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I need to power a Bluetooth speaker (Beatbox Portable) with a battery pack while also allowing DC power in.

I also want to use the input DC power to charge the four cell lithoum ion battery pack.

Can I use buck and boost converters as in the circuit below?

D1 and D2 are safety diodes to prevent current from flowing in the opposite direction.

enter image description here

The below image is a 2nd option that I'm still trying to achieve. I am not sure if I will be able to as the space inside the speaker is limited.

Other side questions:

  1. What happens if the BMS is triggered due to a short circuit or low battery voltage?
  2. Will connecting the main DC input (18.5V) reset the BMS?
  3. Is it OK to leave the BMS connected to the load?
  4. Can this charger board work for five cells in this application?

enter image description here

I'm still in the concept and testing phase. I haven't chosen any component yet, but I was looking at the XL6009 buck+boost converters.

Here is the DC power supply:

enter image description here

Another Potential Solutions:

1- Using this USB-C charging board for 4S or 5S cells with a manual switch to select between DC input or battery pack.

enter image description here

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    – SamGibson ♦
    Commented Nov 14, 2023 at 16:12

1 Answer 1

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You may want to consider using a battery charger IC with the ability to seamlessly switch between DC Input and Battery Input. Its normally called Dynamic Power Management (DPM) and Dynamic Power-Path Management (DPPM).

MPS Power Path Managment Example

MPS have a nice primer page explaining some of the concepts

I'd highly recommend designing a circuit or using a module that implements the battery management and power path functionality as it'll make your life much easier as battery charging can be a pain to implement and you'll save yourself a lot of space with a more integrated solution which is something I think you'd find valuable being space constrained in your application.

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  • \$\begingroup\$ Thank you for sharing this. This is what I want exactly. but I'm looking for a ready-made solution to just plug in. I don't want to do a custom PCB. I'm constrained with the battery compartment for the battery space. inside the speaker, I've some space for the Buck/Boost converters. (the battery compartment fits 6 D cell batteries). Can't something similar to the DPPM be achieved with Buck/Boost converters and a BMS?.... \$\endgroup\$
    – P LA
    Commented Nov 14, 2023 at 12:31

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