The basic USB Lamp Circuit is an excellent choice for portable lighting.
It is user friendly and draws power from a USB port that gives 5 volts.
Additionally, it features a rechargeable battery, which enhances its versatility for various portable lighting applications needs.
Remember the USB port can only deliver up to 100 mA so it is wise to limit the number of LEDs to stay within this range.
The circuit consists of essential components such as a transistor, diodes, capacitor, resistors and LEDs all collaborating to create reliable illumination.
Circuit Working:
Parts List:
| Component Type | Specification | Quantity |
|---|---|---|
| Resistors (1/4W unless specified) | 560Ω | 1 |
| 22Ω 1W | 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 | |
| Power Source | Ni-Cd Cells 1.2V × 2 | 1 |
| Switch | On/Off Switch | 1 |
| Input Connector | USB port male connector | 1 |
The circuit gets its energy from a USB port that provides 5V.
Resistor R3 controls the current flowing to LED1 indicating if the power is on or off.
Diodes D1 and D2 both 1N4007 types prevent any backward current and assist in managing the charging process.
Capacitor C1 helps to stabilize any fluctuations in voltage.
Transistor Q1 BC557 manages the charging and discharging of the battery.
When switch S1 is activated the energy stored in the Ni-Cd battery powers the white LEDs (LED2 and LED3)
This arrangement allows the LEDs to operate independently of the USB power as the rechargeable battery can supply energy when needed.
Formulas with Calculations:
Below are the formulas with calculations for Simple USB Lamp Circuit for Portable Lighting
Charging Current (I):
Using ohms Law:
I = V / R
where,
- i is the charging current in amperes
- v is the voltage in volts
- r is the resistance in ohms
The charging resistor R2 22Ω 1W limits current.
Circuit operates a USB voltage of 5V
I = 5V
22Ω = 0.23A
Power dissipation of R2 resistor
P = I ^ 2 * R
P = (0.23) ^ 2 * 22 = 1.1 W
A 1W resistor is chosen to handle this power safely
Led Current Limiting:
I = (V_battery – V_led) / R1
where,
- i is the charging current in amperes
- v_battery is the voltage of the rechargeable battery
- v_led is the forward voltage drop across the led
- R1 is the series resistor 560Ω in the circuit diagram
How to Build:
To build a Simple USB Lamp Circuit for Portable Lighting following steps are needed for connections which should be followed:
- Assemble all the components as mentioned in the above circuit diagram
- Connect resistor R3 one terminal to USB port one end and other terminal of R1 resistor connect to anode of LED1 and cathode of LED1 connect to GND
- Connect resistor R2 one terminal to the junction of USB one end and one terminal of resistor R1, connect the resistor R2 other terminal to emitter of transistor Q1
- Connect anode of diode D2 between resistor R2 and capacitor C1 and cathode of diode D2 connect to base of transistor Q1
- Connect resistor R1 one terminal between the base of transistor Q1 and cathode of diode D2 and other terminal of resistor R1 connect to GND
- Connect the collector of transistor Q1 to anode of diode D1 and cathode of diode D1 connect to positive of Nicd battery and negative of battery connect to GND
- Connect switch S1 one end to positive of battery and other end of switch connect to anode of LED2 and cathode of LED2 connect to anode of LED3 and cathode of LED3 connect to GND
- Connect the other end of USB port to the GND of the circuit
Conclusion:
This Simple USB Lamp Circuit for Portable Lighting is a easy and efficient way to meet low power lighting needs.
It makes good use of USB power and also has a battery backup feature.
The design is affordable and simple to assemble, which makes it perfect for DIY fans and electronics lovers.