I am trying to create a wearable device using the ESP32-C3 Mini Development Board and would like to use a 3.7v rechargeable Li-Po battery to power it. I have been unable to find a definitive answer for how to do so for this specific board but here is some general information I have found about other boards:
- An LDO regulator with at least 500mA is needed to drop the voltage down from
3.7v to 3.3v
- The battery will connect to the 3.3v pin of the ESP32 board
My questions are:
- Would this be the correct way to achieve what I need?
- What would be the best regulator to use?
Thank you so much!
You are going to have a bit of a problem here. I assume you need 500mA. At full charge that LiPo could be up to 4.2V for a while until the max charge drops off then it will settle down to 3.7V gradually falling to 3.2 or 3V where it should be charged.
Your main drop will be from 3.7V which is only 0.4V and I have not heard of a LDO regulator that is that fine.
What is the absolute maximum your board will accommodate. It is possible you may be able to power the board directly. I did accidentally come across a device recently which had its own power smarts on board. Buck/Boost which would handle any input from over 4V down to 1.8V. Can’t remember what that device was now. Maybe your board falls into that category.
Whatever the outcome, if this is wearable I imagine the battery will be quite small and you are not going to get much wear time at 500mA.
Thanks for your reply. I haven’t been able to find exactly how much my board can accommodate as there is not much information about powering it using batteries (makes me think that it wasn’t made for that purpose ) but from reading other forums, I get the sense that it can’t handle too high a voltage. I did see some boards with inbuilt regulators so one of those might be the way to go!
Thanks for your help
There is a good discussion of a suitable device, with appropriate warnings, here. It uses 3 LDO regulators in parallel to give a rated 1A, although the testing suggests that it actually does somewaht better than that. It is available froim a number of suppliers. Quality may vary but it is cheap enough be worth trying out. Note that the usual description is ‘3V’, not ‘3.3V’, but the regulators are clearly 3.3V devices.
I’ve use the LM1117-3.3V(or alternatives) on designs, it works well, though when you turn on the radio (higher current draw) it chews power much faster.
EDIT: Sorry just re-read your question, all of the dev boards feature a similar regulator onboard (Assuming you are using the following: ESP32-C3 Mini Development Board | Sparkfun WRL-18036 | Core Electronics Australia )
Connecting a Schottky diode through the 5V pin and the battery will prevent back-charging - though have losses, using a FET would be advantageous to reduce losses.
Leaving my reply below:
Here’s the portion of the powerchain that powers the ESP32-C3 board I made:
I handled charging by using an external LiPo charger: Makerverse USB-C LiPo Charger | Core Electronics Australia
If you’re after a small form factor board featuring an ESP32 chip I’d check out the ‘Tiny’ range of the Unexpected Maker boards: Unexpected Maker Australia
The Vcc range of the C3 is quite small at 3.0~3.6 VDC so not suitable for direct insertion of a LiPo.
The highest efficiency regulator across the whole range would definitely by an SMPS though the complexity and time spent would vastly outweigh buying a bigger battery.
What constraints are you working against? Happy to help out!
Here’s a photo of the completed board:
That regulator IC has a minimum input of 4.7V for 3.3V output, refer TI data sheet. So not much use for Tavi’s application unless he uses 2 LiPos in series. The data sheet says minimum input is 2.7V but for that you get 1.25V output. In other words the drop across the regulator is 1.4V. Similar to LM317 (1.25V minimum output but a higher voltage drop across the regulator).
If Tavi has a suitable current requirement and can charge cells externally maybe 2 AAA or AA size cells in series might do the job if his device has an on board regulator like the TLV1117 which should be able to handle this voltage.
Note. Edited reference to LM317 01/10/22
EDIT. Just looked up TI data sheet for the regulator depicted above in Liam’s circuit. That TVL1117LV33DCYR differs from the TVL1117 I looked at previously that it does seem to maintain 3.3V for an input down to 2V. A bit hard to tell but that is how it reads to me. Specs say min 2V, max 5.5V so if Tavi’s device uses one of these regulators it should operate OK with 1 LiPo.
There seem to be quite a few variants of the basic TVL1117 co some research and care is required here.
I have been using these boost/buck converters for my ESP32C3 project.
So far, no issues.
I use a single 18650 LiPo. If you monitor the battery voltage you can use the fully-charged to fully discharged range of the battery.
There is a very similar board available that has a mini pot on board for a fully adjustable output instead of a fixed one.