1. Hand analysis and plotting videos
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Circuits A and B: Diode circuit waveforms, part 1
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Circuits C and D: Diode circuit waveforms, part 2
2. Class time
2.1. Review hand calc process
From day12
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Example 2 (instructor)
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Example 3 (students)
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Example 4 (students)
2.2. Simulator solution
Open CircuitLab
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Draw and solve the circuits of day12 Examples 1, 2, 3, 4
Open this CircuitLab schematic, the same as the diode waveforms handout:
Double-click on D1 and D1a to see the parameters that are configured.
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D1 is CircuitLab’s “ideal diode”, and behaves the same way as the ideal or constant-voltage models from the color figure depending on the value set for
V_D. -
D1a is set to the default realistic diode model for a 1N4148.
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Hover over the nodes and you will notice that everything is 0 V. This is because the DC solver is using the t = 0 seconds value for the voltage sources, which is 0 V.
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Click the Simulate button near the lower left corner.
2.3. Time-domain simulation
The simulation is already configured to run a Time Domain simulation from 0 to 10 ms with a time step of 10 μs.
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PSpice, LTspice, and most other simulators call this a Transient analysis.
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YOU must choose a good value for the Time Step!
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Too large of a step gives bogus and misleading results.
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Choose a small enough time step so that the waveform has enough samples to trace an accurate shape of the “fastest” edges in your circuit.
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Too small of a step means that the simulator needs to compute a TON of points … which can take a long time.
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How many time steps will the simulator compute in this situation?
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What happens if
Time Step == (Stop Time - Start Time)?
The node voltages to plot are already configured.
2.4. Run the simulation
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Run the simulation, which opens the waveform data plot.
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Deselect all of the waveforms except for V(in).
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Add back V(a).
The V(a) waveform is an exact match to the hand analysis solution! This is a great way to check your hand drawings!
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Add V(aa) also, then remove V(in) so you only see the two Circuit A waveforms.
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Is 0.6 V a good choice for \(V_{D,\mathrm{on}}\) in this particular circuit?
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Is there a one-true-best value for \(V_{D,\mathrm{on}}\)?
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