Power Regulators Question

Hi All, can you please push me in right direction about this power regulator dilemma I am facing:

I need 3.3v source to power my project, which is a single Atmega Chip on a breadboard, blinking Leds, showing some things in LED display, and maybe reading some sensor values, final setup is not determined as I am still playing, but the idea is to power everything from AA batteries.

From what I found out in my research there are different types of power regulators, one can take voltage that is higher than what I need and bring it down to 3.3v(step down) and those that can take voltage that is lower than 3.3v and bring it up (step up), also those that can do both.

Another thing I noticed is that AA batteries are not always give away steady 1.5V, they may start at 1.6V when fresh and as they losing their charge they can do down to 1.2V or lower. So power regulator definitely required if I want to have steady 3.3v to power atmega chip.

What kind of power regulator would you suggest I install to power my circuit from 2AA batteries? From what I understand I do not need step down because 2 AA batteries will never give me over 3.3V, but at the deplete their voltage can drop to 2V so I need only a step up regulator, correct?

If I power everything from 3AA batteries, and use step down/step up regulator to get 3.3V, would the fact that now I have 3 batteries instead of 2 give me longer battery life?

Another thing is: If one thing in my project, like a Loud Speaker , or electric motor, or extra bright LED, uses 250mA, is it necessary to make sure that power regulator is rated to that current?

And one more question, how low can AA batteries's voltage go down before it is completely depleted? Asking because it seems that some regulators (at least in datasheets) claim that they can take voltage as low as 0.8V and some other claim that they can take it as low as 1.2V.

Thank you for any info.

Another thing is: If one thing in my project, like a Loud Speaker , or electric motor, or extra bright LED, uses 250mA, is it necessary to make sure that power regulator is rated to that current?

At least that current, you normally have a spare capacity of 20% or so on a current rating.

If I power everything from 3AA batteries, and use step down/step up regulator to get 3.3V, would the fact that now I have 3 batteries instead of 2 give me longer battery life?

Yes it will give you 50% extra, because you have 50% more power available.

how low can AA batteries's voltage go down before it is completely depleted?

Down to zero, which is the definition of being depleted. However once you take the load of a battery it can recover a bit. So give it a rest for an hour and it mite work for another minute.

What kind of power regulator would you suggest I install to power my circuit from 2AA batteries?

A step up or boost regulator.

Minor detail, but it's called a "voltage" regulator, rather than "power" regulator. ( don't ask me why. That's just the conventiion)

Alkaline AA bateries are rated 1.5V but they have about 1.6V when new and can be used down to 0.9V, when theu are considered dead. It means if you use: - 2 AA your voltage will vary between 3.2V and 1.8V: you will need a step-up; - 3 AA your voltage will vary between 4.8V and 2.7V: you will need a step-up/step-down, or just a step down, assuming that 2.7V is still enough to power your atmega chip; - 4 AA your voltage will vary between 6.4V and 3.2V: you will need a step-down

Since AA batteries are cheap and assuming that there is no space constrains, i would go for 4 AA bateries and use a step-down. Or you can use a 3.3V LDO, they are much simpler than switching regulators and if input voltage is near the output their efficiency is as good as switching regulators.

Check this, i use a lot on my projects. It is cheap, very efficiency and you can add more or less batteries without have to change regulator

https://www.pololu.com/product/2122

geologic: Or you can use a 3.3V LDO, they are much simpler than switching regulators and if input voltage is near the output their efficiency is as good as switching regulators.

Check this, i use a lot on my projects. It is cheap, very efficiency and you can add more or less batteries without have to change regulator

https://www.pololu.com/product/2122

Just ordered the one you suggested, also, what do you think about this one? https://www.adafruit.com/products/2745 Its specs also look good to me, however they only mention that it is for powering project fro Li-ion battery or usb, no mentioning of the AAs or any other standard batteries. Would this thing work for my project?

The

alexmg2: Just ordered the one you suggested, also, what do you think about this one? https://www.adafruit.com/products/2745 Its specs also look good to me, however they only mention that it is for powering project fro Li-ion battery or usb, no mentioning of the AAs or any other standard batteries. Would this thing work for my project?

The Pololu 3.3V Step-Up/Step-Down Voltage Regulator S7V8F3 recommended by Geologic can use a wider variety of voltages, from 2.3V up to 12V, and can put out over 1A from an input of 3V to 12V.

The Adafruit LM3671 3.3V Buck Converter Breakout can put out 600mA from an input of 3.5V to 5.5V.

Thus, the Adafruit is more limited, and could not (for example) use 2 or 4AA batteries, and would only be able to discharge 3AA batteries down to 1.16V per cell. It also is more limited in its current capability by about a factor of two (600mA vs. >1000mA) compared to the Pololu.

Hamsterman

raschemmel: Minor detail, but it's called a "voltage" regulator, rather than "power" regulator. ( don't ask me why. That's just the conventiion)

Probably because they regulate the voltage, not the product of voltage and current.

Probably because they regulate the voltage, not the product of voltage and current.

Sounds good to me.

I have mentioned the Polulu supplies here in the past. I only mention them because I use them and have always had good results using them, but... if the regulator says 12V input MAX... honor it. I did fry one by accidentally giving it 15V.

Thanks everyone for great info, can't wait for my order to get shipped/arrive to start playing with it.

Also, this is perhaps stage 2 or my research about voltage regulators, but, since we talking about it. If Atmega328p has fuses (brown out detection) set to stop working when voltage gets lower than 2.7V then if regulator steadily pumping 3.3V there is no need for the fuses to monitor voltage because voltage that comes into Atmega chip will either be 3.3V or 0V ?

Also, this is perhaps stage 2 or my research about voltage regulators, but, since we talking about it. If Atmega328p has fuses (brown out detection) set to stop working when voltage gets lower than 2.7V then if regulator steadily pumping 3.3V there is no need for the fuses to monitor voltage because voltage that comes into Atmega chip will either be 3.3V or 0V ?

You are new at this aren't you ?

The "BrownOut " detection is not something designed to detect planned events. It should be obvious from the name (brownout) that it is designed to detect UNPLANNED events, meaning that IN A PERFECT WORLD, you would never need it. If something shorts your circuit power the brownout detection will trigger a reset.

raschemmel:
You are new at this aren’t you ?

Yes, very fresh, but picking up very fast :slight_smile: thanks for all the support in this forum.

raschemmel: Minor detail, but it's called a "voltage" regulator, rather than "power" regulator. ( don't ask me why. That's just the conventiion)

Probably something to do with it regulating the output voltage don't you think?

Probably something to do with it regulating the output voltage don't you think?

That would be my first guess although Jimbo's comment about it having to do with NOT regulating Voltage x Current is probably also valid. I've never actually heard anyone else call them "power regulators" so I figured that was a giveaway that the OP was a Newbie.

Yeah, I didn't actually say I didn't know why. I just said "don't ask me why".

I just assume that a “power regulator” is a voltage regulator designed to handle largish power, above a watt or so.

I just assume that a "power regulator" is a voltage regulator designed to handle largish power, above a watt or so.

Strangely enough, Google thinks "power regulator " is a voltage regulator.

And when you click on the first link labeled "Power Regulator (on ebay)" it's a link to a bunch of variable step down voltage regulators.

I have another question, can't quite understand that from reading I am doing right now:

I have one power source in form of 2AA batteries right now. from that source I am going to power an arduino with some peripherals such as couple sensors, an lcd, maybe something else small that will use only about 10mA total, so obviously if I chose my voltage regulator to be rated to provide let's say twice that amount I'm good.

On another hand, from the same battery source in parallel I will be powering a siren and strobe light, and those things have induction coil in their circuit and according to the reading I've done so far my understanding is that there is a chance that coil can fire some high voltage(current) back into the power source, which I guess may cause other circuit that has arduino in it to also receive that spike, is that correct? What shoul I do to prevent any potential issues?

2 AA batteries is only 3 V. That’s not enough.

raschemmel:
2 AA batteries is only 3 V. That’s not enough.

I am running it right now without any issues, arduino pro mini 3.3v

I didn't say it wouldn't run. I said it's too low. It's too low because it's only 300mV above the 2.7 V brownout reset voltage.