Here is super easy USB Powered Small Battery Charger Circuit.
No microcontroller or no fancy parts required, just simple resistor, NiMH cells and diode system.
Good for learning, good for small projects.
Safe for small rechargeable cells and great for DIY makers.
Circuit Working:
Parts List:
| Component | Type | Quantity |
|---|---|---|
| Resistors | 1.2k , 10Ω 1 watt | 1 each |
| Semiconductors | LED any 5mm | 1 |
| Diode 1N4007 | 1 | |
| SPST Switch toggle | 1 | |
| Two Ni-Cd cells 1.2V each | 2 | |
| USB Male connector | 1 |
In this circuit the USB gives 5V.
Switch connect or disconnect charger.
Diode 1N4007 stop reverse current from battery to USB.
R2 resistor limit charging current.
R1 resistor and LED show charging is active.
Battery slowly charge through resistor.
LED glow means current flow.
When battery is full the current drop naturally because of resistor limit.
This circuit is simple trickle charger and not a smart charger.
Formulas with Calculation:
Formula for charging current:
R2 = 10Ω
Charging current I = V / R
I = 1.9 / 10
I = 0.19A or 190mA approx
This current is safe for AA or AAA NiCd or NiMH slow charge.
LED resistor R1 = 1.2k
LED drop approx 2V
Voltage across R1 approx = 5 – 2
Current = 3V / 1200
Current = 2.5mA approx
This is enough for indicator LED.
How to Build:
To build a USB Powered Small Battery Charger Circuit following are the connection steps:
- Collect all the parts as shown in circuit diagram.
- Connect USB 5V pin to switch.
- Join Switch output between one end of resistor R1 and R2.
- R2 resistor other end connect to anode of diode D1.
- Cathode of D1 connect to battery positive.
- R1 resistor connect from charging line to LED anode.
- LED cathode connect to ground.
- Battery pack two cells connect in series.
- Make sure polarity correct.
- Positive to charger line and negative to ground.
Conclusion:
This USB Powered Small Battery Charger Circuit is very simple.
Useful for slow charging small batteries, but is not suitable for Li ion battery.
Its can be used only for NiCd or NiMH batteries.
It is with low cost and easy to build and is good for hobby learning.