor divider voltage will change with the battery voltage, as the comparator is powered from the battery. The solution might be to use a zener diode as the reference or the circuit on LED. Admittedly the zener takes more power to provide the reference, but it is not influenced by the comparator supply voltage until it falls below the zener voltage. With a little thought, it should be possible to convert the circuit to a boot strap arrangement, where the comparator and reference are powered from the switched side of the MOSFET, making the MOSFET effectively the switch for the product (the load).
In any comparator circuit it is worth considering if additional hysteresis needs to be added to stop the circuit chattering around the switching point. This can be achieved by adding one more resistor to the existing circuit or maybe two, if a zener or LED is used as the voltage reference.
It is good design practice to connect unused inputs to the voltage rails, unless the data sheet say this is unnecessary. This is to stop unused parts of the comparator drawing unnecessary power or going into oscillation. This also assumes the inputs are specified to include both rails in their input range.
In testing this circuit, the battery rail should be adjusted to show correct switching operation across the full range of the battery voltage, remembering that for a practical circuit, the comparator is likely to be powered from the battery it is testing.
In the configuration shown in the video, the battery voltage is emulated by a potentiometer, not by adjusting the supply voltage to the whole circuit. This is valid approach only if a separate supply is used to power the monitor circuit, as might be the case in monitoring a battery charger with mains supply or a bank of batteries in a telecom or IT installation.
Particular attention needs to be paid to the switching point, where the circuit might burst into oscillation for a number of reasons associated with supply rail smoothing/0regulation or lack of adequate hysteresis in the comparator.
It is also necessary to consider what happens if the unit is not switched off when the low battery voltage is reached.
If the comparator remains powered by the battery, two undesirable events may occurs:
1) the small, but not insignificant, current drain of the monitor circuit may drain the battery beyond the point of recharge.
2) if the monitor is used to switch off the products supply using the power MOSFET, the monitors operation may become unpredictable below the normal operating range of the active elements in the circuit, unless this condition is considered as part of the design. This is all the more reason to design the circuit as a boot strap, so that it turns its self off below a critical battery voltage.
Making the circuit do exactly what is required is not as trivial as the simple voltage monitor circuit might suggest. There are a number of design tricks needed to implement the boot strap and make it fail safe under all circumstances. In a real product design, it would also be necessary to consider where to place capacitors to ensure that the circuit would not be susceptible to RF interference.
As a demonstration of the principles, the video is very good, but a practical design requires a slightly more complicated circuit.
Waoo!
@@geoepi321975 I did not cover the on/Off switching. With the suggested circuit, turning it on is easy, just pull the MOSFET gate low for a moment. This allows the monitor circuit to take over and hold the circuit on. Turning off is a bit more tricky. It is relatively easy if there is a momentary push button for on and another for off. It is then only necessary to make the battery voltage appear to be low, by pushing the off button to short the monitor point to ground at the input to the comparator. The circuit will then switch off. It is still necessary to check that pushing both on and off at the same time does not produce any undesired switching action. With a little consideration, either the last button released will win or off will win.
Making the on/off switch toggle is a little more complicated. A momentary switch can be used to produce a toggle action. The trick here is to use the current state of the circuit (on or off) to select the next state. Given there is one comparator still unused in the comparator psckage, this gives the scope to engineer an on/off toggle. Though I would not be surprised that with a little thought, and understanding of the switching principle, that the suggested circuit can not be made to toggle just using steering diodes and a debounce capacitor.
As I said, the trick is to use the current state to trigger the next required state. In this case, pressing the on/off button conditions the circuit for the next state, which is activated upon the button's release. This has the advantage that debounce is inherent to the design.
Consider the following possible solution out of many:
We know turning the circuit on is simple, just use a switch wired or in parallel with the first ( monitor) compatible output on the MOSFET gate input (forming a wired OR). This is used to force the MOSFET on while the button is pressed. Once on, the comparator is powered, the voltage monitor output takes over driving the MOSFET gate, provided the battery voltage is detected to be sufficiently high.
To turn the circuit off: while in the on state, the button is pressed and held down for a sufficient time to allow a capacitor connected between the second comparator +input and the switched positive rail to be charged via a series resistor and diode connected to the button.. Once this +input voltage falls below the -input reference, the second comparator output will switch low, pulling down the voltage monitor input of the first comparator to which it is connected. This fools the monitor circuit into detecting the battery voltage is low. The first comparator then removes the drive to the MOSFET gate, turning it off, switching off the circuit. Once off, the capacitor on the second comparator is discharged either by a high value resistor across it, or a reverse biased diode to the switched supply rail. The latter has the advantage that the circuit is ready to switched back on as soon as the switched supply rail is truly off. This is because in the off state the switched supply rail is at ground potential, providing a discharge path for the capacitor.
The switching action is as follows: press the button momentarily while in the off state, and the circuit turns on. Hold the button down for a short delay in the on state, and when its released the circuit will turn off.
The circuit does not need lots of additional components, as the same reference voltage can be used for both comparators.
Notes: it is necessary to connect a high value resistor between the MOSFET gate and the unswitched positive rail to ensure the MOSFET is held off when neither the button or the first comparator are driving it to the on state.
As a consequence of the pull up resistor on the MOSFET gate, it is necessary to use a diode to isolate the +input of the second comparator from the unswitched supply voltage on the MOSFET gate..
My apologies to anyone who has watched me repeatedly edit the above postings. My excuse is that I am using a small android tablet to write these posts and edit on line, rather than compose them off line before posting.
Yes
@@gapadad2 yes?
Great video Paul. I'm experimenting with the LM393 using infrared red receiver
Seasons greetings Paul, you're a lovely bloke and a pleasure to listen to
Way cool! I'm using solar panels and a buck converter to charge a 50AH LiFePO4 power pack, but it has no under voltage protection to avoid thermal runaway. With this circuit, I could also add a thermal sensor to the other half of the LM393 to avoid charging below freezing. Thanks!😎
there is a problem. when I use a LIPO with full charge the voltage is 4.2 Volt. the refence voltage will be 2.1 Volt. then I adjust the potentiometer, so the ligth will be on. if the LIPO is empty, the voltage will be 3 volt. the reference voltage will be 1.5 Volt. But the voltage on the potentiometer will be 2 Volt. than I drain the LIPo more. with 2.6 Volt the reference voltage will be 1.3 Volt, but the voltage on the pot will be 1,8 Volt.
Every drop on the Lipo takes a drop at the reference Voltage and the potentiometer Volt !
Thanks Paul! I´ve never considered using an n-channel mosfet on the positive side... Hmm... Great Christmas day projekt... Have a great X-mas paul! ...And a happy newyear too. :)
I love these kind of videos of yours please keep doing them. Great comments from the folks watching as well. Happy Christmas
merry xmass to you too
Have a Merry Christmas, and a wonderful Happy New Year
What if you used a zener diode on the comparitor power pin so once it shuts the circuit off the comparitor would bleed the voltage down a tiny amount more and the zener would stop flowing current ?
Now use a Zener Diode or other V Ref device to provide a Accurate Voltage Reference. A 3 volt zener would be handy working on li Ion Cells for the Low Cut Off . Handy Circuits these are. Did you know you can use various color LED to provide a Voltage Reference ?
Merry Christmas to you too. And have an excellent new year!
And if the solar panel that puts out 10 amps of current..? How are you supposed to connect that to a lm324n..? Capacitor in parallel with the panel? Seeing how capacitors don't allow DC current through...
Hi,,Is it ok to connect the load at the source terminal?
Hope you have a great Christmas and a happy New Year, all the best Joe
Can you just use the other comparator? Want to use as hi low battery indicator green when batteries fine and red when batteries low.
And now expert level: use multiple of those comperators to show high, medium and low level of the battery and then a 4th stage to cut off. Would make an interesting follow up video I think?
Thank you for the follow up video. Your channel has inspired me to start building and experimenting with circuits. Merry Christmas!
Merry Christmas and a happy new Year!
Merry Xmas to you and your family too Paul and thanks for all videos created and shared again this year. Always fun to watch and learn something new. Cheers!
Thank you for another bit of education for me. Have a Very Merry Christmas and hoping the new year bring good things for you.
Nice and simple. Thanks Paul.
Merry Christmas and stay warm. ⛄⛄⛄
Ok question here..i dont think the LED should be in the source line?, because N channel works by voltage difference between gate to source. Since the LED will create some voltage (granted its only .7V), this forces you to have to make the gate an even higher voltage to stay on correctly. The LED should be in the drain I believe, that way you avoid any gate voltage offset like you are going to get with how you have it here. I just dont want people to see this video and put thier loads into the source and then not be able to turn the mosfet fully on because now there is a gate to source offset, that resistor will add even more voltage offset, i am wondering if you are even turning on the mosfet fully beause of this
Measure the voltage at the source pin to ground and see what it is, then subtract that from the gate voltage. For this mosfet it has to be 4 to volts to turn on fully for min rds (on) otherwise if its lower than that its on partial and you waste energy in the switch.
what if we don't have 10 volt supply voltage but we only have the battery itself? lets say a 12 volt battery with a led indicator for a voltage below 11 volts?
Love this practical case on a great circuit to use in projects. Expand on it as you see fit! Merry Christmas to you and the family!
Brilliant, my friend...well done
I know it is a bit more work for you, but a schematic being shown somewhere in the video here is very helpful for me and it stops me from looking elsewhere in others videos for the answer.
Merry Christmas Paul & family. Thanks for all of your 2019 videos.
Hey Paul! Merry Christmas to you and your family! Thanks for sharing your knowlage! I learned so much from you! Best wishes from Austria!
Greetings from Hong Kong. Thank you for making so many great videos throughout the year! Merry Christmas and happy holidays to you too!~
Thank you so much and Merry Christmas , from Québec !
so, where is the circuit? just breadboard..
Thank you sir. Love for you from India
Great practical use for the circuit. It might be helpful to link a couple circuits together to show that they can be parts of a larger circuit. Merry Christmas Paul and happy new year. You are my favorite UA-camr and a great friend.
Merry Christmas Paul
Thanks for all the great videos. Much appreciated
Merry Christmas, its always a pleasure watching your videos.
Excellent ideas here.Happy Holidays to you too.
Merry Christmas Paul hope you have a wonderful holiday season.
Merry Christmas to you Professor Paul!
Is there a similar circuit for a 240v volt battery?
Thanks
hi, this circuit will not work in practice, you need to add a Schmitt trigger to the circuit, once you disconnect the power of the circuit the voltage rises and it connects again
Hello! Where can I find the previous video?
God Bless You Too... Thank You, Merry Christmas and Happy New Year
Thanks for another great vid, Paul. Merry Christmas!
Happy holidays! Take care and have fun! Keep up the good work.
Nice demonstration Paul. Merry Xmas. Patron 👍
great christmas gift, thankyou
Cool, simple and a usable circuit. And your explanation is superb. Thanks!
Thanks for your insights on this channel. God bless you and Merry Christmas.
You know that battery voltage drops over time/usage and your comparator compares two lover voltages?
Could you show this circuit cutting off a battery under load please?
Wish you a Merry Christmas to you and your family too. 😊
Merry Christmas Paul!
Merry Christmas to you Paul! And thanks for telling us the secret how to protect our batteries. However I am still wondering how to use this is if the total circuit (for instance a 9 Volt power supply for a DSO-150) is powered by 4p lion cells. How can the power supply shut off the 18650 cells when it sees only 3 volts?
Thank you 🙏 Merry Christmas 🎄
Merry Christmas Paul ..
Sir how to use this circuit for 7.0ah battery charger
I have this question for you... say my supply voltage is dropping as in trying to monitor a battery voltage as supply then what happens is the voltage divider is also following this drop thus the reference voltage and then the battery just keeps running the load (in this case a small 100mA fan)... so I'm guessing here is that I need to put in a zener diode and current limiting resister to hold that reference voltage at 10.5vdc so this circuit can cut off the fan load and thus save the supply battery from over discharging !! Can you please help on this one.
@ Steve Surick I came to the same conclusion. If we are going to monitor the battery, the trimpot should be regulating the whole circuit simulating voltage drop from the battery. Otherwise the voltage divider does not give a valid reading. Admittedly, I have not tried the circuit.
Thank you Paul ;)
For you and your family also Merry Christmas.
Really interesting circuit, dude! Thanks a lot! 😃
Merry Christmas, everybody! 😊
Love it. Tell me. How would you use this circuit in an actual project you need to put this circuit in, can you give me/us an EXAMPLE. If this make any sense too you. Or can you do another video which shows how this circuit would actually function in a project device... Keep these's great electronic circuits coming. THUMBS UP.
And a really Merry Christmas & Happy New Year to you and yours!
By the way, nice video as always!
Brilliantly Clear as Always...🎄
Another excellent video, Have a Very Merry Christmas
Hey Paul!
Thanks for
Have a nice Holiday, Paul!🎄
You too Robert!!!!
Great vid and a merry Christmas to you and your family.
👍👍👍
nice!! that was cool the way you showed what it could be used for.. i think it wount'nt be a bad idea to do the same with some(not necessarily all) of your "classic circuits you should know"
Merry Christmas! God Bless!
Thank you sir for really good videos. I was looking to build a solar power battery charger and this looks like what I want to add to the circuit.
Merry Christmas!!!!
This circuit is not worked with battery because load or no load voltage is different when battery is low. Please test and correct this circuit.
I wonder how to go about having things cut off entirely at under voltage. Presumably the battery is still draining a little bit even after the load circuit is "off". Happy Christmas!
thanks for the lesson as always fam
Good stuff. Merry Christmas to you and yours!
Same to you buddy!
Merry Xmas & a Happy New Years to you & yours as well. So can we replace the mosfet with an optocoupler? Thanks & have a great one.
Merry Christmas
And to you and your family
It is better to use a zener as voltage reference in this case.
Where is the schematic
Merry Christmas to you and your family also. :-)
Wait you don't use your UT61E anymore?
Is there adequate hysteresis in order to prevent switching oscillation on the cusp of voltage cut-off?
there is no hysteresis here, it is a simple demonstration circuit and will not work in real life
Merry Xmas
A zener diodes does the same thing for over voltage cut a low cut
Thanks for the video
Merry Christmas :)
Merry Christmas 😄
I don't understand how this can work as a battery cutoff. I assume you are using the pot to simulate the battery getting lower over time by lowering the voltage into the opamp. However the voltage divider is still based on the full 10v input to create a constant 5v reference. In a true battery scenario wouldn't this reference voltage also drop as the battery voltage decreases? I am a hobbyist so perhaps I'm missing something.
@DJ Mick: Excellent point. If you want cutoff at a specified voltage, you'll need a reference. I'm used to seeing Zener diodes used for this, or sometimes a series stack of several diodes (adding up their forward drops).
LM393 spec sheet from TI does not show a voltage reference within the chip.
That is correct, you would need some kind of reference like zener or 431 reference which is very commonly used in all kinds of power supplies for output regulation
Amazing. Thank u!
Great video! ☺
p.s that green led lit up before you connected the gate!!!! or am i seeing things..
It is very difficult to see because Paul's hand is in the way. Two things that sound plausible to me: 1. The jumper wire from the gate shorted to the V+ side of the circuit while moving it around. - or - 2. The jumper wire from the gate of the MOSFET touched Paul's finger and in turn Paul touched the V+ side of the circuit. In both cases this would be enough to charge the gate of the MOSFET and turn it on.
2:37 Lit as Paul made finger contact with the bare end of the wire. Either providing a path to earth through his body, or hand brushing against another component. Worth analysing for sake of beginners, and just out of curiosity.
yes Dustin I think no.2 is what might of happened coz I looked at it over a good few times to see if the jumper its self touched a +V but couldn't see right. I think maybe his finger touched and it was very close or even contacting his finger too. I knew I wasn't seeing things!! thanks for answering!!
Khakoo is right. Inductive coupling through mu body opened the channel. If you want to see a very explanation of this effect watch Julian Ilet's MOSFET experiments.
I will do Paul thank you, ya know iv never played with mosfets!! I must get some the next time I online buying stuff. and some Jfets. actually now I remember you were playing with a Jfet one time showing how sensitive the gate was by connecting an antenna(piece of wire) to the gate and using touch to activate. il check out Julian's page, nice one.
You are great
You need to use the schematic more for explanation.