Electronics Tutorial - High side drivers in Buck Converters

#66 In this video I look at Switch Mode Power supplies - in particular the Buck Converter. And to get a bit more focused, I look at the high side switch and how the driver for this component should look like. I analyse both N channel and P channel high side switches.
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[@BLU-qj4bl]

This is the only video that deals properly with the switching of bucks. I have came across tons of videos and articles but this one is the absolute top, well explained and well made. Thanks.

[@tepponen666]

Finally I understood what is the operating principle of bootstrap capacitor :) Thanks a lot mate!

[@FesZElectronics]

Happy I could shed some light on that! Cheers!

[@ramu1020]

Very good explanation. It would be intersting to give some other possible configurations to drive N channel Mosfet as a high side switch.

[@WalidIssa]

Brilliant

[@WalidIssa]

I'd like to add, at 11:50 the gate voltage is 24V and most Vgs < 20V ... Another point is after adding the push-pull, the ground of the PNP transistor is better to connect it to the MOSFET Source (S) terminal which makes it floating and works with any higher voltages.

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[@Ahmadnaweed786]

well done! only one thing. I don't think it's because of the cost I think it's because of the resistance to use n channel instead of p channel. in most of the p channel ones we can see that Rds-On is higher.

[@alocin110]

This is really well explained with practical cicuits. I was just wondering with a bootstrap capacitor what would be the value of capacitor if we are switching a P-channel MOSFET at 500KHz, does it have to be smaller or 1uf is good. Also there are some ICs that is widely used for High Side Switching of N-channel. Could you do a demo using one of the HSS driver IC. Thanks for your video. I liked it and subscribed to your channel.

[@aguywithjeep.7498]

I am watching electronics channels since long time, but don't know why utube reffered to ur channel after so long. Gr8 vid Bro

[@andynicholson1867]

why do you assume I am a normal person ? I was wondering how easy it would be to train ants to pass a laser sensor at the correct frequency and reduce thier food if they pulse to fast and and speed them up if to slow the sensor being the switch , hmmm maybe it would be easier to be normal ... I see your point. Great stuff!

[@p_mouse8676]

Nice video as always! Would be interesting to expand this with an half bridge circuit.

[@FesZElectronics]

That's a great idea! I will get to that as soon as I can.

[@HyperspacePirate]

Thanks, this was also really helpful for building a half-bridge driver without using a P-MOSFET for the high side switch and avoiding the hassle of a gate drive transformer.

[@MuhammadHanif-bx4pb]

it's kinda trade off between gate drive transformer vs bootstrap circuit. with the gate drive you get a galvanic isolation but with bootstrap you don't. with the gate drive you get slow rising slope but with a bootstrap you can get a sharp one. with the gate drive you can get any range of voltage but with the bootstrap you have double the supply voltage only. with the gate drive you can have multiple output while bootstrap you must build for each of the high side mosfet.

[@sahinyusuf]

i watched many videos about high side mosfet drivers, but this one is the best. Thank you very much, you made us undestand it very well. :)

[@ihtsarl9115]

It would be nice if you can show how is the voltage higher at the boot strap capacitor and diode ?

[@med7075]

I wanna ask one thing. In the push-pull configuration, do we need some resistor in NPN (collector) ?. Because i think if I dont put some resistance, the current through the push-pull configuration will be so high (short). Anyway, great video!

[@FesZElectronics]

I'm not sure why having high currents would be a problem? anyway, current running trough the switch closes trough the inductor, so any current will be limited by that circuit element. Or maybe I misunderstood your point.

[@med7075]

​@@FesZElectronics for example, in that push-pull configuration. When the NPN bjt is ON, then current will flow through NPN bjt right? because we have no resistor attached on the npn (in emitter or collector) I thought that it will make the current so high and may damage the NPN transistor. or maybe because we are driving the gate of MOSFET, the main focus is voltage ?? hmm im still kinda confused tho. anyway, sorry for my bad english :)

[@med7075]

sry i just remembered that in bjt, collector current are controlled by base current. I think this clear my confusion

[@sadeghmollaii9873]

Beautiful, thanks

[@user-tm3wg1uq9c]

thx

[@SMV1972]

Спасибо , очень полезный урок

[@grigbarbulescu4218]

Very well explained!

[@pablomarco5118]

AMAZING! THANK YOU!

[@sc0or]

Well. The title says “drivers”, but in fact only one type of the drivers was covered.

[@ammadjaved9428]

Question... If we increase the input voltage yhan 20V then gate voltage also becomes 20V which is highest value in many cases. How this situation could be avoided?

[@FesZElectronics]

That's a very good question! Basically you do not use the supply voltage to drive the transistors, but make a lower voltage that is fixed regardless of input supply - say 5V. I implemented this in kzbin.info/www/bejne/nKi4l6dsmtyNotE

[@johnnytifosi]

Using the last example of bootstrap push-pull driver at a high side MOSFET of a half bridge, I get excessive voltage spikes at the C-E terminals of the BJTs, equal to the total voltage of the half bridge plus the driver circuit voltage (5V). Can I limit it to 5V?

[@edinfific2576]

The reason why N-channel MOSFETs are used more often than P-channel is not only the price, but also the lower RdsON resistance of an N- vs. P-channel. Otherwise, great video and explanation.

[@FesZElectronics]

If you compare the same size transistor (same silicon chip) then you also have worse electrical proprieties. I guess I insisted on price in the idea that 2 similar spec transistors will have a considerable price difference - if you try hard enough you will get the same Rdson regardless of N or P chan.

[@FambiTech]

this circuit works for only 12v? if we increase the battery voltage above 30v, same voltage vale will be impressed in the gate of the mosfet....which is not acceptable?

[@ahmedzangana5251]

@FesZElectronics great job! and thank you for this high-quality explanation. Can you help with this problem? please. I have a buck converter, and even with this configuration of gate drivers, the MOSFET switching-off delays at high frequencies (100 kHz and above) make the duty cycle wider and the output voltage higher than expected. For example, with an input voltage of 120 volts and a duty cycle of 0.2, I got a 24.7031 output voltage at 100 kHz and a 26.4402 output voltage at 200 kHz. Is this normal, and I can't run the MOSFET used in my circuit at these frequencies? If not, does anybody have knowledge about this phenomenon and the way to fix it without using feedback?

[@WillSampson704]

This is a very well-done video. I really appreciate you making this. I do have a question remaining... How would this totem pole driver work in a high voltage buck? (hundreds of volts, say ~300V) Would you be able to add resistors in series with the totem pole's collector and emitter (so as to not exceed the VCE maximum of the bjt's) without compromising the desired high frequency switching response?

[@santoshbabu517]

hi sir im lloking for high volt AC to Dc converter 220 v AC to 90 V DC. Will circuit explained by you will work for same. any reference or help. or if possible plz make a video on that.

[@ccv3237]

You have done an excellent explanation about efficient switching in converters, etc. Thank you very much for your time and generosity. I will subscribe, and gladly give you a thumbs up. Your English was also well pronounced, and well paced, the way these teaching videos are supposed to be, enhancing its understanding. Please continue your excellent tutorials.

[@SomeTechGuy666]

Why didn't the performance of your real circuit match what was happening in LT SPICE ? Did you use different components or not model a parasitic ? Good video.

[@abhishekmaurya6562]

[@LaboussoleNano]

Thanks for your video, what is the current output in general for BJTs pushpull drivers?

[@bradleykingston551]

Worth watching. very insightful

[@sebastianiragorri6884]

This is very very nice! What about explaining H-bridges with mosfets?

[@mr1enrollment]

adding an explanation of depletion mode versus enhancement would be helpful.

[@arneg0]

This is a good video!! Is there a way to share the ltspice file? I'm trying to recreate this to play around with and it's hard for me😢

[@bradleykingston551]

can i build this bootstrap circuit and push pull driver just as it appears on the simualtion? If so what should i take into account?

[@maxim25o2]

Wow, that was greate explanation and so easy to understand!

[@elenduemmanuel9556]

Please can 311V be the input to the entire circuit? Plus the driver

[@themouseisinthehouse]

This has very well explained bootstrap. It helped me a lot. I am wondering will the capacitor be able to sustain its charge when the duty cycle of the switching is high? Maybe 80% and up?

[@FesZElectronics]

Usually converters that use a bootstrap have a limited maximum duty cycle (expressed in the datasheet) so that the capacitor stays charged. The capacitor value will depend on the energy it needs to deliver and this maximum duty cycle. Its common though for such converters to allow maximum duty cycles of around 95%

[@muhammedcihadakkaya7140]

more beneficial than many application notes.. Thanks a lot :)

[@bohuserik5151]

Fine! Simple and smart thinking, with common sense!

[@DeltaSigma16]

Sehr gut

[@mustafaerdogan3380]

What is the electronic analys program name?Also , i need a 24V PMOS High side driver. I couldnt find very well circuit. I made some circuit , but not work ver well. Only for on / off. I cant see pwm on motor. I think, i need a fast closing time. I used C12V zener for Vgs under 20V.

[@mustafaerdogan3380]

i think, i found program name to simulate circuit. Name is LT Spice, i think.

[@felixaudet5860]

High side switching, apparently has less ( A lot less? ) EMI compared to low-side switched buck converters. Can you confirm, and or elaborate on that?

[@FesZElectronics]

I'm not sure what you mean by "low side switched buck"; In general, regardless of the converter type you will have EMI noise. The only thing that you might change is whether the main part of this noise is on the input (in buck converters) or output (boost converters). Linear Technology has a great Application Note 139 where this topic is discussed in detail.

[@farrell2395]

can i use open collector for drive a p channel mosfet on mppt buckboost ? the switching frequency is about 30k-62.5khz

[@FesZElectronics]

Of course - that should work - just keep in mind that the p-mos needs to be switched off during the off time. You can use a resistor for this or the circuit in fig 27 of the NCP3063 datasheet ( www.onsemi.com/pdf/datasheet/ncp3063-d.pdf )

[@grigbarbulescu4218]

Salut. Ar fi interesant un video despre stabilitate si vizualizarea diagramelor Bode pentru circuite simple (op. amps) sau chiar surse de alimentare, folosind LTspice.

[@FesZElectronics]

Am deja :D kzbin.info/www/bejne/jmXcknWtlrRknc0

[@sumanjha1951]

Awesome! Thank you for explaining so well

[@elhadjiamadouwade4840]

Very good explain I have a question I would like to use VN820B5TR-E STMICROELECTRONICS for my simulation LTspice Can you help me or to propose me a model similar on library LTspice please THANKS

[@adithyapai6158]

Good one I would recommend you do a video on reading and understanding > extraction datasheet parameters > and modelling of buck , boost converters in LTSPICE. And even average modelling of smps if possible. Keep it up👍

[@akashtanwar1939]

That would be awesome. He did try and model a device from its data sheet, but, that device was such an unknown device that it didn’t help much. Would be great if he could emphasize more on modeling.

[@0124akash]

Please explain uc3842a ic

[@roberttso1079]

Great tutorial! Thank you!

[@quevineuxcrougniard2985]

C'est vachement balaise ! Merci infiniment.

[@realchristopher4334]

I have been 'secretly' watching this man's videos. But I hate them all because they are boring. But I love them because they have damn many examples (When I mentally ask how about this that circuit, before I get frustrated there he shows another circuit which answers me. And shows another variation, and then another as he scrolls to the right of LTSpice. I am like 'WTF! He mind-reads!?!?!?) and clear ones as well! And he does not deliberately show fancy hard-to-find and expensive components simply because they are superior. Electronics and science are fun only when we can easily acquire the materials and do something with them. Mental masturbation for too long is unhealthy. We learn the best by doing. So yes, I have love-hate relationship with this channel. Some KZbinrs are great in many things including explaining and hence making their videos and themselves charming. Sadly however, all they show is their hands, head, body, wires, mess, covering the thing that they are explaining, tiny text, tiny stuff. I refuse to give them thumbs down because I think it is unfair for them due to many valid reasons; they are not horrid anyway. I try to think positive that they merely are doing it for their own record or documentary, a selfie thing, not for other people to see.

[@widya1836]

but if the voltage i want to switch is 42v how i turn on the p ch mosfet correctly since vgs is limited by 20v, if i shorted the gate to ground then vgs its more than 20v right?

[@FesZElectronics]

Usually a zenner diode (~15V) is placed in parallel with the G-S of the mosfet if the driving voltage can exceed the limit. As the driving is done trough a resistor, the zenner will always limit the Vgs regardless of signal amplitude.

[@tylergeneharrison3594]

Awesome video dude! Absolute gold!

[@SamCPower]

Great video, as usual.

[@shakaibsafvi97]

Excellent Work !

[@yakupemre1]

I appretiate your all tutorials. Thanks for that. I have a question. What do you thing about that what is the most reliable driving method for h-bridge power IGBTs, in narrow frequency range and up to 40khz? For example, I had wached your video which is about pulse-transformer before. Do you think, is it feasible?

[@snakezdewiggle6084]

Opamps work well also. ;)

[@virajytube]

I appreciate your all videos! One question: how can you drive a non-switching NMOS using bootstrapping?. In my circuit, I just want to turn on load for some predefined period.

[@FesZElectronics]

Hello @Viraj Adam ! Well, you need the switching action to charge up the bootstrap capacitor, otherwise there is no energy in it to drive the NMOS. You could try using 2 signals, one just to switch constantly and charge the bootstrap, and another to use this voltage to drive the transistor. Or an altogether different approach is needed - maybe some sort of opto-coupler or some other principle.

[@virajytube]

@@FesZElectronics Thank you, FesZ

[@דפוסבסמת]

شكرا الك

[@santoshbabu517]

Nic tutorial

[@raghavkumar6877]

Super helpful video man, please making such niche videos. There are none like these on the internet :)

[@FesZElectronics]

Glad you liked it!

[@VitorFThome]

Dude, i just copied your circuit and swaped the load of 6 amps for a 10 ohm resistor (so load current would be lower) and an interesting thing happened, the Vgs didn't got to 24v, could you explain why this happened?

[@FesZElectronics]

Well, the Vgs is not load dependent as long as the supply is working correctly. The bootstrap capacitor will be charged with the input voltage (in these circuits) minus the drop on the bootstrap diode minus minus the low side diode in the switching node. And when the gate is being driven, there is a voltage drop on the driver (again 0.7V). So when the circuit is working normally you get ~24 -0.7-(-0.7))-0.7V~23.3V; If there is very little load, the circuit with fixed duty cycle will not work well.

[@VitorFThome]

Ty FesZ! You are actually my favorite yt channel about electronics atm, great content! I’m building a DC motor H bridge driver (without a mosfet driver ic because those don’t exist here where I live and take a long time at shipping lol).

[@FesZElectronics]

Just take into consideration that if you plan to run a motor without PWM (always on, or off, or in reverse) , this sort of high side Nchannel will not work. You need constant switching to keep the bootstrap charged.

[@ashanzlx]

Wow,very clear.

[@coucouj2781]

I finaly understand how to properly drive a n-channel mosfet with a signal generator :)

[@aykutcandan2662]

hi,ı tried bootstrap but I saw 3v over the source pin. but when ı separate the bootstrap cable ı could measure 15v over the source pin

[@carlosalba007]

wow 😍👍✔

[@kinmak9862]

Thank you very much for this excellent explanation, best electrical engineering channel

[@anshaggarwal2060]

Could u make a Video explaining the filter capacitors u mentioned at the starting of the video? A suggestion from some link/ video would be also OK. Thanks in advance

[@023-mohammadsyawal7]

what aplicagtion do you use for simulation

[@FesZElectronics]

I use Ltspice in all my videos - its a free simulation program

[@mubbashirshirazi3758]

@fesz electronics please tell me if it is ok to use the bootstrap configuration when the input voltage of the buck converter is greater than 12 v i.e if it is 75v and if this bootstrap configuration is not ok for the desired application than what could be the remedy for the problem of driving gates

[@mohammadrezaadib8999]

really awesome :) 🙏🏻❤ well explaination.

[@FesZElectronics]

Glad you liked it! Thank you!

[@gasparhenrique3112]

Congrats man.

[@w1qg]

Excellent job, very clear. It would have been nice if the final N chan driver was bread-boarded.

[@rohitdewani]

Your p mosfet driving circuit is not working in real life

[@FesZElectronics]

Maybe you can give some details on the circuit you built? The arrangement should work.

[@ramkumar-ro2vm]

Why did we choose bjt instead of mosfet to drive the high side mosfet?

[@FesZElectronics]

I did not have a special reason; it was just as an example; in general I find using BJT easier to understand but I am aware that in most transistor driver IC's the driver is built with FET's.

[@ameristanbouli5063]

thanks a lot

[@elenduemmanuel9556]

Base on the bootstrapping, for the capacitor to charge, current has to flow through the load. Which then means that current goes through the load Continuously

[@TheSriram1990]

Good explanation.Kindly do share the LTspice schematic in the video description that you use for teaching.

[@andressanmartinmorin1898]

niiiice

[@Tommybotham]

Can you please make a video on actually building your own DIY variable buck converter? My problem is that I simulate the circuit in LTSpice, it works. Then building the physical circuit, it either doesn't work or is badly inefficient and its frustrating. This is for N-Channel type MOSFET.. I know I can just follow a video (electronoobs, GReatScott) on building a DIY, but they almost always use P-Channel and they seem to skip steps. I want to step down 24V to 0V - 23V for example using a Teensy 3.5 as my PWM.

[@FesZElectronics]

Usually you get differences between the simulation and real life if you use different components, or the models are not that precise. On the other hand when talking about switching power supplies, the exact circuit construction can have a big impact. You need to keep the power loops as small as possible as well as the supply ground as compact as possible (the connection between the input cap, diode and output cap must be thick and short). Do you have a particular schematic that you wanted to try and had issues with?

[@bakriaderradji91]

Thanks a lot

[@republicoftutorials6068]

Super helpful there is just one tutorial about Buck Converters bootstrap on the KZbin, Can you please answer one question, its about "C3" capacitor on your circuit i want to know which terminal is positive the one connected to D3 or D2 ?

[@FesZElectronics]

The positive terminal should be one connected to D3; current flows trough D3 to charge it. I would like to point out though that in practice, bootstrap capacitors are commonly quite small in value. So you can just use 100nF-1uF ceramic unpolarized components.

[@shaggygoooxide]

Thank you! I really enjoy all your videos and this is no exception. Can you say more about your "active load"?

[@irsarasheed9842]

I have another question. Can we introduce faults in components in LTSPICE, like we can do in MULTISIM. zone.ni.com/reference/en-XX/help/375482B-01/multisim/settingplacedcomponentsfaults/#wp245032 Please guide me. MULTISIM provides option for these kinds of faults for every places components. Is there a way to introduce faults in components in LTSPICE?

[@FesZElectronics]

Hello Irsa! I'm not sure this feature is present in LTspice. The simulator is more basic and more bare bones. You can simulate faults the "hard way" though. By actually adding the fault as an extra component (in case of short circuit, add a small resistor or a wire) or by cutting traces (for open fault)

[@andresgongoraYT]

Great explanation. Thanks!

[@projectsiva9536]

Usefull information 👏 Excellent explanation

[@farrell2395]

can i use that bootstrap capacitor on inverting buckboost converter?

[@ihtsarl9115]

Great Video and Very Instructive thanks

[@suhaimiannuar6008]

nice la bang.

[@mikemarachov3230]

You are great! Thank you! Where can I find examples of power mosfet driving circuits?

[@electroLuke]

I was working on my DSD audio player project, designing a reconstruction filter in ltspice and I just bumped into your tutorials... Such a satisfactory click of a subscribe :). Man... you're way to much underrated, wth, great content ! Might have to binge it later xD

[@FesZElectronics]

I'm happy you are enjoying my videos! Keep safe!

[@akashtanwar1939]

Him? Underrated? I rate him very highly.

[@armanhossain2491]

Seriously Bro,your videos are just awesome.So much informative.Can you make video on High side current sensing amplifier .I found a circuit in Art of electronics.page no 278 but can't understand it.

[@FesZElectronics]

Hello Arman. Can you please provide a link to the document (the "Art of electronics" has multiple editions) and/or chapter and figure number so we are both looking at the same thing.

[@brianoc22]

Hello, I really enjoy your videos, I have one question though. Doesn't the source node drop below 0 volts in the buck converter? If so how will the mosfet remain off completely with an effectively positive GS voltage? Thanks!

[@FesZElectronics]

Hello Brian! Well, the switching node does go below 0 in a buck converter, but only to about the forward voltage of the diode - that being schottky its usually less then 1V even for really high currents. Depending on the Mosfet, the Vgsth (gate source opening threshold) is usually more than 1V, unlike a bipolar transistor that needs 0.7V; so even with the offset of 1v you still can get away with not putting the transistor into conduction. The design can be improved by referencing the push-pull driver to the switching node and adding some resistors - I did this in the next video on the topic - kzbin.info/www/bejne/nKi4l6dsmtyNotE

[@Danixu86]

Nice... I've always drove the N channel mosfet on the low side instead the high side. I also have another question: How to drive those mosfets if the source voltage is higher than the max gate voltage?. Maybe you can create two voltages sources, where one of them is at the correct level to avoid the gate damage, but that's the problem, you need two sources.

[@FesZElectronics]

Hello Daniel. Regarding the voltage issue - you can simply make a basic stabilizer with a zenner, nothing fancy - I tried this in kzbin.info/www/bejne/nKi4l6dsmtyNotE

[@teambacon]

I can see your channel becoming as big as GreatScott!. Really brilliant content!

[@gaynzz6841]

Not really. The topics on this channel are too complex. "GreatScott" is a complete buffoon by the way. He steals stuff from others and can't do anything on his own.

[@gaynzz6841]

Nah, most people prefer to watch TIkTok videos (and Greatscott is on the same level as those)

[@teambacon]

@@gaynzz6841 two years ago I would have disagreed

[@gaynzz6841]

@@teambacon I liked Scott too at first. But it seems the bigger a channel gets, the more they let it get to their heads. I do wish Fesz a lot of success, but I just can't imagine him doing these high quality videos and all the research if he had 1.5M subscribers.

[@foobarables]

You're driver circuits are incomplete in that Vgs follows the supply voltage. Some modern MOSFET's do not like to be driven with gate source voltages larger than 7...12V. Better circuits exists which limit Vgs to an appropriate voltage.

[@martingiese5154]

Thank you for this explanation! I’ve simulated this setup for bootstrapping, but it seems to break down if not enough current is drawn by the load: at some point the current in the off-state is not enough to charge the bootstrap capacitor, so there is not sufficient voltage to open the gate 😕 So what do we need to do to keep the boostrap cap charged consistently, independently of the voltage?

[@FesZElectronics]

In some converters, there is a minimum on and off time defined - so you cannot have the switch closed for extended periods, or open for that matter; regardless, if the load is very small, the converter should still work, but there will be a very large voltage drop on the high side switch - this will happen until the capacitor is re-charged. You can always use some other charge pump circuit to create a higher voltage, something that does not rely on the power converter switching, although this is not ideal and just adds complexity.

[@martingiese5154]

@@FesZElectronics True. Still, you need tovhave enough current in the open state, right? I see that the IC gate drivers charge the cap through the low side switch that replaces the diode.

[@SanjaySharma-pw6ww]

Nice video on buck converter 👍

[@overratedgaming3831]

What’s is the purpose of diode d2?

[@overratedgaming3831]

There doesn’t seem to be any use for it

[@FesZElectronics]

Are you referring to D2 present at 13:00 ? Its the regular flywheel diode in the buck power stage.

[@overratedgaming3831]

@@FesZElectronics yes, thanks for the quick response, was stumped on the reasoning but had initially forgotten about the voltage spikes caused from an inductive load. this is probably the most useful video on mosfet drivers one can find on KZbin