P-FET Reverse Voltage Polarity Protection Tutorial

[perazaroberto2]

YOU ARE NUMBER ONE . THANK.I APPRECIATE THAT.

[cybersmythe]

The only thing I was disappointed in with this video is the fact that all the RVP I've seen in circuits have been in the form of a diode placed across the battery oriented to conduct only when the power is connected backwards. The result is a brief but brilliant light coming from the fuse when you plug the 12V in backwards. I like the MOSFET solution better, if only because it means fewer trips to the hardware store.

[n0n570p]

I think I'll just try to connect the battery sober

[VolcanicDrum]

Really nice! thank you!

[iNf3rNuSdI4bLuS1]

nice, but gotta watch it 3 more times, too much info at a time, can't process!!

[pappapaps]

wh.. what?

[SquirrelFromGradLife]

Thought about doing a video on inverters? Or do you know a really good resource on them?

[Lao999Sonnabot]

This is a good lesson, yet we still cannot make idiot proof because idiot is getting better. Electronic and Vodka won’t mix.

[SomeGuyInSandy]

Nice ;)

[Nathanxiangdarby]

Ok I'm ready for another video......

[6527mjap]

maybe you can teach us make a electronic switch that uses tact switch

^.^

[zombiepancakes21]

I love your channel and i'm really into electronics. I was wondering if you went to college to learn all of this, and if so, where? Also what do you do for a living, does it have anything to do with electronics or is this a hobby?

[hellokn100]

Thank you so much.

[Pagweb]

I got a battery charger that works even when connected the opposite way to the wall. How do you do that?

[zombiepancakes21]

@Pagweb This is with a DC current, in AC current the polarity is constantly changing polarity anyway so it doesn't matter how you plug it in. Well, thats how I think that works

[jdflyback]

@xanokothe cell phone chargers rectify mains voltage and pulses it through a really small transformer(somtimes just a little bigger than your thumb) with a transistor. This is just based on what Ive seen when I took one apart.

[ftpaddict]

5:40

lol, typo

[Mrluke1308]

Hey afroman do you know if there are any quad ic timers if so can you tell me where to get them

[bahstrike]

4:10 Waait a minute..

[xanokothe]

"Elerical" Characteristics... How can we trust a datasheet with English "erors" dammit!

[GiorgioCapocasa]

Great as usual :)

However, I'm subscribed to your channel; how come this video didn't show up on my homepage? Is it only me?

[jayagk]

I love your videos.

[squiggyreck]

Cool. Never new u could u a mosfet like that.

[R4ND0M1C]

There is any problem due to ESD?... I think that putting an MOSFET to close where the people can touch them, can distroy them due to electrostatic discharges.... Is that correct?

[Afrotechmods]

@R4ND0M1C Yes

[medabrundibar]

@R4ND0M1C That is, why you have to use at least the resistor in the gate, but best even the Zener, even for lower voltages then Vgsmax. That serve as a voltage limiter clamp (together with the MOSFET on-chip gate protection clamp and the gate capacitance, witch goes in nF range), so even with the ESD discharge, the gate voltage is clamped to way safe value.

[xyxy1024]

Nice video!

Wouldn't it be more efficient to use an N-channel MOSFET, connecting D-S at the negative terminal and the gate to the positive one? As far as I remember, N-MOSFETs have lower Rds(on).

[MrWafflesMonster]

This is an excellent video, I might incorporate a reverse polarity protection circuit into my next project

[snomimons]

"0 dislikes" that's what I like to see. awesome video!

[trance183]

If I may, I would love to see a video about radiant energy, like using a crystal radio to power a small LED. Thank you.

[CoolDudeClem]

Please just answer me this one question because my head is still spinning trying to figure this out. If I was using this mosfet to turn something on or off and I was running it at 60 volts, if there was 0 volts at the gate it would be on right? But would I need something around 56 volts at the gate to turn the mosfet off? How could I put that kind of voltage at the gate if the limit it 25 volts?

[Afrotechmods]

@CoolDudeClem I implied several times in the video that if Vgs is 0V the FET would be off. It needs -4V or less to turn on. The circuit at the end of the video with the zener diode will clamp a large gate voltage down to the zener voltage.

[CoolDudeClem]

This has made everything so clear, I have been trying to figure out p-channel mosfets for months now in a circuit simulator circuit simulator and getting really confused as to why things were not working the way I thought they would, and that's all because it doesn't show the ''parasitic diode'' in the mosfet.

[DracoXul]

I'm a bit new to electronic design but couldn't you use a bridge rectifier or four diodes and then it shouldn't matter which way the battery is put in, it will work?

[Afrotechmods]

@DracoXul You could do that, but then you get double the voltage drop and therefore twice the heat in all situations. Personally I think it's better to have something that just doesn't work when you plug things in backwards, then you can just flip the battery around. 99% of the time you are going to plug it in the right way around anyway.

[outwit2010]

It is possible to make AC rectifier from mosfet?

[hristijank2]

wow this gave me idea... u can make the simplest amplifyer with that mosfet

[Afrotechmods]

@hristijank2 People do it all the time. JFETs are better for preamps though.

[V8Jagnut]

good vid sir.

[colt4547]

@Afrotechmods that is exactly what I saw in the sim, and would expect. Thanks for the videos. Your time and effort making these videos are greatly appreciated. Thank you.

[megaman1025]

Great I am a master at this...now I just have to learn electricity in physics...lolz

[mediaguardian]

The P-FET data sheet said the GS voltage has a min of -2.0 V and a max of -4.0 V. First, what is the significance of the min and max (since you simply use the -4.0 V value in your video)? Second, from the sign of the voltages in the table it appears that the author(s) consider -2 V is less than -4 V. What did you mean when you said the difference must be -4.0 Volts or "less" for the transistor to switch on? At first I assumed you meant getting more negative? Now I am not sure.

Thanks,

Jim

[Afrotechmods]

@mediaguardian Above -2V, (i.e. -1V, 0V, +2V etc.) the mosfet is in cutoff mode ("off"). Between -2V and -4V (specified min and max) the behaviour could easily vary from batch to batch and you could end up in the linear region where the Rds is several ohms to several kilohms. Then -4V or less (-5V, -6V etc) you enter saturation mode ("on") with lower resistance as you approach -25V. So in a switching application the designer knows to stay well beyond the -2...-4V range

[mtdeezy]

I've been trying to make a circuit with transistors that will switch alternating current, but nothing has been working. Can you make a video showing how to do it?

[thenaimis]

@mtdeezy You can't use transistors to switch AC, I believe you need a triac to do that. I don't "know" any more than that, my only experience with triacs is seeing them used in EL wire sequencers.

[HWGuyEG]

@thenaimis

If I remember you can make AC gates with pairs of transistors and flip between two gates to rectify a circuit.

Anyone know a good place to buy CMOS logic gates?

[KyleCarrington]

Awesome. Thanks.

[toolhog10]

Good vids, reminds me of E&M class.

[colt4547]

Another great video. Is there a reason you designed this circuit using a P-channel MOSFET as opposed to an N-channel? Can't you flip the MOSFET to the negative rail and use an N-type?

[szekelymihai]

@colt4547 the P-MOS has the negative threshold voltage, so he exploits that in leaving the circuit open

[colt4547]

@szekelymihai I understand. If the MOSFET were N-channel and was moved into the negative rail couldn't you use it's positive threshold to control the state of the MOSFET by connecting the gate to the positive rail? LTSpice thinks so.

[Afrotechmods]

@colt4547 You absolutely can. But the downside is that you introduce a few milliohms of resistance on your ground rail, which may or may not be a problem depending on what you are doing.

[LiKBeAsT]

@Afrotechmods Thanks for the video!

1 question though: Ground keeps confusing me. I understand it pretty well when it comes to mains, but buffles me on circuits.

With a battery supplied circuit, I assumed ground was the (-) pole. However in your vid you have a "separate" ground and it's the same even with reversed battery, thus making the whole P-FET thing work. What would (practically) be the ground in that case?

Any chance of a new video about ground explanation? :)

Thank you very much!

[Afrotechmods]

@LiKBeAsT I've thought about doing such a video. There are just too many things to make videos on... Anyways when we are not talking about ground meaning the earth's ground, ground can be anywhere you want in the circuit. It is a reference point. You can choose the ground node to be anywhere you want and do your design & analysis based around that. However, using certain nodes makes things easier than others. Most of the time it's easiest if GND = battery's -ve terminal.

[LiKBeAsT]

@Afrotechmods I suggest you keep that thought :D

So when it's not earth's ground it is just a node by convention and we can choose which ever one we want (without being too supid:P) ?

With the reversed battery in the video, the ground is at the same node as the +12V, but we still say Gate is at 0V. If ground was not there, and someone would ask me about the V at G, i 'd probably say +12V.

I assume it has to do with reference points (in the end it's always Vab of a,b), but...

[Afrotechmods]

@LiKBeAsT "So when it's not ... choose which ever one we want (without being too supid:P) ?" Yes.

The mistake you are making with the battery is that you are viewing the + terminal as an absolute value of +12V. Voltage is always relative, between two points. The batt's + terminals is 12 volts higher than the batt's -ve terminal. So if we declare GND to be at the batt's + terminal, the -ve terminal has to be at 12 volts less than that.

[LiKBeAsT]

@Afrotechmods Thank you very much! Yes, that was my mistake! And as a result I though that ground "had to" be something specific.

I owe you one :P

Everything crystal clear now!

Keep up the great work with your videos!

[LiKBeAsT]

...but it's still not 100% clear to me.

Once more, I enjoy your vids and keep up the good work :)

[lacosteaef]

Time to make my killing machines



[6527mjap]

this is awesome.

[the1cyrus]

amazing info !!!!! thank you!

[pfsupercars]

I love your sense of humor. Almost choked on my coffee watching this video, another great educational video.

[Bylga]

Great video! Thank you so much!

[Z2m8l0]

Awesome, that was really, really usefull! Hope you will post videos more often...

[Drd4all]

Great info, thanks !



[Kankki1]

Wow this is really awesome. Awesome trick! :D

[llewgnal]

Some of the finest tutorials on Youtube, Thanx

[MrChickenPicker]

Great videos.  Very informative. Keep up the good work!

[shoeb2015]

good one .Keep em coming!!

[xato909]

Vodka + Electronics = possibility to build time machine

[zanuha]

@xato909

No man, you need to fall and hit your head on the toilet while hanging up a clock.

[Teejaa6]

THIS VIDEO MADE MY DAY A COMPLETE ONE.THNAKS

[alauta1996]

One way is to use fuse and diode. The cathode of diode is connected to Vcc and the anode is connected to ground and the fuse is connected between Vcc and cathode. This works when the power supply is connected wrong way so the current is flowing trough the diode and burning the fuse. You can use any almost any rectifier diode for this. For example if you have power supply rated to one amp you must use diode which can handle at least one amp and a fuse with one amp or lower rating.

[TomTerrific02]

@alauta1996 does your circuit allow a spike downstream? How about protecting a microcontroller? It seems your suggestion would be great to a robust circuit but not so good for a circuit that would release magic smoke if subjected to reverse polarity for few micro second (fuse action time). Just a thought here, I'm wet behind the ears still.

[TomTerrific02]

@TomTerrific02 maybe spike is not a good term, replace with reverse polarity.

[alauta1996]

@TomTerrific02 Yes it isn't the best way to protect your microcontroller but it works well with Amplifier ICs and I have seen this solution in few amplifier circuits. Its good solution with devices which needs fuse. There is also small delay in diode but that can be fixed with fast diode like BYW72 or MBR150. I recommend also to use fast blow fuses to lower the risk of magic smoke.

[RavenRof]

Thank you!

[TerminalJack505]

Cool. I'll have to remember this. It could come in handy one day.

[FussyCashew]

Thanks man, I always learn something watching your vids

[IncoherentRussian]

i love working on circuits drunk, and i thought i was the only one^^ Good video

[DarkLevis]

Great explanation

[peterismobiel]

You've done it again!

[Flankymanga]

man your videos are allways awesome to watch!

i really look forward to watch more from you!

[Ards777]

Good video

[IROHINE]

Thumbs up for the Typo he found in the video. It made me smile.

[1strog]

In the past, mosfets and co. was black magic for me. When I saw your tutorial videos, I understood it + the datasheets of mosfets make sense now.

I really appreciate your time spending such good clips and hope to see more of them.

[MrAndrimnir]

Thanks for the tutorial afrotechmods! It's great!

[oxiigen]

this tutorials are really fantastic! simple, clean and efficient. thank you!

[naturestrikeback]

As usual you done a good job

[silverstream314]

Great video as always!

[MrJANTJE123]

Q: does this work by making ac to dc or is it not switching fast enough?

A:?

[MrSpanerd]

@MrJANTJE123 I believe you have to check how fast the transistor can switch!

[TheMagicalTouch]

i watch these and make a face, like i know whats going on, just to look smart :D

[robertd1p2]

Clear, concise and very thorough, what a great

resource – no wonder you Teach! muchas gras.

roBot

[MudDeveloper]

Fantastic! Thanks very much.

[rabidgerbil38]

Finally I've got the intelectual resources for a more efficient killing machine, but is there a mosfet that shoots lasers too?

[covertads]

Very nice, keep these up!

[Pagweb]

What software did you use to create the schematics for this video?

[Afrotechmods]

@Pagweb LTSpice

[Demoman42]

Good luck connecting that mosfet when you had to much of vodka :D Thanks for advise ;]

[cia150]

thanks

[slamdvw]

Neat! Thanks!

[adolphbot]

I solved this by using a bridge rectifier. Nothing has caught on fire... yet.

[jesterjunk]

.

Reverse Polarity is something that is likely to happen eventually to anyone including the most seasoned electronics experts ... but thinking ahead like this can ensure that when the event does happen there will be little grief over it, but that isn't an excuse to be careless regarding polarity.

.

[Mrsameero]

Great vid, simple and informational as always :)

[frank26080115]

do the thing where you make a bridge rectifier with 4 MOSFETs instead of 4 diodes

[laharl2k]

@frank26080115 i second that. i want to se afrotech's ultra high efficiency bridge rectifier.

now that i think of it, why don't they make brigde rectifiers ICs like this? the only possible problem i see is that if the output voltage gets to low the pfet will start to limit the current and and the diference will be disipated as heat as un a constant current regulator. You have to make sure the psu is powerfull enought. but on the other hand you get short circuit protection.

[laharl2k]

@frank26080115 oh i forgot about the diode, so no short circuit.

[MrNathanShow]

I love your vids

[tlfort]

awesome...1st view