I am measuring a power mosfet with a multimeter. The voltage at the source with respect to GND is ~291V. The voltage at the drain with respect to GND is ~16V. The P-type mosfet is rated for 250V, so I'd expect it to be completely avalanching from S to D, but that is not occuring. When I measure the voltage with black probe on drain, and red probe on source, I get only ~2V. The mosfet is either broken, or I'm reading the mosfet wrong with the probes. Sound familiar to anyone?

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    \$\begingroup\$ Sounds like you have strong E fields, and high source impedances. \$\endgroup\$ – analogsystemsrf Dec 1 '18 at 3:08
  • \$\begingroup\$ What is Mosfet Part number ? Rated for 250 volts doesn't mean that the device will fail at exactly 250. \$\endgroup\$ – Marla Dec 1 '18 at 3:09
  • \$\begingroup\$ mouser.com/datasheet/2/427/sihfr921-108641.pdf \$\endgroup\$ – snowg Dec 1 '18 at 3:10
  • \$\begingroup\$ @analogsystemsrf Chip broke or naw? Is it impossible to measure Vsd with a multimeter from the terminals of the chip itself? Is measuring from ground individually the 'correct' way? \$\endgroup\$ – snowg Dec 1 '18 at 3:12

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