Charging a Li-ion battery does not need big smart charger, but we can do it with one small 555 timer chip; also this 555 Pulse Generator Li-ion Battery Charger Circuit makes fast little pulses that charge the cell gentle and safe.
Anyone can build this circuit with very few parts and with very low cost, as its a perfect beginner project to learn battery charging in simple way.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt) | 1.2k, 10k, 1k, 100Ω | 1 each |
| Capacitors | Ceramic 0.1uF, 0.01uF | 1 each |
| Semiconductors | IC 555 Timer | 1 |
| Standard LED any 5mm | 1 | |
| Diode 1N5819 Schottky | 1 | |
| Li-ion Battery 3.7V 700mA | 1 | |
| Power Supply 12V DC | 1 |
The above circuit diagram shows IC 555 runs in astable multivibrator mode, it make square wave around 680 Hz and output pin 3 give pulse around 10 volt peak to peak.
Then pulse go through diode D1 1N5819 and this diode prevent battery discharge back to circuit.
Now resistor R3 limit charging current and R4 work like extra safety resistor and then LED show charging pulse activity.
After that, capacitor C1 is a timing capacitor for frequency and capacitor C2 is a filter capacitor for stable 555 operation; finally battery get small fast pulses and this help charge slowly and safe.
Formulas with Calculations:
Formulas for IC 555 astable mode:
Frequency f = 1.44 / ((R1 + 2R2) x C1)
Duty cycle approx = (R1 + R2) / (R1 + 2R2)
Use values:
- R1 is 1.2k
- R2 is 10k
- C1 is 0.1uF
Calculate frequency:
f = 1.44 / ((1200 + 2 x 10000) x 0.0000001)
f = 1.44 / ((1200 + 20000) x 0.0000001)
f = 1.44 / (21200 x 0.0000001)
f = 1.44 / 0.00212
f = 679 Hz
So frequency is about 680 Hz.
How to Build:
To build a 555 Pulse Generator Li-ion Battery Charger Circuit follow the below connection steps:
- First, take all the parts as shown in circuit diagram.
- Next, pin 1 go to ground.
- Then, pin 2 receives the RC network input from R2 and C1.
- After that, pin 3 is output pulse go to junction of resistor R3, LED and diode D1.
- Now pin 4 go to Vcc 12V.
- Further, pin 5 connect to small capacitor 0.01uF C2 to ground.
- Pin 6 connect to resistors R1, R2 junction and C1 capacitor.
- Also, pin 7 go to R1 and then goes to Vcc and then pin 8 go to Vcc 12V too.
- Finally, resistor R4 connect from cathode of diode D1 and battery positive and battery negative go to ground.
Conclusion:
Overall, this 555 Pulse Generator Li-ion Battery Charger Circuit is for learning, as it give slow safe charge using pulse; but it is not for fast charging.
Moreover, this low cost circuit is easy to build and works well for charging a small single-cell battery.