Designing a radiation hardened switch mode power supply for use in space is a challenging task, radiation effects, the lack of atmosphere, thermal amplitudes, mechanical shock and vibration, EMI compliance, reliability and cost are some of the design constraints. Several converter topologies are studied as well as the design trade-off's imposed by each of the topologies. Commercial integrated circuit radiation hardening by design techniques are presented. A novel controller IC capable of withstanding radiation environment is currently under development.