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
Printed circuit layout for the LED dimmer
Parts placement layout for the LED dimmer
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Ricardo J
Does anyone have equivalent part numbers for the transistors in this circuit? I can’t seem to find them listed. Thanks!
Both the transistors used in the circuit are high current types. Use any high current NPN like BD 130 even though it is rated 1 A only. If more current is required use 2N 3055
Hi my doctor for an air conditioner remote control using SMS requires need help getting it introduced me to your site or internal circuit? Thanks
Correction NPN transistor BD 139
Thanks for the quick response! I’ll use the BD139 for T1. Any suggestions for T2?
Use BD139 as T2
Thanks again for the information! — I’m planning to use this circuit to dim 39 white LEDs in parallel (a current draw of approximately 780mA). What wattage rating would you suggest for P1, P2, and R1? Should the pots be linear or log taper?
P1 and P2 can be 100 and 500 Ohms Linear pots(Volume control type) and R1 1W
Thanks for your help. Just to clarify, should the minimum power rating for the pots be 1W, or will a lower wattage rating be sufficient (1/4W, for instance)? Also, when you say “volume control type” does this imply the pots should have an audio taper, or will the circuit work best with linear pots?
linear Potentiometer with a knob for adjustment. Not presets
i need a mini project
thank
your cercuit is good and they support me with many information but I need mor details. thanks
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
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?
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.
Woops correction:
If R1 = 1K, it may power up to about 10 LEDs @ 20mA each.