I'd suggest posting a file that recreates your issue.

On Friday, July 6, 2018, Van Horn, David <
david.vanhorn@backcountryaccess.com> wrote:

> Sorry, this is a resonant royer, without the second winding for driving
> the transistors.
>
> Similar to the first schematic here:
> https://www.eevblog.com/forum/projects/efficient-magnetics-
> design-for-offline-resonant-push-pull-(royer)-converter/
> Just add a bridge rectifier on the output and a feedback path to a
> comparator that drives the power control fet (Q3) in this circuit.
>
> I'm nowhere near regulation, but if I alter the circuit to regulate at 40=
V
> instead of 400V it actually works in spice, turning "Q3" on and off
> appropriately.
>
>
> -----Original Message-----
> From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> On Behalf Of
> Jason White
> Sent: Thursday, July 5, 2018 12:31 PM
> To: Microcontroller discussion list - Public. <piclist@mit.edu>
> Subject: Re: [EE] 3V - 400V royer converter
>
> 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
> > 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
> > 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
> small"
> > 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<mailto:david.vanhorn@
> > backcountryaccess.com>
> >
> > --
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>
>
> --
> Jason White
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