I have connected by lithium-ion battery to a tp4056 IC charger with builtin circuit protection(shown below).

enter image description here

Which means the circuit will automatically disconnect the load when the battery voltage goes below 2,4V. My problem is when the battery goes below 2,4V the IC disconnects the load from the battery, but then the voltage picks up to around 3,2V and then reconnects the load. When the load gets connected again the voltage drops back below 2,4V and then disconnects the load. So basically when the battery drops below 2,4V the first time my load then keeps on reconnecting to the battery via the TP4056 IC. Hence I want to design a switch that when the battery drops below 2,4V initailly the swtich closes and disconnects my load. BUT when the battery voltage increases after disconnecting the switch must remain closed. How do I design such a switch? and the charger IC is connected to a 5V boost then to my load to give my logic part of the switch

initially: output=5V

voltage drops below 2.4: output=0V

voltage goes back up: output=0V

  • \$\begingroup\$ So that I understand what you're talking about, you want something that if the voltage reaches below 2.4V you want it to disconnect from the load and have it stay disconnected permanently? How about a latch? \$\endgroup\$ – user103380 Jun 7 '18 at 20:18
  • \$\begingroup\$ @KingDuken the former question is exactly what I want. As for the latter question on the latch, how would that work? \$\endgroup\$ – Joey Jun 7 '18 at 20:20

In electronics, the behavior of having a different voltage for a disconnect and a reconnect (or any particular usage similar) is called hysteresis. In you're case, you want to toggle off your circuit when the voltage is bellow 2.4v (this is done automatically by your circuit). However, you want to prevent a power up of the circuit unless the input voltage is greater than 4 volts (slightly above the rebound voltage that your battery is doing).

The specific circuit that you will be looking for is a Schmitt trigger. Depending on your choice of component around it, you will be able to enable and disable your circuit at will.

You can make one out of transistors, op-amps or simply buy a pre packaged Schmitt trigger IC that is ready to go.

  • \$\begingroup\$ I have researched a Schmitt trigger but in order to have to different thresholds you would need a Schmitt trigger with a Vref. But my Vref changes, since the output disconnects. So I cannot use 5V as my Vref. How do I solve this? \$\endgroup\$ – Joey Jun 7 '18 at 21:24
  • \$\begingroup\$ Looking at the schematic of that particular board, there is nothing that you can use on board to achieve that. You will need some kind of external circuitry. Since the external circuitry is merely there to do logic purpose, it can be designed with an external battery that will outlast by far the lipo battery. Normally, the ''schmitt trigger'' should have been deployed inside the DW01A battery protection IC or at least around it. In all cases, my go to move would be to put an external power source to actually drive the trigger mechanism. \$\endgroup\$ – Simon Marcoux Jun 8 '18 at 14:15

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