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It would be probably good to protect N-MOSFET with its drain connected to a long (~1 m) piece of wire against ESD. The transistor has its drain-source maximum voltage 20 V, so I decided to choose MMBZ16VALFHT116 (datasheet) transient voltage suppressor with VBR = 16 V. (This one is marketed as a bidirectional TVS, but it looks like there are two unidirectional TVSes.)

Is this TVS correct for this use case?

Do I understand that there are two unidirectional TVSes in the SOT-23 package? (The datasheet uses ordinary diode symbol for them, as I understand it.) Can this be used as one bidirectional TVS (by leaving the anode unconnected)?

I am new to using TVSes.

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  • \$\begingroup\$ Yes you can use it as a bidirectional TVS...but why would you want to use it as a bidirectonal TVS to protect a MOSFET? That just protects the MOSFET less since it's not a bidirectional device. \$\endgroup\$
    – DKNguyen
    Aug 20, 2022 at 16:16
  • \$\begingroup\$ I have multiple FETs, so I will use them as unidirectional TVSes. I ask for the bidirectional usage because they are ① sold as bidirectional and ② I can use them at other places as bidirectional ones. \$\endgroup\$
    – jiwopene
    Aug 20, 2022 at 16:20
  • \$\begingroup\$ Oh they are marketed as bidirectional? Anyways, it's fine. \$\endgroup\$
    – DKNguyen
    Aug 20, 2022 at 16:21
  • \$\begingroup\$ Yep. A shop with tens (maybe hunderds) of thousands various components is probably unable to make sure that all of them have proper descriptions. ☺ \$\endgroup\$
    – jiwopene
    Aug 20, 2022 at 16:23
  • \$\begingroup\$ Is it safe to use the 16V TVS to protect a N-MOSFET with V<sub>GS</sub>=20V? \$\endgroup\$
    – jiwopene
    Aug 20, 2022 at 16:24

1 Answer 1

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A regular back-emf diode will do the job (from MOSFET drain to the positive power rail). I guess your power supply might be no more than 12 volts (given your 20 volt maximum rated MOSFET) and, if a positive ESD pulse "hits" the drain connection, the diode will conduct current safely to the much sturdier power rail (where it should get absorbed by power supply filter capacitors). But, it might be prudent to have a 10 nF ceramic capacitor close to the MOSFET's associated power rail down to to 0 volts (just in case).

Should the ESD pulse be negative, the body diode of the MOSFET will conduct energy to 0 volts.

I'm not recommending a TVS in these circumstances because a diode is far less ambiguous in what peak voltages might be produced. And anyway, you would probably want to fit a diode in case of back-emfs should the LED wiring produce a back-emf due to wiring inductance.

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