What is the 18650 lithium-ion battery protection board design method?

　　Author ：Iflowpower – Fournisseur de centrales électriques portables

In the case where the lithium ion battery protective board is normal, VDD is high, VSS, VM is low, DO, CO is high, when VDD, VSS, VM is changed, DO or CO end Level will change. 1 30 millio, so its on-resistance has little effect on the performance of the circuit. The consumption of the protection circuit is in this state.

μClass A, usually less than 7μA. 2 The voltage value is 4.1V), and it is turned to constant pressure to charge until the current is getting smaller.

During the charging process, if the charger circuit is lost control, the battery voltage will continue to charge after the battery voltage is over 4.2V. At this time, the battery voltage will continue to rise, and when the battery voltage is charged to more than 4.

3V, the battery is chemically Side reactions will exacerbate, causing battery damage or security issues. In a battery with a protective circuit, when the control IC is tested to the battery voltage reaches 4.28V (this value is determined by the control IC, the CO pin will change by the high voltage to zero voltage, so that V2 The turning circuit is turned off, thereby cutting off the charging circuit, so that the charger can be charged to the battery, and play a charging protection.

At this time, due to the presence of V2 itself, the battery can discharge the external load by the diode. When the control IC is tested to the battery voltage, there is a delay time, and the length of the delay time is determined by C3, usually set to 1 second, and cause alert due to interference. judge.

3, the over-discharge protection battery is gradually decreasing with the discharge process, when the battery voltage drops to 2.5V, if the battery is continuously discharged Will cause permanent damage to the battery. During the battery discharge, when the control IC is tested to the battery voltage below 2.

3V (this value is determined by the control IC, the DO pin will change from the high voltage to zero voltage, so that V1 is passed by the guide Turn to turn off, thereby cutting the discharge circuit, causing the battery to discharge the load, and play an over-discharge protection. At this time, due to the existence of v1 vs. VD1 itself, the charger can be charged by the diode.

Since the battery voltage cannot be lowered in the over-discharge protection state, the current consumption of the protection circuit is low, and the control IC will enter low power consumption, and the entire protection circuit consumes less than 0.1μA.

When the control IC is tested to the battery voltage is less than 2.3V, there is a delay time, and the length of the delay time is determined by the C3, usually set to 100 milliseconds, and the alert is caused by interference. Judgment .

4, short-circuit protection battery When the circuit current is large to the load discharge, the control IC determines that the load short circuit is determined if the U0.9V is made to make U0.9V (this value is determined by the control IC.

) The DO pin will quickly change from the high voltage to zero voltage, so that the V1 is turned off to turn off, thereby cutting off the discharge circuit, and serves to short circuit protection. The short circuit protection is extremely short, usually less than 7 microseconds. Its working principle is similar to overcurrent protection, but the judgment is different, and the protection delay time is different.

In addition to the control IC, there is a nicker component in the circuit, which is the MOSFET, which plays a switch in the circuit. Since it is connected between the battery and the external load, its conduction impedance has the performance of the battery. Impact, when the elected MOSFET is better, its conduction impedance is small, the internal resistance of the battery pack is small, the load capacity is also strong, and the electric energy consumed when discharged.

5, overcurrent protection due to the chemical characteristics of lithium ion batteries, battery packages specify that their discharge current is maximally exceeding 2C (C = battery capacity / hour), which will cause permanent damage to the battery when the battery exceeds 2C current discharge Safety issues. During the normal discharge of the load, the discharge current is connected in series, due to the MOSFET's conduction impedance, a voltage occurs at both ends, the voltage value u = I * RDS * 2, RDS is a single The MOSFET is turned on, the V-foot on the control IC is tested on the voltage value. When different ICs have different values), the DO pin will change by the high voltage to zero voltage, so that the V1 is turned off to turn off, thereby cutting off the discharge circuit, so that the current is zero in the loop, and enables overcurrent protection use.

In the control IC test, there is a delay time between the control IC test, and there is a delay time. The length of the delay time is determined by C3, usually 13 milliseconds, and the error is caused by an unfair. In the above-described control process, its overcurrent test value is not only on the control value of the control IC, but also depends on the on-impedance of the MOSFET.

When the MOSFET is turned on, the same control IC, its overcurrent protection Small the value. .