Nowadays LED lights are increasing rapidly because of their reduced cost and long durability. Generally, one can see the LED lights increasing and decreasing their intensities depending on the number of persons entering or leaving at a particular place or a room. It depends on the fading of LEDs. Here is a simple circuit that slowly fades out when it is applied with some voltage. This article explains the circuit that starts fading depending on the incoming voltage.
UP/DOWN Fading LED Lights Circuit Principle:
The circuit mainly consists of a transistor and a capacitor. Light Emitting Diode conducts in forward bias condition i.e. LED glows only when positive terminal is connected to the positive end and negative end is connected to the negative of the battery. In this proposed circuit, LED conducts only when the negative terminal is grounded as the positive terminal is applied with some voltage. When the button is pressed, the capacitor starts charging and discharging which causes the LED to fade up and down.
Also get an idea about how to make LED Christmas lights blink.
UP/DOWN Fading LED Lights Circuit Diagram:
- Capacitor – C2
- Resistors – 4 (R1, R2, R3, R4)
- Transistor ( BC 547)
- ON/OFF switch
UP/DOWN Fading LED Lights Circuit Design:
In this circuit, the power supply is connected to the On/Off switch. A 10k resistor is connected after the button to bring the button to the pull down mode. This makes the button initially low and when it is pressed, it becomes high. Switch is connected to a diode PN junction diode 1N 4007. Diode allows conducting in forward bias condition only. Diode is then connected to a resistor of resistance 330K, which is in series to another resistor of 60kOhms. Another resistor of 36k ohms is connected before the transistor for protection.
Transistor used here is a NPN transistor of series BC547. This NPN transistor is initially in off state i.e. it will not conduct. Voltage from emitter to collector flows, only if the base region is applied with some voltage. The minimum voltage required at the base of the transistor is 0.7v. When this voltage is applied, transistor breakdown occurs and voltage starts flow from emitter to collector. You may get more knowledge on NPN Transistor by reading the post – Transistor Biasing and Characteristics
Capacitor is connected in series to the resistor of 60K. The capacitor used is 220uf and 16v rated electrolytic capacitor. This capacitor is required for producing pulses to On/Off the LED.
UP/DOWN Fading LED Lights Circuit Simulation Video:
How UP/DOWN Fading LED Lights Circuit Working?
- Initially switch on the circuit.
- Then press the button.
- You can see the LED fading up. When a button is pressed, voltage flows through the diode and it then flows through a series of resistor having 330k and 60K ohms.
- A capacitor connected in parallel to the resistor is charged. This gives some voltage to the base of the transistor which starts conducting.
- Before the transistor, a resistor of 36 kohms is present to protect from over voltage.
- Thus voltage from collector flows to the emitter, which is connected to the ground.
- Thus, negative terminal of the LED is connected to the ground.
- And LED slowly starts glowing, as the capacitor continuously produces the pulses.
- When the switch is released, the LED starts slowly fading out as the capacitor is discharged.
UP/Down Fading LEDs Project Output Video:
Applications of UP/DOWN Fading LED Lights Circuit:
- This can be used in the shopping malls for fading out the lights in the places where there is no crowd.
- Fading LEDS can be used in security applications to alert something.
- These can be used in home applications.
- These can be used in cars as indicators with some changes.
Limitations of the Circuit:
- LED lights should be powered correct voltage otherwise they may be damaged.
- LEDs can change color due to age and temperature.