Simple reverse polarity protection?  - Page 1
Forum section: electronics / beginners

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: February 13, 2023, 05:26:57 pm
content: Just stumbled upon this LM74610 IC (https://www.ti.com/lit/ds/symlink/lm74610-q1.pdf) and it kind of seems like an amazing and simple reverse polarity protection IC with a somewhat high voltage support of 42v, but I'd love to find one that supports 60v? Anyone used it before (or similar) and recommend it? AFAIK, I don't know it would be possible to add external circuitry to this IC to allow for higher voltage support?

author: Peabody
author_rank: Super Contributor
timestamp: February 13, 2023, 06:11:33 pm
content: I guess most don't like to do it, but you could just use an N-channel mosfet by itself in the lower rail, and then the reverse voltage maximum would depend on the mosfet specs. It would work the same as a P-channel in the upper rail, but with the lower RDSon of an N-channel, and no charge pump stuff.

author: MasterT
author_rank: Frequent Contributor
timestamp: February 13, 2023, 06:53:04 pm
content: 1N4007 is the best option.

author: shapirus
author_rank: Super Contributor
timestamp: February 13, 2023, 06:56:41 pm
content: load current?

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: February 16, 2023, 09:36:04 pm
content: Let's say a load current of 10A, as I'd rather not use a simple diode for reverse polarity protection. Preferably an IC which controls an external mosfet, similar to the one I linked?

author: Psi
author_rank: Super Contributor
timestamp: February 16, 2023, 09:45:14 pm
content: You don't need an IC, just a P-MOSFET that's happy with 10A continuous, a ~10V zener (to clamp the gate to 10V), a resistor pulldown and maybe a cap.Google mosfet reverse polarity protection.If you really want a control IC, google ideal diode controller

author: Zero999
author_rank: Super Contributor
timestamp: February 16, 2023, 10:36:29 pm
content: Quote from: Psi on February 16, 2023, 09:45:14 pmIt might not even have to be P-MOS. N-MOS can be used if the load has a completely separate ground.

author: BadeBhaiya
author_rank: Regular Contributor
timestamp: February 18, 2023, 10:27:58 am
content: You are right, NMOS usually have better Rdstoo, so for reverse polarity protection they would be ideal. Minimum losses ftwAs you said, the only possible problem with using an NMOS as a reverse polarity protection (and even when load switching) is that it makes the ground for the load at a higher potential than the actual ground. It should be fine for loads which don't care about it.I don't think OP is doing anything RF or similar related where a good ground reference is critical. Unless he's planning on pumping 10A into an antenna, in which case...good luck

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: February 18, 2023, 07:07:48 pm
content: Quote from: BadeBhaiya on February 18, 2023, 10:27:58 amNope definitely not. Also had never seen the use of a zener diode +PMOS for reverse polarity protection, so I may go that route! Thanks!

author: Psi
author_rank: Super Contributor
timestamp: February 18, 2023, 09:14:31 pm
content: Splitting the ground to use an n-Fet usually comes back to bite you.Someone will attach a few new devices to your product, some on the input and some on the output.Then someone will link those two device together with an audio cable or something and BAMB your nFet is bypassed and your reverse polarity protection does not work and there's no signs this has happened until that cable goes up in smoke.

author: Zero999
author_rank: Super Contributor
timestamp: February 18, 2023, 10:45:50 pm
content: Quote from: Psi on February 18, 2023, 09:14:31 pmIt depends. If V1 is just a battery inside an internal holder, then no problem, but if it's an external power source, such as a USB connector, or power jack, then yes, it can be a problem and P-MOS is definitely the way to go.

author: MrAl
author_rank: Super Contributor
timestamp: February 19, 2023, 12:18:49 pm
content: Quote from: LooseJunkHater on February 13, 2023, 05:26:57 pmHi,Diodes and chips like this only work with passive loads. If you intend to do any battery charging you have to use an inline fuse. That's because if you use a diode inline for reverse protection and you reverse the connections to the battery being charged, a high current still flows.I believe that's the caue with a series mosfet also because they have internal diodes that do not shut off.

author: Zero999
author_rank: Super Contributor
timestamp: February 19, 2023, 01:51:21 pm
content: For completeness, here's the reverse polarity protection circuit, with a P-channel MOSFET.

author: Kalvin
author_rank: Super Contributor
timestamp: February 19, 2023, 02:21:15 pm
content: Removed my previous post about MOSFET's body diode. Zero999's circuit is correct, as the body-diode is in conductive direction by default (when the battery polarity is correct), and the MOSFET will "short circuit" the body diode and remove the 0.6V body diode's voltage drop when the correct battery voltage is applied to the circuit.When the battery is connected with wrong polarity, the MOSFET's body diode will be in blocking direction and the MOSFET will not conduct.

author: Peabody
author_rank: Super Contributor
timestamp: February 19, 2023, 03:42:13 pm
content: Quote from: MrAl on February 19, 2023, 12:18:49 pmWith respect to the standard P-channel mosfet circuit, if the concern is only about reverse polarity of the battery (inserting it backwards), then it seems the presence of a charger circuit wouldn't change anything. Current could flow in either direction through the mosfet while it is on, but if polarity is reversed, the orientation of the diode would still block current flow because the mosfet would be off.Edit: I could be wrong about that.Edit2: It appears I am indeed wrong.https://www.edn.com/reverse-voltage-protection-for-battery-chargers/

author: Xena E
author_rank: Frequent Contributor
timestamp: February 19, 2023, 08:51:08 pm
content: What about a diode in series with a relay coil? If the polarity isn't correct the relay doesn't pull in and the supply isn’t connected. No insertion loss, only power cost being the relay current.Low tech but almost fool proof: is that simple enough?Regards,X

author: Zero999
author_rank: Super Contributor
timestamp: February 19, 2023, 09:39:48 pm
content: What's this got to do with relays? Perhaps you replied to the wrong thread.If an ideal diode circuit is required, then how about a MOSFET plus a couple of BJTs?The stackexchange thread linked below recommends the DMMT5401, which isn't expensive.https://electronics.stackexchange.com/questions/223935/understanding-an-ideal-diode-made-from-a-p-channel-mosfet-and-pnp-transistorsAll that's needed are some zener diodes to protect the MOSFETs' gates.EDIT:Attachment deleted, but the image is left in the post. It might be automatically deleted later by the server software. I try to avoid deleting content, but I often re-use attachments and don't want to risk posting the same bad circuit again!

author: shapirus
author_rank: Super Contributor
timestamp: February 19, 2023, 10:09:00 pm
content: Quote from: Zero999 on February 19, 2023, 09:39:48 pmreverse polarity protection, which is exactly what is discussed in this thread. relay will only close its contacts when the polarity of the power supply is correct.

author: Zero999
author_rank: Super Contributor
timestamp: February 19, 2023, 10:47:49 pm
content: Quote from: shapirus on February 19, 2023, 10:09:00 pmOh I see. Although Xena E wasn't explicit, it should have been obvious. Thanks for spelling it out to me. The relay could do with a back-EMF diode.

author: EPAIII
author_rank: Super Contributor
timestamp: February 20, 2023, 09:37:39 am
content: Would it be better to reverse the diode and have reverse polarity pull the relay off? That way, quiescent current would be zero when all is OK and only draw relay current when the polarity is reversed?Just spit-balling! Probably a short delay while the relay reacts to the reverse polarity situation.Quote from: Xena E on February 19, 2023, 08:51:08 pm

author: Zero999
author_rank: Super Contributor
timestamp: February 20, 2023, 10:54:58 am
content: Quote from: EPAIII on February 20, 2023, 09:37:39 amThe problem is the relay will be too slow for most applications. Perhaps if it's just to prevent a motor running in reverse, it will be tolerable, but it's nowhere near good enough to protect semiconductors, which will be destroyed, in the 10s to 100s of ms, before the relay switches.

author: Xena E
author_rank: Frequent Contributor
timestamp: February 20, 2023, 11:49:18 am
content: As the OP suggested 10 Amps load consumption I suggested the relay, it not being a micropower application. One of our DC powered products uses a similar crude but effective protection system, but with the refinement of an economiser circuit to drive the contactors coils to reduce the coil current after hold in, but that's not necessary to discuss here with the vauge application information given by the OP.As zero nine nine nine said, if theres anything sensitive connected as a load, coil suppression and relay operation on correct polarity is the safest option.Regards X

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 20, 2023, 01:05:39 pm
content: As posted before, there are plenty of options for a small discrete circuit.But IC's for "ideal diode circuits" are quite common too. There are variants for higher voltages, and even IC's that implement four of them and are designed for an "ideal" bridge rectifier. Especially at higher currents, the voltage drop over normal diodes becomes quite a heat source.

author: MrAl
author_rank: Super Contributor
timestamp: February 20, 2023, 02:22:21 pm
content: Quote from: Peabody on February 19, 2023, 03:42:13 pmThat's an interesting link thanks.The only thing i dont like is the author did not give any part numbers for the MOSFETs did he?MOSFETs have an integral body diode that conducts when the voltage is reversed across them drain to source. That means certain configurations will not work very well because if the battery is connected backwards the MOSFET diode conducts, which would be the same situation as with a simple series diode.What i ended up doing on one of my power supplies was first connect a diode in reverse (anti parallel to the output polarity which means cathode on positive and connect anode on negative directly across the output terminals) so that if the battery is connected in reverse the diode conducts thus shunting all the current to ground which protects the power supply. Since the diode can then see a ton of current (even 100 amps or more) a fuse also has to be inserted in series with the output of the power supply. The new output then comes from ground (as usual) but then the positive terminal comes from the other end of the fuse. This way when the reversed battery draws a ton of current the diode conducts and the fuse blows.It is also possible that the diode still gets destroyed though and would probably become a short, if it does blow that is. After i added this i never actually tested it to see if the diode would survive, but it's an easy test just use a simple high current diode and fuse and connect a lead acid battery such that the diode conducts and the fuse blows open, and dont have to connect that to the power supply to test this setup.Thanks again for the link.

author: JohanH
author_rank: Frequent Contributor
timestamp: February 20, 2023, 03:03:29 pm
content: I wonder if a Sic JFET could be utilized for reverse protection. They are great for current limiting (also large DC currents), but I'm not sure how low the current can be limited to, as you would essentially want it to be zero in the reverse direction, without causing a voltage drop of a ballast resistor in the other direction.https://www.allaboutcircuits.com/industry-articles/utilizing-sic-jfets-in-circuit-protection-applications/Interesting concept in the above article for an essentially two terminal solid state circuit breaker without need for external power. From the article:Quote

author: shapirus
author_rank: Super Contributor
timestamp: February 20, 2023, 05:18:31 pm
content: Quote from: Zero999 on February 19, 2023, 10:47:49 pmthat is definitely implied. it was only a quick and dirty example.

author: Wolfram
author_rank: Frequent Contributor
timestamp: February 20, 2023, 05:19:03 pm
content: Quote from: Zero999 on February 19, 2023, 09:39:48 pmCorrect me if I'm wrong, but wouldn't this circuit have issues with exceeding the reverse BE breakdown of Q1 when the input voltage is negative? The Q1 BE junction will be reverse biased in series with the forward-biased BE junction of Q2, and once this voltage exceeds some five-six volts you'd be outside of the maximum rating of most common small signal transistors. For the DMMT5401 specifically, max Vbe reverse voltage is 5 V.

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 20, 2023, 07:03:18 pm
content: I have a bad experience with a relay as a reverse protection. Relay contacts don't like to work with a DC current, so I guess a Mosfet-based design may work more reliably despite all Mosfet volnerabilities.

author: Zero999
author_rank: Super Contributor
timestamp: February 20, 2023, 09:01:36 pm
content: Quote from: Wolfram on February 20, 2023, 05:19:03 pmYou're right. Well-spotted. I should know better than to copy circuits without thinking through how they can fail.It's obviously not shown up in my simulation because V2 is no more than 5V away from V1. The obvious solution is to use another matched pair of transistors as diodes, to block the reverse voltage.

author: BillyO
author_rank: Super Contributor
timestamp: February 20, 2023, 09:16:15 pm
content: Isn't the word simple in the title?

author: shapirus
author_rank: Super Contributor
timestamp: February 20, 2023, 09:21:58 pm
content: Quote from: BillyO on February 20, 2023, 09:16:15 pmpost #6 should've been the final one.(ideal diodes is actually an interesting topic to discuss, but it doesn't really belong here.)

author: Zero999
author_rank: Super Contributor
timestamp: February 20, 2023, 09:29:58 pm
content: Quote from: BillyO on February 20, 2023, 09:16:15 pmI know, but I had to correct the error.Quote from: shapirus on February 20, 2023, 09:21:58 pmI disagree about it not belonging here. One of the good things about this place is threads drifting off-topic. You don't have to keep following a thread, if it no longer interests you.

author: Xena E
author_rank: Frequent Contributor
timestamp: February 21, 2023, 12:04:42 am
content: Quote from: Vovk_Z on February 20, 2023, 07:03:18 pmThat raises a very good point.Switching at load can cause contact welding and also problems with sustained arcing on DC, designers must pay attention to manufacturers specification of the components... a contactor rated for swtching 240VAC at 20A for instance, isn't ever suitable for the same voltage and power at DC. Selection of fuses also follow this caution.

author: BrianHG
author_rank: Super Contributor
timestamp: February 21, 2023, 12:27:38 am
content: Quote from: LooseJunkHater on February 13, 2023, 05:26:57 pmHow about these guys with 65v automotive support (Back to back mosfet controller for polarity protection with ORing selection for multiple sources):https://www.ti.com/product/LM7481https://www.ti.com/product/LM7480https://www.ti.com/product/LM74900-Q1Note that 2 channel ORing controllers also exist for either multiple battery sources, or mains supply VS battery source with a forced switch selection input pin.https://www.ti.com/power-management/power-switches/ideal-diodes-oring-controllers/products.html#p238max=65;100&p339=External%20single%20FET&p1498=Catalog&p1694=ORing%20controller

author: BrianHG
author_rank: Super Contributor
timestamp: February 21, 2023, 01:00:53 am
content: Don't forget about FERD diodes from STMicroelectronics. You might find some in the 0.2v to 0.3v drop at reasonable currents and they cost less than the ideal diode controllers. Though, the reverse leakage current can be as much as 1ma.

author: Smokey
author_rank: Super Contributor
timestamp: February 24, 2023, 12:36:42 am
content: https://www.ti.com/lit/ds/symlink/lm74502.pdfAnother option:LM74502, LM74502H Low IQ High Side Switch Controller with Reverse Polarity and Overvoltage Protection3.2-V to 65-V input range (3.9-V start-up)• –65-V input reverse voltage ratingNote: This part does not have reverse current protection...

author: Smokey
author_rank: Super Contributor
timestamp: February 24, 2023, 02:20:55 am
content: Here is an app note from TI about ideal diode controllers. Good comparison between the controllers and the discrete solutions (both P and N):https://www.ti.com/lit/an/slvae57b/slvae57b.pdf

author: BillyO
author_rank: Super Contributor
timestamp: February 24, 2023, 04:08:07 am
content: Sigh!I do have a 21 page schematic that only uses a mere 321 devices, but I thought the simplicity of the solution would draw ridicule, So, no.Ahh, diode?