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led dimmer

5V LED Dimmer Circuit

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.

LED Dimmer Schematic

led dimmer schematic

Printed circuit layout for the LED dimmer

led dimmer pcb

Parts placement layout for the LED dimmer

led dimmer parts

21 Comments

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  • Salim kumar

    Hlo D.Mohankumar sir plz help me to build a emergency led lamp with LDR

  • StigArne

    Planning to be used on a xmas tree.
    Output from transformer is 30V and max 0.4A.
    15 Leds in a string.
    So, I need to adjust the 30V output to something between 0 and 30.

    Suggestions for components choises ?

  • Ernie

    I like this circuit which i’ll build & put in an enclosure, i’ve substituted a few components & left out the 100r pot. i’m using an TIP122 for the Darlington & a BD139 for the other transistor also a logic 1K pot. The circuit works fine but regards the pot it basically has no affect untill its turned half way round. Then there’s only a small bit of ajustment left between Off & On of the led. I was wondering if there’s a way to make the pot work more evenlly.

  • bimolchandra;Imphl

    Any modification if I use 6v 4.5Ah battery

  • abhayadevs

    I need a large LED array of 5MM LEDs of 100Nos. Here, if i need high curretn i can go for 2N3055, but should i change T2, P1 and P2 to support enough base current?

    • Jim Keith

      Yes, the circuit may be scaled up to your higher current requirement.

      If R1 = 10K, it may power up to about 10 LEDs @ 20mA each. Or if R1 = 100Ω, it will drive 100LEDs.

      However, the next problem is that T2 now dissipates excessive power and it must be kept cool because the Vbe junction voltage is a function of temperature and this the 0.7V “voltage reference.”

      What I would do is to create a composite connection out of T2 by adding a PNP power transistor with its collector grounded. This way, the PNP transistor dissipates most of the power and T2 remains cool.

      Check out this youtube primer:
      youtube.com/watch?v=cHf73C8b9kA
      Use the first composite connection he describes.

    • Jim Keith

      Woops correction:
      If R1 = 1K, it may power up to about 10 LEDs @ 20mA each.

  • Lambert Joe

    If I change source voltage to 12V, is there any modification need to be done in order to ensure amperage n voltage not exceed the limit?
    Tq

  • elfaki Yousif

    your cercuit is good and they support me with many information but I need mor details. thanks

  • rafi

    i need a mini project

  • D.Mohankumar

    linear Potentiometer with a knob for adjustment. Not presets

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