USB Lamp Circuit for Portable Lighting is good for portable light.
It is easy to use and takes power from USB port of 5V.
It have rechargeable battery which are more useful.
USB port give only 100 mA so use LEDs less.
Circuit have transistor, diodes, capacitor, resistors, LEDs for good light.
Circuit Working:
Parts List:
| Component Type | Specification | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | 560Ω | 1 |
| 22Ω 1 watt | 1 | |
| 1kΩ | 1 | |
| Capacitors | Ceramic 0.01µF | 1 |
| Semiconductors | BC557 PNP Transistor | 1 |
| 1N4007 Diodes | 2 | |
| Red LED 5mm, 20mA | 1 | |
| White LED 5mm, 20mA | 2 | |
| Ni-Cd Cells 1.2V × 2 | 1 | |
| On/Off Switch | 1 | |
| Input connector for USB port male connector | 1 |
Circuit takes power from USB port of 5V.
R3 resistor limit current to LED1 for power ON/OFF show.
D1 and D2 1N4007 diodes stop reverse current and help charging.
C1 capacitor make voltage stable.
Q1 BC557 transistor control battery charge and discharge.
When switch S1 is ON then Ni-Cd battery give power to LED2, LED3.
LEDs can work without USB and battery give power when we need.
Formulas with Calculations:
Formulas for USB Lamp Circuit:
Charging Current (I):
I = V / R
where,
- V is 5V USB
- R2 is 22Ω
- I = 5 / 22 = 0.23A
Power in R2:
P = I² × R = (0.23)² × 22 = 1.1W
This is used for 1W resistor for safe limit.
LED Current Limit:
I = (V_battery – V_led) / R1
where,
- V_battery is rechargeable battery voltage
- V_led is LED forward voltage
- R1 is 560Ω as from diagram.
How to Build:
To build a USB Lamp Circuit for Portable Lighting following steps are needed for connections which should be followed:
- Assemble all parts like in circuit diagram.
- Connect R3 one end to USB positive and other end of R3 to R1 then to anode of LED1 and LED1 cathode to GND.
- Connect R2 one end to same USB positive junction where R3 joins and other end of R2 to emitter of Q1.
- Put D2 anode at junction between R2 and C1 and D2 cathode to base of Q1.
- Connect R1 between base of Q1 and D2 cathode and other end of R1 to GND.
- Connect Q1 collector to anode of D1 and D1 cathode to positive of Ni-Cd battery and battery negative to GND.
- Connect S1 one end to positive of battery and other end of S1 to anode of LED2 and LED2 cathode to anode of LED3 and LED3 cathode connect to GND.
- Connect USB GND to circuit GND.
Conclusion:
USB Lamp Circuit for Portable Lighting is a very useful project for beginners.
It uses USB 5V and battery backup.
Circuit is cheap, easy to build and is good for DIY.