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I just try Micro-Cap SPICE simulator and trying to check it with LTspice.

I'm simulating this MOSFET in LTspice with 10Hz 12V gate voltage and the gate current due to MOSFET capacitance peak to 200mA as in the following plot:

enter image description here

When I simulate the exact circuit in Micro-Cap the voltages are the same but the gate current is not how it is in LTspice not even close. Here is the setup in Micro-Cap:

enter image description here

As you see the bottom green plot shows the gate current which is like noise:

enter image description here

What could be the reason I'm getting very different gate current wave-forms?

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  • \$\begingroup\$ I guess that in LTSpice you're using the model of the IRF530. Are you also using such a model in Micro-Cap or are you using some "generic" MOSFET? There can be a huge difference depending on the model. You can imagine that the behavior (and model) of a large MOSFET that can handle 100V, 10 A is quite different from the behavior of a MOSFET that sits somewhere deep inside a microcontroller on a chip with 1 million other transistors. \$\endgroup\$ Commented Mar 9, 2020 at 10:15
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    \$\begingroup\$ You probably also need to make the minimum time step smaller in microcap. \$\endgroup\$
    – Andy aka
    Commented Mar 9, 2020 at 10:23
  • \$\begingroup\$ @Andyaka In Transient analysis window the Maximum time step was set to zero, I changed it to 1u now I can see peaking currents although not exactly the same but similar behaviour. So you were right it was about time step. \$\endgroup\$
    – pnatk
    Commented Mar 9, 2020 at 10:31
  • \$\begingroup\$ @Bimpelrekkie Im not using generic Im using exactly the same model. \$\endgroup\$
    – pnatk
    Commented Mar 9, 2020 at 10:34
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    \$\begingroup\$ use step time < 10% of expected rise time or use a faster clock for fewer steps and faster analysis \$\endgroup\$ Commented Mar 9, 2020 at 11:19

2 Answers 2

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You probably also need to make the minimum time step smaller in microcap

In Transient analysis window the Maximum time step was set to zero, I changed it to 1u now I can see peaking currents although not exactly the same but similar behaviour. So you were right it was about time step.

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Your circuits above are not the same. Look at the 10K gate pulldown resistor.. it is right on the gate for the microcap sim, but it is before the 47 ohm gate resistor on the LTSPICE. Also it adds some confusion discussing the circuit because you didn't make the schematics have the same reference designators but that won't affect the results.

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