In my project, I am designing a board which is supplied by a battery. The battery is a LiPo, 3.7 V, 1000 mAh, so its voltage range is 3 - 4.2 V.

All the components on the board need a fixed voltage of 3.3 V. In some configuration the board can draw 1 A, but most of the time it draws about 50 mA.

I need to convert the battery voltage to 3.3 V. I was thinking of 3 options:

  • Option 1. Using a buck-boost converter
  • Option 2. Using a buck converter and electronically cut the power supply when it is approaching 3.3 V (let's say 3.6 V)
  • Option 3. Same as option 2 but with an LDO

Do you see better options?

My conclusions are as follows:

  • Option 1 is the most expensive option, and price does matter.
  • All the 3.3 V buck converters I have found only accepts input voltages starting at 4 V. Is it a normal behavior that bucks need a voltage gap to work?
  • Option 3 seems to be the best option. But when the board draws 1 A, I would need to dissipate maximum (4.2 V - 3.3 V) * 1 A = 0.9 W, which is too much because the board is very small so it would badly dissipate heat, and heat does matter...

Which options would you use in such a case? Do you have advice?

  • 3
    \$\begingroup\$ If you need 3.3 V out with only 3.0 V in, then buck-boost is the only one of your options that can possibly do the job. \$\endgroup\$
    – The Photon
    May 16, 2022 at 16:05
  • 1
    \$\begingroup\$ You should also consider the efficiency required (that is -battery life?) and the fact that a switching regulator is producing a noisy output comparing to LDO, and needs certain design considerations to reduce the effects. Given all the points, you have all of the information to decide yourself. \$\endgroup\$
    – Eugene Sh.
    May 16, 2022 at 16:05
  • \$\begingroup\$ How often does the board draw 1A? For how long? What are the discharge curves for your battery? Most Lipos stay > 3.5V until they're almost fully discharged so a LDO might work. \$\endgroup\$
    – vir
    May 16, 2022 at 16:07
  • \$\begingroup\$ It is okay if I do not use the battery all the way down to 3 V. Cutting it at 3.6 V is acceptable. It can draw 1 A 25 % of the time, sometimes during dozens of minutes. I do not have the discharge curve of the battery but I think most LiPo 3.7 V battery discharge curves are more or less the same, am I right? \$\endgroup\$ May 16, 2022 at 16:10
  • 1
    \$\begingroup\$ Related/similar: electronics.stackexchange.com/q/330922/2028 \$\endgroup\$
    – JYelton
    May 16, 2022 at 16:22

2 Answers 2


It looks like LiPo batteries stay above 3.3V in normal charge levels, and drop to 3.0V when they're below ~80% capacity.

Image source: https://learn.adafruit.com/li-ion-and-lipoly-batteries/voltages

Based on this, you can stick with an LDO since it's the cheapest and easiest way to step down a voltage, assuming you don't mind the efficiency losses when your battery is >4.0V. LDOs will dissipate any unused power as heat; the greater the difference between Vin and Vout, the lower the efficiency. A benefit when compared with switching topologies is a much smaller ripple on Vout, which is good for sensitive electronics.


Consider using a boost converter chip in a SEPIC configuration. This can act as step up and step down in one circuit.


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