The charging device charges four 2Ah nickel-cadmium batteries.
The working principle circuit is shown in the figure. The diodes VD7, VD8, and the transistors VT2 and VT3 form a constant source to limit the charging power.
The three-terminal integrated block 7806 and the diodes VD9 and VD1O constitute an imaistor. In the early stage of charging, the voltage across the battery GB is relatively low, the charging current is large, and the charging current is limited by the constant current power supply, which is about <200 mA. As the battery terminal voltage rises, the charging current gradually decreases, the value genset loses its effect, and it is charged by the 7806 constant voltage. Transistor VT1 and LED VD5 form a charging indicating circuit. At this time, VD5 changes from bright to slightly bright. When the battery is fully charged, the collector and emitter junction resistance of the transistor VT3 increases, and the base potential drops, causing the base potential of the transistor VT2 to rise, thereby causing the base potential of the transistor VT1 to rise, and VT1 is turned off, and the light emitting diode VD5 is dim to off.
Among them, the diode VDIO is a reverse intercepting pipe to prevent the battery GB from being reversed. In order to ensure that the battery has a charging voltage of 6V, a diode VD9 is added to the ground of the 7806 to compensate for the voltage drop of the VD1O.
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