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I have the following driver circuit used for switching very high current n-channel mosfets

Here's their datasheet https://www.littelfuse.com/~/media/electronics/datasheets/discrete_mosfets/littelfuse_discrete_mosfets_n-channel_trench_gate_ixfn420n10t_datasheet.pdf.pdf )

Here's the circuit that I am trying to build

enter image description here

After trying to build a prototype on a breadboard, I've found that there is no voltage drop across the 1k resistor that is connected to the 2n7000 transistor. As a result, Vgs=0 no matter what the output of the inverter is (High=5 V, Low= 0V). Here's the datasheet of the 2n7000: https://www.onsemi.com/pub/Collateral/NDS7002A-D.PDF

Can anyone tell me what I'm doing wrong with this circuit? I don't think I can ground the source of the 2n70000 because then the driver will share a common ground with the very high current power supply.

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  • \$\begingroup\$ Are you connecting the source to the emitter of the optocoupler? \$\endgroup\$ – user115094 Jun 18 '19 at 16:54
  • \$\begingroup\$ @Blue_Electronx wouldn't that just ground the source? If I do that I get Vgs=0 for inverter output=0, and Vgs = 2 V for inverter output= 2 V. For some reason, the inverter output lowers dramatically. In addition, the 10 V regulator gets messed up and starts outputitng 3.5 V. \$\endgroup\$ – Physean3 Jun 18 '19 at 17:45
  • \$\begingroup\$ Define “very high current”. How fast are you switching? \$\endgroup\$ – winny Jun 18 '19 at 19:13
  • \$\begingroup\$ @winny roughly 400 A. I'm switching about once every 30 s \$\endgroup\$ – Physean3 Jun 18 '19 at 19:24
  • \$\begingroup\$ What do you measure on your +5V, + 10 V rails? How do you power the inverter going to the 2N7000 gate? \$\endgroup\$ – winny Jun 18 '19 at 21:34
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The source did, in fact, need to be connected to ground although the 10k resistor was drawing too much current. Switched to a 180k resistor and everything started working as expected.

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