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Car Emergency Start Power: Lithium Battery Protection Board Works

Update:24-12-2018
Summary:

The car emergency start power source is believed to hav […]

The car emergency start power source is believed to have been used by most car owners. The internal battery core is a lithium battery. The lithium battery protection board has different circuits and parameters according to the use of IC and voltage. The following Lin Sheng uses DW01 with MOS tube 8205A. Explain and make sure that you are using the car emergency start power safe:

The normal working process of the lithium battery protection board in the car emergency starting power supply is:

When the cell voltage is between 2.5V and 4.3V, the first pin and the third pin of DW01 output a high level (equal to the power supply voltage), and the second pin voltage is 0V. At this time, the voltages of pins 1 and 3 of DW01 will be respectively added to the 5th and 4th pins of 8205A. The two electronic switches in 8205A are connected to each other because their G poles are connected to the voltage from DW01. Both electronic switches are on. At this time, the negative pole of the battery core and the P-end of the protection board are directly connected, and the protection board has a voltage output.

Lithium battery protection board over-discharge protection control principle:

When the battery is discharged through the external load, the voltage of the battery will gradually decrease, and the voltage inside the DW01 will be monitored in real time through the R1 resistor. When the voltage of the battery drops to about 2.3V, the DW01 will consider the voltage of the battery. When the voltage is over-discharged, the output voltage of the first pin is immediately turned off, so that the voltage of the first pin becomes 0V, and the switch tube in the 8205A is turned off due to the absence of voltage on the fifth pin. At this time, the B- of the battery cell is disconnected from the P- of the protection board. That is, the discharge circuit of the battery cell is cut off, and the battery cell will stop discharging. The protection board is in an overdischarged state and remains there. After the P and P- protection voltages of the protection board are indirectly charged, the DW01 immediately stops the overdischarge status after detecting the charging voltage by B-, and re-outputs the high voltage on the first pin, so that the overdischarge control tube in the 8205A is turned on. That is, the B- of the battery cell and the P- of the protection board are reconnected, and the battery core is directly charged by the charger.

Lithium battery protection board overcharge protection control principle:

When the battery is normally charged by the charger, as the charging time increases, the voltage of the battery will become higher and higher. When the voltage of the battery rises to 4.4V, the DW01 will assume that the voltage of the battery is in an overcharged state. Immediately disconnect the output voltage of pin 3, so that the voltage of pin 3 becomes 0V, and the switch tube in 8205A is turned off because there is no voltage on pin 4. At this time, the B- of the battery cell is disconnected from the P- of the protection board. That is, the charging circuit of the battery core is cut off, and the battery core will stop charging. The protection board is in an overcharged state and remains there. Wait until the protection board P and P- indirectly discharge the load, so although the overcharge control switch is closed, the internal diode is in the same direction as the discharge circuit, so the discharge circuit can discharge, when the voltage of the battery When it is placed below 4.3V, DW01 stops the overcharge protection state and re-outputs the high voltage on pin 3, so that the overcharge control tube in the 8205A is turned on, that is, the battery B- and the protection board P- are reconnected. The battery can perform normal charging and discharging.

Lithium battery protection board short circuit protection control principle:

During the external discharge of the protection board, the two electronic switches in the 8205A are not completely equivalent to the two mechanical switches, but are equivalent to two resistors with small resistance, and are called the conduction internal resistance of the 8205A. The on-resistance of each switch is about 30m\U 03a9 is about 60m\U 03a9. The voltage applied to the G-pole is actually directly controlling the on-resistance of each switch. When the G-pole voltage is greater than 1V. When the switching tube has a small internal resistance (tens of milliohms), which is equivalent to the switch closing, when the G pole voltage is less than 0.7V, the conduction internal resistance of the switching tube is large (several MΩ), which is equivalent to the switch. disconnect. The voltage UA is the voltage generated by the internal resistance of the 8205A and the discharge current. When the load current increases, the UA must increase. Because the UA0.006L?IUA is also called the tube voltage drop of the 8205A, the UA can simply indicate the magnitude of the discharge current. When it rises to 0.2V, it is considered that the load current has reached the limit value, so the output voltage of the first pin is stopped, the voltage of the first pin is changed to 0V, the discharge control tube in 8205A is turned off, and the discharge circuit of the battery cell is cut off, and the battery is turned off. Discharge control tube. In other words, the maximum current allowed by the DW01 is 3.3A, which achieves overcurrent protection.

Short circuit protection control process:

Short-circuit protection is a limit form of over-current protection. The control process and principle are the same as over-current protection. The short-circuit is only equivalent to adding a small resistance (about 0Ω) between P P- to protect the board. When the load current instantaneously reaches 10A or more, the protection board immediately performs overcurrent protection.