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We have designed a board for mass production . This board has a few components on it, that works with 3v3 , such as MCU, Wi-Fi, and a few more sensors.

We used to have a battery, 3.7v to power the board directly, and later on, we have decided that we must use a regulator, because its more safe . the regulator is AMS1117

After some research, we found out that this regulator(and others) must have 1V more in its input,relative to its output .

So, using a battery pack of 3.7v lithium, will not work properly for such regulators(3.3v) , even when its charged with 4.2v .

We found out that logically ,connecting the battery directly (no regulator) to the board is much clever, because you can "enjoy" the battery power as long as it is > 3.3v .

Our only concern is that we are not using a regulator, and its not healthy .

Is that a good thing to do- "professional" ?

do you think of more options,such a zener diode instead of a regulator ?

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  • \$\begingroup\$ Check the datasheets of your components, and when everything is able to run at the highest possible voltage then you can do it. \$\endgroup\$ – PlasmaHH May 4 '15 at 11:30
  • \$\begingroup\$ Look up SEPIC voltage converters. en.wikipedia.org/wiki/Single-ended_primary-inductor_converter \$\endgroup\$ – Scott Winder May 4 '15 at 18:20
  • \$\begingroup\$ I don't understand what you mean by "Healthy"? and how does "professionalism" translate to design? \$\endgroup\$ – Volcano May 4 '15 at 21:16
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If you're asking questions like this, you're not ready for "mass production", whether you wish to be professional or not.

You need to look at the supply voltage range of everything, and then see if the range of your battery's voltage from full to flat will work. If not, then you will likely need either a very-low-dropout linear regulator (hint: the AMS1117 isn't), or a type of buck-boost switch-mode regulator that can provide a stable 3.3V supply from a source that can be either above or below the output (i.e. as the battery goes from full to flat). For a linear regulator option, even if the battery voltage drops below the regulator's drop-out voltage (for a 3.3v LDO regulator's output, lets say it's 3.5V, 200mV above output), then you might be able to get away with that - the regulator won't really be in regulation, but depending on your load profile that may or may not matter much.

When you say a "3.7 lithium" battery, its range between full to flat will be ~4.2V full, to no less than 3.0V flat. And you don't charge lithium with a constant voltage source. Well, at least not at first - lithium battery charging is at least a 2-stage process, first constant-current, then constant-voltage, using a charge management chip specific to Lithium chemistry.

You are not ready for mass production, not even close.

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  • \$\begingroup\$ My question was not if i am ready or not for mass production, you have no idea what is our product, and who is involved ( you even might know them) . Your answer does not provide any new information to me, you assume that i didn't think about the range of my parts, and its not true. just because the range is ok, i did asked this question . another thing, dont be so angry with yourself . its not good for you . \$\endgroup\$ – Curnelious May 4 '15 at 12:28
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    \$\begingroup\$ The tone may be a bit harsh, but the point is sound. If you need to ask a technical question like this, you aren't ready for mass production, or any type of production. You are making a prototype. That being said, you can certainly find LDO regulators that can run much closer to 3.3V than the one you've chosen. \$\endgroup\$ – scld May 4 '15 at 13:18
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If I were you I would use a regulator, and it is not too hard to find one that suits your requirements. As you have little difference between the Vin and Vout, you can go with an Low-Drop Out regulator, such as this.

I found this in less than 10 minutes. It has an excellent WEBENCH to help you make your design.

Here is the recommended schematic:

enter image description here

As you can see it can take 3.5V - 4V input voltage while providing the stable 3.3V. I do not know how much current does your application need, this one can supply up to 400mA.

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Just off the top of my head, you may use some off-the-shelf DC-DC converter module like this one: 3.3V fixed output, 2.7-11.8V input range with nice efficiency especially with load currents <500mA.

enter image description here

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