Simple Adjustable LED Dimmer Circuit

Want to fine tune your LED lights?

An adjustable LED dimmer circuit is your answer.

This handy bit of electronics lets you control how bright your LEDs shine giving you the perfect level of light for any situation.

By tweaking resistors, transistors and a special knob called a potentiometer the circuit adjusts the flow of electricity to the LEDs, making them dimmer or brighter as needed.

Circuit Working:

Parts List:

Presented here is a simple LED dimmer setup comprising 2 transistors,1 resistor and 2 potentiometers.

Traditional LED segment displays typically draw around 25mA per segment necessitating the use of resistors to limit current.

To regulate current across a six digit display, a minimum of 42 series resistors would be required.

However, this LED dimmer project addresses these challenges by offering brightness adjustment using minimal components.

Eliminating the need for series resistors simplifies PCB design and assembly.

Essentially, the circuit acts as a voltage regulator with adjustable output voltage.

LED brightness is directly tied to the output voltage which is variable thanks to the voltage regulator.

Potentiometer P1 allows for coarse adjustment while P2 enables finer brightness tuning.

The regulator circuit can vary its output from 0 to 4.3V.

To set up the circuit, start by zeroing the potentiometers then gradually adjust them until the desired brightness is achieved.

In a typical six segment display the total current should not exceed 1 ampere.

For instance, if each segment draws 25mA then seven segments in a six digit display would total around 1050mA slightly over 1 ampere.

Due to high current consumption transistor T1 requires proper heat sinking to dissipate excess heat.

Formulas:

The following formulas and computations are relevant in creating an adjustable LED dimmer circuit using the specified parts:

Current Passing thru the LED:

The LEDs required operating current ILED and forward voltage VLED must be known in order to calculate the current passing through the LED.

The resistors and transistors in the circuit have an impact on the current flowing through the LED.

I_LED ​= ​V_CC​−V_LED​​ / R_LED

where,

The equivalent resistance in series with the LED, or in this example, the load line resistance affected by the potentiometer and transistor, is denoted as RLED.

Resistance of Potentiometer and Control of Current:

The base current of the BC547 transistor is regulated by the potentiometer, and this in turn regulates the base current of the 2N2222 transistor.

This has an impact on LED brightness:

Base Current of BC547 IB:

I_B = V_Pot−V_BE(BC547) / R_Pot

where,

• The voltage across the potentiometer, which is movable between 0 and 5V is known as Vpot.
• ​VBEBC547 is the BC547 base emitter voltage, which is normally around 0.7V.
• The potentiometers resistance 1k is represented as Rpot.

BC547s Collector Current IC:

Using the current gain β, usually between 100 and 200, and assuming the BC547 transistor is in the active mode:

I_C​ = β × I_B​

2N2222 Transistor for Current Control:

The base current supplied by the BC547 transistor determines the collector current (I_C2N2222) of the 2N2222 transistor, which functions as a switch.

Collector Current of 2N2222 (I_C2N2222):

I_C2N2222​ = V_CC​−V_LED​−V_CE(2N2222)​​ / R_LED​

where,

• VCE2N2222 is the 2N2222s collector emitter saturation voltage, which is normally 0.2V when saturated.

2N2222s Base Current (I_B2N2222):

The BC547 transistor affects the 2N2222 base current:

I_B2N2222 ​= I_C2N2222​​ / β_2N2222​

where,

• β_2N2222​ is the current gain of the 2N2222 transistor (typically around 100).

The basis for comprehending the circuits operation is provided by these computations.

Depending on the real world circumstances and component values, adjustments can be required.

How to Build:

To build the LED dimmer circuit , you will need to follow the below mentioned steps:

Identify Components:

• Gather all the required components listed above.

Circuit Layout:

• Plan the layout of the components on your breadboard or PCB.
• Ensure you have space for the LED segment display and potentiometers.

Connect Transistors:

• Connect the transistors according to the circuit diagram.
• Typically, transistor T1 is used for current regulation.

Add Resistor:

• Connect the resistor in series with the LED segment display to limit the current.
• The value of this resistor depends on the LEDs requirements and the desired current limit.

Install Potentiometers:

• Connect the two potentiometers.
• Potentiometer P1 is for coarse adjustment, and P2 is for fine adjustment of brightness.

Wire the LED Display:

• Connect the LED segment display to the circuit, ensuring the correct polarity.

Heat Sink for Transistor T1:

• If necessary, attach a heat sink to transistor T1 to dissipate excess heat especially if the current draw is high.

Power Supply:

• Connect the power source to the circuit.

Testing:

• Turn on the power and test the circuit.
• Start with the potentiometers at their minimum settings and gradually adjust them until you achieve the desired brightness on the LED display.

Adjustments:

• Fine tune the potentiometers to adjust the brightness as needed.

Safety Precautions:

• Ensure the circuit operates within safe voltage and current limits to prevent damage to components or overheating.

Note:

• Remember to double check your connections and follow safety precautions when working with electrical circuits.
• If you are unsure about any aspect of the circuit or its construction it is advisable to consult with someone experienced in electronics or seek professional assistance.

Conclusion:

Overall, an adjustable LED dimmer circuit provides flexibility and customization options for controlling LED lighting making it a versatile solution for various lighting needs.

References:

Dimming Techniques for Switched-Mode LED Drivers

LED Dimmer only using NPN BJT and potentiometer