Buck-boost configurations

Figure 1-14 Improperly Referenced Buck-boost Configurations...

Blog Entry 3 A more simple solution to implement is to use the 3478 Low-side N-channel controller in a SEPIC configuration. This application utilizes two inductors (instead of a Flyback transformer) to attain the Buck-Boost function. The 3478 requires an external user-selectable Fet switch, so you can choose the one that suits your load current requirement. The datasheet provides an application rationale for SEPIC configuration on page 19, Figure 13. The output voltage can be set to 12V by changing the value of the feedback resistor. 

For either configuration, we see that whatever polarity is present at the input, it gets reversed at the output. Therefore, the buck-boost is often simply called an inverting topology (though we should keep in mind that that allows for two different configurations). 

A related issue is the case when a buck IC is used in a so-called inverting configuration . We should realize that in doing so actually the topology has in effect changed from a buck to a buck-boost. So now we just cannot get 5 A of load current from a declared 5 A IC. How much load current is possible depends on the specific input-output conditions. So again, our peak current is not close to 5 A, nor should the inductor rating be 5 A . Or we will certainly be frozen into a July 4th timeframe forever. 

Small Research Laminator. The Process Development Area (PDA) of FSA received two ARCO Solar-developed laminators at the end of the contract. One of these laminators was modified for use with a strip heater. This configuration, with a boost-and-buck autotransformer power supply, was used successfully for some process verification and materials survey experiments. Assessment of future research needs and present equipment capabilities led to additional modifications of the laminator. 

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