Inductive spiking, and how to fix it! 

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A lot of YT videos take 30 minutes to present sixty seconds worth of content. You did it in under five minutes. Good job.

This video is the reason why I love your channel. I understood inductive spiking in less than 5 min. My lecturer spent 90 min explaining this concept and showering us with total BS formulas with no meaning and at the end everyone left the class without understanding the what the inductive spiking was. Cheers, keep it up.

Every afrotech video is gold; not just good tutorial how-does electronics work but how it should be taught

I don't know who you are but have been around electronics all my life and this is one of the most informative videos I have ever had the pleasure to watch! I cannot thank you enough. It's application at work is far reaching! Thank you!

You are so underrated. There are not many youtubers who deserve to hear this ( there is so much crap online nowadays) but you are my favorite

Genuinely appreciate your efforts to simplify the concepts & educate the viewers.

Compliments on a clear presentation of the function of a Free Wheeling Diode. I will link this explanation for the electronic laymen/vintage car owners, who I am currently working with to solve a vehicular electrical problem where the stimulus is release of the horn or backing light relay, but no FWD is present. You and I both know what the first line of defense must be...snub that spike!! Cheers from Connecticut!

Best tutorial on this I've ever seen! And thanks for mentioning importance of diode speed; I never understood that before.

this is the best explanation about the Snubber, Flyback and voltage spiking on you tube because it shows all in practical way. Thanx a lot!!

Love this guys voice and sense of humor.

I'm in the process of converting an automobile to full electric, and I have been building an open source DC Motor controller. This video was hugely helpful to me in understanding WHY I need to add capacitance across the bus bars of the IGBTs. I had already done so, but I was just a monkey imitating what a thinking person had done before me. Now I at least have an inkling of the theory underpinning it. Thank you.

Very interesting. About 8 years ago I had some projects with the ignition coils on my car and I observed the Voltage on the primary side of them with an O-scope and it had the same pattern.

Everyone learning about transistors NEEDS to watch this, took me forever to find a video that explained this in a way that make sense!

What an incredibly lucid, humourous explanation. Thank you.

1N4148 is a good catch diode for low power inductive loads (

I really enjoy your videos super clear concise and formative please keep up the good work

Simple and easy to understand. Your videos are flawless!!!

I was building a driver for flyback transformer and my diode just disintegrated and I had no idea why. Luckily I decided to watch some of your videos again. Apparently the schematic I was using was faulty and I just put my diode the other way around which led to a build up of huge energy on the negative side of it. Thanks man! I'll replace it and see if it works this time :D

"Every afrotech video is gold; not just good tutorial how-does electronics work but how it should be taught" This.

And this clearly explains what an brilliant (but not so great at teaching) instructor tried to explain in an hour last week in less than 5 minutes. Love it.

Wow. Good tutorial and information. I am currently dealing with this and now I understand better. I am working on trying to use a mosfet to control a heated bed for my 3d printer. The printer is old and did not include a heat control. Thanks very much for your time and energy.

Cannot love your channel enough. Great work.

Thank you very much for all your lessons, including this one!

What about in an H bridge where the high voltage pulses drive crazy the microcontroller, the mosfet driver and also other parts of the circuit?

@Afrotechmods By the way, my motor was a 60W motor DC motor. A short story : when I was young, I had blown up a BLDC driver circuit that I had had build just by the way you suggested. I had a diode to block reverse currents to the power supply. The brilliand thought was an addition of the last moment when I said "Hey, when we plug it, someone may put the power supply cables in reverse and blow it up", so I put the diode. It was not still that bad, because the board in order to stop the motor....

Very nice video. Well done. Very helpful illustrations. Clear and concise explanations. Bravo.

Wow. You explained all I needed to know in under 5 minutes!

Afrotechmods, So i built your 555 timer PWM circuit, and put it on my variable tension friction drive bike project i built. I had the backwards diode in the circuit, it ran fine, I had 24 volts on this 280 watt motor with a powerful fet, and i hit a bump in the road and my solder connection on my diode broke off and i basically had no protection for that fet so the fet exploded in the housing, i went back home, and realized it was over 100 volts of spiking on the drain. Inductive spiking is very real.

I noticed even with the diode you didn’t have a square wave it was more of a chair shape. I just wondered how you explain that. I have just built a similar mosfet driver for a spindle motor upgrade on my mini CNC on my channel so your video came around just in time. Thanks

Thanks. I went ahead and purchased some of both your recommended diodes. I'm playing around with joule thiefs and other things, so hopefully there will be useful for something.

Very interesting. I just watched a video about waterhammer, a phenomenon in fluid dynamics, where a huge spike in pressure occurs when a valve is closed too quickly. The resemblance of the diagramms are uncanny

Awesome as always . Makes me understand stuff so much clearer

If I’d had RU-vid back in college, my life would have been easier! Nice job!

thanks so much , this is way more helpful than what i learned from the textbooks

Very good tutorial here. Brilliant explanation. They should show this at my school. Some people in my class just won't *get* this stuff...

Yup that'd work. I would also recommend a bulk capacitor after that diode though to cut down on EMI.

Very well explained . The motor I am using is 3kv dc motor 24 volts it is a golf cart motor . and max current is almost 150 amps , please advise what kind of a freewheeling diode will be good to save the IGBT it blows up very now and then

I love your videos! So informative and some humor thrown in as well.

@KIBProductionz Actually, you would get a negative voltage spike at the node where the FET and the inductor are connected to each other. This phenomenon forms the basis of a buck-boost converter.

at first my head started to hurt but then it was all clear. your tutorials are very very very very good.

3:11 when transistor switch is off, there is no way for the current to go through the power source because that power source is connected only by one end to the inductive load. So energy does not go back to the power source at this moment. Here energy only recirculates through the inductive load.

@Afrotechmods I tested all. I used an IRF630 (200V) prepared for the worst. With the basic configuration there was no overshot because the back emf of the motor continued to produce voltage as a generator with the same voltage and direction as the power supply when it was disconnected, dissipated by a smooth ramp as the speed of the motor decreased until 0 after 500ms. When forcing the motor to stop, there was a small overshot in the end of the ramp of about 1V, it was the current flowing.......

@Schmiki24 All power MOSFETs that I know of have that diode. However other FETs such as a JFET do not have the diode. Whether you should add your own additional diode in parallel depends on your application. Parasitic body diodes tend to be kinda "crappy", i.e. slower response time and higher forward voltage drop than a nice discrete schottky diode. So if you were building an H bridge, putting some good schottkys in parallel with each mosfet could get you a little more efficiency.

Very informative and concise as always. Keep 'em comming!

@Afrotechmods .....but it was observed in both sides of motor which suggests that it was not produced by the motor (if it was the case then the voltage in the motor should be raised, but instead if followed the usual ramp). The overshot was due to the inductance of the cables that continued to bring some current even after the FET was off, current that charged the Drain-Source capacitance of the FET and stayed for some time unable to return to the power supply.

@Afrotechmods .....in the free wheeling diode. Because the current to the windings of the motor was not slowly dissipated and through the immediate stop it had a large ΔI/δt it produced the free wheeling current. It is the same overshot of 1V that appears in the basic circuit when you turn off the transistor briefly before the ramp. By using a diode in series with the power supply, there were no dramatic results either. When stopping, it was a very brief overshoot of about 10V....

500 comments already, maybe someone has written about it, but: we should keep in mind that, although parallel diode is "a must", adding it makes the current in the coil fade away quite slowly. U = -L(di/dt), so if U is like 0.7V on a silicon diode (or even less on a Schottky diode), the current remains significant for quite a while after the transistor gets switched off. In many cases this might be not important, but if we need fast reaction, it is advisable to use a Zener diode in series with "normal" one (cathode to cathode or anode to anode), in order to increase U in the formula above. Alternatively an appropriately calculated resistor may be used. I personally learned that when I was designing solenoid driver for kind of a printing head, and the first version, where a regular silicon diode was used, dosed much more ink than was desirable and than would result from the duration of the driving pulse. (In turn, when a Zener diode is used, power dissipated on it must be taken into account, especially if pulse repetition rate is high).

Afrotechmods: I need your help...bad. I have a brush DC motor with a PWM controller to manage motor speed (the pwm uses mosfets to send the flyback voltage back through the motor. The power source is 2 x 12 VDC batteries in series. All works well. I'm trying to measure volts, amps, and RPM using an arduino. I have a buck converter hooked to the battery and dropping the voltage to 5VDC to power the arduino, and i'm using a simple voltage divider to drop the 24 VDC to around 4 so my arduino can read the batttery voltage (then in software i compute the voltage based on R1 and R1. My amp meter is a hall effect sensor with a low pass filter to smooth the output signal. I have several issues 1) My issue is the arduino "locks up" and I suspect is just spiky, noisy voltage. I added a home made inductor (wire wrapped through a washer, and connected it in series to the ground (read that somewhere) and while the arduino no longer locks up, it does restart (as if the battery were unplugged and plugged in again. I still suspect the issue is very spiky voltage caused by the pwm controller. I can only hope my buck converter is filtering out all the junk, but I now suspect connecting the noisy battery directly to the arduino input w/o any type of filtering, may be causing other issues. 2) a plot of the input voltage (the ~4 VDC signal) over time is a sine wave--again I suspect its due to the noise and spikes of the pwm controller I've tried dozens of things to shielding wires, twisting wires. etc. maybe i can 1) add a low pass filter to the positive (before the buck converter and input to the arduino or 2) connect the input the the point between the batteries. It feels like #2 will give the cleanest DC signal. Thoughts?

Beautiful illustration

Excellent. I like the short form. But It would be nice to give a guide what parameters the diode should have (calculate). And maybe mention about AC inductive loads, and RC snubbers, or something. For a next video.

I love your videos, very educational and entertaining :)

This is very useful. Thank you for this explanation. Could you explain the same for a high side? How would the diode protect the MOSFET on a high side driving an inductive load. Please let me know. I would appreciate it.

The best description I've seen on this topic. Thanks so much for sharing so clearly.

@ntomata0002 Also, try running a large motor, then switch the transistor off, then forcibly slow down or stall the motor and you will get a massive spike on the supply line unless you have sufficient capacitance to deal with it.

@Afrotechmods I believe that my experimental results was in accordance with the theory of electronics and closer to ideal results because I used more ideal components (a good quality servo motor, MUR415 ultra fast diodes and twisted cables for the power supply). If you used slower diodes, or a motor with noisy brushes it is possible to have additional spikes and not so ideal response.

This can also be applied to a regulator (boost, buck, and linear), since reverse current is still an issue. Simply use the diode concept on the input and output of the regulator. Look into power diodes for higher currents common to switchers.

Should there be a 0.1 uF ceramic in parallel with the diode? I wish to switch a large motor (24 vdc, 5 amp). Oh right...love your work. so helpful to so many.

Hi Afrotechmods, thanks for your video sharing but I have a question. If I parallel a diode with a dc motor, the spike will be reduce? or it is normal for the motor's PWM waveform contain spike or noise when it running? Appreciate for your reply, thank you very much^^

Love your videos! I had never though about trying this on one of my flyback transformer drivers, particularly my 555 based driver where I keep killing MOSFET's.

Hahahaha, you crack me up! I enjoyed these tutorials so much!! Please don't stop uploading... I'd even pay for info like this! YOU ROCK!!! Where do you and this info come from??

Best one soo far!!❤

Thanks for the information, I have one doubt is diode is require when the motor is connected after MOSFET source to ground.

@ntomata0002 Next, if you add a bulk capacitor after the power supply's series diode, you will see all those spikes go away. This is because it only takes a small amount of capacitance to 'absorb' the freewheeling current in a small motor. So by doing this experiment you can prove that current not only recirculates back into the motor but also a small amount will be returned to the power source, and in most cases a capacitor or rechargeable battery will absorb it without a big voltage spike.

@Afrotechmods I spotted it after watching the video again, by the oscilloscope outputs it looks like the inductance to your motor was strong and the roll inertia weak, my motor was the opposite, the inductance current clamped by the diode was dissipated within some msecs, while the motor continued to roll for 500msec working as a generator (producing voltage but no current).

Great and easy to understand explanation, Thanks!

Wow you make such great videos, i learned a lot from just watching a couple of them. You really know your electricity, but whats different is you can actually explain it so even idiots like me can understand it, thanks

Salute to the gentelman! Well concised video short and simple which covers essentials matters cheers

Thanks again for another great video. Keep them coming.

Wow very nice explanation 😀👍👍👍 I have a problem on my walkman.. the speed of motor for tape is not stable.. and i try make test tape at 1khz of sound and measure the speed of cassette is not stable.. i changes motor and pwm control nothing changes still same when i analyzed the circuit there are small mosfet and pwm and the motor act like inductor coil.. i measure the drain of mosfet yes! There are voltages spikes when the 2 coil of motor is ON and turn again into another coil has voltages spikes.. i see i have diode open. And i changes new the problem is sold 👍

without the diode i get a 128V spike with the diode i get about 38V spike on tiny dc motor being switch @1Khz , my mosfet can handle it but how can i reduce that spike more? 38 seems a bit too much still

Hi! Good idea on this video. I've been struggling with my car heater speed circuit and I was actually suspecting this was the reason for the main transistor blowing up every time. Do you have any experience with these type of circuits? It's an old car so it uses one of those big round cap type of transistors to hold the 12v motor voltage back when turning at lower speeds. Thanks in advance.

This explanation is gold !!

@ntomata0002 Nope, just a plain simple small DC brushed motor. There is some brief footage of it in the video at 4:16

Such a good and well explained video

Great clarity. I'm subscribed.

@steveBB30 Well you shouldn't be using a low side mosfet like in this diagram to switch any AC voltages so it's not really applicable.

EXCELLENT EXPLANATION!!! Thank you very much for this..

Another excellent video/explanation. Thank you very much - again!

your videos are easy to understand. thanks

appreciate the valuable information, i am 128hz pwm a 12v 18 amp dc motor, what is a suitable diode value? thank you

@ntomata0002 You can also try this for dramatic results: Put an extra diode in series with your power supply, and do not use any bulk capacitors. Then connect the motor & flyback diode as normal after this extra diode. This diode will tell you if any current ever goes back to the supply. If no current goes back to the supply then this diode will make no difference right? But view the voltage just after this diode, and you will see large positive voltage spikes on the flyback diode's cathode!

yay i always happy when you upload a video :3

@ms63129 All circuits are RLC circuits in some way or another. The parasite resistances, capacities and inductancies might be too small or too large to practically figure them in a model but that doesn't mean they are not there. The shape of the voltage spikes, as seen in 1:36 clearly corresponds to an RLC circuit.

@ntomata0002 I probably should have mentioned the motor's mechanical inertia too. If you have a motor rolling along, then you turn the fet off, that motor is going to act like a dynamo for a short while until it stops.

Thanks for all the information. Suppose the engine will change direction from time to time. Like CW CCW. Do I need to connect the two opposite diodes in parallel with the motor? What kind of diode should I choose for a 24V 15A (nominal) 895 model number 12000 rpm high torque Dc motor. Please help, I'm trying to build an electric skateboard thanks.

Hi Afrotechmods, i have exactly the same configuration as your schematic above, with an n-channel mosfet FQP30N06L. and my load is 12v 50w incandecent light bulb. My PSU is a 12v 70w SWPS. I have a 1N4007 diode across the lightbulb and switching the mosfet on and off at 100Hz. i am still seeing 78v spikes at the drain. could you have a clue as to why this is happening? your help would be greatly appreciated!

Best 5 min video ever

Excellent video as always. Thanks!

@pawningcity I already have one... search for PWM tutorial

How do you determine what value of diode to use, especially when you don't have a DSO that can capture the spike when it happens to look at the measurement? A small solenoid would have a smaller spike than a big motor, but in either case how do you know if you've selected a diode that will provide protection without itself being blown up by the spike?

I love your channel please keep it up

@pufarinu It's a parasitic diode, created by the process used to make the MOSFET. i.e. it's not deliberately put there. It may be a good thing or a bad thing depending on the application.

@ForViewingOnly those voltages will force the transistor to conduct (like sparking inside it, if the volts are higher) and they can damage the thin iron oxide layer (the gate)

Hi... Does placing the N-Channel MOSFET on the other side of the load protect the N-Channel MOSFET from the motors inductive energy?

I have a 240v ac drill press which i want to add to the start circuit/button an LED light which is designed for 240v ac operation. The LED is a ring light module with an inbuilt voltage controller/regulator. Will i need add any protection for the LED circuit ??

So I have crisp clean V but have L spikes of -.3--1.0 amp; will this help smooth those out aswell? I keep hearing so many different things I dunno what to believe.I do know I've hooked up electrolytic and ceramic and still bad amp spikes but nice voltages..

I know this stuff but still I enjoy watching your videos :D Thumb up

Excellent explanation, thanks for posting.

Very well thought out tutorial!