Cheap LDO for battery usage

[jmd]

Hi !

This is my first post on mysensors.
I tried to find the answer of my question on the existing posts, without success. If you know where I can find it, don't hesitate to tell it to me

I'm trying to build my first node, powered by AAA batteries, for at least 1 year.

I tried to find :

• A step up converter with 5V output
• A step down converter with 3.3V output
• A step down converter with 5V output

As I'm running on batteries, I'm looking for high efficiency components.
As I'm not rich, and it's just a hobby for me, I'm looking for cheap components (on aliexpress).
As I want to power some power-hungry components, I'm looking for an output between 100mA / 200mA...

For the step down converter with 3.3V output, I found the HT7333-1, less than 4€ / 50 pieces. What do you think ?
For the other two, I have no clue at all. I think that a lot of nodes need stable power supply. I'm surprised that I didn't find the answer.

Thank you a lot !

[flopp]

662k is a cheap LDO step-down

Here you find more information

https://www.mysensors.org/store/#power

[Michael Moebius]

Hello,

I was just trying to find something similar, but I'm more interested in the step-up part, to use with one or two AA/AAA to power my circuits. That was the closest thing I found from "reality": https://www.kickstarter.com/projects/340271897/whisper-node

I tried to build a step-up circuit myself but wasn't that easy... looks like those switching regulators don't work very well in breadboard, they're all SMTs with very fine pitch and they need other components like the inductor that can add some cost. Also found those ones ready to use: https://www.pololu.com/product/2561, it's not the most expensive but I'm not sure if they will keep the power consumption low at stand-by.

You mentioned 100mA and one year... are you planning to sleep those power-hungry components most of the time correct?

[Pavel Hrudka]

Hi.
Last few days I spent my free time with searching for step up converter.
I need to powet DHT22 from batteries, It needs 3.3V.

You can either get one on alliexpress or build one.

Using nowdays ICs which are very efficient and need only four or five components was my choice.
I found MAXIM-DALLAS MAX856CSA+ or LINEAR TECHNOLOGY LT1300CS8#PBF which are both step up converters with choice of voltage (3.3/5V) using digital input.

Both are able to handle your currents.

Nice tutorial can found here

You can also find some tutorial on instrucatables .

Also nice post about this is here.

I know you wanted step down regulators but if you head to pages of Linear technology (http://www.linear.com/) or Maxim (www.maximintegrated.com) you will find what you are looking for.

Happy digging!

[jmd]

Thank you for your answers.

@flopp : I didn't noticed before the 662k, with seems great to get 3.3V (step-down). Unfortunately, it seems more difficult to find the same chip in 5V.

@Pavel-Hrudka :The MAX856CSA and LT1300CS8#PBF are way too expensive for my usage. But I will take the time to read the tutorials.

@Michael-Moebius : My node actually sleeps almost all the time. I just need to read the sensor 2 or 3 time per hour.
Which step-up component did you try to use ?

For now, I use a cheap MT3608 regulated to get 5V, and power-it on/off with an NPN when needed.
I also use an HT7333 as 3.3V regulator (step-down).
I still didn't find the components I dream of

[AWI]

@jmd said:

@flopp : I didn't noticed before the 662k, with seems great to get 3.3V (step-down). Unfortunately, it seems more difficult to find the same chip in 5V.

The 662k is part of the XC6206 family.. find the XC6206P502MR where the 50 in the last part tells you something about the voltage

What kind of circuits are your power hungry ones?

[Michael Moebius]

@jmd : I tried to build myself a step-up circuit using the MCP1640, inductor, capacitors and resistors to deliver 3.3V from a single AA.

It worked well, but only for very low currents, anything over 20mA was not working. So I research and found out that those switching power regulators, specially the step-up ones need to be carefully designed and are very likely to under-perform or not work at all in a breadboard or protoboard. The MCP1640 even have a suggested PCB design which you must follow to get it working at full performance.

[Mike Musskopf]

Hi,

My name is Mike and I'm the person running the Kickstarter campaign mentioned on this topic (https://www.kickstarter.com/projects/340271897/whisper-node). Glad to see people are looking into my project as an alternative for low-power applications. Anyway, I'll try to give my 2 cents about the battery powered nodes and the regulators.

@Michael-Moebius The MCP1640 is a great chip, but you're correct saying that it's complicated to built the module itself. The problem of assembling it on a breadboard or protoboard, is that you will probably end-up having very long leads/traces, this will cause lots of inductance, preventing the switching regulator to work well. There's also the interference the circuit can cause to others and to itself as those regulators run at high-frequency.

I've a look on the Pololu product you mentioned and it seems to be ok for a step-up regulator to produce, let's say, 3.3v from a single or dual AA, but the efficiency chart there show a bit of problem at lower currents when using a single AA. That might cause some unexpected battery consumption when the board is sleeping... but only a real-life test would give the answer.

@jmd Could you pls provide some additional details about your project:

• Which board/MCU are you using?
• Have you already discovered the power consumption of your circuit when its active and when sleeping?
  *Collect the active current can be trick as it might be a very sort spike, in this case you can rely on datasheets OR change your code into a loop to, lets say, keep reading a sensor continually just for you to measure the current.
• Do you really need 5V?

Sorry to ask so many questions, but when designing things to run for long periods every single mA counts! Also, stay away from 5V if possible, use 3.3V or even lower voltage is possible, that will save lots of battery.

If you really need 5V to power-up a special sensor (which there's no substitute which could run at 3.3V), the best approach is to have 2 power rails: a 3.3V rail powering the board and MCU and a 5V rail to power the special components. This second rail you'll need to keep off and turn on using the MCU only when necessary using a Mosfet, Power Switch or a Regulator Enable Pin.

Another thing related to 5V is that you probably won't be able to get if from a single AA, you'll need at least 2 cells to produce some usable current from a step-up. Remember that the battery voltage will drop during its life, so make sure you always calculate things using the lowest voltage (expect 0.9V by the end of the battery life http://data.energizer.com/PDFs/E91.pdf)

If you decide go to the LDO solution, bear in mind you'll always need to supply greater voltage, so the regulator will "burn" the extra power and deliver the selected voltage. For example, if you need 5V you probably will need to have 5 Alkaline cells so you can use the batteries down to 1.1V each (the extra 0.1V is for the LDO drop-down itself). People normally do the mistake of using 4 AA thinking they'll have 6V, but that's only true for the first 25% of the battery life

As a rule of thumb, if your project will spend most of the time sleeping you need to chose a regulator that is more efficient at lower currents. Always check the datasheets for "quiescent current" as well the current X drop-out charts. That will give you an idea about the minimum consumption when nothing is running.

I've posted some details how I tested the power consumption of the Whisper Node board on this forum: https://www.element14.com/community/thread/49699/l/new-ultra-low-power-arduino-board-with-built-in-rf-rfm69, you should be able to adapt some of that for your project.

Regarding price... switching regulators are not the cheapest part of a circuit. Depending of your needs it can easily be more expensive than the MCU itself

@Pavel-Hrudka Great options, although I couldn't find much information on the MAX856 and LT1300CS8 datasheets when running under 1.5V... The MAX seems to be better for lower currents, while the Linear has a good output power. Anyway, both manufacturers usually produce very good quality components.

For the Aliexpress option, there's no silicon model, but byt the look of the module design I would say it'll not have the best performance... I can see a diode which can add some undesired voltage drop as well a huge (22uH) non-shielded inductor, which doesn't look ideal to for efficiency. At the end you get what you paid for...

Cheers,
Mike M.

[hek]

Hi @Mike-Musskopf.

Will you open source your module? Can't find any info on the KS about this?

[Mike Musskopf]

Hello @hek I haven't stop to think about this yet. Is very likely I'll be making most of the details about the project available but need first to focus on bringing it to life.

Cheers,
Mike M.

[jmd]

Hi @Mike-Musskopf. Thank you for your help !

I'm using an Arduino Pro Mini 3.3V, without the power led (removed), but with the built-in regulator.
The sensor I want to use is a HC-SR04, witch only work at 5V.
I use 3 AAA batteries, powering my Arduino Pro Mini, and a step up converter for the sensor.
The power-up converter (and level converter) are power on / off through a NPN (I don't have any mofset yet).
Moreover, I'm using an NRF24L01+ to send the value of the sensor (3 or 4 times a day, with each time 5 reading in a row to compute an average value).

When the Arduino pro mini is sleeping, and the sensor not powered on (NPN as switch), and the NRF radio in sleep mode, it seems like I'm using 70µA (with my cheap multimeter).
I'm using more than 1mA when awake.

For step-up converter, I'm using a cheap MT3608 from aliexpress on PCB, but I don't like it because it's big, and have to be adjusted through a potentiometer.
I'm looking for a step-up converter as cheap as the MT3608, but more compact, to output 3.3V (for my other projects, with less than 3 batteries) or 5V.

Thank you

[Mike Musskopf]

Hey @jmd, the Arduino Pro is a much better option than a stardard one. Now regarding the 5V, if you only need it for the ultrasonic sensor, you might be better using the US-100 instead. The potentiometer is to adjust the voltage divider as all those regulators you normally need a feedback Voltage, you should be able to replace it with a single resitor, just need to look on the datasheet to get the correct value.

About the transistor, that's a great trick to use with those devices that don't have a sleep mode. Sometimes you need a N and P channel mosfet combination and place it as a high side switch.

Anyway, if you still need a 5v for something else, have a look on those modules: https://www.pololu.com/category/132/step-up-voltage-regulators. They're a bit more expensive but the quality of the components and the reduced size might pay off. You get what you pay for... BTW, switching regulators are not generaly cheap... On my project power regulator circuits cost more then the MCU and Flash memory together!

Also the sleep current seems to be right as you have the LDO there. Now the awake consumption is too little... That might be because you're waking up and going back to sleep too quickly and the multimeter won't have enough time to get a real reading. One suggesting is to make you code to keep transmitting in a 10 seconds looping, so you can get a more realistic readings. After that change back to the original but also calculate how many millis you code is being awake. With those two figures you'll be able to estimate better the real consumption.

Now, be aware that 3 AA batteries will deliver something over 4.5V only when brand new... which is ok for the LDO. But as soon the juice start to drain the voltage will drop as well. An Alkaline battery will deliver only 0.8V at its end of life, or 2.4V for three in series: http://data.energizer.com/PDFs/E91.pdf

If your Ldo needs, for example, at leas 3.6V to run, that's 1.2V per battery, which is around 50% the Alkaline life.... Just wasting the other 50% of energy.

My suggestion would be to take off the LDO regulator from your Arduino Pro and put a step-up to 3.3V... Power it with two Alkalines and you'll be fine with the US-100 sensor.

Hope it helps...

Cheers,
Mike M.

[jmd]

Hi @Mike-Musskopf
I didn't realize that the Alkaline batteries will not be used over 50% of their capacity with my circuit.
It is a very good point !

Do you also recommend the pololu step up converter at 3.3V ? Do you know other good references ?
Could you confirm that only switch regulators do not consume a lot of energy ?

I also order a US-100, which I didn't know before your answer.

Thanks ! It's very helpful !

[rollercontainer]

My thoughts: Every voltage conversion isnt effective. So why not dump all regulations? ^^

• ATMega328P DIL with internal Clock, 1Mhz, BOD disabled (min 1,8V)
• NRF24 (min 1,9V)
• SI7021 (min 1,9V)
• 2 AA batteries

[Mike Musskopf]

Hi @jmd

I've never used the Pololu ones but those are the only interesting ones I found so far... I basically use Dev boards like this one: http://www.microchip.com/DevelopmentTools/ProductDetails.aspx?PartNO=adm00458 for testing. I'm normally building the step-up circuit myself so I have better control of everything and reduce costs. But for one off or if you can't build the PCB your self modules are the best option!

Back to the Pololu, they seems to be pretty well built and most models are based on this chip: http://www.ti.com/lit/ds/symlink/tps61200.pdf, which seems to be very nice! All info you need will be in the PDF!

@rollercontainer , I totally agree that any regulation will have some lost, but at the same time not all components work at low voltage range, like the ultrasonic sensor US-100 on this project, it requires at least 2.4V. One alternative is to run everything directly from the battery as you suggested and have a separated rail with the step-up output at 3.3V and enable it only when necessary... or just run everything at 3.3V and simplify the design

Cheers!
MIke M.

[m26872]

Just a word of caution when power supply the nrF24L01+ (or clones which most of them probrably are) in general and with booster/step-up in particular. Forum experience is that they are extremely supply quality sensitive. Slightest ripple, EMI or weak supply will likely impair their performance. So, don't expect it to work until it's tested.
There are endless issues reported in the forum, but here's some early findings I remember (follow the post#3 link too): http://forum.mysensors.org/topic/486/my-2aa-battery-sensor/3

[alexsh1]

@Mike-Musskopf said:

If you decide go to the LDO solution, bear in mind you'll always need to supply greater voltage, so the regulator will "burn" the extra power and deliver the selected voltage. For example, if you need 5V you probably will need to have 5 Alkaline cells so you can use the batteries down to 1.1V each (the extra 0.1V is for the LDO drop-down itself). People normally do the mistake of using 4 AA thinking they'll have 6V, but that's only true for the first 25% of the battery life

That may or may not be the case. Depends on the batteries. I am currently using rechargeable lithium ones. They are rock solid 1.5V until they die, but the only other potential problem if one wants to recharge them in a low voltage environment is that they require 5V (USB) to be charged. Also there are NiZn 1.6V AA rechargeable batteries around, they would require a compatible charger, but preserve high voltage until fully depleted.

[Mike Musskopf]

Hi @alexsh1 , yes I recently find out those 1.5V rechargable lithium batteries. I haven't bought one myself but I'm wondering if they have an internal step-down circuit there from 3.7V there

Most of the rechargeable batteries will have a self-discharge much greater than non-rechargable Alkaline/Lithiun. The rechargeable lithium-ion have not so much... maybe 2%/month, but still adds up if you wish to run your project for 1 or 2 years.

Anyway, my point here is if you just want something to stay running for over one year in your basement for example, any rechargeable battery can add a significant cost and some trouble as you'll need to use a very specific rechargeable cell. It's not very practical IMO. On the other hand cheap non-rechargeable Alkaline and Lithium are common, offering very low self-discharge and are more resilient to temperature variations.

In the other hand if you project is a toy or a hand held device which need new batteries every second week, well, rechargeable lithium seems to be the way to go. In this case maybe just stick a LiPo or a big 18650 battery... just need to pay attention for any possible regulation as those ones the voltage will vary from 4.2V (fully charged) to 3V (discharged)... and 4.2V might fry some 3.3V component

At the end it all comes down to the project design and how it's supposed to run. If you have access to energy harvesting, like a sensor in your roof, even more fun to design...

Cheers!

[jmd]

@m26872 : Thanks for your link. I read your posts, and I'm quite interested about the results you got with the Chinese step-up converter.
You mentioned a dedicated post. Did you found some times to write it ?

After looking for some non-SMD components, I've ordered some Chinese step-up modules for less than 2€ a piece (but min order 5-8 pieces).
I hope that it will be better than the MT3608. At least it will be a more compact solution.

Step-up / step-down:
http://www.aliexpress.com/item/5pcs-mini-1-8V-3V-3-7V-5V-to-3-3V-Boost-Buck-Low-Noise-Regulated/32365767349.html

Step-up only:
http://www.aliexpress.com/item/8-pcs-Ultra-small-DC-DC-0-8-3-3V-to-DC-3-3V-Step-UP/32268496143.html

[m26872]

@jmd I guess you refer to my thoughts regarding the interesting battery voltages after 2AAs have been drained by a booster? - No, I've not yet researched anything more on that.

Did you read this? http://forum.mysensors.org/topic/2027/test-of-step-up-modules-sparkfun-pololu-china-module-any-other

My conclusion is that testing is necessary to says something about the performance of these setups. My "105-test" is still going strong.