Application Note 5766
October 2013
Micheal Scherrenbur
The MAX13256, a 10 Watt transformer driver, is an improved way to convey power across isolation boundaries. As with all transformer drivers, good system performance requires good transformer specification. Though many transformers can potentially work with the MAX13256, not all transformer data sheets are specified with a transformer driver application in mind. This application note discusses how to specify a transformer that meets your application needs.
The MAX13256 is a small, high-performance transformer driver, ideal for isolated power delivery in industrial or medical environments. The MAX13256 is an unregulated DC-DC circuit component, that is, it has no feedback to control the secondary voltage. For this reason, the MAX13256 can be particularly attractive in applications where the secondary power does not need tight regulation. Even when good regulation is requested, following a MAX13256 with a post regulator can still be a cost competitive solution.
So how do you set output voltages? Unlike regulated DC-to-DC architectures, the MAX13256 always drives the transformer with a 50% duty cycle square wave. Consequently, output voltages depend on transformer winding turns ratios. So, care must be taken to select or specify an appropriate transformer for each application.
Finding a suitable transformer can be as simple as choosing an existing product specific for the MAX13256, or searching catalogs of general-purpose transformers for a suitable product. Also, transformer suppliers will manufacture custom designs, sometimes with little or no nonrecurring engineering (NRE), and fast turn-around, so if one of the standard offerings does not meet your needs, you can specify your own. Many transformer vendors accept high level specifications. For those vendors needing some help, you will also learn how to provide them with a basic design.
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MAX13256 secondary rectifier topologies
