Oh sweet, this is the first tutorial on high side switching that simply explains the bootstrap caps - diode and how to choose them! Thanks a lot Julian!
OMG, thank you! I was turning crazy all day trying to undesrtand trully a mosfet on its different configurations. Finally some wonderfull person explains it with clarity and in a practical manner. Thank you again. :)
This man addresses the capacitance issue that, I think, no other UA-camrs mentions! So now I know that capacitance of a discrete capacitor needs to be AT LEAST 2000 times bigger than that of integrated/body capacitance of MOSFET.
The origin of the bootstrap circuit has its real meaning when there was a young very tired boy who wanted to go upstairs to his room to sleep and he told his mother that what he was going to do to avoid climbing the stairs was to put on his boots and then pull the boot laces up with his hands as hard as he could to lift himself up. A circuit diagram would have been very helpful. There is a very interesting bootstrap circuit where the low side MOSFET is used with the high side MOSFET to make a half bridge and the low side MOSFET acts as a two role unit, providing the power output and also the bootstrap control system. Bootstrapping is a logic that most young people should learn about. It is a philosophy that can be put into real practice ...........that of lifting oneself by the laces on his boots!
While a schematic would have added to this; this is a great demo of how and why bootstrapping works :) I could NOT work it out for the life of me before seeing this.
ive been watching this set of videos for the last few months and finally i got some transistors to try. this is awesome! thank you so much and i hope to see more, maybe something with two transistors being used at once for polarity swapping?
I should've watched this before I whacked a PNP in a blinker relay :/ I needed the high side switch there and was forced to use a PNP 'cause I ran into the same problem (gate-source equilibrium you talked about). I didn't have any P-channel MOSFET's and I had limited time to make that damn blinker relay. Now I will use a bootstrap for applications like that, charge leakage won't matter there 'cause the MOSFET will be on for a short period of time, then off and when it's off, the bootstrap cap will recharge. Really nice tutorial, thanks for sharing!
It says 10volts for gate to source because thats the MOSFET "fully on", but you can drive them at any level under that, usually down to 4v,(or some drive at logic level) and it just passes less current.
Yes you are right, the SM72442 (the little brother of the SM72445 ) is 6€ and the SM72295 is 4.5€ from elements14. The circuit seems to be complicated also to my eyes, but i like the i2c interface and the integrated current and voltage sensors (except for shunt resistances on the high side). I'll study the datasheet again to understand whether all those external components are needed for my use.
Yesss!!! I was able to do it by my self after this video, understanding what I was doing :D My dream of a solar powered rc airplane is now one centimeter closer :) I'm still not sure whether to use a buck converter as you are doing or try the couple SM72445 SM72295
Actually, there are P-channel FETs available today that have every bit as low on-resistance as N devices. Check out the Infineon MOSFETs on Mouser.com, for a given voltage rating, they have comparable on resistance to N channel ones. They're available in any package you want, including TO-220. They're even a similar price! P channels will probably always be somewhat more expensive--but they've gotten much cheaper. Thing is, they still have a lot higher gate charge than N channel devices, so make sure the gate drive circuitry is up to snuff.
+BasementEngineer n channel msofets are still very popular for highside because of the price and because of the Vgsmax. Also because that makes it easier to create symmetrical H Bridges
thanks for the explanation.i have two n channel mosfets and want to control the high side of a circuit with one or if needed both of them with a signal of an arduino which can output 3V. Drain to source voltage is 5 volts. How could i make an arrangement of mosfets to achieve this?
Hello. Thank You for the great tutorial. I have a question regarding a low side technique, I am currently connecting an IGBT in parallel with a resistor and is supplied from a 9v battery. The igbt is driven from an L6384E gate driver such that its low side (pin 5) is connected to the IGBT's gate. am not connecting any c_boot since am only using the low side. The problem is that the switch is overheating unexpectedly, and there appears to be a 0.5v on the emitter of the igbt. Could you please explain as to why my IGBT is overhrating?! Thanks in advance
Nice job on this 4-part series. It was very helpful. I have a small issue perhaps you can help with.. I'm building a motor controller to switch on and off a DC motor (around 75 amps). My N-channel MOSFET has the TO-220 tab connected to the drain. So... when i bolt the MOSFET to the heat sink then bolt the heat sink to a chassis, it will short out (the chassis will be used for grounding things like lights, horn etc). I guess i need to insulate the MOSFET to the heat sink or the heatsink to the chassis? My mosfet is a Texas Instruments csd18535kcs rated at 200 amp (i'll be putting 3 in parallel just to reduce the load through the MOSFET.
+Kris Kasprzak Yes, it is common for the mosfet's drain to conflict with common ground. In these cases, you give it its own heatsink, but don't insulate the mosfet from the heatsink, that defeats the point of it. Insulate the heatsink from the chassis.
thanks for the nice and simple presentation. I have a simple question, can I use normal electrolytic "polarized" capacitors? and after bootstrapping, does mosfet go hot any more??? thanks again
Julian what's the voltage of Vgs on the boot strap ( Did you say 20 V ?) because there is a rated maximum voltage typically not exceeding 15V or they blow up .
hello Julian, great vids on mosfets. But all are used as a simple switch. How can power transistors be replaced by them ? I am constructing a powersupply using lm723 (Vin-230V, Vo-100VDC, Io-1A, about a 100Watts!) Oh its fig. no. 7 in lm723 datasheet
Hi Julian, really great videos !+!+! Three questions: 1. My application needs to be on for many hours. For how long will the MOSFET stay on with that setup? 2. Or could I use an easy circuit (eg a joule thief) to constantly charge the cap? 3. Acually I need a rectifier with an extremely low voltage drop (below 50mV at 1A). So this setup using an 10mOhm N-Channel MOSFET would come close. Unfortunately, as I have learned from your tutorials, there is a reverse diode that is destroying my hope for the rectifier. How could I overcome that problem?
Maybe try floating a photovoltaic output optoisolator between load and gate? They work akin to a current controlled adjustable voltage source. Input side is a LED... Glows when current past through... Output side a series stack of solar cells... When illuminated generates a voltage which can be floated on top of any other voltage.
can i use an L7809 instead of the 9V battery? Will it work if i connect the input of the L7809 voltage regulator to the 12 V supply, the GND of the voltage regulator to the source and the output of the L7809 to the gate?
No it will not work, if you tie the ground of regulator to the source then as the source voltage increases the voltage across the regulator's IN and GND will decrease.
What if i connect the GND of 7809 to the Negative terminal of the battery instead of connecting it to the source of the MOSFET and then connect the 9V lead to the gate of the MOSFET(sort of like an isolated power supply)?? Thanks for replying :)
I was following along nicely until you said that when the Source rises to 12v, the bootstrap capacitor rises even further, to 24v (and thereby maintains the voltage differential to keep the MOSFET switched on...) I can't get my head around why the capacitor would charge to a voltage higher than the available 12v supply :-/ What am I missing?
Graham Smith The bootstrap capacitor it's charged only at 12V, the voodoo magic here is the ground reference, in high side switching you need a voltage above the source. So you need to see the source pin like "ground" o 0V point, so when you connect the capacitor "-" to that point and the "+" to the gate the mosfet see 12V difference between G and S, so it works. It's like putting two batteries (12V) in series, 1° end is "-", the "+" of that battery is connected to the "-" of the 2° battery and the "+" of that battery is the free terminal. So when you put your multimeter between the "-" of the 1 batt and "+" of the 2° batt sees 24V, but! If you put the ground tip of the MM at the 2 (+,-) connections and the "+" of the 2° batt sees only 12V!. The ground reference it's the magic here. I hope you understand it, I'm not a great teacher nor native english speaker
fersunk - thanks for your explanation. I think I understand the concept now, I just can’t get my head around how he’s making it work - don’t worry though - I’ll put it on the back burner and come back to it when I have a little more experience with MOSFETs.
Graham Smith - The cap doesnt charge to a voltage higher than the supply, it charges to 12 volts. When the mosfet is ON the load has 12 volts across it. This 12 volts adds to the capacitor 12 volts because they are in series ( you may need to draw a schematic to visualize) so the total is 24 volts. When the lamp is off (FET open) the source is pulled to ground, this is when the cap charges to 12 volts.
@@noweare1 hey, I know this comment is old, but I figure worth a shot. So in this case, the capacitor acts as a voltage adder, since 12v is at the source, feeding through the capacitor(towards the diode) and the capacitor is charged, and stacks with the voltage present at the lamp to add up to 24v and fully driving the MOSFET? Can the capacitor be charged from either side since it's a tantalum, and not an electrolytic? Or do I have a misunderstanding of electrolytics as well?
Ah btw yesterday I was able to the mosfet as pwm modulator pretty much as you did but I have "huge" rise times (100uS), probably i'm not driving the optocouplers correctly
Hi Julian, Love your videos! I'm designing a power boost circuit but I wondered if you could (or anyone else) point me towards a power mosfet WITHOUT an in body flyback diode? - google won't help me
If I'm understanding this series correctly, the reason you can't find one is because they don't exist. The diode is simply a by-product of creating a MOSFET, and you can't create one without also creating the diode.
Rather than adding more components to create a desired full-on lamp. Wouldn't it've been easier to move the lamp between +12V and Drain? And connect Source to Ground. This way Vgs isn't affected by Source voltage lift.
Argh, I'm so confused! Surely you should connect the Source or Collector pin of a transistor to the positive of a battery...? Doesn't the electricity flow from the positive side to the negative side?
I think there is a possible beginning of an explanation about the power lost (1:50) at ua-cam.com/video/5A-THexe6u8/v-deo.html, around 11:25, even though that I don't see it fully (I fail to see the involved oscillation, if there is one). Interesting to know that the intrinsic diode of the MOSFET can conduct, even in reverse, for a short time...
Thanks Julian for another great video! Unfortunately I have problem with representing this circuit with bootstrap in LTspice for better understand. i.imgur.com/W5Sm55l.jpg - mosfet is not fully on What is wrong with my circuit? Could You make simple schematic and share here with me? :) Cheers!
Oh sweet, this is the first tutorial on high side switching that simply explains the bootstrap caps - diode and how to choose them! Thanks a lot Julian!
OMG, thank you! I was turning crazy all day trying to undesrtand trully a mosfet on its different configurations. Finally some wonderfull person explains it with clarity and in a practical manner. Thank you again. :)
This man addresses the capacitance issue that, I think, no other UA-camrs mentions! So now I know that capacitance of a discrete capacitor needs to be AT LEAST 2000 times bigger than that of integrated/body capacitance of MOSFET.
Masha-Allah. Zazakallah Khyer. You are very helpful for every engineering students.May you live a long life with Full of gladness and health.
The origin of the bootstrap circuit has its real meaning when there was a young very tired boy who wanted to go upstairs to his room to sleep and he told his mother that what he was going to do to avoid climbing the stairs was to put on his boots and then pull the boot laces up with his hands as hard as he could to lift himself up.
A circuit diagram would have been very helpful. There is a very interesting bootstrap circuit where the low side MOSFET is used with the high side MOSFET to make a half bridge and the low side MOSFET acts as a two role unit, providing the power output and also the bootstrap control system. Bootstrapping is a logic that most young people should learn about. It is a philosophy that can be put into real practice ...........that of lifting oneself by the laces on his boots!
these videos are beautiful, They have helped me in immeasurable ways, thank you.
While a schematic would have added to this; this is a great demo of how and why bootstrapping works :)
I could NOT work it out for the life of me before seeing this.
absolutely brilliant mate. very clear and easy to follow.
ive been watching this set of videos for the last few months and finally i got some transistors to try. this is awesome! thank you so much and i hope to see more, maybe something with two transistors being used at once for polarity swapping?
Very informative, have been helpful in my study when trying to understand how MOSFET drivers work
I should've watched this before I whacked a PNP in a blinker relay :/ I needed the high side switch there and was forced to use a PNP 'cause I ran into the same problem (gate-source equilibrium you talked about). I didn't have any P-channel MOSFET's and I had limited time to make that damn blinker relay. Now I will use a bootstrap for applications like that, charge leakage won't matter there 'cause the MOSFET will be on for a short period of time, then off and when it's off, the bootstrap cap will recharge.
Really nice tutorial, thanks for sharing!
I like your idea to put a small LED voltmeter into the circuit for illustration! Just ordered some ;-)
This was best video I saw on this topic
Thank you
It says 10volts for gate to source because thats the MOSFET "fully on", but you can drive them at any level under that, usually down to 4v,(or some drive at logic level) and it just passes less current.
Yes you are right, the SM72442 (the little brother of the SM72445 ) is 6€ and the SM72295 is 4.5€ from elements14.
The circuit seems to be complicated also to my eyes, but i like the i2c interface and the integrated current and voltage sensors (except for shunt resistances on the high side).
I'll study the datasheet again to understand whether all those external components are needed for my use.
Not the hero we deserve but the hero we need
Yesss!!! I was able to do it by my self after this video, understanding what I was doing :D
My dream of a solar powered rc airplane is now one centimeter closer :)
I'm still not sure whether to use a buck converter as you are doing or try the couple SM72445 SM72295
Actually, there are P-channel FETs available today that have every bit as low on-resistance as N devices. Check out the Infineon MOSFETs on Mouser.com, for a given voltage rating, they have comparable on resistance to N channel ones. They're available in any package you want, including TO-220. They're even a similar price! P channels will probably always be somewhat more expensive--but they've gotten much cheaper.
Thing is, they still have a lot higher gate charge than N channel devices, so make sure the gate drive circuitry is up to snuff.
+BasementEngineer good to know. This video was made in 2013.. still informative though.
Michael Rinkle I just had a look a while back, apparently P channel devices are now below 2 milliohms for a 40V blocking voltage :)
6h
Ione Ribeiro
???
+BasementEngineer n channel msofets are still very popular for highside because of the price and because of the Vgsmax. Also because that makes it easier to create symmetrical H Bridges
thanks for the explanation.i have two n channel mosfets and want to control the high side of a circuit with one or if needed both of them with a signal of an arduino which can output 3V. Drain to source voltage is 5 volts. How could i make an arrangement of mosfets to achieve this?
Hello.
Thank You for the great tutorial. I have a question regarding a low side technique, I am currently connecting an IGBT in parallel with a resistor and is supplied from a 9v battery. The igbt is driven from an L6384E gate driver such that its low side (pin 5) is connected to the IGBT's gate. am not connecting any c_boot since am only using the low side. The problem is that the switch is overheating unexpectedly, and there appears to be a 0.5v on the emitter of the igbt. Could you please explain as to why my IGBT is overhrating?!
Thanks in advance
Nice job on this 4-part series. It was very helpful. I have a small issue perhaps you can help with..
I'm building a motor controller to switch on and off a DC motor (around 75 amps). My N-channel MOSFET has the TO-220 tab connected to the drain. So... when i bolt the MOSFET to the heat sink then bolt the heat sink to a chassis, it will short out (the chassis will be used for grounding things like lights, horn etc). I guess i need to insulate the MOSFET to the heat sink or the heatsink to the chassis?
My mosfet is a Texas Instruments csd18535kcs rated at 200 amp (i'll be putting 3 in parallel just to reduce the load through the MOSFET.
+Kris Kasprzak Yes, it is common for the mosfet's drain to conflict with common ground. In these cases, you give it its own heatsink, but don't insulate the mosfet from the heatsink, that defeats the point of it. Insulate the heatsink from the chassis.
Well done, so what diode did you use for the tantalum elko cap ?
Many thanks.
Regards. Stefan.
thanks for the nice and simple presentation.
I have a simple question, can I use normal electrolytic "polarized" capacitors?
and after bootstrapping, does mosfet go hot any more???
thanks again
Very helpful for my project.. Thank you.
Hey, good news.
But that TI chipset and the evaluation board look very complicated - I don't suppose they're cheap either.
Thanks, Julian! Can I ask: is there any reason why you choose a tantalum capacitor over other types?
Not really, I just happen to have several thousand of this particular capacitor.
Julian what's the voltage of Vgs on the boot strap ( Did you say 20 V ?) because there is a rated maximum voltage typically not exceeding 15V or they blow up .
Can you please also show the schematic, connections aren't really clear ?
Very nicely explained.
Nickolay Pelov *66
hello Julian, great vids on mosfets. But all are used as a simple switch. How can power transistors be replaced by them ? I am constructing a powersupply using lm723 (Vin-230V, Vo-100VDC, Io-1A, about a 100Watts!) Oh its fig. no. 7 in lm723 datasheet
Hi Julian, really great videos !+!+!
Three questions:
1. My application needs to be on for many hours. For how long will the MOSFET stay on with that setup?
2. Or could I use an easy circuit (eg a joule thief) to constantly charge the cap?
3. Acually I need a rectifier with an extremely low voltage drop (below 50mV at 1A). So this setup using an 10mOhm N-Channel MOSFET would come close. Unfortunately, as I have learned from your tutorials, there is a reverse diode that is destroying my hope for the rectifier. How could I overcome that problem?
Maybe try floating a photovoltaic output optoisolator between load and gate? They work akin to a current controlled adjustable voltage source.
Input side is a LED... Glows when current past through... Output side a series stack of solar cells... When illuminated generates a voltage which can be floated on top of any other voltage.
Thanks for the tutorial!
super. was waiting for this
Thank you this was really helpful
Hi! I would really like to know what is the capacitance of the capacitor of your setup
Good. Thanks you very much for your tutorial !
Another excellent video, thanks (:
How did the 9 volt battery turn on the fet when it looks like the gate is tied to the negative terminal of the load (& power supply).
My bad it looks like its connected but its floating in the air lol, never mind
I hope you do a dc -dc converter using H bridge tutorial sometime soon.
please, i'm trying to understand this. I want lamp always on and off only when triggered by io
can i use an L7809 instead of the 9V battery?
Will it work if i connect the input of the L7809 voltage regulator to the 12 V supply, the GND of the voltage regulator to the source and the output of the L7809 to the gate?
yes
Thank you :)
No it will not work, if you tie the ground of regulator to the source then as the source voltage increases the voltage across the regulator's IN and GND will decrease.
What if i connect the GND of 7809 to the Negative terminal of the battery instead of connecting it to the source of the MOSFET and then connect the 9V lead to the gate of the MOSFET(sort of like an isolated power supply)??
Thanks for replying :)
I was following along nicely until you said that when the Source rises to 12v, the bootstrap capacitor rises even further, to 24v (and thereby maintains the voltage differential to keep the MOSFET switched on...) I can't get my head around why the capacitor would charge to a voltage higher than the available 12v supply :-/ What am I missing?
Graham Smith The bootstrap capacitor it's charged only at 12V, the voodoo magic here is the ground reference, in high side switching you need a voltage above the source.
So you need to see the source pin like "ground" o 0V point, so when you connect the capacitor "-" to that point and the "+" to the gate the mosfet see 12V difference between G and S, so it works.
It's like putting two batteries (12V) in series, 1° end is "-", the "+" of that battery is connected to the "-" of the 2° battery and the "+" of that battery is the free terminal.
So when you put your multimeter between the "-" of the 1 batt and "+" of the 2° batt sees 24V, but! If you put the ground tip of the MM at the 2 (+,-) connections and the "+" of the 2° batt sees only 12V!.
The ground reference it's the magic here.
I hope you understand it, I'm not a great teacher nor native english speaker
fersunk - thanks for your explanation. I think I understand the concept now, I just can’t get my head around how he’s making it work - don’t worry though - I’ll put it on the back burner and come back to it when I have a little more experience with MOSFETs.
Graham Smith - The cap doesnt charge to a voltage higher than the supply, it charges to 12 volts. When the mosfet is ON the load has 12 volts across it. This 12 volts adds to the capacitor 12 volts because they are in series ( you may need to draw a schematic to visualize) so the total is 24 volts. When the lamp is off (FET open) the source is pulled to ground, this is when the cap charges to 12 volts.
@@noweare1 hey, I know this comment is old, but I figure worth a shot.
So in this case, the capacitor acts as a voltage adder, since 12v is at the source, feeding through the capacitor(towards the diode) and the capacitor is charged, and stacks with the voltage present at the lamp to add up to 24v and fully driving the MOSFET? Can the capacitor be charged from either side since it's a tantalum, and not an electrolytic? Or do I have a misunderstanding of electrolytics as well?
Ah btw yesterday I was able to the mosfet as pwm modulator pretty much as you did but I have "huge" rise times (100uS), probably i'm not driving the optocouplers correctly
how we know capacitor value ?
Hi Julian, Love your videos! I'm designing a power boost circuit but I wondered if you could (or anyone else) point me towards a power mosfet WITHOUT an in body flyback diode? - google won't help me
If I'm understanding this series correctly, the reason you can't find one is because they don't exist. The diode is simply a by-product of creating a MOSFET, and you can't create one without also creating the diode.
It would help to include the simple schematic on the corner of the screen as this make it easier to imagine.
Perhaps include a circuit diagram at some point to show what you describe?
Nice video, however sound works stereo until 4:35 when it only outputs on right channel.
I know, sorry about that, it's a problem with the Movie Studio Android app.
Rather than adding more components to create a desired full-on lamp. Wouldn't it've been easier to move the lamp between +12V and Drain? And connect Source to Ground. This way Vgs isn't affected by Source voltage lift.
+tikiteyboo Yes, that's correct. I think in practise there are cases where you can't get away reconfiguring things though.
Argh, I'm so confused! Surely you should connect the Source or Collector pin of a transistor to the positive of a battery...? Doesn't the electricity flow from the positive side to the negative side?
electrons flow from the negative side to the positive.
Wow, that was an old comment. Yeah I understand electronics a lot more now and this makes perfect sense :)
:)
3:18 is IS a viable circuit actually, it would be called a class-A amplifier
help guys plz I can't connect switch to MOSFET
I think there is a possible beginning of an explanation about the power lost (1:50) at ua-cam.com/video/5A-THexe6u8/v-deo.html, around 11:25, even though that I don't see it fully (I fail to see the involved oscillation, if there is one). Interesting to know that the intrinsic diode of the MOSFET can conduct, even in reverse, for a short time...
4:27 for bootstrap tutorial
In the video, nothing special, just a 1N4148.
Hi Good day... how about the exact info of tantalum capacitor
difficult understand without a schema
Thanks Julian for another great video!
Unfortunately I have problem with representing this circuit with bootstrap in LTspice for better understand.
i.imgur.com/W5Sm55l.jpg - mosfet is not fully on
What is wrong with my circuit?
Could You make simple schematic and share here with me? :)
Cheers!
The gate is connected to the capacitor at startup and the capacitor never gets a chance to charge.
The Lightning Stalker Thanks! Somewhere I found information that bootstraping work only with PWM /PFM signal. Is it true?
Dominik M It is most effective when the FETs don't stay on longer than a few tens of seconds.
If anyone could test this app i'd be grateful! Locate androidcircuitsolver on google