I'm designing a circuit that charges a battery with solar power. Im using the TP4056 for this. My question is the following. I want to use a transistor as switch to cut off the power if the battery is fully charged. (to prevent overcharge). And to drain the battery. (for demo purposes)

The transistor is controlled by an arduino pin.

I have the following schematic:

enter image description here

The solar panel is 5.5V and 170mAh.

  1. Am I correct that there is no current flowing between the panel and the charger ?
  2. How do I determine what the exact transistor should be if I want to interrupt the circuit. (5.5V before transistor, 5.5V after transistor) ?
  3. Is this even necessary. Does the TP4065 automatically shuts off ?

Many Thanks in advance !

  • \$\begingroup\$ why don't you use the CE pin on the TP4056? \$\endgroup\$
    – jsotola
    Mar 2, 2021 at 19:51
  • \$\begingroup\$ I do not have access to it. The tp4065 is integrated in this : 5.imimg.com/data5/SE/CK/MY-5015976/… \$\endgroup\$ Mar 2, 2021 at 19:55
  • \$\begingroup\$ TP4056 cuts off power when battery is fully charged. \$\endgroup\$
    – user208862
    Mar 2, 2021 at 19:55
  • \$\begingroup\$ @MichalPodmanický And will the TP keep the battery charged or does the battery need to drop below a certain voltage ? \$\endgroup\$ Mar 2, 2021 at 19:57
  • \$\begingroup\$ TP will keep the battery at almost full level. \$\endgroup\$
    – user208862
    Mar 2, 2021 at 20:02

1 Answer 1


It's called a High Side 1A switch that can handle this, with a 0V input enable.

enter image description here

Any resistor will do for < 200mA but needs 10mA for low Vce(sat) on the PNP and 1 Ohm on the Pch FFET

  • \$\begingroup\$ When I lookup the TIP42C I see that it has a voltage of 100V although the circuit is only 5.5V. Whats the reason behind that ? \$\endgroup\$ Mar 2, 2021 at 20:21
  • \$\begingroup\$ Any PNP will do with decent Beta \$\endgroup\$ Mar 2, 2021 at 20:21
  • \$\begingroup\$ Any PNP will do because there is no current or ? \$\endgroup\$ Mar 2, 2021 at 20:23
  • \$\begingroup\$ The base R draws current and the Vce replaces a fixed resistor which the datasheet recommended digikey.com/en/products/detail/motorola/2N2907/12094713 \$\endgroup\$ Mar 2, 2021 at 20:26

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