In my product i am using a wifi module requires 3.3v and a bunch of other components requires 5v. For this i am using 3.7v 3000mAh battery. So here i have a doubt whether to use which case or any other suggestions

case 1: To use two 3.7v battery in series becomes 7.4 so that i can use a 3.3v regulator to convert from 3.7 and a 5v regulator to convert from 7.4V as in below fig.


simulate this circuit – Schematic created using CircuitLab

case 2: Use one 3.7v battery and use a 3.3v regulator and 5v booster(if this please suggest a good circuit or module). If i use this does the power consumption increases and batter level reduces in short time? or it doesn't?

  • \$\begingroup\$ It depends on current consumption for each regulated circuit. You haven't mentioned this. \$\endgroup\$ – Andy aka Dec 29 '15 at 11:41

Never put a load across only a single cell of a battery. You will pull the battery out of balance leading to shortened operational life. Put the 3.3V regulator either across the entire battery or after the 5V regulator.

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Do not do case 1 -- unbalancing batteries like that is one of the worst things you can do.

Your choices are:

Buck-boost regulators for 3.3V and 5V from a one-cell topology (remember the cell can range from ~2.8V to 4.2V, though you should not be operating below 3V), or

Buck regulators to 3.3V and 5V from a two-cell topology

One-cell is simpler to manage, but a buck-boost regulator is harder to compensate and stabilize than a conventional buck. An example controller is the LTC3785, though I feel like you're better suited with a module.

Two-cell allows you to buck only, but you need to ensure your two cells are closely matched / from the same lot. Buck regulators are easy to stabilize, and modules are easy to find. The OKI78SR series are simple 780x compatible modules that are available in 3.3V and 5V outputs.

In either scenario, you should be using switching-mode regulators to maximize the amount of power you can utilize from the battery or batteries. If you provide the necessary specs of each rail, we can recommend you modules.

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  • \$\begingroup\$ i will be using a PIC16 bit controller, INA125 and a load cell everything consumes 5v and i will be using one 3.7v 3000mAh battery \$\endgroup\$ – Honeybee Dec 29 '15 at 4:59
  • \$\begingroup\$ I'm looking more for "I have a Wi-Fi module, P/N xxxxx on 3.3V' expect 2-3A" and "I have X, y, z on 5V, expect 1-2A" type information. You stated you have a 3.3V load in addition to your 5V load. \$\endgroup\$ – Krunal Desai Dec 29 '15 at 5:01
  • \$\begingroup\$ Wi-Fi module ESP8266(3.3v), PIC16F877A(4.1-5v), INA125P(1.24V, 2.5V, 5V or 10V-460microA), LOAD CELL 750g(known spec excitation voltage 5v) \$\endgroup\$ – Honeybee Dec 29 '15 at 5:07
  • \$\begingroup\$ @NaveenRaja, He's going to need the expected current outputs of the batteries and the expected load currents of the different components. Such as "I need 1A on 3.3V and 2A on 5V." Some topologies don't work for certain load-source configurations. \$\endgroup\$ – Dave Dec 29 '15 at 9:11
  • \$\begingroup\$ 215ma on 3.3v, 4.5mA on 5v,20nA on 5v,6mA on 5v \$\endgroup\$ – Honeybee Dec 29 '15 at 11:54

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