The basic component is the operational amplifier MCP6001 acting as a comparator. It has a number of advantages that were used in this project: Small supply voltage (1.8 to 6 V). Low power consumption (typically 100 μA). Rail-to-Rail output....Electronics Projects, Protection Circuit of Li-Ion or Li-Po Battery "battery charger circuit, power electronic projects, " Date 2019/08/04
The basic component is the operational amplifier MCP6001 acting as a comparator. It has a number of advantages that were used in this project:
Small supply voltage (1.8 to 6 V). Low power consumption (typically 100 μA). Rail-to-Rail output. Small housing (SOT23-5).
Its output directly controls the gate of the IRLML6402 MOSFET-P transistor, which switches on the load. The role of the reference voltage source is made by the LM385-1.2 system providing a stable voltage of 1.235 V. The resistor R1 causes the current flowing through it to be about 28 μA at a voltage of 3.5 V.
The minimum value of this current has been determined by the manufacturer for 10 μA, so the correct work of the element is ensured in a wide temperature range. The elements surrounding the US2 system set the thresholds for switching on and off the load, in particular the resistor R5, which causes them to be extended.
The difference between them must be large enough so that the system does not fall into oscillations caused by the disconnection of the load with high power consumption from the cell with a significant internal resistance. Resignation from any parameter adjustment by the user enabled miniaturization of the device. Reading of catalog notices of various cells showed that the minimum voltage to which the cell can be unloaded without fear of its damage, is in the range 2.7 … 3 V.
Battery Protection Circuit Scehematic
It follows that the 3 V shutdown threshold will be suitable for all cells. In turn, the maximum current consumed is limited by the transistor and is about 2 A depending on the ambient temperature. The battery protection circuit is assembled on a single-sided PCB measuring 26 mm × 15 mm. The device does not require any start-up activities. The following values were measured in the model copy:
switching threshold: 3.06 V, switch-off threshold: 3.38 V, voltage drop at 1 A current consumption by load: 67 mV (UZAS = 3.5 V), power consumption without load: 140 μA at UZAS = 3.5 V and 130 μA at UZAS = 3 V.
The plate can be protected against the influence of environmental factors by covering it with varnish and pressing into a section of a heat-shrinkable tube.