I just finished a prototype of a circuit I've been working on for several months. I want to retrofit a selection of vintage lamps with modern LEDs with standlight capability as well as the option to flash. I breadboarded it, had a PCB made and just finished soldering the parts on last night. The circuit charges a supercapcitor which powers a LED boost driver when stopped to provide anywhere from 2-5 minutes of standlight (depending on flash setting). A 555 timer provides the blinking option.
A couple of pictures:
The PCB is about 1.6" in diameter.
To fit the LEDs in the lamps I've made an E10 bulb with a copper heat sink:
I have yet to install the whole contraption on a bike yet, but it seems to be working well on the bench. The schematic is here.
The only issue is that the 6.8V Zener diode that regulates the input voltage gets very hot while in flashing mode. During the off cycle it clips the dynamo output and shunts its current. Kind of wasteful, but easy to implement. It's a 5W Zener, so it should be able to handle the dynamo output with the load disconnected, but I'm still a little worried about it. At some point I'd like to implement a kind of charge pump that stores the dynamo output during the off period of the flash and adds a burst of current during the on period. No idea how to do that though...