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Originally Posted by Diabolical Artificer
I'm wondering whether Vds & Vgs are too great. Vds will be 120v Vgs a tad under that.
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Vgs will be whatever it needs to be, probably 4 to 5V. It is protected by the Zener, ZD1. You didn't say how much load current you are expecting to pull...
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I'm also wondering if there's a better protection circuit,
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It's OK except for something missing: there needs to be a 1k resistor in series with the base of Q2. Without it, it is possible to blow the base of the transistor, leaving the MOSFET unprotected. But if you add the resistor, your MOSFET will be safe from momentary output shorts. It is fast acting, no need to worry about capacitance or Zener sluggishness, that's just leading you down the garden path.
But it will not surivive *sustained* shorts. If you want to survive sustained shorts then add a 100mA fuse and don't be clumsy.