LCD-LED Display

Simple LED Constant Current Source Schematic Circuit Diagram

Chip manufacturers are always coming up with ever more sophisticated constant current driver chips for LEDs. We have included this design for those of you who prefer a more cheap and cheerful solution.

Simple LED Constant Current Source Schematic Circuit Diagram

Current through the LEDs produces a voltage drop across resistor R1. As the current rises to a level to produce a voltage drop of 0.6 V across R1 it will cause T2 to start conducting and shunt the gate voltage of T1 to the ground. This produces a constant current I = 0.6 V/R1 through the LEDs.

The control input allows the LEDs to be switched on by applying a voltage in the range of 5 V up to around 12 V and switched off by applying a voltage of 0 V. When this input is driven by a pulse width modulated signal it gives the possibility to change the LED brightness.

The supply voltage for all the series-connected LEDs can be as high as practical providing the maximum drain-source rating of T2 is not exceeded. The choice of T2 and any necessary heat sink will depend on the power dissipated in this device. This can be calculated from:

(Supply voltage minus the voltage drop across the LEDs) × ILED

The resistor is a passive electrical component that creates resistance in the flow of electric current. In almost all electrical networks and electronic circuits, they can be found. The resistance is measured in ohms (Ω). A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor.
The resistor absorbs the electrical energy in the process where it acts as a hindrance to the flow of electricity by reducing the voltage, and it is dissipated as heat. In today’s world of electronic circuits, heat dissipation is typically a fraction of a watt.
Types Of Resistors
  • Thermistors.
  • Varistor Resistors.
  • Photo Resistor or LDR (Light Dependent Resistors)
  • Surface Mount Resistors.

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