transformer for LT SwitcherCAD

Without getting too wordy about things have a look at....

For the general idea for an ideal transformer in SPICE.

You take that idea and then add 'parasitics' as required.

You might get leakage inductance by playing with the coupling coefficients but it is easier to make them all 1 and then add series inductance to the appropriate windings.

DNA

I have never used SWCAD but do know it is optimized especially for switchers. In a pinch, certainly you can find an ideal transformer, then parallel it with an inductor equal to the magnetizing inductance, and in series, with the whole assembly, add a combo of R+Ls where R is the winding resistance and Ls is the leakage inductance, which can be taken to be 1% of magnetizing inductance. Add a secondary series R+L as well. This will give a first order approximation. For an exact simulation SWCAD should have provisions for a Jiles-Atherton [sp?] transformer simulation, mainly to simulate core losses, and this requires information pertaining to core material and geometry- much more detailed. You can also estimate the loss and represent this in the first order model by a resistor Rm in parallel with the magnetizing inductance, which is still useful for obtaining bounds.

Think I found this on the yahoo gloops LTSpice

Lp N003 N004 Lp Ls N005 N006 Ls Llp N001 N003 Llp Lls N005 N008 Lls Rp N004 N002 Rp Rs N006 N007 Rs Cs N008 N007 Cs Cp N001 N002 Cp Rc N003 N004 R K1 Lp Ls 1 .backanno .end

martin

Just another first order with no core loss or nonlinearity representation...

The easy part is you use an inductor for each winding then link them all with the K directive.

This provides an ideal transformer, you can then model the losses wich are frequency dependant with L/R/C circuits around the winding inductance, or even use the parasitic parameters of the inductors.

Some inductors specify eqv circuits in their data sheets. I dont know about transformers, especialy if you are winding your own, maybe there is a normalised circuit equivalents for each type of magnetic material ? obviously it would vary a lot depending on construction gap etc.

I supose you could even model the magnetic path in circuit terms, theres a good ltspice forum on yahoo might have the answer already.

Colin =^.^=