buck boost regulator in one..

[podoljano]

Hi guys, im building a simple battery USB charger which has to provide a constant 5V output @ 0.5-1A. The charger has to be able to handle input voltages higher and lower than the output voltage (3-10V). I have been reading about boost/buck converters however on most of the datasheets i have seen they only talk about these devices being used for ETHER a boost, or buck circuit. However i need the circuit to do both, meaning when the input voltage exceeds the desired output voltage the buck will do the work, and when the input voltage is below the desired output the boost converter steps in..
I would very much like to use the MC34063 ic for this operation due to its low price and avilability in my country, however im not sure if it is able to do the job.
Can anybody give me some hints on this issure, maybe refer me to some reading material on the subject, or recommend another ic.

Best regards
Nikolaj

 

[BradtheRad]

A buck-boost can do what you want, assuming the control IC can alter the frequency and duty cycle.

Screenshot of the same circuit, showing waveforms if it were driven with a 3V supply (left) and a 10V supply (right).



The buck-boost changes a positive supply to negative polarity. There are strategies to work around this, if needed.