Regulating batteries - which is the better solution?

[johankj]

Say you had 4 x 1.5V (AA) batteries in series, which you wanted to regulate down to about 5V (roughly, like not higher than 5.1 but not lower than, say 4.5), which of these would be of preference with regard to battery life, quality of regulated output, size/cost, any other advantage/disadvantage?

1. 5.1V Zener-diode in parallel.

2. Small-signal diodes in series.

3. A voltage regulator, like a 7805.

4. Other suggestions?

Brand new AA batteries kick out at about 1.6V, which is 6.4V, and then degrade from that. I want to maximize the life-time of the batteries, while maximizing their usable voltage-range.

 

[dknguyen]

Linear regulator. But if maixmize lifetime is realy REALLY important a switching regulator is more efficient. But you are only burning off 1.4V with a linear regulator so it might not affect lifetime very much. It would definately be cheaper and smaller to use a linear regulator.

 

[eng1]

Say you had 4 x 1.5V (AA) batteries in series, which you wanted to regulate down to about 5V (roughly, like not higher than 5.1 but not lower than, say 4.5), which of these would be of preference with regard to battery life, quality of regulated output, size/cost, any other advantage/disadvantage?

1. 5.1V Zener-diode in parallel.

2. Small-signal diodes in series.

3. A voltage regulator, like a 7805.

4. Other suggestions?

Brand new AA batteries kick out at about 1.6V, which is 6.4V, and then degrade from that. I want to maximize the life-time of the batteries, while maximizing their usable voltage-range.

A 7805 is not suitable because it needs 2 or 3 V accross it. I would use an LDO regulator. Choose amongst low quiescent current LDO regulators in order to maximize the lifetime of the batteries.

 

[audioguru]

You need a buck-boost switching regulator since the battery voltage will drop to 4V.

 

[Papabravo]

An SMPS for your first project is a bit ambitious. I would get comfortable with a an LDO (Low Drop Out).

The MIC2951 and the MIC5206 are both good choices to start with for current up to 150 mA.

 

[Diver300]

audioguru is right when he says that the voltage will drop to 4V. Alkaline batteries loose voltage from about 1.6V new to 1V when dead.

Many designs do not work right down to 1V so batteries get thrown out when they still have quite a lot of energy left in them.

However, I would also agree with Papabravo that as buck-boost regulator is a difficult thing in itself to make, and a good linear regulator is the best choice to start with.

As your circuit will work down to 4.5V, you can take the batteries down to 1.125 volts so you are getting 80% of the life out of the batteries. If your circuit needed 5V to work you would only get about half of the battery life.

The MIC2951 is a good choice, as it has low drop-out and a low ground current, both important for battery life.

 

[dknguyen]

https://www.dimensionengineering.com/AnyVoltMicro.htm

 

[Krumlink]

Justt peel that little sticker and copy the circuit

Just dont tell the police!

 

[Hero999]

You need a buck-boost switching regulator since the battery voltage will drop to 4V.

That depends on the type of batteries used and the minimum working voltage of the circuit connected to it, if it'll work down to 4V then I don't see why not.

 

[Sceadwian]

SMPS isn't particularly ambitious, many manufactors make buck-boosts that will work for applications like this that are simple IC's, you just supply the inductor and some filter components. A switch mode IC will suck the last bit of juice out of batteries.

 

[johankj]

Thank you all for all the input regarding this. I have not decided what to go with yet, as I will concentrate on the main-board for the moment, and then design the power circuit later.

However, the buck-boost switching regulator looks very interesting.

 

[HarveyH42]

Go to the National Semiconductor website. They have an online wizard, that will design the power supply for you, and suggest specific chips for your needs.
I haven't been there in about a year, but sure it's still there. Imagine it sold a lot of chips.