lithium 3400mah 3.7v 18650 battery.Lithium battery power supply system monitoring circuit analysis

　　Many battery-powered systems require a visual indicator to indicate when the batteries need to be replaced. LEDs are generally used for such indicators, but they consume at least 10mA of current. This large current will accelerate the discharge of the battery and shorten the useful life of the battery. Figure 1 uses a sampled data technique

　　Many battery-powered systems require a visual indicator to indicate when the batteries need to be replaced. LEDs are generally used for such indicators, but they consume at least 10mA of current. This large current will accelerate the discharge of the battery and shorten the useful life of the battery. Figure 1 uses a sampled data technique to reduce the average power consumption of the monitoring circuit. The circuit has a standby current of 5A and consumes 30A when low voltage is indicated.

　　During a sampling period, the LTC1041 sets the range controller to power up its two internal comparators; samples the VIN, SETpOINT, and DELTA inputs; stores the comparison results in an output latch; and then powers down. This process takes about 80s. The external RC network formed by R1 and C1 determines the sampling rate.

　　The controller's Vpp output switches to VCC during the controller's active 80s on-time and to high impedance during the shutdown period. A quick settling baseline sets the trigger point. R2 must be small enough to supply the minimum required current to the LT1009. R3, R4 and R5 divide the battery voltage and feed it to the input of a comparator. The resistors provide a lower trip point of 5.5V and an upper trip point of 5.95V. The internal comparator has a low current bias point, allowing the use of large value resistors for the voltage divider. R5 sets the comparator hysteresis. The comparator drives an internal RS flip-flop. When VINSETpOINT+DELTA, the flip-flop is reset (ON/OFF=ground).

　　Low temperature lithium iron phosphate battery 3.2V 20A -20℃ charging, -40℃ 3C discharge capacity ≥70%

　　Charging temperature: -20~45℃ -Discharge temperature: -40~+55℃ -40℃ Support maximum discharge rate: 3C -40℃ 3C discharge capacity retention rate ≥70%

　　When the controller reaches the lower flip-flop, the flip-flop latches, causing Q1 to conduct. Once latched, the Vpp output drives Q2, causing the LED to blink on each sample cycle. The circuit drives the LED for 80s with 75mA current every 220ms. The result of this operation is an average power consumption of 27A. The LED may flash once during power-up because the latch voltage cannot be determined. Bypass capacitor C2 ensures low supply impedance under transient loads.

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