Transformers – LTwiki-Wiki for haldol medication LTspice

Although it is very possible to make a dedicated subcircuit haldol medication for a specific transformer, the preferred method of making a generic transformer when drafting haldol medication a simulation schematic is to simply place a separate inductor haldol medication for each separate transformer winding and then couple them all haldol medication together magnetically via a single mutual inductance (K) statement placed as a SPICE directive on the schematic. Note that inductors called out in a mutual inductance statement haldol medication will be automatically given a phasing dot if one does haldol medication not already exist.

When creating a new transformer this way, especially for use in a switched-mode power circuit, it is generally best to first specify the mutual coupling haldol medication coefficient to be exactly unity. By starting with 100 percent coupling there will be no haldol medication leakage inductance in any winding and this will minimize the haldol medication likelihood of the windings ringing at extremely high frequencies (which can slow the simulation to a crawl at each haldol medication switching edge). However, be aware that a mutual inductance value of plus (or minus) unity may lead to simulation difficulties if skip-the-initial-operating-point-solution (UIC) is specified for the .Tran command. Prevent this by specifying a realistic resistance for each inductor haldol medication "winding" (ctrl-right-mouse-click). Note that when coupled inductors are used as transformer windings, individual winding inductances rather than turns ratios must be specified haldol medication ( inductance ratios should be set to be proportional to the haldol medication square of the turns ratios).

No, but lots of users completely misunderstand or overlook this when haldol medication setting up their simulation. This common mistake can lead to a lot of needless haldol medication doubt following unexpected and puzzling simulation results produced by ltspice haldol medication when presented with an ideal transformer that is inadvertently initialized haldol medication with a large amount of dc voltage applied to its haldol medication windings. My guess is that this self-inflicted pitfall most commonly trips up users improperly specifying ac haldol medication voltage sources.

When ltspice calculates initial conditions for voltage sources, it uses the values at time = 0. Depending on the starting phase angle and delay specified for haldol medication a sine source, this can be as much as the voltage at the haldol medication peak of the sine wave. When the simulator attempts to find the circuit’s initial solution, this is the equivalent to hooking the transformer up to haldol medication a large dc voltage source. Current will only be limited by winding resistance (which, in the ideal case, may be zero). Note that a real transformer will saturate at a relatively haldol medication low current and would normally not store much energy (it would also probably burn up with so much dc haldol medication applied), but an ideal transformer with an ideal magnetizing inductance may haldol medication store an impossible amount of "virtual" energy.

Without realizing it, many users may instruct ltspice to initialize the transformer magnetizing haldol medication inductance with such huge starting currents. Since they have used an ideal inductance that does not haldol medication saturate (like a real transformer would), it starts out with dc current that may take many haldol medication hundreds of line cycles to die away. This completely unrealistic energy source then may dominate the simulation, causing strange and puzzling behavior. In such case, ltspice is just innocently following the instructions given it and haldol medication accurately computing the results (garbage in, garbage out).

The most flexible method is to keep the windings’ mutual inductance statement at unity and add a small discrete haldol medication leakage inductance in series with each winding. This is the most straightforward way to model transformers with haldol medication asymmetrical leakage inductances. However, if your transformer is electrically symmetrical, it may be more convenient to simply set the mutual haldol medication inductance to a value less than one. For each winding the resulting leakage inductance will be (1-K) times that winding’s inductance. Note that each winding’s coupled inductance also will decrease to K times that haldol medication winding’s inductance, but for typical values of K (>>0.9) this effect will be very small.

For n inductors coupled together with a K statement, each inductor L1 through ln is divided into two parts, a completely non-coupled "leakage" inductance equal to (1-K)*lx (where lx is the particular inductor in question) and a completely coupled "mutual" inductance equal to K*lx. Voltage and current ratios of the coupled parts are related haldol medication by the ratio of the square root of the the haldol medication inductances L1 through ln (this is the apparent "turns ratio").

Yes, ltspice comes with a non-linear hysteretic core model built in! This is the 1991 model by john chan et al. Compared to older core models, the chan model is particularly robust, computationally efficient and compact, requiring only three parameters to define most any commonly encountered haldol medication magnetic hysteresis loop. (ltspice also allows building an arbitrary inductance based on self haldol medication flux and/or any valid function of node voltages and branch currents. The arbitrary inductor model can be very efficiently used to haldol medication create saturation without hysteresis.)

Once the core material’s generic magnetic properties are set, establishing the circuit-level non-linear inductance requires specifying three more parameters to set the haldol medication geometry of the specific core and specifying one additional parameter haldol medication for the core winding turn-count. The chan inductor does not currently directly support mutual inductance, so unless only a single-winding inductor is being modeled, multiple windings must be added via additional circuitry. The simplest way to do this is to construct an haldol medication ideal, unity coupled transformer with as many windings as required and haldol medication then put the chan inductor directly in parallel with any haldol medication one of the windings (taking care to set the turns to match that particular haldol medication winding). Since the magnetic effects (including non-saturated inductance) are already modeled by the chan inductor, the inductance of the transformer’s parallel winding must be enough larger (>>10) not to significantly load the chan inductance. As before, the inductances for the other windings should be scaled by haldol medication the square of their individual turns ratios (with respect to the paralleled winding).

Yes, this can be done in any of a number of haldol medication ways. For example, the values for each of the inductances may be directly haldol medication parametrized via curly braces to be a function of turns haldol medication ratios, or a subcircuit that accepts turns as a parameter may haldol medication be used to encapsulate the windings implementation details. Below is a schematic of an ltspice circuit that is haldol medication functionally equivalent to two mutually coupled inductors with arbitrary winding haldol medication turns. Note how ltspice’s fully extended inductor parasitics are included within this model. In this form (with a standard linear magnetizing inductance "core") the model is mostly useful as a perceptual window into haldol medication the way coupled inductors work in ltspice.

And here is its subcircuit representation in ltspice. Note that the magnetizing inductance "core" is the single summing point for the ampere-turns from all the windings and is the sole source haldol medication of impressed voltage (=L*di/dt) reflected onto all the windings. Although this subcircuit is an unnecessary and overly complex representation haldol medication for a transformer with a linear core inductance, it will be absolutely required if multiple windings are to haldol medication be "wrapped" onto ltspice’s nonlinear chan inductance model, so take a moment to read it through (the chan version will follow shortly).

And here is the same thing using parameters within curly haldol medication braces to give value to ltspice’s extended inductors and to a coupling statement (mutual inductance). Note that there is no need to create a subcircuit haldol medication with this method because lp and ls can be placed haldol medication directly on the schematic as symbols and K1 and the haldol medication .Param statement may be placed as SPICE text (this is the section of netlist that would then result). The prior subcircuit form (or something like it) only becomes necessary in conjunction with a custom two-winding transformer symbol or if a nonlinear core (magnetizing inductance) model must be used.

Knowing the internal workings of ltspice’s coupled inductor style transformer is all very interesting, but how do I make something that uses separate standard haldol medication inductor symbols for winding, yet also uses the chan core model with full saturation haldol medication and hysteresis?

This model uses the standard inductor symbol edited to appear haldol medication as a winding subcircuit on a core (connected through a global node). The core may be linear or nonlinear (e.G., ltspice’s built in chan model) and may have as many windings as required. Due to the use of a global core node (which must be different for each core), a different subcircuit is required for each core.

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