I'm attempting to create an isolated 12V supply. This works from an 11V - 14.4V input (i.e. normal lead acid battery) and should produce about 12V @ 500mA. One essential point of this supply is that it *must* be isolated from the input because the other side is connected to the mains in some way. I've been working on this design in LTSpice, but it's hideously unstable. It starts off at 12V, but then sags down to around 4V, with very high ripple. Does anyone know why this might be so?