Should you use LTspice ?

If you are designing electronics circuits and don’t know about LTspice, it is time to learn about it. LTspice is a free software that allows you to simulate multiple circuits and make sure your circuit is behaving properly. Do note that we are not associate with LTSpice in any way and we are suggesting this software because it is actually a useful software to have when designing circuits. Multiples electrical engineers are using this software for their jobs to simulate input filter, logic circuit, current transient, etc. This allows designer to find any problems with their design. It is strongly suggest to download and learn to use this software if you eventually want to design circuits or if you are currently designing circuit. This software should be in your toolbox if you ever need it. Most manufacturer have models for LTspice which you can use in your simulation to get more accurate results than using a generic components. The results could vary based on the quality of the models made by the manufacturer but it will generally give you decent results.

Below, we have an example of a Bode plot for a ferrite bead with capacitor filter done in LTSpice. These types of circuit are often use for filtering high frequency power supply noise and to reduce EMI. The circuit below is often suggest on the internet or in datasheets. There is multiples example of this circuit and some will include more capacitances, resistors and some will use an inductor instead of a ferrite bead. You need to be careful with theses types of circuits since they can be resonant if they are not properly design. The circuit below is actually an example of a very bad filter design. If you look at the frequency response, you will see that this filter is resonant. This is why LTSpice can be useful since you can simulate the frequency response of the circuit to avoid any issues. You can find the SPICE model of the ferrite bead, capacitors, etc. on manufacturers website and simulate the circuit with the real model that you are using on your board. This will allow you to find problems before completing your design. Troubleshooting theses kind of issues can be hard and it is best to avoid them in the design phase.

Figure 1 : Power supply filter example in LTSpice
Figure 2 : Power supply filter frequency response example in LTSpice

You could fix this issue by using a different ferrite bead or using different damping methods. You could simulate your new circuit in LTSpice to see if it is now behaving properly. LTSpice is very useful for validating modification done to the original design and to see the impact of your modification. There is multiples methods of damping and you can find multiples article online written by manufacturers that suggests various damping methods. For our example above, you could have added more capacitors after the ferrite bead to damp the resonance of the circuit (shown below). This is not the best since we still have a resonant filter but it is better than before. You could also add a resistor in series with a capacitor in parallel with the existing capacitor to solve this issue.

Figure 3 : Power supply filter with more capacitance example in LTSpice
Figure 4 : Power filter with more capacitance frequency response example in LTSpice

As you can see from the example above, LTSpice is an important tool when designing circuit since its allows you to simulate circuit and find potential issue before the design is complete. We gave only one example above but you can simulate multiples things with LTSpice. We took a simple example that most electrical engineer and student will understand to show you how useful LTSpice can be. For more advanced user, you could simulate transient response to verify voltage undershoot/overshoot, etc. We recommend that you learn how to use this software to increase the quality of your design and to potentially avoid any issues with your circuit after the design phase.