While researching different types of regulators for a battery powered application, I learned about jeelabs and how they use a step-up voltage regulator to suck every pick of juice from AA batteries. The LTC3525 they use will take anywhere from 1.5V to 4.5V, so it also works as a step-down when the batteries are fresh.
The bad thing is the LTC3525 only comes in SMD package. Not very home newbiew solder friendly. Can someone recommend a similarly efficient step up regulator that's more prototype board friendly?
There's a MAKE Article and Youtube about making a bracelet that uses sunlight on photodiodes to charge 3 caps that a Joule Thief made mostly from a small choke (you don't even have to wind coils) to light a led you can see in daylight.
The full article: Solar Joule Bracelet - Make:
The YT: https://www.youtube.com/watch?v=ghB2irHIN8I
A joule thief will only be if use if you're powering less sensitive electronics with it, or the ripple will mess up the operation of most ic's.
There's a MAKE Article and Youtube about making a bracelet that uses sunlight on photodiodes to charge 3 caps that a Joule Thief made mostly from a small choke (you don't even have to wind coils) to light a led you can see in daylight.
The full article: Solar Joule Bracelet - Make:
The YT: https://www.youtube.com/watch?v=ghB2irHIN8I
Probably won't be for my project, but really interesting video. Thanks!
Thanks for the pointer to Pololu. A question about how they rate efficiency and quiescent current.
Their data sheet lists efficiency as 80% for a given condition (input voltage above 3.3V for example). Let's say the input voltage is 3.3V and output voltage is also 3.3V. Does that mean that if the load (the wireless module) consumes 4uA, at 80% efficiency, you'd expect the whole thing to consume (1 / .8 * 4uA) = 5uA? Most of the time the wireless module is sipping current, so an overhead current of a couple uA from the regulator is no big deal. I can live with that, but I don't think I'm interpreting the datasheet correctly, because this next statement doesn't make sense:
Maximum quiescent current: 1 mA
*The highest quiescent currents occur at very low input voltages; for most of the input voltage range, the quiescent current is well below 1 mA
Let's say the input voltage is really low (like 0.8V) and you get into the inefficient condition for the regulator. Is that 1mA quiescent current apply to when output current is 0? Or when output current is at the rated 200mA? Not sure what they mean.
I don't really care about how efficient the regulator is at 150mA, since I'm only running at 150mA for a couple seconds a day. I'm more concerned with the low load conditions.
Is it weird this table of voltage regulators list "max INPUT current"? Isn't OUTPUT current what's important? Is that a typo?
And they do it again in their specs, swapping input and output:
Here, they list "maximum output current":
Then they switched to listing the maximum input current for a smililar regulator. Did they mean output in this case? It's a little confusing
Thanks again for the help.
jremington:
Some of Pololu's boost regulators work down to 0.5 V. Pretty hard to beat that, especially considering the low price. Pololu - Step-Up (Boost) Voltage Regulators
I think it is a type/ Basically the energy (U * I) out = eneryg going in corrected with inefiiciency losses. OS if the voltage goes down the current goes up.
I built a project recently myself where I have an ADXL345 (6 DoF sensor) running at 3.3V (constant in sleep mode) and a Tiny84 direct on the battery. The ADXL345 gets fed by the regulator. The nice thing about the linears is that they will push the Vin to Vout when Vin is below 3.3V + dropout. So the only reason for the regulator to work is as long as the battery voltage is above 3.3V (i am using 3 x AAA in series = 4.5V). Once it gest below the regulating voltage only a few uA's are lost in the regulator
There is a boost circuit (MCP1640) sleeping when everything else is (Boost is disabled).
Now when the ADXL345 detects a change in the axis (rotation), an interrupt wakes the CPU. That in turn reads the ADXL. If the direction change is relevant, the boost circuit is switched on. That in turn switches a 433 Mhz transmitter on and data is sent.
And then everything goes back to sleep. The whole process takes about 2 seconds (mostly because of some delays I think I need).
Current consumption:
in sleepmode about 120uA.
in activation 15 mA And that is including a LED.
Expected lifetime with average 3 x AAA batteries is more than a year.
The circuit has been running now for about 6 weeks with triple amount of activity on a daily basis. Voltage drop has been 3mV sofar
arusr:
While researching different types of regulators for a battery powered application, I learned about jeelabs and how they use a step-up voltage regulator to suck every pick of juice from AA batteries.
The problem with that approach is that it trashes rechargeables to discharge them
so deeply and I never use anything else.
MarkT makes a good point about rechargeable batteries. It is counterproductive to try to squeeze "every drop" out of them.
If you have questions about Pololu products, post them on the Pololu user forum. The engineers are very knowledgeable and will respond quickly during normal working hours -- sometimes on the weekend, too!
MarkT:
The problem with that approach is that it trashes rechargeables to discharge them
so deeply and I never use anything else.
Oh yeah, thanks for pointing that out. I plan on using disposable AA - I have too many of them from costco, so I'd like to get as much out of them as possible. I do have a bunch of slow discharge NiMH, but I use them for flashlights. I'll have to see which has better cold/hot weather performance. I think slow leak currents are a good way to use disposables, in terms of getting the most amp*hours out of them.
Keep in mind, too, that in my experience, disposable batteries are more likely to leak, the closer they are to fully discharged. Carbon zinc or so-called "heavy duty" batteries leak a corrosive acid. Alkalines leak an alkaline (as expected) that is less corrosive but still damaging.
I'm not saying don't do this, I'm saying don't leave the batteries in after doing this.
I wonder how efficient the average joule thief is.
Why use something less than 100% efficient to charge something that is less than 100% efficient at storing energy which then must power a switching regulator which is also less than 100% efficient? Why not just use a single switching regulator from the disposable battery?
