2
\$\begingroup\$

I find the following reverse polarity protection circuit everywhere online.

Reverse polarity protection using PMOS and Zener diode:

Reverse polarity protection using PMOS and Zener diode

Can you replace the Zener and resistor with a voltage divider as in the following circuit?

Reverse polarity protection using PMOS and voltage divider:

Reverse polarity protection using PMOS and voltage divider

What would be the drawback in this circuit? I plan on using a 24V supply and 10k for both resistors. My MOSFET has a gate source voltage of +/- 25V (DMP4015SSS.)

\$\endgroup\$
2
  • \$\begingroup\$ "I plan on using a 24V supply and 10k for both resistors" Umm... that way you get 12V on the gate no matter if you connect 24V to + or -. \$\endgroup\$
    – Lundin
    Mar 22 at 10:25
  • \$\begingroup\$ Also I suspect that having a 1.2mA continuous reverse current in case of polarity change is not ideal. \$\endgroup\$
    – Lundin
    Mar 22 at 10:30

3 Answers 3

2
\$\begingroup\$

One drawback of your zener-less solution is that the voltage divider will raise the required voltage to turn on the MOSFET.

If you will only use 24V supply, that's probably not an issue. But for a wide input voltage range it might be an issue.

\$\endgroup\$
2
\$\begingroup\$

For low f and true R loads with limited V1 range, cct 2 is OK but for inductive effects and Miller capacitance, Vgs max can be exceeded with only a Thevenin R protection.

But for high voltage switching of R2 to ground, it can be effective if parasitic flyback effects of the load and feedback to the gate are clamped, snubbed or damped during turn off.

\$\endgroup\$
0
\$\begingroup\$

If your circuit operates with a voltage lower than the maximum supported voltage between the gate and source of the MOSFET, you may not use the zener diode. At higher voltages it is recommended to use it to protect the MOSFET and avoid damaging it.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.