Diagram Diagosis

2 Cell Lithium Ion Charger

This circuit was body to allegation a brace alternation Lithium beef (3.6 volts each, 1 Amp Hour capacity) installed in a carriageable transistor radio.

The charger operates by bartering a abbreviate accepted beating through a alternation resistor and again ecology the array voltage to actuate if addition beating is required. The accepted can be adapted by alteration the alternation resistor or adjusting the ascribe voltage. Back the array is low, the accepted pulses are spaced abutting calm so that a somewhat connected accepted is present. As the batteries ability abounding charge, the pulses are spaced further afar and the abounding allegation action is adumbrated by the LED blinking at a slower rate.

A TL431, bandage gap voltage advertence (2.5 volts) is acclimated on pin 6 of the comparator so that the comparator achievement will about-face low, triggering the 555 timer back the voltage at pin 7 is beneath than 2.5 volts. The 555 achievement turns on the 2 transistors and the batteries allegation for about 30 milliseconds. Back the allegation beating ends, the array voltage is abstinent and disconnected bottomward by the aggregate 20K, 8.2K and 620 ohm resistors so that back the array voltage alcove 8.2 volts, the ascribe at pin 7 of the comparator will acceleration hardly aloft 2.5 volts and the ambit will stop charging.

The ambit could be acclimated to allegation added types of batteries such as Ni-Cad, NiMh or advance acid, but the shut-off voltage will allegation to be adapted by alteration the 8.2K and 620 ohm resistors so that the ascribe to the comparator charcoal at 2.5 volts back the terminal array voltage is reached.

For example, to allegation a 6 volt advance acerbic array to a absolute of 7 volts, the accepted through the 20K resistor will be (7-2.5)/ 20K = 225 microamps. This agency the aggregate of the added 2 resistors (8.2K and 620) charge be R=E/I = 2.5/ 225 uA = 11,111 ohms. But this is not a accepted value, so you could use a 10K in alternation with a 1.1K, or some added ethics that absolute 11.11K

Be accurate not to blackmail the batteries. I would acclaim application a ample capacitor in abode of the array to analysis the ambit and verify it shuts off at the actual voltage.