Simple USB Lamp Circuit

This circuit explains how to construct a little nightlight that runs on the USB port on a desktop or laptop.

Designing this circuit requires only a few essential components like:

Similar to USB socket which is found on the end of the cell phone charger.

An LED which produces a tiny light with low power consumption.

A resistor which includes a small component that controls the LEDs brightness.

When one requires a little additional light in a small area or during power shortages this is a useful circuit.

Circuit Working:

Parts List:

Standard A connecters another name for USB Type A connectors are rectangular and flat in shape.

The original USB connecter type A is widely used with all USB generations including 3.0, 2.0, and 1.1.

The USB Type ‘A’ connection is included in all USB models and is mainly used for host controllers in PCs and hubs.

The USB A socket is rarely used as an upstream connector on any device instead, it is designed for downstream connections to host controllers and hubs.

This circuit is simple and simply uses an LED, a USB Type ‘A’ male connector and a single 5 ohm 1 watt resistor.

The 5 ohm 1 watt resistor is perfect for powering a 3.3V 1 watt white LED since it restricts the current to 25mA.

Any unused or extra USB cable will work well for connecting this circuit.

This design is used for a laptop or computers in case of an sudden power loss.

This USB lamp circuit is connected to a portable USB port to provide quick and easy lighting in areas such as small fuse boxes or computer motherboards where it is difficult to carry a large emergency light, torch or flashlight.

Formula:

The following formula from ohms law is essential for understanding a USB lamp circuit:

R = V / I

where,

• Resistance indicated by the letter R represents an elements resistance in the circuit in ohms Ω.
• The voltage across the component is measured in units of V.
• I represents the current flow of the component measured in amps A.

Ohms law serves as the base for the calculation used to figure out the resistor value for an LED circuit:

R = (V_source – V_LED) / I_LED

where,

• Ohms Ω or R is the resistors resistance.
• The power source voltage or V is usually the battery voltage expressed in volts.
• The forward voltage drop of an LED or VLED is measured in volts V this value is found in the datasheet for common LEDs and ranges from 1.8V to 3.4V.
• The datasheet for the LED also mentions the desired current ILED which is measured in amps A and is normally between 10 mA and 30 mA for small LEDs.

How to use the formula:

Generate the data:

Find out the power sources voltage from the datasheet.

Vsource the LEDs designed current ILED and forward voltage VLED.

Put the values in:

Replace the values in the formula.

Find out the resistance:

Calculate R by solving; the result will be the resistance value in ohms which the resistor needs.

How to Build:

Building a USB Lamp Circuit follow the below mentioned steps:

Find the Type ‘A’ USB Connector:

• Always ensure that the plug is a male USB Type ‘A’.
• This rectangular flat connection is often seen in USB cables.

Assemble the parts:

• Gather the brilliant white LED and the 1 watt 5 ohm resistor.
• Check that the resistor can manage the LEDs power rating.

Choose a right resistor:

• To keep the current at 25mA and assure the LED functions properly a 5 ohm 1 watt resistor is essential.
• Check the features of the LED one is using and use the above mentioned ohms law calculation to modify the resistance.

Connect the resistor to the LED:

• Connect the resistors first leg to the LEDs longer leg anode.
• The resistors other leg is connected to the power Vcc line through USB Type ‘A’ connections.

Connect the LEDs shorter leg:

• The ground line of the USB Type ‘A’ connection should be connected to the LEDs shorter leg cathode.

Put the Circuit Together:

• Jumper wires can be used to put the circuit together on a PC if you have one.
• Follow the instructions in previous steps to connect the components.
• The components are soldered together on a PCB while not in use.

Connect to a USB port:

• Connect the male USB Type ‘A’ connection to a laptops USB port or any other USB power supply.

Check the circuit:

• After being connected the LED should begin to light up providing emergency light.

Use:

• Connect the USB Lamp Circuit to a USB port for quick lighting in situations where standard emergency lights are not possible such as during a power failure or in small rooms.

Conclusion:

A project that could offer fans or beginners with an enjoyable and informative introduction to simple electronics is the USB Lamp Circuit.

It shows how useful USB connections are for powering tiny electrical devices and goes beyond data transfer and power charging.

References:

USB-Powered PC Lamp