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Author Topic: Looking for some input or suggestions on building a smart circuit !  (Read 619 times)
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 Hi all, I'm looking to build a self-adjusting voltage regulator. My goal is to use any size lipo 2s or 3s to power a otg cable. where i'm short on knowledge is what ic would be suitable for adjusting the regulator. i'm not even sure what this would be called because i didn't find many people with a need to do this. keeping a stable voltage till the battery has reached it discharge limit is what i'm looking to do.
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What output do you want? 5V?
You need a boost regulator circuit that will take battery output and boost it to desired level for as long as battery can supply current.
Example:  http://www.pololu.com/catalog/product/798
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Most likely a switching regulator of some kind. Most can take a range of input voltages. There are boost regulators, where Vout > Vin, "buck" regulators where Vout < Vin, and buck/boost regulators that do it all.

Figure out your exact requirements, then visit the usual suspects (TI, Microchip, NXP, ST, et al.) to find a suitable part.
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 I'm looking for a stable 5v out but the input voltage would be between 7.4v and 11.8v i have a lot of 2cell,3cell lipo packs around 1200~2600 mah's so i figure i'd use them
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All kinds of step down regulators are possible.
Which you select depends on how much output current you want.
Some examples:
http://www.pololu.com/catalog/category/131
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Take a look at UBEC's

http://www.hobbyking.com/hobbyking/store/__767__766__UBEC_Regulator-UBEC.html

Some of them have low voltage alarm
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Are you looking to totally drain the batteries?

You could use a boost/buck circuit basically whatever the voltage 3v or 9v, it spits out 5v, the more efficient ones are switching, but if you want cheap and cheerful use a 7805 voltage
regulator and supply 9vdc and you'll get a clean 5vdc out.

if you want to really drain the battery, get hold of a buck/boost circuit and regardless of the voltage providing it's got enough juice left in the battery it will be boosted to a constant 5v regardless of input voltage.
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Only a buck regulator is needed. His 2S battery is nominal 3.7V/cell and will never be below minimum 3.2V/cell (6.4V total). 
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Lacey, Washington, USA
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Yes, if you go below 3.2V a cell, you'll damage the batteries. So buck only required.

The Dollar Tree stores here carry 12V to 5V USB chargers. Has everything you need, although you may need to adjust a couple of components. They use the MC34063 switching regulator. The inductor in the ones here are shrinkwrapped, and so rewindable. There are many online calculators to help you with the right values.

This one lets you input a voltage and a range as a percent, plus or minus.
http://dics.voicecontrol.ro/tutorials/mc34063/

6.4 to 11.8V would be 9.1, +-30%.

A 7805 will not do, as it requires a minimum of 8V to regulate the output to 5V. A shame to waste half the power, in any case.
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