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I'd like to solve the above-mentioned problem by using a buck-boost or SEPIC DCDC converter. I haven't successfully found any suitable ICs though. SEPIC converter with input voltages from 4.5V to twenty-some volts doesn't seem the best choice as it would be necessary to have the aimed 5V 300mA output as soon as possible. (Minimum input of 2...3V would be better.) I was thinking on designing a voltage doubler / multiplier between the generator and the converter so that the input voltage is more convenient (4.5V input is reached faster). Unfortunately I don't have any previous experience on voltage multipliers, so I'm not quite sure it would solve my problem.

Efficiency is vital, so I'd prefer keeping it as high as possible. The voltage source will gain the power from the rotating shaft of a small car, thus the voltage will increase monotonously in time until reaching the maximum value of approx. 6V.

Thanks in advance for your help!

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closed as too broad by placeholder, Bence Kaulics, PeterJ, Voltage Spike, uint128_t Jun 23 '16 at 1:06

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ To design and build such a device requires much skill. What your describing is much like those built for LED strips or LED hockey puck lights, in that the supply outputs a constant current, not a constant voltage. Surf the web for "LED power supply". Also, some large hardware/lumber supply stores carry LED lights and power supplies. Don't build what you can buy. \$\endgroup\$ – Sparky256 Jun 22 '16 at 19:31
  • \$\begingroup\$ MAX1699x page 16 fig 2. It seems to have 2.5 Input voltage min. I didn't look much more, but it seems there are ICs that can do just what you want. I wouldn't be surprised Linear Technology also had tons of ICs like that. \$\endgroup\$ – dim Jun 22 '16 at 19:35
  • \$\begingroup\$ @dim. That IC is a good choice if the OP has the skills to build a SMPS. \$\endgroup\$ – Sparky256 Jun 22 '16 at 19:42
  • \$\begingroup\$ @Sparky256 well, given the question, I hope he has. Otherwise, it is pointless. \$\endgroup\$ – dim Jun 22 '16 at 19:45
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I think there might be a DC-DC converter for your on world's largest web store (mostly from China). It costs about half the pack of cigarrets and just might be a suitable find for you. Try searching for: "1-6.5V to 5V buck boost" and you should find something useful.

In case you're not going to plug in any USB devices, just unsolder USB connector and find right wires to wire your application.

I hope it helps.

ps: I've used one when I did my solar charger for a phone. Works great!

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