This $0.70 Component SAVES your Circuit?! (Surge Protection) EB#59

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.

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.

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

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.

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!

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.

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

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.

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

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

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 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.

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

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.

Thanks for another clear and informative video Scott

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.