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I’m working on a piece of portable audio electronics and I’m running into some charging and power supply issues.

Project:

• Small 3-board build: power, signal (5 V), amp (needs ~9 V).

• Battery: 2 Li-ion cells (LP653042 3.7V 820mAh 3Wh) (amazon.com/dp/B08HJ53Q3C?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_5&th=1) with an 2S BMS board (amazon.com/dp/B07KSQY67X?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_5&th=1).

• Original power board parts: D1 = 1N4004 from DC jack to system bus, U1 = 7809 (9 V rail), U2 = 7805 (5 V rail).

Power Signal Amplifier PCB Layout Assemble original circuit boards

Problem:

I realized after designing the PCBs (and after doing some research) that the 2S board is only for battery management and needs a charging board and a constant current source in order to charge the cells safely.

Changes I’m making (tentatively):

• Replaced D1 with a TP5100 module (to feed the 2S board) (amazon.com/dp/B0C78184C1?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1) module.

• Replaced U1 (7809) with an XL4015 module (amazon.com/dp/B0CYZH5VJ4?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1).

• Added a Schottky (1N5819) on the BMS from B− to P− (to help wake the FETs).

PCB front with modifications PCB back with modifications

Constraint I just realized:

• On my PCB, the U1-OUT net is tied to P+ and due to the physical design of the PCB, it would be difficult to cut the traces to or from P+, so the output of the 7809 (or the XL4015 if used in its place) would have to simultaneously go to the S2 board, 7805, and power amplifier board.

What I’m trying to figure out:

• Given that U1-OUT = P+ on this PCB, what’s the safest, least invasive way to handle charging and the rails?

• Is there a clean approach that doesn’t require cutting traces?

• If a small mod (single trace cut or lifted pin) is the right answer, where would you do it?

• Any gotchas with using TP5100 vs XL4015 for a 2S charge path in this situation?

• Suggestions for current setpoint (cells are modest capacity) and blocking/backfeed considerations?

The more I think about this/try to troubleshoot this, the more confused I get. Ultimately what I am trying to accomplish is to complete this circuit so it safely charges the cells with minimal (if any) PCB reworking, and a stable ~9V for the amp circuit and 5V for the signal board. Help would be greatly appreciated!

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  • \$\begingroup\$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. \$\endgroup\$ Commented Nov 16 at 1:22
  • \$\begingroup\$ @Community How do I modify the circuit so it can safely charge the li-ion batteries described above, with minimum modification to the PCB (if any), and ideally using one or both of the TP5100 or XL4015 I already got if needed. \$\endgroup\$ Commented Nov 16 at 7:55
  • \$\begingroup\$ Please consider cropping your images to the relevant portions. Too much scrolling! \$\endgroup\$ Commented Nov 17 at 17:49
  • \$\begingroup\$ Quick bump: still stuck on my 2S Li-ion + 2S BMS portable audio build. Given that my 9 V rail (U1-OUT) is tied directly to P+, should I be using the TP5100, the XL4015, or both — and where in the chain (before/after the BMS, feeding P+ vs just the amp rail)? Looking for the simplest, safest way to wire this without major PCB surgery. Thanks! \$\endgroup\$ Commented Nov 17 at 23:12

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