Powering MDBT42Q through a lipo circuit

[espruino-discuss3]

Posted at 2019-06-26 by vorillaz

Hello y'all. I recently bought the MDBT42Q breakout board for quick prototyping as well as a few bare modules. As my prototype on the breadboards works, I want to design and order a few PCBs.

In the bare module documentation, it is noted that:

A 3v non-rechargeable lithium cell is ideal for this (LiPo batteries have a voltage that is too high and will need the voltage dropping with a diode or voltage regulator).x

I was hoping if someone has any examples of circuits powering the MDBT42Q module. My goal is creating a prototype with a LiPo charger on board via a USB port, so any help, schematics or advice will be highly appreciated.

Thanks in advance.

[espruino-discuss3]

Posted at 2019-06-26 by Robin

Wed 2019.06.26

Hi @vorillaz,

By chance did you take a peek at the breakout board schematic using a simple voltage regulator?

Link below image at:

http://www.espruino.com/MDBT42Q
https://github.com/espruino/EspruinoBoard/blob/master/MDBT42/pdf/mdbt42q_breakout_sch.pdf

If battery life is of concern, as the regulator will draw current continuously, a buck step down converter could be used to improve that slightly, although they can be a bit noisy.

A separate circuit using a MOSFET could be utilized to completely cut off power to all parts.

[gfwilliams]

Posted at 2019-06-27 by @gfwilliams

As @robin says, checking the schematic is a good bet.

'Normal' voltage regulators have a quiescent current (the power drawn by them even when not supplying any power) that's quite high, often 1mA or more. The MCP1703T used in the MDBT42 breakout is a bit pricier but provides a decent amount of power while also having low quiescent current.

In terms of charging, there are a bunch of chips you can use - generally now they're all pretty straightforward to use - just the chip and some capacitors. I've used MAX1551 in the past as it's easy to get hold of.

When you use USB it's also good practice to add a 500mA PTC (self resetting) fuse near the USB plug - just to ensure that if there was any kind of short you don't end up damaging your PC :)