2 quick questions about voltage regulators

  1. What voltage regulator do arduinos (uno, mega) use? Is it the AMS1117?

  2. I need a low dropout regulator to power a 5v heater (max. 0.5 amps). I want to use as few AA batteries as possible to power it (lets say 4x1.5V).

Does anybody know a regulator that you would recommend?

Try to look at the L4941.

Hi,
How long do you think you can draw 0.5A from a few AA's?

Tom... :slight_smile:

Simple, say 2Ah, 0.5A, 4 hours(!)

Of course finding a decent AA battery with good capacity is the trick. Limit yourself to batteries for
which there is a datasheet.

For instance: http://data.energizer.com/pdfs/e91.pdf
http://www.eveready.com/SiteCollectionDocuments/RE15-1300.pdf

Hint: go for high performance rechargables with datasheets, and abandon the
hope of 4 cells, 6 is more like it.

Well... I'm definitely using Energizer ultimate Lithium (for various reasons, such as temperature). Which is also the reason I want to use as few as possible, as they are very expensive.

I am using a mq131 gas sensor. It needs 5 V for its heater. Does anyone know if it really matters weather or not it is exactly 5 V? Otherwise I could just hook up 3-4 unregulated batteries maybe?

bestanamnetnogonsin:
Well... I'm definitely using Energizer ultimate Lithium (for various reasons, such as temperature). Which is also the reason I want to use as few as possible, as they are very expensive.

I am using a mq131 gas sensor. It needs 5 V for its heater. Does anyone know if it really matters weather or not it is exactly 5 V? Otherwise I could just hook up 3-4 unregulated batteries maybe?

Data sheet says 5.0V (+/-0.2V) so yes, it has to be 5.0V

Changing the heater temperature will change the sensivity on the sensor and you can no longer rely on it.

Normally when a sensor like yours is used in portable equipment it is NOT heated all the time - it is just heated once in a while - a sample is taken and it's powered down again.

// Per.

A voltage regulator with an enable input might be a good choice.

MarkT:
A voltage regulator with an enable input might be a good choice.

The number of voltage regulator modules that use a chip with an enable pin but don't break it out (just tie it to the input voltage) is infuriating. They don't even use a pullup resistor where you would have a chance of tapping in on it. No they have to save that extra $0.00001 and just tie it with a dead short.

But wouldn't it have cooled down if I don't take a sample for some time? It says it needs a burn in time of like 24 hours...

The L4941 seems absolutely excellent. How come the arduino board doesn't use something like that? I mean the dropout seems to be only a couple of hundred millivolts...

  1. It wouldn't fit on the board.
  2. It probably costs a few cents more.
  3. It's still a linear regulator.

For your heater application, I would definitely go for a Pololu boost-buck regulator. It will be much more efficient than a linear regulator and it will keep powering your heater when the batteries are completely shagged at 2V total for the pack. You don't get the claimed AH capacity unless you draw them right down. Many of the Polou regulators also have a shutdown input so you can turn it on and off with the Arduino.

bestanamnetnogonsin:
The L4941 seems absolutely excellent. How come the arduino board doesn’t use something like that? I mean the dropout seems to be only a couple of hundred millivolts…

Low dropout regulators are more expensive and some are very finnicky about the ESR of the capacitors on
the rail - get it wrong, they oscillate. Unless you need that LDO performance, you tend not to want to pay for it,
either in money or in compromised performance in other specifications.

Also the L4941 is only available in huge package sizes, so would need lots of board area.
And it has 4mA quiescent current, rather large percentage of an Arduino board’s current draw.

Ok well that explains it. Would still be handy in for example battery powered projects though.

You say the capacitors are tricky. I was planning on using it without any. I guess that still works right? (as with most regulators)

No. It may not work. I have had LDO regs completely non functional with the wrong caps.