Cuk Converter (2)

Published:2011/8/10 21:26:00 Author:Li xiao na From:SeekIC

By Georg Gerads

Inductor

Unlike most comparable high-power switched-mode regulators, the design of the inductor is not critical with the Cuk Converter, since it conducts a continuous current instead of being switched. The Epcos type E42/21/20 core, which is made from N27 core material, is quite suitable, readily available and a real bargain at less than 7 pounds (including mounting hardware). The core accessories include a plastic coil former and a sheet-metal clamp for securing the core. In our lab prototype, the job was handled by an LCC type E-45220A core. Spacers cut from i.5-mm PCB material create a gap with a width of 1.5 mm. which in the case of an E-section core corresponds to an air gap of 3 mm in the magnetic path. Type ETD49 and E47/20/16 cores are also suitable, but the base of the coil former for these types doesn’t match the circuit board layout.

Regardless of which type of core is used, 32 turns of 1-mm diameter RF litz (multi-stranded) wire must be wound on the former for each winding, with the wires for the two coils simply being wound in parallel.

Solid enamelled copper wire can also be used, but the insulation breakdown voltage of enamelled copper wire is not all that high. Consequently, the primary winding should be wound firs:, followed by the secondary, and paper strips must be placed between the layers of the windings.

In either case, pay particular attention to the direction of the windings, since otherwise things will go bang.

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