A simple and effective charging equalization circuit for Li-ion battery

a simple and effective charging equalization circuit for Li-Ion battery

This equalization circuit is made up of three identical parallel-regulated circuits, one for each battery.

Schematic diagram of the circuit is as follows:

Each regulated power supply is regulated to 4.2V. The principle of equalization is that when the battery voltage is less than 4.2V, the shunt regulator circuit does not work, charging current from the battery through:

If the battery is unbalanced, which has a first filled (reached 4.2V), then the shunt regulator circuit began to work, the shunt, will be the voltage has been stable to 4.2V, that is, the charging current will not be filled with the battery:

The principle is so simple, then look at the principle of parallel voltage regulator circuit. The following is a single circuit, the TL431 is the reference voltage, by adjusting the variable resistor, the voltage is adjusted to 4.2V.

If the battery ends less than 4.2v,tl431 does not absorb current, that is, the following ib=0, so ic=0, three-stage tube shut down, charging current is still through the battery.

If both ends of the battery reach 4.2v,tl431 start absorbing current, ib>0, the charging current (ie IC) through the transistor, will not pass the battery, that is no longer charging the battery.

In addition, this circuit in the three series diode IN4001, is the role of pressure, can reduce the dissipation of power on the transistor TIP42. If the three diode IN4001 is not received, then the power dissipation on the transistor TIP42 P=4.2VX the charge current, plus the p= (4.2v-3x0.7v) x charge Current.

The right-most LEDs are illuminated, indicating that the voltage has reached 4.2V, i.e. the battery of the equalization circuit is fully charged.

The actual circuit board is done:

Circuit debugging is also relatively simple, is not to pick up the battery, the equalization circuit directly connected to the constant current supply (if the power supply does not support constant current, you can string a resistor, slowly put the supply voltage up). Then one adjusts the variable resistor so that each balance circuit is 4.20V at both ends.

The actual use of the effect is good, each battery voltage is strictly limited to 4.20V.