thank you for this very usefull video. I know what to do with all those useless mosfets I got on dead PC motherboards

What if my load is a battery? Will PMOSFET also protect me from plugging the charger to the battery the wrong way? Or will the voltage from battery keep PMOSFET open and everything will go in flames?

@@niceshotapps1233 The charger already provides a diode bridge rectifier and a fuse. Plug it the wrong way a the fuse will simply blow

@@CaptainDangeax Aparently when the load can provide its own voltage, one mosfet is not enuough. You need at least two and two resistors to avoid blowing fuses or something more valuable. www.analog.com/media/en/technical-documentation/application-notes/AN-171_AN-1568.pdf

@@niceshotapps1233 My point is why would you use such a protection on a battery charger ? Of course it's perfectly fit for any electronic appliance with external power supply, but for a battery charger, I don't see the point as I already wrote

Ok, I’m here. Sorry for the 4 year delay but please understand there’s a major backlog for KZfaq commenters requesting awards. With that being said... Hear Ye Hear Ye! We gather here today to recognize Afrotechmods for his stellar video tutorials that have gone above and beyond in helping others. His no bullshit approach combined with clear and concise dialogue alone was far more than his competition could come up with yet even that wasn’t enough for Afrotechmods. In a game changing manner, Afrotechmods set the bar higher than Willie Nelson at Snoop Doggs pool party by making a video without a single fucking digression, a feat many KZfaq viewers believed to be impossible. We Salute you, Afrotechmods!

True

Why dont YOU give him an award?? Allways the others should do it...

+George Kot Thanks!

Agreed!

or use a diode on the + and - backwards so that it will short circuit ur power supply if connected backwards for dirt cheap and effective reverse polarity protection :)

If your 'power supply' is a non protected lithium polymer battery, that's not going to be pretty

With a proper rated fuse or polyfuse this could work

lol

Hey man. The circuit in this video. Why does D and S revesed? Usually, PMosfet, S to + and D to load!!! This is crazy Plz help 😣

sony10 , yes , I agree that at first glance, the circuit appear quite weird. But when you look closely pay attention to the polarity of a P channel Gate compare to Source. Keep in mind that a MOSFET is a variable resistor ( at least when utilized at low voltage ) . This means that , when ON, (short) , you can feed current both polarities, it still will act as a short circuit. This is why it appear weird when you look at a circuit that show a P channel connected as if it was a N channel. In this circuit the PMOS is utilized in reverse polarity. It need to be this way because of the internal inevitable substrate intrinsic diode that would be turned ON if you were to use an N channel and made a mistake of reversing polarity. You don't want any current circulating if in reverse battery connection. Hence, wether using a P or NMOS you want the internal diode in the direction of the current flow. Most circuits utilize a MOSFET configuration with current being blocked by the internal diode. In this circuit you want it configured such that when the battery polarity is correct the current would flow through the internal diode (if the gate was not energized) because in case of reverse battery polarity ( an undesirable error ) you certainly do not want any current flowing. So, you Then have to connect the PMOS in reverse, which is totally allowed according a MOSFET specification sheet. Once the battery is connected properly the internal diode will bring the Source to a higher potential then the Gate ( even if the Drain is of higher potential, it's not prohibited) you now have a Gate that could be connected to a voltage potential lower than the Source ( a condition to turn ON the PMOS) . Once the Gate is put to a lower potential it turns ON the PMOS and the voltage lost in the internal diode becomes almost zero because you now have a PMOS turned ON ( a short circuit ). Hope that make any sense to you. At least, that is how I see it.

sony10 , the short version. A MOSFET can be utilized both polarities. As long as the Gate is at lower voltage then the Source you have a ON (short) MOSFET , which is what you want here in this circuit. D higher voltage than S is totally allowed if you do not exceed the forward internal diode maximum current mentioned in the specification sheet of your device.

@@jimviau327 tks alot And tks again!!! Im thinking.... This one is crazy

@@jimviau327 now I can die in peace ✌️

If your battery is isolated from 0V a N MOSFET on the negative works just as well😊

If the battery is connected in reverse as in 3:21 then the Drain of PFET is below ground, then the Source pin doesn't have much chance of ever going above ground so PFET should never turn on.

If you think of protective fet as of part of the battery, it doesn't make any difference, is it pfet at positive battery terminal, or a nfet at negative one. In other words, just assume your ground and positive rail after fet, and never think of reaching battery's terminals, and you are good. So I would think of using nfet at bottom always, they often go under 10 mOhm of rds on. Also, nfet is very convenient when you want to control its gate with a MCU for soft on-off feature.

+nRADRUS 2. True, but we want a common ground, if somehow possible. lg, couka

Use a charge pump on the gate. Really simple to implement because its not drawing any current. You can buy a small IC that provides the voltage you need. To protect the charge pump IC you can just implement pMOS or a simple diode on its VCC terminal. Since it draws current in the uA range, the losses are negligible. The losses in implementing the charge pump to have a high side nMOS is usually much lower than using a pMOS

@@ericcartmann true but look at the datasheet again, it's spec'd at 0.026 ohms @ ~24 amps/10 volts, ( heat sunk to 25 deg C of course ) in any case at 2.0 amps it's much much less. personally i prefer Geranium diodes over Si... lower Voltage drop . . . & i have a ton of those laying around in metal cases.

@@robozstarrr8930 The problem with those metal cases is they are made of zinc, and zinc whiskers. Most of them have already shorted themselves out and they are no longer manufactured.

Be _very_ careful about that on a complex system (with multiple boards, for example) because you may short the "Protected" Ground with the real ground over multiple boards and fry them all T.T

Yeah Bob you're right for once somebody mentioned something about the crappy generic music that people put on these electronic videos..thanks :)

Still there

Milan Lukic In fact, for PMOS, if Vds>0.7 or so, it just turn on and act as a diode (no matter what the voltage is on the Gate). you can get this info. from it's symbol...

Milan Lukic MOSFETs generally work on the fact that a channel is created between drain and source when the gate charge attracts charges into the channel, reversing its behavior. When a channel is created, it doesn't matter which way the electrons flow in it.

Milan, you’re right. The Drain-Source should be swaped. MOSFET has a internal diode that points from source to drain in N channel devices and drain to source in P channel devices. Therefore in a PMOS current flows from Source to drain not the other way around.

ElectroBOOM Medhi! You are one of my heroes

@@SakarPudasaini10 you are a godsend

That's funny. That is until I started to really thinking about it, it's not such a bad idea after all. If we made the whole world with drunk proof electricity then no more Boo Boo's with all of that going on No More, No More, as the Raven said, LOL.

Poka yoke, always best indeed. Thought a protection can't do any harm...

Until the drunk installs the batteries backwards.

Think of a little guy inside with a voltmeter and a rheostat. The voltmeter measures the voltage between the gate and source. As that voltage increases, he turns the resistance down on the rheostat. It's the same as the model for a BJT, except that the little guy there has an ammeter instead of a voltmeter.

Maxx Smaxx the zip