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I would like to create a reverse voltage protection for my 12v 0.1A - 3A (load is changing) DC circuit with minimal voltage drop. According to this Instructable Link. There are 3 ways to do it. Using a Diode, a Schottky diode, or a MOSFET.

It would seems the mosfet is the way to go, but i am not well versed with mosfets and do not know too many of them, so are there any other COMMONLY available mosfets that i can easily find? it would seems the one in the guide is quite hard to find.

worse comes to worst. i will just have to settle for schottkies. Is parralleling 2 schottkies recommended to achieve the current demand?

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  • \$\begingroup\$ Never parallel diodes. If searching for FETs, most distributors (e.g. Digikey, Mouser, Newark) have parametric search functions, where you can enter the specs that are important to you and get a listing of all the devices they offer that meet your needs. \$\endgroup\$
    – Hearth
    Feb 11 '19 at 0:22
  • \$\begingroup\$ Sadly in my location Digikey, Mouser, etc is not a very good option since it would take a long time to arrive (1-2 weeks). I was hoping for FETs that I can find in my local electronic stores. \$\endgroup\$
    – Jake quin
    Feb 11 '19 at 0:29
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    \$\begingroup\$ One diode will inevitably take the vast majority of the current, due to minuscule differences in things like doping concentration and temperature. Diodes are very nonlinear devices and keeping them balanced is very difficult. It's easier when they're on the same die, of course. \$\endgroup\$
    – Hearth
    Feb 11 '19 at 0:34
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    \$\begingroup\$ For some applications a reverse-biased diode and a resetable fuse might be enough. \$\endgroup\$ Feb 11 '19 at 0:36
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    \$\begingroup\$ @Huisman The forward voltage of a silicon diode decreases when the temperature increases, so you have the opposite of a balancing effect; it makes it worse. \$\endgroup\$
    – Hearth
    Feb 11 '19 at 1:08
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The instructables link shows low side switching; while that can be ok, it can interfere with low side (ground) referencing.

Here is another way to do it:

schematic

simulate this circuit – Schematic created using CircuitLab

I have used back to back parts here to prevent body diode conduction. When Vin is normal, the MOSFET gates are pulled down and they conduct.

If Vin is reversed, the MOSFETs are turned off.

It is possible to do this with just M1, incidentally. The advantage of using both devices is that it is now possible to turn the circuit off completely without powering the supply off (with some small circuit additions).

The key parameters for the MOSFETS: Vgs should be rated at 10V for low Rds(on), Vds should be 20V to get a bit of headroom.

Look for the lowest Rds(on) that is available and make sure the part can handle the power (look at the thermal characteristics).

It is not uncommon to see a large (1M or so) resistor at he junction of the source terminals to the negative side of the power for balance.

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  • \$\begingroup\$ Can you elaborate on the benefit of M2 as opposed to only using M1? \$\endgroup\$
    – Jurkstas
    Feb 11 '19 at 12:35
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Depending on your purpose you can place an E-fuse or an electronic Fuse IC they come with more features not only reverse voltage protection but current monitoring, overvoltage, undervoltage, overcurrent, hot swappable supply and etc.

For example take a look at these selections from Texas Instruments

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