I had lighting strike the radio antenna of a cellular remote oil well monitor that I had built a long time ago. It skipped right over the lightning arrestor on the antenna cable and blew the ground track off the entire circuit, through the cellular modem, through the serial cable connecting the modem to the PLC, through the PLC circuit board, through the ground wire and into the electrical circuit on the engine skid that was supplying power to the automation panel. Was a hell of a thing. The ENTIRE circuit from top to bottom vaporized. There was nothing left of the tracks at all.

I repair control circuits for some industrial equipment, and they regularly use both a TVS diode and GDT in parallel on each line. The TVS diode handles the lower voltage transients, while the GDT protects against higher incidents like lightning surges. It works very well, and it's easy to test and cheap to replace if it does blow.

Here's a video idea: Signal integrity When and how to use shielded wires, coaxial wires, differential twisted pairs, ect and avoiding issues like ground loops (like connecting the shield only on one end) ect

When designing automotive type electronics that had to meet EMC standards, the electronics had to withstand ESD discharges up to 15kV. Something as simple as a 1000pF cap at the input was often sufficient protection. Signals that couldn't tolerate that much capacitance were good candidates for a TVS diode. For power line transients, which are much longer in duration and contain much more energy, a larger TVS was usually the solution (perhaps in a SMB package). The datasheet will tell you how much energy a TVS package can handle. MOV's weren't used, and I get the feeling that they are more oriented towards mains power where lightning strikes are a risk.

these should be compiled to a playlist "things i should have known before starting electronics". this is a huge lifesaver. good work as always.

Varistors are way slower than TVS diodes and aren't fit for fast transients such as ESD & EFT. Another thing to remember is Kirchoff's law, any current pulse will return to its source. Therefore instead of trying to suppress a pulse it is often more practical to divert it from the sensitive components using spark gaps etc

"Doesn't happen often that lightning strikes near you." I live in Singapore and I've had a thunderstorm every afternoon for the last three days. Yesterday the lightning strike was so close you could hear the crackle before the bang. But at least the humidity stops you getting static shocks from the carpets in the office. Something you might be able to advise on is the problem that I have, which is when there is a lightning strike nearby my RCD trips, none of my neighbours seem to be affected. I've always thought it was because I have an induction hob and the coil is picking up the EMP from the lightning and creating a current flow in the neutral line, as normally the hob is switched off at a wall switch, (which I assume only isolates the live), and hence causing a differential L to N current flow. You could probably have used an electric fencing unit to create a known and constant voltage, or a car ignition circuit.

I'm familiar with GDT as a "Comgap". As in communications gap. Back in the landline days, they were a required component (in Canada at least) across tip and ring on a phone line. Every modem had one for example. It was to supress lightning strike level voltages from reaching the consumer. If it happened to protect a circuit, that was just a side effect. They were often used in combination with a MOV. Old-school rotary phones generally didn't need them as the ringer coil would take the punishment instead.

As a notebook repairman, I am very familiar with diode arrays, it is very common to find them protecting the USB, HDMI and other connectors on the boards, many versions of notebooks for home use differ from the corporate versions in that although they have the tracks, They do not have the chip installed, this small saving makes the notebook much more delicate, plus now all those connections go directly to the SOC, system on chip, practically killing the processor in the event of any incident.

Hi GreatScott. Good video! I would like to add a few things: 9.44 the fuse in series with a varistor that you have drawn is not a thermal fuse, but an ordinary fuse, which would open when a varistor is damaged due to a high surge current. A thermal fuse is usually added in series to the varistor, so that if a varistor gets damaged and it conducts some small current it gets slowly hot - in that case a thermal fuse would open. some manufacturers even include a themal fuse in a varisto case, so the varistor has 3 pins. But you mentioned that the fuse blows when¸ an overvoltage event takes place, which is wrong. this would be a terrible design. actually we have to choose fuses, which have a high I^2t rating so that they DON'T blow during expected surge events. Your testing is only with ESD pulses, for which TVS diodes are best. Varistors and GDTs are used for surge pulses (indirect lightning strikes and inductive overvoltage events) which contain much more power. the 8/20us pulse is a typical indirect surge testing shape, which has 8 us of a rise time and 20 us of duration. there is also 10/1000us which has much more energy. ESD protection and surge protection are very different things. Usually for surge protection we use several of these protection components. for example we start with GDT, then varistor and then with the TVS diode. All three seperated with an inductor. Current and voltage on the device gets smaller with every component. 11.46 this is a thermal fuse and it opens when the varistor gets hot. the failure mode of a varistor is that with every surge pulse it conducts more leakage current. and when this leakage current is smaller than the current fuse in series, the varistor gets very hot and it ca cause a fire. that is why standards determine there has to be a thermal fuse there, which opens when varistor gets too hot. then it is time to change the protection module. Note that an ESD pulse has a rise time of 1 ns and duration of approx 50 ns. But a surge pulse has a rise time of 8 us and duration of 20 us or more. The problem with varistors is that the current through the device is increasing quite slowly with voltage rise. But a TVS diode's current increases much quicker with increasing voltage. at 7.58 you drew the correct V/I characteristic. but when you dig in a datasheet you see that the current rise in varistors is very slow. For example the varistor you showed MOV-20D681K conducts 1000A at 1600V and 1A at 800V. so it need additional 800V to get from 1A to 1000A. Usually a varistor is not used as a ESD protection device. I think it protected your circuit due to varistors parasitic capacitance, which conducts ESD current and not really due to the varistor voltage limiting.

Thank you for the video! The MOV surprised me in this experiement, I didn't expect it will protect against sparks due to its slower reaction. I designed an off-line converter with an LNK-304 and lacked the mov. When my father plugged in a washing machine to the nearest socket the IC blown away. Never lack the MOV!

9:37 Quick correction, that isn't a thermal fuse, it's just a standard electrical fuse. A thermal fuse is tripped when the temperature of a component gets too high. For example on motors to stop the windings from burning, electric heaters to stop your house from burning, hotplates to stop the hotplate from burning and so on. The resettable thermal fuses are usually found on components like electric heaters, hotplates, dehumidifiers and other devices, though are a first line of defense, they reset after the temperature drops (though microcontrollers have taken their place in some applications) but they'll also be found as second line of defense devices on industrial electronics (or higher end consumer stuff) where you have a uC and temperature probe (thermistor or thermocouple) monitoring the temp, but if the uC crashes, the resettable thermal fuse cuts the circuit, then if that fails a thermal fuse (attached using thermal paste) blows, giving the device 2 chances to recover and one chance to need fairly simple repairs.

A thing I like to do to protect low current inputs is a high value series resistor and a capacitor to gnd behind it. The resistor limits the current and the capacitor just eats the charge, so there is nothing left that the internal protection can't handle. Great for button inputs, as this also covers debouncing or acts as a low pass for "slow" analog inputs

This video is really helpful. I suffered a power spike a couple years ago when the transformer outside my house blew up. lost a few appliances, namely my robot vacuum, looking at the board there were large scorch marks and some exploded components, after some research I discovered it was a varistor. easy enough to replace and still working to this day

Love this. Been researching ESD protection options and came across TVS diodes recently. This video really sold me

Thank you for this video, i love almost every video Great Scott produces. MOVs are commonly used with a few other components in AC power supplies such as class Y capacitors. I would love to see these covered in similar videos. Please and thank you.

Nice video, very informative. There is one thing I was missing. When adding such a protection to your pcb, you should pay attention to your layout and routing. You must route your wire through the pads of the tvs/mov to get the best results. And ideally they should be close to the connector.

One of the most useful channels on YT thanks GreatScot this is really a great video.

Good video. I want also mention, for low speed input lines often simple ceramic capacitors are used to protect the input from ESD loads. Usually 10 to 100nF are used.

Thanks for another clear and informative video Scott

I built a home energy monitor using CT clamps, and I learned they incorporate a TVS diode inside the clamp. Because without any load on the other end of the clamp, the 100A of current on my main line running through the core can generate theoretically millions of volts, and the whole thing just explodes in a puff of smoke without even touching any metal wires. I learned about their existence because I didn't understand any of this and unplugged my CT clamps from their load while current was running through them. The TVS diodes did their job, shunting the voltage to I think 22 volts, and making a hell of a racket, both noise and vibration, while they did so. Both clamps were unharmed and continue working accurately to this day.

I never knew about transient voltage suppression components. Thanks for walking us through-it was very interesting!

I would like to add some observations and know more. I have seen many SMPS with MOV for protection. First failed component I always saw is MOV with dark discolored and often cracked like 2 separate disks for each terminal. It happened over a few years in India and often with power surges. Specifically they open circuit after 3-5 power surges. Which is around 2 months of time. I tried observing this because another SMPS had a fuse installed instead of MOV with almost same rating. These SMPS were used to power small LED panels for a business display sign with a LED driver always.

Great video, Scott. Packed with loads of interesting info. Thanks for sharing.

I have experienced two direct strikes on antennas fitted with lightning arresters and direct grounding wiring. The equipment survived without damage but proper protection is a bulky affair with thick cabling required to provide a low impedance path to ground. All the power circuit protection devices tripped, but no damage was done and everything worked after the tripped breakers were reset.

When using a MOV on high side of power supply, you need to take account their failure mode: slowly conductive. So either couple them with thermal fuse close to them, or a combo MOV+ThFuse, or you can end up with a fire event in case of repetitive surges.

Love it, thanks for these practical helper videos

I wonder how effective spark gaps are, given they're pretty much free to add to a PCB. Our TV's power supply got quite a few of those, and after a lighting strike nearby, the cable TV box burned and it made the favor of killing the TV's motherboard through HDMI, along with the Switch dock on that same TV. Replacing the motherboard made it work again, but after a while the power supply also went bad, and I could see on the mains pins a tiny welding like dot on the metal casing (clearly an arc mark), along with a missing spike on the spark gap PCB track. It was already more than 10 years old at this point and it still survived that lighting strike.

Man, I've been a fan of yours long enough to know your real name. Haha, I think it's about 10 years that I have been a subscriber (when you still responded to messages on facebook within 24hrs, haha). I started watching you when I was in high school at 14 years old. Actually, you played a very big role in me studying BEng Electronic Engineering. I am now 24 working as an electronic engineer. I recently did an ADC protection design for one of our products where I used TVS diodes. I actually learnt what those are from you years ago. If I ever find myself in Germany, I'd really like to have lunch with you. I don't think you realise how much of an effect your videos have on some individuals. Much love from South Africa.

Wait a moment... That isn't ElectroBoom job?

It's very educational to have all of these in one video. Well done.

Small Neon Bulb can also serves as surge & lightning protector and suitable for small outdoor antennas. Its break over voltage is about 90v

Ngl, this is the first time I've heard of a MOV, and the timing couldn't be more perfect!

The GDT can create a lot of interference and scramble sensitive logic circuits digital logic since when the tube fires, the voltage across it collapses very quickly to a lower voltage, creating EMC surges. TVS diodes and MOVs tend to create much less EMC interference because they clamp the voltage and don't exhibit the voltage collapsing effect. So whenever we have to use a GDT (for example, when extremely low leakage current and stray capacitance is critical), we have to incorporate other protective devices in such a way to minimize the EMC surges.

nice video greatscott. thanks for sharing.

As far as your microcontroller supply line goes, simply adding the 100n decoupling cap that should be there anyway will pretty much protect it against ESD. The pulse is high voltage but very low energy (standard ESD model often uses 150pF) and thus the decoupling cap will act as a capacitive divider and "eats" the ESD pulse.

The main reason the MOV is protected by a fuse in series is not because the fuse will blow in the case of an overvoltage event. As the MOV starts to age due to surges, its resistance decreases, which in turn increases the current flow through the MOV, leading it to heat up and you end up in a vicious circle that will end in the MOV bursting or cathing fire and the circuit, without the fuse, drawing way more amps than anticipated. In order to protect that from happening, the MOVs are now protected by a fuse.

Good content! Thanks for sharing

Thanks, sometimes I think you are looking over my shoulder with the timeliness of your videos. Right now, I was designing a circuit that needed this type of protection, and here you are with helpful advice.😀

We used to add MOVs to anything with an inductive load (PLC control systems working at 24VDC). Even contactors or solenoid valves can be a problem. Inductive spikes were a particular problem with high speed counters or servo-motors which use incremental encoders. An extra count here and there can really foul things up for the position of a pick and place robot.

Very interesting and informative. thank you for the great videos keep it up

Thank you for the deep-dive and clarifying these parts. What is the best practice for TVS application in a digital circuit? Just on the power rails? Power rails and any connections that touch the outside of the product housing? What about cap touch LCDs that get touched (obviously) - their power rail too?

Interesting, educational and entertaining as always! Thanks for making and sharing!!!

We usually work in solar systems and we use surges all the time in both AC (grid input) and DC (pv input) but not these types it is similar to the red one but a glass insulator breaks open and allows everything to flow to ground instead of dissipating as heat and it is connected in parallel with the circuit. AGAIN IT IS USED FOR DIRECT LIGHTNING STRIKES AND CAN ONLY POP ONCE BEFORE DISPOSAL.

TVS packs are the electronics tinkers best friend!! In many years since I first used one I do not think any of my projects have ever been without one. Though I have moved in the last few months to a new location there are so many things they want me to do here. First was the safety light in the stairs and then the active emergency LED lights in various rooms that are going through a minor upgrade. But the use of the TVS ane other types of protection devices is common in this lab. Peace

Hey GreatScott!! I would love to see a video about ferraite cores.. how do they work and when/how to use them 😊 i think its a quite intersting topic

Thanks for sharing a great video and topic

At 6:12 there is a mistake: increasing the air gap doesn't increase the voltage across the board but only the voltage across the air gap, doing this just increases resistance and reduces the current.

Awesome! Thanks a bunch for another lesson, dude! 😃 Stay safe there with your family! 🖖😊

This turned up at the moment I needed it.

Nice video 😎 Off topic: you make new coilgun with capacitors and igbt/scr ? 🙃

Fun fact: some CRT display video output amplifiers used neon bulbs to protect against the CRT arcing through the video output electronics. Quite like a GDT as shown in this video, but you could see them flash occasionally while in action.

Fantastic video, thanks for sharing!

Amazing video, learned alot!

Just woke up and learnt something about overvoltage protection. This will be a great day!

Thank you @greatscottlab This video was very educational. What book would you recommend getting similar information for electronic tinkerers? I typically find very theoretical books on electronics or super simple books which mostly around: how to tinker with arduino with components. I saw a video from Adrian Black once, where he exchanged elcos agains ceramic caps and worked with a conversion table. I really would like all these practical helps in a single source like a book or similar.

Hi Great Scott! Very interesting program. Great that you opened the two overprotection circuits. Interesting to see what they are doing to protect from the surge. HOWEVER, the really interesting teardown would be the OBO Bettermann Surge Protector. I have been wondering for many years what is the magic in there and why they are pretty much the only source for this class of surge protector and what they use in there to justify such a steep price. Last time I looked at them some 20 years ago they were over 300 € each. So, if your budget for a program stretches tgatbfar could you examine the OBO device. BTW the OBO device is the one that is use by pretty much all the railways around the world for serious surge protection. So, what is their magic sauce?

Thank you for this informative video. Hopefully it solves my home made MPT Solar Controller which has failed twice now, due to local lightning strike ⚡

You can make a zenner diode go there, you can even create a zener diode serial array. This way you have a full wave antenna that bounces until it adds up to the next zoltage. So you wrap up full wave zeener diodes inside the blade antennta, at each stage, well it is mhz, so the audio is much louder in real time.

If you ever saw or will see such an IC on a PCB then there is a big possibility that it is a transient voltage suppressor IC

Increasing the gap voltage doesn't change the voltage applied to the board by much since most of the extra voltage simply gets lost in the arc. It does increase the peak discharge current though. As for why the MOV manages to save the circuit despite having much higher voltage, that is down to your generator having pFs of output capacitance discharging into the MOV's nF of parasitic capacitance, forming a capacitive voltage divider that drags the discharge voltage low enough to save the input pin from excess ESD current. Also, IO pins have their own internal protection from the output FETs' body diodes that can usually handle human-body-model ESD as-is as long as the chip has a path from power+ground pins (depending on ESD polarity) to actual ground. Chips on an assembled grounded PCB can be surprisingly difficult to kill as Linus demonstrated in his Electroboom special.

Awesome!!! Thank you!

Very nice video! One overvoltage protection circuit (not sure if it'd be a surge protection then?) that I found interesting is the crowbar circuit. I saw it first on the output side of a 3.3V PSU, but don't know too much about their effectiveness, are those too slow to act as surge protection?

Thanks for the video. What would be equivalent protection chip for 3.3V? Many of us are switching to ESP32.

Excellent video , could you put all 3 in parallel? That would give speed and high energy?

I dicovered TVS and varistors while reasearching for a DIY TIG welder, they seem to be used at the output of the Diode rectifier to avoid the HF/HV starter from blowing the diodes

Very interesting video. Definitely learned something.

Very interesting. Thanks for an informative video. This isn't something you often think about when building a circuit.

That was Great, Scott!

Hi Scott love your videos. Are you maybe able to make one about zigbee and possible ZigBee Circuts? I find the tech really facinating but doesnt quiet understand how to use it myself... LG

Nice informative video once again

About 10 years ago I accidentally connected a 12v dc circuit to 240v ac, when it didn't work I soon realised my mistake and connected it back to the proper 12v dc again and it worked. I've never quite understood how the 240v didn't fry it. that same board is still working to this day.

It would be interesting to see you build some "crowbar" circuits for smaller electronics so we could see how they also work in protecting electronics.

GDT is used in telecom wire communications mostly great scott

Hi Scott This video is really interested, I am about to built a PoE injector for my wireless point to point device , I wonder if I added the GDT over the data line is that will effect the data rate ? the connection speed of the data is 1Gbps , is that make work in less data rate ?

Danke vielmals für das Video. Genau das war gerade Thema in unserem Repair-Café (der Kollege konnte die TVS nicht identifizieren) und ich frage mich selber schon länger, welche Optionen ich zur Absicherung einer Schaltung noch hätte. I will stay tuned :-) - Liebe Grüsse allen Klein und Gross

Thanks 👍

Varistor are common in circuit specially in smps but there is problem. If there High enough voltage it will arc between the pads of circuit. I have literally fried 3 smps in similar way. When I opened it up the copper pad were the witness. So tvs diodes are perfect for such applications.

It probably should be mentioned that MOVs have a limited number of "hits" they can take. Or to put it another way, they get less effective each time they are activated. It would be very informative and intuition-building to see you demonstrate that effect!

This is probably the best video I've seen about a concept I knew about but hadn't delved into. You mentioned that a MOV is often alongside a fuse in a power supply that blows when such an event occurs. I'm wondering what the fuse adds in such a circuit beyond fragility. Is it for non-transient high voltage events?

.... Another repeatable and controllable source of high voltage spikes would be the inductive spike from opening current path to an inductor (normally suppressed by flywheel diode)...

Idea for next videos: Recently I found out that I can power my Black pill from my smartphone with simple TypeC-TypeC cable (yes, it's all about 5.1K resistors). Could you please research on it and investigate max power capabilities smartphone can have, which other embedded devices it can power, can it power small motor, can it be burned down, does smarphone has protection agains overcurrent and so on? For me it appeared like an interesting topic as I am currently developing 2 small projects where my devices are not required to run 24/7 but only when only man uses it. So I could get rid of wall power adapter or Li-ion battery

I have had overvoltage(home) in sockets but the ptotecton has not blown due to low power demand aka no load but low power devices and those devices have got lots of damage, some insta out of commission others over time.

Great info!

Great video!

Spark gaps on PCBs are also commonly found in the primaries of power supplies for this purpose. Thought they deserve an honorable mention :))

Question is what pins/components need TVS protection? Does each signal on a PCB need protection?

I learned something new through your video

Is there a video of you making the HV generator?

Them huge capacitors on the spinning magnet wheel.... Memories of the simple schoolgirl engine & beyond. Bedini would be proud. Now just catch the collapsing spikes in a lead acid battery, to feed back to the capacitors. Not perpetual motion, but tuned right, a heat pump that can run for a surprisingly long time.

I have had a MOV absolutely blow it's guts up in a shower of sparks in a power supply for my PC, it was green in colour and ceramic and was within the power factor correction side of the circuit. I was having constant over voltage events of around 255V for a year and I think it wore out or something. All I did was flip the switch at the wall

Haha, I just got a bunch of 6 leg micro packages in and spent hours manually soldering those legs without a breakout board! Broke 3 legs off before I could get one working and said f this and ordered break out boards.

Thanks. The amount of boards that blow.... and now i know what those funny things are - i thought they were caps but didnt behave like caps.

Reminds me of “load dump” in car electronics. Never really figured out what to do about it and figured if it happened I’d have bigger problems than my relay drivers failing. Fused MOS might have been a good solution.

9:25 ".... dies immediately...." (shows a working circuit) 🙃🙂9:39 ".... that blows when overvoltage takes place", you mean current. Such fuse blows only when there is excessive CURRENT. 9:50 Aha! I spotted one (GPT) in an inverter, didn't know what it was until now. It was tied between the 230v output AC lines (N & L).

question. does the cheap SPD have an LED in series (leak current) with MOV? if so would it not work in reverse flow and not react fast enough?

Great video, but you probably should have mentioned the fact that MOVs wear out as they provide over-voltage protection.

Thank you. I have a Ethernet switch had on solar power and the 12 volt regulator went bad and it did about 24 volts then and 2 surface mounted components right by the power input blow up L2 and L3. From this video I order 2 SZSMF4L12AT3G Zen TVS 400W 12V UNI from mouser. I hope that fixes it. Looked up "12 volt TVS diode" I guess for 12 volts it should be 12 volts right or maybe a little more for leeway? Thank you.

@GreatScott -- I don't know how deep on this topic you're interested in going, but -- in light of your summary at 10:31, it would be interesting to explore how to use these components in combinations. (Along with "spark gap" which is essentially DIY GDT.) It might seem using these in some combination might handle multiple over-voltage/arc scenarios, but does the right protector step in at the right time or voltage to avoid the other protector getting overstressed?

I guessed it correctly at the title. Never seen one that small but i have seen it everywhere on good quality electronics as a blue coin battery shaped module.