STANDALONE BATTERY CHARGER
Figuer.1
- Here first I divide battery charging circuit into three parts
1.
First,
which gives us constant 5volt output
2.
Second
is battery charging circuit
3.
Third
is indicator circuit
FIRST PART OF BATTERY CHARGER
Figure.2
- In this circuit, First plug in 9V-500mA AC out step down transformer and fit it’s output wire with bridge rectifier which gives ~9v DC output voltage then it pass through 100uF capacitor which filter out remaining AC plus. Then it is put into LM7805 IC chip which gives us 5V constant output. Here 0.22uF capacitor is put between first and second port of IC chip and 0.1uF capacitor is put between second and third port which also filter out remaining AC plus and gives us constant pure DC 5 volt.
{
{ [ You can also use step down transformer which gives 12 v - 1 A AC output,and different nearby valued of capacitors]
[ If you design for 12 V battery charger then use LM-7812 which gives you 12 V output voltage]
[There are exiting LM-78XX IC chips....If you want put 5 volt then there is LM-7805,If you want to put 6 volts then there is LM-7806.etc.
[ Before we go to second part of battery charger first you have to know about op amp , which is use as comparator]
SECOND PART OF BATTERY CHARGER
Figure.3
- Now, After getting constant voltage of 5 volt this 5 v is supplied to op amp LM-741, to Battery and to resistor of 24k ohm and 1k ohm. We supply 0.2volt reference voltage to op amp’s inverting port or at second port.
V(1)=V*R1/R1+R2;
0.2=5*R1/R1+R2;
{{Relation between R1 and R2}
R2=24*R1;
- If we use R1 =1k ohm then R2 =24k ohm. Now V (ref) = 0.2v and non-inverting port is connected with collector port of transistor. And battery’s negative port is also connected collector; battery’s positive port is connected with 5volt which is supplied by LM 7805.
- During this battery is being charged under constant 5volt and vary current, and thus battery is being charged, collector voltage also varies as battery voltage varies so feedback of collector voltage is pass to op amp’s non inverting port so again it compares and it gives positive output so charging is till now going on, but once battery is at a high voltage of 4.8v difference is become 0.2volt so now at op-amp’s non inverting and inverting port both have same value but different sign so it gives null, so now current passing through battery is so small(9mAh) that battery charging is stopped.
THIRD PART OF BATTERY CHARGER
Figure.4
- Here, as seen in the figure.4 collector voltage (V2) is also supply to the first op amp’s (LM741’s) non-inverting port and second op amp’s inverting port. For first op amp, Reference voltage is again set with voltage divider method which is show in figure.5 and figure.6
Figure.5 Figure.6
- For low battery indicator reference voltage is set at 3.5v with 10k ohm and 4.7k ohm resistor.
- For high battery indicator reference voltage is set at 1.5v with 22k ohm and 10k ohm resistor.
- 5v power from LM 7805 output is supplied to two op amps and to two series combination of resistors.
- Here Red LED is connected with output of first op amp (At sixth port) in forward bias which indicates Low battery.
- And Green LED is connected with output of second op amp (At seventh port) in forward bias which indicates High battery.
FINAL CIRCUIT
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