This is a very simple LED dimmer circuit which has 2 transistors, 1 resistor and 2 potentiometers. Typical segment displays LEDs consume around 25 mA for each segment and should be limited to this value by using resistors. If a six digit display is to be current limited, at least 42 series resistors are needed. To counter the above described problems, this led dimmer project allows you to do the adjustment of the LED display’s brightness using just a few components.
The series resistors are not needed anymore for the segment display which simplifies the pcb design and contruction. The circuit is simply a voltage regulator with variable voltage output.
The brightness of the LEDs are dependent on the output voltage. Since the voltage regulator is variable, the brightness of the LEDs is also variable. Potentiometer P1 is used for rough adjustment while P2 is used to trim the brightness in finer resolution. The output of the regulator circuit can be varied from 0 to 4.3 volts.
Before tuning the circuit, set the pot to zero point, then slowly adjust the pots until the desired brightness is achieved. In a typical six segment disply, the maximum current must not exceed 1 ampere. For example: if one segment consumes 25 mA each, then 7 segments of a six digit display will consume around 1050 mA. That is a bit more than 1 ampere! The transistor T1 must be heatsinked because high current consumption will produce a lot of dissipated heat.
Printed circuit layout for the LED dimmer
Parts placement layout for the LED dimmer