frequencyltspiceperformance
I am trying to simulate the follwoing circuit in LTSpice IV. What I am looking for is overall performance in frequency domain.
I downloaded and readed a lot of LTSpice guides, but none of them were speaking about how to do for this kind of circuit. If you know how-to, I would really appriciate yuor help! Maybe it is stupid but I do not know what voltage source (AC, DC, sine or …) I should use and I do not know which simulation type will be what I need.
Here is the real behavior of almost the same circuit, installed in a real device.
The differences are that the driving source impedance is unknown (V1 is ideal in the simulation), and the load impedance corresponding to R3 in the diagram is unknown.
The behavior is nowhere near the rosy picture painted by the simulation. (On the other hand it is good enough that the everything works in the DUT).
The horizontal divisions on the graticule represent 500 nS intervals. The upper trace is the transistor's collector: one division is 5V. The bottom trace is from the base: one division is 2V. As can be seen, the rise time is quite slow, taking over 500 nS to rise to more than 90%. What might be considered a solid high logic level is probably not established for some 250 to 300 nS.
Try this instead
In the model you had the series resistance was too high, the off resistance too low, you also had series inductance and a series voltage.
An ideal switch has zero resistance when on and infinite resistance when off and no series inductance. LTspice wont let you have this but the model here is much closer.
When I run this simulation the output voltage settles around 52.7V
You also want to pick a different diode: I used a 1N4148 because you did but it wont handle the current.
Best Answer
This tutorial has a good overview of sweeps in LTSpice.
To summarize: Give your voltage source the value
AC 1(where you currently have 1V for a DC source), and the sweep will take care of setting the frequency.Add a
.acdirective, either by using theSshortcut key and typing the Spice directive (The format is.ac [oct|dec|lin] [step size] [start frequency] [stop frequency], where dec/oct/lin refer to a decade, octave, or linear sweep rate) or through the Simulate->Edit Simulation Command menu.That tutorial also talks about sweeping parameter values to simultaneously plot the response with various capacitor and resistor values with the
.paramand.stepdirective. These two tools together are very useful when designing a filter.