I was doing a report for my lab in VISIR simulator, but I get a strange output for a RL circuit. The goal, is obtain a frequency to fit the permanent regime in a half of input period, therefore, for a RL circuit where R = 2200 ohms and L = 820 μH, the right input frequency would be a number about f = 268 KHz, in accordance with goal the frequency must be f= 1/(10*Tal). so the expected outpout should be: enter image description here

But I'm getting this:

enter image description here

Could someone explain to me where I'm getting wrong?

the circuit image is following below: enter image description here

  • \$\begingroup\$ can you post the circuit diagram you're working with? \$\endgroup\$
    – ppmbb
    May 6, 2020 at 22:51
  • \$\begingroup\$ I do that right know, sorry to don't post before I forget this detail. \$\endgroup\$ May 6, 2020 at 22:53
  • \$\begingroup\$ what is Tal in f= 1/(10*Tal)? \$\endgroup\$
    – ppmbb
    May 6, 2020 at 22:59
  • \$\begingroup\$ time constante of any energy storage element \$\endgroup\$ May 6, 2020 at 23:37
  • \$\begingroup\$ what is the saturation current for the inductor you are using? Can you reduce your input amplitude? \$\endgroup\$
    – Aaron
    May 6, 2020 at 23:39

2 Answers 2

  • 1) wrong Gen. frequency T= 1.8cm * 50ns ~ 90 ns = 11MHz shud be much lower f or greater period Tau = L/R= 820u/2k2= 373 ns vs your 90ns

  • 2) note rise time automatically indicates load capacitance

    • from self-capacitance ( normal) and/or virtual probe. (30pF ?)
  • 3) Both indicate you are operating too high a frequency for this L/R ratio and neglecting capacitance which you can tell from the half-sine PW < 100 ns or self-resonance with low Q around 5 MHz or so.

I can synthesize your waveform @ 8Mhz using different values. enter image description here

Always calibrate your instrument with a known square wave and resistive divider then add stray effects like capacitance and inductance.

  • \$\begingroup\$ You can use this and change the values tinyurl.com/yaadd22e or use slider variables \$\endgroup\$ May 7, 2020 at 1:34
  • \$\begingroup\$ I was using a remote lab, the output was been detected by a virtual oscilloscope, so it has a considerable internal capacitance and resistance that we have to consider, Is this? \$\endgroup\$ May 7, 2020 at 9:43
  • 1
    \$\begingroup\$ +1 You can hear the resonances calling to you from the partial sinewaves :-) \$\endgroup\$
    – Russell McMahon
    May 7, 2020 at 13:06
  • \$\begingroup\$ @LucasVital All probes have some capacitance < 30pF and wires have inductance > 5nH /cm. Perhaps that simulator has specified even real self-winding capacitance on coils . That simulation may be due to unspecified values or in the fine print. Store that in your experience bank, and next time calibrate the components with known expected behavior like 0 0,50,100 Ohm source to 50 Ohm load to see expected attenuation and rise time and f-3dB = 0.35/Tr (10~90%) \$\endgroup\$ May 7, 2020 at 16:06

Simulating your circuit I get this, which is similar to what you expect I think. So in principle it seems to be ok, but maybe is some VISIR detail on how you connect the circuit, oscilloscope prove, grounding... Try connecting the function generator GND directly to right terminal of inductor.

enter image description here


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ I did what you have suggested, but the result remains the same. \$\endgroup\$ May 6, 2020 at 23:33

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