I'm trying to build a constant current source for 2mA (IEPE accelerometer). The simulation works as expected:

LTspice opamp current source

But the real circuit is sourcing only about 240µA. Vgs is around 2V; I thought this will work with DMP10H4D2S.

Any ideas what's wrong?

  • 1
    \$\begingroup\$ Since you have the simulation working, measure and compare all the DC voltages. Which voltages are different? \$\endgroup\$ – Bimpelrekkie Jan 3 at 15:09
  • \$\begingroup\$ The maximum gate-source voltage for the DMP10H4D2S is 20 volts and your circuit is potentially able to exceed that (especially so if you have disconnected the load resistors). \$\endgroup\$ – Andy aka Jan 3 at 15:18
  • \$\begingroup\$ Is your symbol for the FET meant to show the physical arrangement of the pins? Because normally on SOT-23-3 pin 1 is on the side with 2 pins, so it looks like you have assigned pin numbers differently from the way most manufacturers assign them. \$\endgroup\$ – The Photon Jan 3 at 16:48
  • \$\begingroup\$ Even if the symbol is supposed to show the physical arrangement of pins, you've mixed up the source and gate pins, according to the Diodes Inc datasheet. \$\endgroup\$ – The Photon Jan 3 at 16:49
  • \$\begingroup\$ The SPICE footprint is different: 10: drain 20: gate 30: source \$\endgroup\$ – solderjoint Jan 3 at 17:35

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