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TINA simulation issue with DC Analysis

hat cat
Prodigy 70 points
Other Parts Discussed in Thread: TINA-TI

My circuits are simple

[1] Just take a diode 1N183 , connect 5V DC to cathode and measure DC voltaage at anode. Do DC analysis

 Why do I see 5V at anode ?

[2] Take a Enhancment type Pchannel MOSFET( 2N6804)  connect 5V on Souirce and 5V on Gate, measure drain voltage, Do DC analysis.

Why do I see 5V at Drain?

[3] ake a Enhancment type Nchannel MOSFET(2N6755) connect 5V on Drain and 0V on Gate, measure source  voltage, Do DC analysis.

Why do I see 5V at Source ?

  • TI__Intellectual 2405 points

    Hello Hat Cat,

    I am not sure exactly what issue you are facing. I have simulated all three cases mentioned by you. While doing DC analysis in TINA-TI, go to 

    Analysis >> DC Analysis >> DC Transfer Characteristics and select the proper voltage source to be swept and the range to sweep from and sweep upto.

    1. If you do a DC analysis on diode and voltage source series combination, with some load, you will see, V(cathode) = V(anode)- I(load)*Ron(Diode).

    2. For a p-channel MOSFET, if you sweep gate voltage with source at 5V, the drain voltage will be equal to source voltage till the device is ON. As threshold voltage approaches, the voltage at drain will start dropping to zero and when MOSFET is completely OFF, the drain voltage will be zero.

    3. Similar explanation will be applicable as the case 2, except for it will be NMOS behavior.

    PFA the schematic and all three results from TINA-TI. Let me know if you have any specific questions.

    6170.Test.TSC

    Thanks!!

    Best Regards,

    Mahavir Jain.

  • in reply to Mahavir Jain
    Prodigy 70 points
    Hello Mahavir,

    Thanks for reply.
    In your schematics there is assumption of having 10K load.

    If you remove the resistor or even make it 100Meg , it does not work.

    Please let me know if I am missing something !!

    Thanks
  • in reply to hat cat
    TI__Intellectual 2405 points
    Hello Hot Cat,

    The point of having certain load resistor is to allow current to flow through device. Without load resistor it will be as good as open circuit. Also, if you put very high value of load resistor (e.g. 100Meg), the current through device will be very low (5/100meg = 50nA). Hence, you will not be able to see considerable impact, as the diode ON resistance is very small value (few miliohms), so it will appear as if no voltage drop happened across it.

    Hope this clarifies your doubt.

    Thanks!!

    Best Regards,
    Mahavir Jain.
  • in reply to Mahavir Jain
    Prodigy 70 points
    Hello Mahavir,

    But why any resistor is required , I can have cpacitive load with initial condition=0

    Take simple case of NMOS, as pass gate transistor switch.
    Drain=5V ,Gate=0V, on Source you should see 0V or some very low value for convergenece, in regular spice simulation used for IC design, you will not see any voltage on source,, with simply DC node voltage analysis,
    But TINA shows 5V !!!.

    Please let me know, if there are some settings or model tweaking required.

    Thanks
  • in reply to hat cat
    Prodigy 70 points
    Hello Mahavir,

    I think the DC analysis has or DC model have some issue or operating point analysis.
    The Transient simulation are working as expected.

    Please look into this.
    Thanks
  • in reply to hat cat
    TI__Intellectual 2405 points
    Hello Hot Cat,

    In DC Analysis in these tools, the simulator assumes Capacitor to be Open Circuit and Inductor to be short circuit. Now if the Source is open circuited, the MOSFET is as good as a resistor with voltage source at one node and open circuit on other node. In that case voltage will be same at both nodes, since no current is flowing through the device. And this will be true irrespective of Gate voltage.

    Please use transient analysis for your case and use Voltage generator instead of VDC source (Battery). In voltage generator you can select Piecewise Linear mode of signal and define time and amplitude as per your expected waveform.

    Hope this helps resolve the issue.

    Thanks!!

    Best Regards,
    Mahavir Jain.