Before I read Sean's email: Post the LTSPICE file, I recall facing a similar issue recently in a power supply design class I took. I think the issue was something simple like a 1milliohm series resistance in the default LTSPICE inductor & switch models. Changing it to 1 nanoohm fixed that. After I read Sean's email: if you need to model saturation you can do it but I think you'll have to define your own model/subcircuit. On Thu, Jul 5, 2018 at 1:12 PM, Van Horn, David < david.vanhorn@backcountryaccess.com> wrote: > I'm having some trouble with an exercise in LTSpice, for a DC-DC converte= r > from 3V (Lithium cell nominal) to 400V > Basically, no matter how I set up the transformer I don't seem to get pas= t > 40V. > It's been a while since I built a Royer converter, and I think I'm missin= g > something in the transformer design. > > Taking a WAG at the inductor design, I have a center tapped primary of tw= o > 10uH inductors. > I defined the relationship as Pin =3D Pout =3D (Vin * Iin) =3D (Vout * Io= ut), > 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 > inductance 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 > statement like .param L2=3DL1*(133^2) I get the dreaded "Time step too sm= all" > message 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 backcountryaccess.com> > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 Jason White --=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 .