Electronic – combine step-up and step-down designs for switched DC-DC convertor

circuit-designdc/dc converterintegrated-circuit

I need to generate 5 volts from unstable source. The voltage on input will be between 2 to 7 volts. The source is hand-crafted dynamo, which I'm doing as an experiment.

I found LT1173CN8-5 DIP8 integrated circuit. In the datasheet (written for all LT1173 series circuits) they show these two examples on page 13:

image description

I'll be going with the left design, since my input voltage is most likely to be less than 5V – random peaks above can be handled by capacitors.

But is it possible to combine designs? Would that cost me efficiency?

Why is the diode on the images above actually placed completely differently?

Best Answer

For your application exists a different category of DC/DC converters called buck-boost converter which handles exactly what you are describing.

They reach efficiency levels of both designs, mostly dipping if the input is close to the output voltage.

They are available from different manufacturers, just like you'd expect.

A word of warning for your special application (I tried something similar and killed my MP3 player with it): in case of no load the voltage of your dynamo will get very high, use some sort of voltage limiting at the input of your buck-boost converter.