There's a lot of post on here about MOSFETs and ESD sensitivity. But whenever the general question is asked, people always go straight to the gate and how sensitive it is.

I've developed an LED driver board, with common-annode LEDs connected. Therefore, I have the drain of the low-side N-Channel MOSFETs exposed - and lots of them. The board has 52 of these exposed:


simulate this circuit – Schematic created using CircuitLab

Since I have so many, I really don't want to have to place 30V+ TVS diodes on every single output. If I have no choice, I guess I will. But I was just wondering - since they do have a parasitic body diode, is there any chance the drain will be okay - at least for EMC testing - by itself?

  • \$\begingroup\$ Does the drain provide a path for electrons to reach the atoms-thick gate? Yes it does. Though not so easy as from the source to the gate. But y'know...static is thousands of volts and even the MOSFET source-drain can only withstand 1500V if specifically designed for it, and the static doesn't even have to go all the way from source to drain to reach the gate. \$\endgroup\$ – DKNguyen Oct 21 '19 at 22:12
  • \$\begingroup\$ FETs are extremely vulnerable to ESD. The datasheet can provide proof of that. BJTs are generally susceptible to ESD but it is still vulnerable. \$\endgroup\$ – KingDuken Oct 21 '19 at 22:17
  • \$\begingroup\$ You should do it anyway. As well as ESD you could also have inductive kickback due to long wires. \$\endgroup\$ – Bruce Abbott Oct 21 '19 at 23:39

Yes, mosfets drains are sensitive to ESD. If you look at the Vds spec in the datasheet, it cannot be exceeded (for the IRF530, it's 100V), even for short amounts of time.

ESD over-voltage conditions can reach thousands of volts. To prevent failure of the mosfet, install ESD protection. One way to do this would be to use a TVS diode that limits the voltage on the drain to less than 100V (maybe 50V would be best).

If its a choice between placing a TVS diode or replacing the mosfet (or having an intermittent mosfet that behaves unpredictably, a TVS diode would be a better choice.

There are a few mosfets, such as the DMN61D8LQ that have ESD/diode protection built in to the part, however, there might not be one with the specs needed for your design.

enter image description here

Source: https://www.diodes.com/assets/Datasheets/DMN61D8LQ.pdf

If the LED's are connected to the outside world and are touchable by humans, then the mosfets need to be protected.

  • 2
    \$\begingroup\$ Alright, I suspected as such - just good to hear it from another person. Thanks. The sources are all grounded, and the gate has no exposure to the outside world. So I'll place a 30V TVS from the drain to source, and hope for the best. Cheers! \$\endgroup\$ – DSWG Oct 22 '19 at 0:45

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