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I opened an USB rechargeable speakers which contain the PCB as follows:

enter image description here It uses a 1000mAh Li-Ion battery with a protection circuit (not in the figure). I couldn't find a battery charger IC in the PCB. I opened the battery external involucrum and noticed a 8205A and DW01 ICs in the protection circuit. These ICs also come along with TP4056 charges as I could notice.

So, I'm still confused about the differences and necessities of both a charger and a protection circuit:

  • Does a charger require a protection circuit?
  • Do all protection circuits require a charger? If so, why having protection circuits attached to the batteries after all?
  • What is missing in a protection circuit to also allow charging? (since both the 8205A and DW01 are present in the protection circuit and charger)
  • How come my speakers don't have a charger IC but still work?

Thanks

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Does a charger require a protection circuit?

  • Yes and no. Most reputable charger have built in safety mechanism, however reputable manufacturer would add them (eg DW01) to give them extra safety. Cheap product just don't have the budget to add in a protection circuitry for their battery.

Do all protection circuits require a charger?

  • You can charge the battery just applying a fix voltage, just like in this case. However this design with the protection will open the mosfet inside the board once voltage exceed preset settings. It's not a good design to keep triggering the safety circuit.

If so, why having protection circuits attached to the batteries after all? What is missing in a protection circuit to also allow charging? (since both the 8205A and DW01 are present in the protection circuit and charger)

  • The circuit is to prevent batteries exploding in the event of overcharge. 8205A is the mosfet that open the circuit. DW01 is the IC that measure the voltage. It is possible to charge the battery with a fix 4.2V voltage thru a resistor without protection, I had done it but I don't recommend if you're not experience to know what's going on.
  • In addition, it also protects the battery from over discharge to a voltage that is too low that may damage the battery. Other PCM also have current limit and NTC to measure the temperature.

How come my speakers don't have a charger IC but still work?

  • Dedicated charger uses CC (constant current) and CV (constant voltage) to charge the battery. For your case it's just CV, the downside is it may charge at a higher current than the battery spec allowed. More details can be Google.
  • Example for your board, if there's 2.2V drop across your 2.2 ohm resistor; that's 1A into the 1000mAh battery. Whereas the batt manufacturer only spec 0.5A charging. The outcome is the battery capacity will drop very fast.

Looking at the PCBA. This lousy design I draw out in the schematic below, the manufacture is hopping the protection circuit will stop the charging when the voltage rises upon a certain voltage. Do not use this product, it's a fire hazard.

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ Lousy it is, but not so dangerous. DW01 will disconnect the battery when it reaches its max at about 4.25 - 4.3V and will prevent damage to the battery. This is not perfect and will somewhat reduce battery life, but I don't think it could cause hazard. \$\endgroup\$ – Todor Simeonov Aug 5 '17 at 6:49
  • \$\begingroup\$ Agree if it's exactly 5V. USB do spec +-5%, so it may go up to 5.25V. Batt needs 4.2V to properly charge and with Vf of 0.6V at the diode, there's a slight possibility of 4.65V at the batt. \$\endgroup\$ – Jason Han Aug 5 '17 at 6:53
  • \$\begingroup\$ Thank you for dissecting the circuit. Would mind answering the other question? I'm still confused about designing my own board with a Li-Ion. The other answers would help a lot. Thanks. \$\endgroup\$ – Contaso Aug 7 '17 at 10:51
  • \$\begingroup\$ Added some. You're welcome. \$\endgroup\$ – Jason Han Aug 7 '17 at 14:03
  • \$\begingroup\$ Thank you so much! I'll probably use one of these along with the battery: hotmcu.com/… It's not yet clear why the OUT+/- connections since the specification says you cannot charge under load (if it is the case why not use B+/-?). Thanks again! \$\endgroup\$ – Contaso Aug 7 '17 at 14:11

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