| Electronics > Projects, Designs, and Technical Stuff |
| Micropower "kickstart" boost converter / joulthief |
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| Amper:
Hi! On my quest of building small micro controller devices with less and less supply im now thinking about supplying an attiny13 with just a single AA battery. Though this calls for operation starting at 1V or less, the controller needs 1.8V for reliable operation and i dont want a continuously running boost converter as it will eat more energy then the entirety of the device. What im looking for is some sort of part/ circuit that will only draw power once its output falls below 1.8V. The main energy harvesting will be done by the micro controller supplied through a diode into one of its pins. The output stage with its two fets and diodes should make it possible to just pull the inductor down from 1V to ground and then set the pin high/ floating again and this way charge a cap located at the vcc pin. Using the brown out detector it should be possible to keep the system running like this with just two passive components and no boost converter. But i have no idea if there is a way that will draw less then .1uA in standby and still start up below 1V. open for any reasonable suggestions ^^ |
| Amper:
Just a quick update, the main boost converter works just fine, though i dropped the direct drive by the controllers pins because it seems lie its not possible to switch from output to input fast enough for the converter to operate nicely and the protection diodes are no shottkys. Parts count now is 6 including passives and it reliably works down to 1V, though 0.7V has worked as well and in theory even less should be possible. here is a video of the thing running on a single empty (sub 1V) 1.2V cell. Between flashes the power consumption is just the 4uA of the watchdog and while the led is on the 25uF cap is recharged to 3.6V. Still looking for a solution for the initial startup voltage source though... |
| rvalente:
Would these guys help you? https://www.microchip.com/wwwproducts/en/en547080 https://www.microchip.com/wwwproducts/en/MCP16252 |
| mikerj:
How about adapting a "joule thief" style circuit, which can typically start up below 1v. Have the bias to the feedback winding controlled by a low Vgs P-MOSFET which is biased on with a (high value) pull-down resistor. This makes a self-starting supply which the micro can disable once it's started up, and then take over the inductor switching itself. Would need some way of preventing the unpowered micro port pin interfering with the switching transistor in joule-thief mode. Main downside is a dual inductor |
| Amper:
@rvalente yes, they look interesting but they still have moderately high power consumption. When turned off 1uA would be allright but im not sure how to do that as they are pulled down in off state Maybe a logic level fet will do that for me, i will consider. @mikerj Thats my original idea and the reason why i mentioned it in the title of the post. The issue is that in the turned off state after applying power there is no voltage available to turn on any p-fet i would know of. Also actively turning it off using the micro is no option as it would require another pin and current to keep the pin active. |
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