3xAA 1.5v batteries to 3.3V

Hi

I'm a bit new to this and have created one of my first projects that I want to have standalone powered by 3x AA 1.5v batteries.
As the voltage is around 4.5v together I cant use the 5v input. So the only option is 3.3v in.
But when i connect it there it won't start. When i regulate the voltage down to about 4.2v it work fine.

So my question is. What is the best way to handle this? With the 3 AA batteries.
What is the best way to regulate the voltage down to 3.3v-4.2v?
I have reaserched alot and from my understanding a buck converter (switching) req. 4.8v to get to 3.3v, so that is gone.
Or maybe a LDO HT7333 might work, but are they efficient enough?
Zener voltage diode? I use that today, but i really don't know if its that good?

I want to keep the price down also, I understand that a stepup-stepdown buck converter would be great, but I cant put a 6-10$ piece into this project.

So please help me in this issue. Thanks

What are you trying to connect to what? What type of Arduino/microcontroller? To what? with what?

Share a photo or a drawing.

If you want to power an arduono on 3.3V, make sure it CAN work on 3.3V in the first place. A Uno has a 3.3V output but doesn't work on 3.3V because it runs on 16Mhz and uses 5V logic.

Freddp:
As the voltage is around 4.5v together I cant use the 5v input. So the only option is 3.3v in.

I'm not aware of any Arduino that has separate 5V and 3.3V power IN. Not sure what you're trying to do due to a lack of details but pretty sure you're doing it wrong.

Anyway, if you just grab a 3.3V Pro Mini and connect the batteries to the Vcc pin you're set. if you don't need the 4.5V you can leave out one battery, those Arduinos work great on just two AAs.

wvmarle:
I'm not aware of any Arduino that has separate 5V and 3.3V power IN. Not sure what you're trying to do due to a lack of details but pretty sure you're doing it wrong.

Anyway, if you just grab a 3.3V Pro Mini and connect the batteries to the Vcc pin you're set. if you don't need the 4.5V you can leave out one battery, those Arduinos work great on just two AAs.

I would recommend to use the RAW pin and not VCC as that pin expects a regulated 3.3VDC connected as input.

So 4.5V on the RAW pin will make a Pro Mini 3.3V 8Mhz run fine, you can use the VCC pin to power any peripherals up to 150mA.

Leroy2007:
I would recommend to use the RAW pin and not VCC as that pin expects a regulated 3.3VDC connected as input.

No need for regulated 3.3V here. The ATmega328P at 8 MHz works on 2.2V up to 5.5V, there's nothing else on that board that has a problem with those voltages, and in fact when you connect it to a standard FTDI adapter the whole thing is running at 5V. For battery power it's often best to even completely remove the regulator (disabling the RAW pin in the process), and the power LED.

Check the schematics and make sure you understand what's going on!

Freddp:
Hi

I'm a bit new to this and have created one of my first projects that I want to have standalone powered by 3x AA 1.5v batteries.
As the voltage is around 4.5v together I cant use the 5v input. So the only option is 3.3v in.
But when i connect it there it won't start. When i regulate the voltage down to about 4.2v it work fine.

So my question is. What is the best way to handle this? With the 3 AA batteries.
What is the best way to regulate the voltage down to 3.3v-4.2v?
I have reaserched alot and from my understanding a buck converter (switching) req. 4.8v to get to 3.3v, so that is gone.
Or maybe a LDO HT7333 might work, but are they efficient enough?
Zener voltage diode? I use that today, but i really don't know if its that good?

I want to keep the price down also, I understand that a stepup-stepdown buck converter would be great, but I cant put a 6-10$ piece into this project.

So please help me in this issue. Thanks

If you have a +5v Arduino variant... you will need +5v input
If you are using a +3.3v Arduino variant.. then your +4.5v battery pack/source if fine.
It cant be both ways, you need to understand what board you are working with... and power it correctly.
If you are using a +5v variant board.. the +3.3v is for OUTPUT.. not to POWER the board.

Thanks for all the answers,

wvmarle:
No need for regulated 3.3V here. The ATmega328P at 8 MHz works on 2.2V up to 5.5V, there's nothing else on that board that has a problem with those voltages, and in fact when you connect it to a standard FTDI adapter the whole thing is running at 5V. For battery power it's often best to even completely remove the regulator (disabling the RAW pin in the process), and the power LED.

Check the schematics and make sure you understand what's going on!

Yes, this is accually the best solution. Insted of 3x AA I went with 2, and it worked great. Perfect, thanks.

Still I ordered some regulators, might come in handy in the future.

xl97:
If you have a +5v Arduino variant... you will need +5v input
If you are using a +3.3v Arduino variant.. then your +4.5v battery pack/source if fine.
It cant be both ways, you need to understand what board you are working with... and power it correctly.
If you are using a +5v variant board.. the +3.3v is for OUTPUT.. not to POWER the board.

The question is then, how come that 3x AA don't work but 2x does? when I do a voltage reading of the 3x AA it = 4.8v, so it should be fine. But it isn't.
2x was about 3.2v and it worked great now.

Freddp:
The question is then, how come that 3x AA don't work but 2x does?

Without you being clear about which exact Arduino you use and how you have it all connected we can not offer any sensible answers.

wvmarle:
Without you being clear about which exact Arduino you use and how you have it all connected we can not offer any sensible answers.

^ this.
Also... I think pics of your ACTUAL set up are required now. You arent painting a very clear picture for us.. and then want advice/feedback?

Freddp:
Still I ordered some regulators, might come in handy in the future.

Probably not! Presuming these are AMS1117 or similar, you are quite likely not to find them at all useful. If you need serious current regulation, it will in the vast majority of cases, be better to use an efficient and cool switchmode regulator. :roll_eyes:

Freddp:
The question is then, how come that 3x AA don't work but 2x does?

Almost certainly you have done something wrong as this makes absolutely no sense. But we can't see what it is.

Leroy2007:
I would recommend to use the RAW pin and not VCC as that pin expects a regulated 3.3VDC connected as input.

I would recommend never using the "RAW" pin. :astonished:

Paul__B:
I would recommend never using the "RAW" pin. :astonished:

Please elaborate. I use the pro mini in a setup with and SDcard, a GPS and some other sensors that are rated at max 3.5VDC. Feeding it with a LiPo battery of 3.7VDC (4.2 when fully loaded) is not going to go well with my attached stuff so I power the Arduino via the RAW pin and use VCC to have a nice, stable 3.3V for all my peripherals.

That would be one of the few reasons to use that pin, but a few important things to keep in mind:

  1. you won't get a "nice and stable" 3.3V as when the battery discharges you may not have enough voltage overhead for the minimum dropout,
  2. the on-board regulator may not be able to supply sufficient current for the SD card (which can draw pretty large current spikes).
    So try to find out which exact regulator you have on your Pro Mini board (I don't think this is standardised between all the clones), and whether that one is suitable for this use.

Check out the LDL1117 - under 500uA (0.5mA) of quiescent current (250uA typical)... with 0.35V dropout!!!

Yes, this means you can get a regulated 3.3v from a 1S LiPo with just a simple linear regulator! Likes small, cheap ceramic caps, too.

Pretty sick product. About the same price as other linear regs too, pin compatible with normal 1117's.

I used to use the ZLDO1117 series, but these blow them out of the water.

Basically, all the linear regulators we used to use are now obsolete (to the extent that a linear reg is ever still an appropriate option - I was putting little note-cards with specs in with all the dc-dc converter boards I had from china, and realized that some of them have an Iq that is better than most linear regs, which is sort of impressive)

Mine use a MIC5205, it runs all the sensors and the SDcard well at this moment. I’ll look into the LD1117, it looks like a very good replacement.

The MIC5205 has dropout voltage of 0.165 V, and ground pin current ~600 uA at 100 mA output, so it is roughly equivalent to the LD1117.

The MIC5205 does 150mA whereas the LD1117 does 1200mA, that's a big difference if you're trying to power a lot of peripherals.

DrAzzy:
Pretty sick product.

Not much of a recommendation then! Is there an equivalent that works properly?