Electronic – Under Voltage Protection for LiPo Battery


I have a 3Cell LiPo battery which I am going to use with an RC Car, and I want to design a circuit to protect the battery cells from going under ~3.3v each. So what do you think of this design?

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As you can see in the schematic, I am using the MCP111-315 which detects voltage drop below 3.08V (active-low, open-drain).

  • Diodes are used to increase the detected voltage level, so it will detect the power at 3.08 + Vf (3.3 is my preferred value). However, the MCP111 only draws 1.75uA (max) and most datasheets only provides Vf for as low as 1mA. Is there a more reliable way to get this ~0.2 voltage drop at such low current? maybe a voltage divider?

  • I am using optocouplers since I don't have a common ground between Cell 1 & 2 and the MCU

  • Any cell that falls below 3.3V should pull the MCU pin down (MCU Internal pull-up resistor is turned on on that pin)

  • C1, C2 and C3 are bypass capacitors for the MCP111, whereas R1 & R2 are series resistors for the optocouplers LED.

Any suggestions on this design or do you have a simpler idea?

Best Answer

There's battery monitoring, and battery protection. They're two different things, and different design considerations apply to each. Sending a signal to a microcontroller is a good design for monitoring -- you can alarm and tell the user their battery is low.

But generating a digital signal isn't stopping discharge, so it doesn't provide any protection to the cells. The only way you can read your digital signal is by powering the microcontroller... which continues to drain and damage the battery.