The University of California in Berkeley, actually promotes a free for non-commercial users version of Spice for Windows.
Spice5
I have tried several other free Circuit Simulators, Quc's {never got it to run on Windows} ngspice and never got it to run on Windows. At least Qucs allowed me to draw a schematic. The simulator side never worked. The first time I tried installing it, it showed up as a little tiny box that wouldn't allow me to access any buttons. I'll wait another year. Unless you're running a dual OS, Linux, or Unix, I doubt that either of those circuit simulators will work.
Now, if you want to design your own circuit boards for Free, the best schematic editor/PCB designer that produces a Gerber File that can be sent to a PCB manufacturer over the internet is KiCad.
Shop around PCB makers and a proto-type custom circuit board can be hammered out. The Gerber file will send your very own personalized traces and layouts to be perfected as circuit boards based upon your specs and design. You can select flow solder holes, multi-layer etc. it's all up to you.
If you would like to write and undersell the monsters of simulation in the world you could go to this site and pick up the source code for spice and there is an analog component that still isn't right and doesn't have a good model, step up and step down transformers. University of California at Berkeley Center for Electronic Systems Design
Start with a Bifilar wound 1:1 toroid. The inductances are mutual and don't change at any frequency or load. But, when you take a step up or a step down transformer and measure the inductance of the primary when the secondary is open you'll get a high value of inductance, and when you measure the inductance with the secondary shorted you'll get a low value of inductance. Some-one has to sit down and plot a few graphs with a decade box because, reflected impedance is really reflected inductance. This means that if you have a transformer that has a primary, tickler winding, and a secondary that it will resonate over a range of frequencies based upon the load. It also means that you can use the primary as a tuner in a radio circuit and change the resonant frequency of a capacitor in parallel with the primary by using a potentiometer on the secondary winding. As it is, you cannot calculate the Q of the tank circuit nor it's range. Since, the Q is calculated as Q=XL/wr, where XL = inductive reactance in ohms at a given frequency, and wr = the DC winding resistance in ohms. Since, L is changing so does XL and Q as a result where the DC winding resistance never changes. As a rule inductors include winding resistance, stray/winding capacitance and that's enough to calculate self resonance. But, that doesn't fulfill the detail and compliment of true or real transformers. There are core dependencies such as saturation and where the windings begin to respond as if there were only a phenolic core beyond that point. There's how the self resonance of the secondary can effect the primary and visa versa. Then there's the issue already mentioned concerning loads. The model transformer is still not right. The BH curves don't even come close to the kind of graphs required to simulate a real transformer. You have to look at the load on the secondary to find the inductance of the primary then calculate resonance and Q.
Have a nice day,
The Flavored Coffee Guy
Spice5
I have tried several other free Circuit Simulators, Quc's {never got it to run on Windows} ngspice and never got it to run on Windows. At least Qucs allowed me to draw a schematic. The simulator side never worked. The first time I tried installing it, it showed up as a little tiny box that wouldn't allow me to access any buttons. I'll wait another year. Unless you're running a dual OS, Linux, or Unix, I doubt that either of those circuit simulators will work.
Now, if you want to design your own circuit boards for Free, the best schematic editor/PCB designer that produces a Gerber File that can be sent to a PCB manufacturer over the internet is KiCad.
Shop around PCB makers and a proto-type custom circuit board can be hammered out. The Gerber file will send your very own personalized traces and layouts to be perfected as circuit boards based upon your specs and design. You can select flow solder holes, multi-layer etc. it's all up to you.
If you would like to write and undersell the monsters of simulation in the world you could go to this site and pick up the source code for spice and there is an analog component that still isn't right and doesn't have a good model, step up and step down transformers. University of California at Berkeley Center for Electronic Systems Design
Start with a Bifilar wound 1:1 toroid. The inductances are mutual and don't change at any frequency or load. But, when you take a step up or a step down transformer and measure the inductance of the primary when the secondary is open you'll get a high value of inductance, and when you measure the inductance with the secondary shorted you'll get a low value of inductance. Some-one has to sit down and plot a few graphs with a decade box because, reflected impedance is really reflected inductance. This means that if you have a transformer that has a primary, tickler winding, and a secondary that it will resonate over a range of frequencies based upon the load. It also means that you can use the primary as a tuner in a radio circuit and change the resonant frequency of a capacitor in parallel with the primary by using a potentiometer on the secondary winding. As it is, you cannot calculate the Q of the tank circuit nor it's range. Since, the Q is calculated as Q=XL/wr, where XL = inductive reactance in ohms at a given frequency, and wr = the DC winding resistance in ohms. Since, L is changing so does XL and Q as a result where the DC winding resistance never changes. As a rule inductors include winding resistance, stray/winding capacitance and that's enough to calculate self resonance. But, that doesn't fulfill the detail and compliment of true or real transformers. There are core dependencies such as saturation and where the windings begin to respond as if there were only a phenolic core beyond that point. There's how the self resonance of the secondary can effect the primary and visa versa. Then there's the issue already mentioned concerning loads. The model transformer is still not right. The BH curves don't even come close to the kind of graphs required to simulate a real transformer. You have to look at the load on the secondary to find the inductance of the primary then calculate resonance and Q.
Have a nice day,
The Flavored Coffee Guy
