Micropower "kickstart" boost converter / joulthief - Page 1
Forum section: electronics / projects

author: Amper
author_rank: Frequent Contributor
timestamp: November 22, 2019, 01:16:17 am
content: 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 ^^

author: Amper
author_rank: Frequent Contributor
timestamp: November 26, 2019, 06:40:02 pm
content: 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...

author: rvalente
author_rank: Frequent Contributor
timestamp: November 26, 2019, 07:47:36 pm
content: Would these guys help you?https://www.microchip.com/wwwproducts/en/en547080https://www.microchip.com/wwwproducts/en/MCP16252

author: mikerj
author_rank: Super Contributor
timestamp: November 26, 2019, 08:01:58 pm
content: 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

author: Amper
author_rank: Frequent Contributor
timestamp: November 27, 2019, 03:32:15 pm
content: @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.

author: Brutte
author_rank: Frequent Contributor
timestamp: November 27, 2019, 05:06:57 pm
content: How aboutATTiny43U?

author: Amper
author_rank: Frequent Contributor
timestamp: November 27, 2019, 06:06:22 pm
content: well.... if had known about that one beforeThanks for suggesting, will order some right now and use my test circuit as a blinky decoration.

author: Amper
author_rank: Frequent Contributor
timestamp: November 27, 2019, 06:58:30 pm
content: Allright, maybe i was to enthusiastic...The 43U is awesome but it has a startup voltage of 1-1.35V which is better then my current setup but saly only suitable for starting the thing up on charged cells.

author: Yansi
author_rank: Super Contributor
timestamp: November 27, 2019, 07:03:34 pm
content: Still very lame - a pro tip!Use a depletion mode mosfet in the joule thief (or a JFET). Will then start from a couple hundred mV.

author: Amper
author_rank: Frequent Contributor
timestamp: November 27, 2019, 07:38:17 pm
content: I wanted to try it but dont have one here right now. Do you have some part number as a starting point?Some other extreme way would be to use an ltc3109 but thats the other end of the extreme scale and wont help much on battery applications. But i do like them a lot, running something from a 10x10mm peltier device just from the heat of a fingertip is pretty awesome, allways wanted to build a writs watch this way.

author: Amper
author_rank: Frequent Contributor
timestamp: November 27, 2019, 10:55:29 pm
content: Allright, i found an acceptable way using a LTC3105 for startup, later pulling its shutdown pin with an ordinary n channel logic fet. It draws 12uA this way which is to much but the basic principle works and now i can look for different boost converters (like the ones posted before). This paired with the tn43U could result in a really sweet setup but ill still try getting it to work with just normal controllers.

author: Amper
author_rank: Frequent Contributor
timestamp: December 03, 2019, 04:39:55 pm
content: Andanother update:I just started playing with MCP1640 and while im pretty happy with them in terms of standby current (1uA as stated in the datasheet is easy to obtain without any voodoo) the efficiency at low input voltages is horrible.At this point i just enable it by a pull up and disable it by the attiny and then put everything to sleep until the brownout detector wakes it up again at 1.8V.right now it consumes 100uA@ 1.5V on average which is way to high and leaving the boost converter enabled consumes an extra 9mA without doing anything else. The 10uA figure stated in the datasheet is only realistic at high input voltages above 3V, i guess they dont supply the internal logic and transistor drivers from the output but use the input as its exclusive power source...

author: Marco
author_rank: Super Contributor
timestamp: December 04, 2019, 09:17:25 pm
content: How about TPS60310?There are of course proper 0.9V MCUs, just not tinys.

author: Amper
author_rank: Frequent Contributor
timestamp: December 04, 2019, 11:45:56 pm
content: I think i solved some issues, one or two software bugs, and a mistake i did in hardware. Also charging the storage more often (every few seconds actually) helped. I guess this way it operates in a better efficiency range. Now i just keep charging to 1.9V and went down to 14uA@1.2Vin and 20uA@0.9Vin. Efficiency wise this is also not amazing but im down to 20uW which is good enough for almost all applications. Though im toying with the thought of using an M41T62 RTC which i may need anyways as the watchdog. This will bring the current at high voltage down to 450nA and will result in roughly 2uA@1.2V. Thats insanely low power.The reason i dont really want a low voltage controller is that i plan on controlling other hardware and even writing to SD will need 3.3V an when i have to have a boost conveter anyways i may as well keep open all the range of atmel cpus.