How to implement Reverse Polarity Protection in your Circuits! ll Diodes & MOSFETS
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- เผยแพร่เมื่อ 7 มิ.ย. 2024
- Go forth and protect your circuits from a potential disaster!
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The key to successful electronics work is keeping the smoke inside your components.
Underrated channel. Definitely needs more subscribers and views.
Subscribed. Usually I'm turned off by funny bits in educational videos, but your deadpan delivery makes it.
Great detailed explanations along with great demos.
I really like that you provide the schematics for your circuits as well.
You've got a new subscriber. Keep up the great work.
Good job sir!
Really glad you are back.
Thank you.
Excellent video. Very well presented... WELL DONE!!! 10/10
Excellent demonstration! This was just the information I was looking for. Thanks for posting.
Nice video. I am missing the double MOSFET protection in this case. Which fixes some issues of the single one with a penalty of some additional costs and board space. Also there are some integrated circuit ones with even more control in a tiny package.
Very well explained with practical demo great video sir
Great informative video and demonstration
So well explained
Well explained.
The LED is also a "Diode", so its a poor test example. In reverse polarity, the LED would not illuminate; regardless of the additional protection diode.
I think two LEDs back to back would have worked great for the examples. One lights up either way.
That's a good point!
That's why he reversed the LED for the reverse polarity tests
Thank you for this great video. I learned a few things. I was wondering if you Know if using a MOSPEC F12C20A and its pair F12C20C or, the U30D20A and its pair U30D20C That are used for rectifiers would work. As you know no matter how you connect the power source ( as long as it is not connected to the commons ) It would only pass positive in one direction to the load. It might not work for a charging situation just for loads like you mentioned? I don't know too much about voltage loss so I am hoping you can tell me if this is worth the effort. I already have the MOSPEC F12C20A and its pair F12C20C.
Well done. Thanks.
thanks! this video really helps. that voltage drop with the schottky diode is irrelevant cause im regulating the voltage to 5V anyways.
Amazing video
have an old amp that uses both negative and positive sources from the caps. Can I use a shotky on the negative side rail as well? Good info. ty.
Would the mosfet be a good solution for protecting a ham radio against reverse polarity?
Do you have any recommendations with as much detail in this video for an AC coil relay with AC inductive loads?
What method should one use for the voltage rail connected to voltage regulator?
Can this be done on a ATX power supply 12v (yellow wire) ? I am wanting to replicate a -12v polarity using a +12v wire . Basically I want to replicate or make another blue wire that is -12v.
Thanks in advanced
Great video. Btw, Did you draw the wrong schematic at the 5:40 mark?
To improve the P-channel mosfet circuit, a second transistor can be added to cut off the mosfet gate when a load voltage is applied
Is there a video for this?
Does the SR540, and SB540 do the same thing? What is the difference? Awesome video, btw!
The third method could we not add a Schottky diode inline if the load were a battery? This way the voltage would flow only one way (basically a mixture so the fet is replacing the fuse in method 2 becoming, in essence, a resettable fuse?
I love it!
I loved the intro
So, I just was wondering what type of protection from your proposals do actually use all those 18650 Chinese cheap chargers.
What kind of protection is suitable for reverse current protection?for example if I connect a buck converter with 3 volt output to a 3.5 volt lithum ion battery this cause a reverse current to buck converter.I destroyed too many buck or boost converter this way🙃🙃
If Mosfet allows current to flow both ways as you said, how in the world that translates into protecting your power supply from reverse voltage, say if you have an inductor ( a coil of wire) in the system while it is switched on and off?
thank u so much sir
Good video
Appears you have made a mistake in the schematic diagram. The diode across the supply voltage should be AFTER the fuse, so when the supply voltage is in reverse polarity it will pop the fuse. What you have on the schematic diagram will cause a short circuit directly to the -ve terminal.
hi, all , me and my so race rc buggys , we have a Lipo charger 16 amps max , if we plug the Lipo battery into the charger the wrong way it blows that chanel on the charger , , can some tell me , if the mosfet way in this video would work , between the charging lead , ????
Love your Videos!! But there is one more way to protect when charging, but requires elbow grease!!! A simple switch and Relay!!! Great Video and I'll definitely share this when needed!!
Wouldn't the delay inherent in relays allow current to flow that could damage the power supply?
Gracias
Can we use relay instead of fuse
I've seen this done with a bridge rectifier to the circuit and they then polarity dont matter. Only draw back is more voltage drop on because of more diodes.
Nice.
Thanks for the info, please tell me about your choice of using 100K resistor and not a 100 ohm resistor to the gate
Reducing energy wasted by the gate circuit. You only need to overcome the gate capacitance of the MOSFET once, after that any additional current flowing is just wasted.
With the Schottky & fuse method, I've seen the Schottky go open circuit after being overloaded, although the equipment was successfully protected.
Unfortunately the user only knew that the fuse had blown and replaced it. The equipment worked perfectly until the next time he connected it up wrong, this time there was no protection at all and his equipment was wasted.
Not a good protection method at all, IMHO.
If a fuse is blown the end user is to blame when it happens, so the same end user needs to check the diode as well as the fuse and replace both if needed. Most will not and happily continue on until the next time the equipment is blown. To be honest there is no real way to protect a device from idiots.
@@generalawareness101 You are making the assumption that the user knows about this method of "protection". Fuses are common devices which are replaced as a matter of practice, diodes are not. The user may realise that the fuse blew because the polarity was reversed and know not to do it again but may not be the only user of the same equipment.
@@chrishartley1210 I think we are talking about two different classes of end user. You are talking about the WalMart type while I am talking about the ones watching this video. The DIYer type.
@@generalawareness101 So does that mean that only the DIYer is allowed to have a reasonable level of device protection? That was my criticism of this method as a means of protection.
@@chrishartley1210 For the three methods mentioned? Yes, only a DIY'er as there is a fourth method I have seen in products that were not made in China. TBH if it is made in China 99% chance that if you fuck up and reverse the wires you will kill the device instantly and release the magic smoke. The Chinese made products don't even connect the ground wire up on most items so it isn't just a reverse polarity issue with their shit. Do I buy their shit? I have no real choice, but I know the first thing to do is open it up, make sure all mosfets are tightened to their heatsinks, that the ground wire is actually attached to the outer case (even if it is make sure it is in contact as some are but are insulated due to paint then they connected it over the paint). Basically the WalMart types do not have the education, or just experience, to handle all of that so releasing the magic smoke is the least of their worries. Most quality made goods (iow not made in China) has reverse protection that works and are really grounded. People scoff at UL but if it doesn't have their seal I will not touch it (unless really cheap and I will go into it to make sure it is not going to burn down my house, or kill me, which both almost happened to me before so I learned the hard way what to look out for).
I was a bob when I hooked up the battery on a VERY expensive generator with electric start. It started but a few seconds after running, the control box let out the magic smoke. I burned up the charging circuit. Hooked the battery up in reverse polarity.
How do you calculate the required / ohm resistor? Can 100k be replace by other value?
Yes it can... Depends on Vgs(th) of p MOSFET enhancement
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In the case of a battery backwards across a power supply, a series diode is not the best solution, regardless of type. The supply and battery are simply in additive series at that point and while the diode may act like a fuse and pop, it still risks overstressing the supply. It's true the supply won't see reverse polarity, the battery still will see a polarity that opposes it's own, and your internal shunt diode wouldn't have popped, but that's not... Well... Ideal... Even tho a battery with a discharge rating in excess of the capacity of the diode will eat that just fine.
It will however save equipment from a flipped supply.
The shunt version is much more robust in either case. The little bit of reverse voltage the equipment sees is minimal, you'll only have a problem if your device runs on very low voltage to begin with.
The MOSFET version is really overkill (especially if you are running heavy enough current to warrant a heatsink) as it doesn't save much in terms of losses for normal operation over a schottky.
Schottky and fuse FTW.
Sometimes I wish videos like this were on the early TH-cam back in the early 201x's. Could have saved myself alot of torture 😂 next video show us how to build a time machine? 😁
I'm working on it ;)
Finding that flux capacitor is the hard part ;)
What about a diode in series with a relay? Wrong polarity... it doesn't allow the relay to pull in and of course the relay contacts must be able to handle the voltage and current. The down side is that the power supply must be a fixed voltage, which is perfect for battery chargers.
Before Schottky diodes were selenium rectifiers... about 50mm square bolted to the chassis of a Pye AM10D radio telephone and its protective fuse was 10 amps. I never saw one of those fail to blow a 10 amp fuse... well not until some prat replaced his blown fuse with a 22 cartridge. The boss went ballistic when I told him about it.
i did a bob...or a boob.... now my 1970 something all original farnel l30b doesnt have working current limit...
Oh no, that's a heart breaker!
Can you make a circuit that reverses the polarity every 0.5 seconds?
use a h bridge to your load with suitable components that switches at a 500 ms frequency. maybe.
Best protection is relay
🤘🤘🤘🤘🤘
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Lolol my diy power supply has reverse voltage protection. And I never have this problem. 😁😁
Hi I am Bob,
Power Supply: Go away!
That could make a great T-Shirt!
Hey, Bob's your uncle.
Amon, I think you may be a bit confused about what "reverse polarity protection" means and what it's intended to protect against. A few places in the video you put a battery where the load would normally be, then declare that the reverse protection doesn't work. This is not the scenario it's *intended* to protect against. Reverse polarity occurs when a source's positive and negative are swapped, not when the source is moved elsewhere in the circuit, or when two sources feed the circuit from opposite ends.
At 3:53, your diagram and description will *only* work to protect the PSU against a reversed battery. I realize you were using your opening scenario as the example, but you said, "battery slash load." If a load is connected backwards using this arrangement (in place of the battery in your diagram), it will *not* be protected, as the diode is still reverse biased by the PSU. For a typical use case -- trying to protect a load against reversed PSU or battery connection -- the fuse must be to the right of the diode, so that if the PSU is reversed, the diode will conduct and blow the fuse.
At 5:30, and later, your schematic shows a battery as source and motor as load, but again, the fuse is in the wrong place. If the power source is reversed, the diode will present nearly a dead short and may overheat or explode, but the fuse will not blow and the load will not be protected (in this case, the fuse must be to the left of the diode to have any effect).
At 7:59, your white-board drawing shows the battery positive connected to the MOSFET's gate and negative connected to its source. This puts the gate at a higher voltage than the source, which will turn *off* a P-channel device. As drawn here, the MOSFET would *not* conduct if the PSU were removed. However, a few seconds later you clearly have the negative of the battery connected to gate and the positive to source, which will of course turn on the MOSFET and light the LED, but your voice-over suggests that this is unexpected. It shouldn't be; it's perfectly normal, and it's not a failure of the reverse polarity protection circuit.
The series diode would be inside the equipment to be protected, not at the supply.
In the scenario given with the battery as the "load", the battery and supply would effectively be in additive series (so if your intent was charging, essentially attempting double the voltage across a forward biased diode), which if both the battery and supply were capable of exceeding the diode rating, would cause it to act like a fuse and pop. If not, the supply would just drain the battery, but the supply would indeed never see the attempted reversal, only the battery would.
This whole thing is more complex than it would seem for just a handful of components lol
The LED lighting up is more complex as well but I'll save that for another day
Agreed on the shunting diode being in the wrong place.
We've all been a Bo(o)b at one time or another..... 😂😂😂
Also the led blocks the reverse lol
Does Bob have his own channel where he gets to make fun of you instead?
I thought his next intention was to show us how to burn out an oscilloscope.
ja ja ja good cows
...What if you need to REVERSE the POLARITY of the NEUTRON FLOW? hehehe
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