AUTO TURN OFF SOLDERING IRON CIRCUIT SERIES
It is good to connect appropriately dimensioned fuse in series with the cell for safety reasons. The value of Rx is calculated: Rx = 0.95 / Imax. For charging current 500 mA, I used the value of 2R2. Select it according to the type of charged cell. This reduces the voltage on the pin adj and so it stabilizes the current. If the drop of shunt Rx reaches approximately 0.95 V (the total voltage drop of the NPN transistor’s B-E and diode 1N4007) transistor starts to open. Stabilization of current is not as critical as the stabilizing voltage, so it is sufficient to stabilize it by a shunt resistor and NPN transistor. We set it without connecting the cell, because the target voltage corresponds to the output voltage with no load. Cells Li-ion and Li-pol do not like storing in a charged or discharged state, they should be stored partially charged. When using the cells, they should never discharge below 3.4 to 3.3 V.
If you reduce the target voltage to 4.1 V, capacity drops by 10% but lifetime (number of cycles) will increase almost twice.
AUTO TURN OFF SOLDERING IRON CIRCUIT FULL
The cell does not need to be charged the full 4.2 V, because it decreases its lifetime. Target voltage of Li-ion and Li-Pol accumulator is usually 4.2 V (for some types 4.1 V) Target voltage is not the same as the nominal voltage. After reaching the target voltage (Umax), the charger goes into voltage mode when the voltage is constant and the current asymptotically approaches zero.Īt the moment the current is small, the cell is charged.
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