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Crank up the Charge

The datasheet of the PCF50633 says Vusb=4V. What will be the input current when charging with 500mA? Let's assume not more than 500mA. So the power requirements are 2W. OK. You will loose some power in the rectifier. Maybe there's no additional voltage regulator needed.

If you want to reduce the power requirement even more, you could replace the battery by something robust, lets say a plumbium battery, and feed the regulated dynamo voltage directly the battery voltage pin. There 2.8V seem to be sufficient.

Dynamo Hub Series Connection

The FreeRunner can be put in series to the continuously running lights. There is no need for a voltage regulator. A powerful Z-diode with 4.xV parallel to the USB voltage input should be sufficient. Maybe a power LED can be used directly. In combination with a homebrown LED light only one rectifier is needed.

Switching Mode versus Linear Regulator

Let's say we power the FreeRunner via USB with 4V and it draws 500mA. Assuming 2V voltage drop across the voltage regulator and the schottky rectifier we get a power loss of 1W. Is this really worth worrying? As said above you can use the same rectifier for your homebrew LED lights.

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