I'm having some trouble with an exercise in LTSpice, for a DC-DC converter = from 3V (Lithium cell nominal) to 400V Basically, no matter how I set up the transformer I don't seem to get past = 40V. It's been a while since I built a Royer converter, and I think I'm missing = something in the transformer design. Taking a WAG at the inductor design, I have a center tapped primary of two = 10uH inductors. I defined the relationship as Pin =3D Pout =3D (Vin * Iin) =3D (Vout * Iout= ), more or less. Vout / Vin =3D turns ratio 400/3 =3D 133/1 turns ratio Since inductance is kN^2, I defined the output inductor to be the inductanc= e of one half of the primary winding (10uH) multiplied by (133^2) Coupling between all inductors in the transformer is 0.95, another WAG. I added 1uH leakage inductance (not coupled ) to both legs of the primary, = but not to the centertap leg. Ancillary problem, whenever I define the output inductor with a param state= ment like .param L2=3DL1*(133^2) I get the dreaded "Time step too small" me= ssage pointing to my mosfets. I have to work it outside of spice, and then use something like .param L2 = =3D 178mH. -- David VanHorn Lead Hardware Engineer Backcountry Access, Inc. 2820 Wilderness Pl, Unit H Boulder, CO 80301 USA phone: 303-417-1345 x110 email: david.vanhorn@backcountryaccess.com --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .