LEDs are super cool and efficient light sources that are everywhere these days.
This post will show how to make an LED light that slowly fades in and out.
It might sound fancy but only few circuits parts and a classic chip called a 555 IC is needed.
What is a LED Fading Circuit using IC 555:
An IC 555 based LED fading circuit smoothly adjusts an LEDs brightness to generate an eye catching effect.
LED dimming or LED fading are two typical terms used to describe this process.
A pulse width modulated PWM signal is generated by the IC 555 in astable mode and the LEDs brightness is then controlled by this PWM signal.
How to Build:
Parts List:
| Category | Component | Quantity |
|---|---|---|
| Resistors | ||
| 47k 1/4W CFR | 1 | |
| 330Ω 1W CFR | 1 | |
| Capacitors | ||
| Electrolytic 100μF 25V | 1 | |
| Semiconductors | ||
| IC 555 | 1 | |
| Transistor BC547 | 1 | |
| Battery 9V | 1 | |
| LEDs | 3 |
Apply positive supply to pin 8 and pin 4 with pin 4 connected to VCC to prevent unwanted resets.
Connect negative or ground to pin 1.
Pin 5 is grounded through a 0.1μF capacitor for accuracy in the voltage divider network.
Pins 2 and 6 are interconnected to get a stable trigger level connection with timing capacitor C1.
Pin 7 is left unused maintaining an open circuit to prevent toggling ON and OFF effect.
Pin 3 is connected to the transistor base and charging capacitor through R1 resistor.
LEDs are connected to the emitter pin of Q1 through R2.
Circuit Functions:
The 555 IC is controlled by the charging and discharging cycle formed by the 100μF capacitor C1 and the 47k resistor R1.
The charging and discharging of the capacitor works as a gradual ON/OFF switch allowing the voltage levels at the transistor base to slowly rise and fall.
The LEDs that generate the attractive fading effect are controlled by this control over current flow.
Role of BC547 NPN Transistor:
In this circuit the BC547 NPN bipolar junction transistor is an important semiconductor component.
The BC547 is suitable for low power amplification tasks because of its maximum current rating of 100 mA and voltage rating of 45V.
It works well in minor signal amplification due to its usual current gain hFE ranging from 110 to 800.
The BC547 which comes in TO92 packaging is widely used in oscillator circuits, signal processing and audio amplification.
It offers simplicity and consistency.
This transistor serves as a switch in this project regulating the LEDs fading effect.
Formulas and Calculations:
Below are the formulas with calculations for Simple LED Fading Circuit using IC 555:
Timing Elements Calculation:
Calculating the charging and discharging cycle depends strongly on the timing components in this circuit especially the 100μF capacitor C1 and the 47k resistor R1.
The formula listed below is used to calculate the RC circuits time constant (τ):
τ = R × C
For
R1 = 47k and C1 = 100μF:
τ = 47,000Ω × 100 × 10 − 6 F = 4.7 s
Frequency Calculation:
The frequency of the circuit calculates the rate at which the LEDs fade in and out by the given formula:
f = 1 /2 × τ
Substituting the calculated value of τ:
f = 1 / 2 × 4.7 Hz = 0.106 Hz
Transistor Base Resistor R2 formula:
For the transistor to be biased in the ON state the base resistor R2 is essential.
Ohms law is used to calculate the base current IB:
IB = VCC − VBE / R2
where,
- IB is the base current of the BJT.
- VCC is the supply voltage connected to the collector side of the transistor.
- VBEis the base emitter voltage drop which is around 0.7V for silicon BJTs
- R2 resistor is the base leg of the circuit through which base current flows.
The circuits timing factors are shown by these calculations which also help in choosing the right component values for transistor biasing and the required fading effect frequency.
Value adjustments for resistors and capacitors is done in response to the particular needs of the project.
Conclusion:
This article provides the techniques of creating an exciting LED fading effect by pairing the old 555 IC with the adaptable BC547 transistor.
To build their own captivating lighting projects it bring a little charm to the world of electronics, the hobbyists can begin by learning about the complex relations between components and the circuit design.