I tried to design a charging circuit based on the TP4056 li-po chip. At a usb voltage of 5V, the battery charging output (Pin 5 of TP4056) 4.3V. This seems acceptable, but there seems to be no regulation in my circuit as the battery voltage will vary with the input voltage


Can anyone suggest what the problem is? I'm too reluctant to plug in my li-pos until I get safe readings from a multimeter. Schematic included below enter image description here

IBATT connector is shorted for voltage tests.

I do not want to overcharge my batteries with a voltage too high. The TP40456 dosent seem to be doing its job properly.

  • \$\begingroup\$ What battery are you using? How much voltage does it put out by itself (not connected to the charger)? \$\endgroup\$ – Bruce Abbott Sep 5 '20 at 6:14
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    \$\begingroup\$ haven't checked the TP4056 datasheet, but these 0.7 V between in- and output might simply be the minimum drop. How are you measuring the voltage if you're not attaching a battery? Obviously, the free-running voltage is not what you'll see when you attach anything that actually loads the charger's output. \$\endgroup\$ – Marcus Müller Sep 5 '20 at 7:31
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    \$\begingroup\$ unshort ibatt and connet an ammeter there, observe current during the tests. \$\endgroup\$ – Jasen Sep 5 '20 at 9:02
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    \$\begingroup\$ Why should it be 4.2 V without load? \$\endgroup\$ – Marcus Müller Sep 6 '20 at 16:58
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    \$\begingroup\$ You said "the battery outputs 4.3V" but you didn't connect the battery. Please edit your question to correct this incorrect information. \$\endgroup\$ – Bruce Abbott Sep 6 '20 at 21:32

The TP4065 could be detecting there is no battery, or a battery that is out-of-spec for normal charging, and do as it sees fit.

It could also be going into CC-charging mode, and then it's a current source and not regulating voltage. Its behaviour in the absence of a battery may well be described in its datasheet, I haven't checked.

Anyway: it will be hard to test properly without a battery connected. Pros use a Battery Simulator; when in doubt, I just take the whole rig outside, use a battery, and stand well back; not as safe, but much cheaper.

  • \$\begingroup\$ Did a few tests and swapped in a TP4056 from a brought charging board. The problem seems to be the actual chip itself, I will try to find another supplier of the same chip. \$\endgroup\$ – T-RexMan Sep 15 '20 at 5:12

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