LTspice IV can help you easily create your own schemes in order to simulate switching regulators.
It is a new SPICE that was developed to simulate analog circuits fast enough to make simulation of complex SMPS systems interactive. Incorporated into the new SPICE are circuit elements to model practical board level components.
Capacitors and inductors can be modeled with series resistance and other parasitic aspects of their behavior without using sub-circuits or internal nodes. Also, a simulation circuit element was developed for power MOSFET's that accurately exhibits their usual gate charge behavior without using sub-circuits or internal nodes.
Reducing the number of nodes the simulator needs to solve significantly reduces the computation required for a given simulation without compromising the accuracy or detail of the switching waveforms.
Another benefit of these new simulation devices is that convergence problems are easier to avoid since they, like the board level component the model, have finite impedance at all frequencies.
Modern switch mode power supplies include controller logic with multiple modes of operation. For example, devices may change from pulse switch modulation to burst-mode or to cycle skipping depending on the circuit's operation. An original new mixed-mode compiler and simulator were written into LTspice that allows these products to be realistically modeled in a computationally fast manner.
But despite LTspice’s close association with SMPS design, it not a SMPS-specific SPICE but simply a SPICE program fast enough to simulate a SMPS interactively.