Slow Start, Fade Lamp Dimmer Circuit

This article for Slow Start, Fade Lamp Dimmer Circuit show how to make light dimmer switch; here the light becomes slowly bright when turn ON and goes slowly dark when turn OFF.

Also, this type of circuit looks very nice for bedroom or living room.

Circuit Working:

Parts List:

Components	Values	Quantity
Resistors (All resistors are 1/4 watt unless specified)	10k	1
	68k	1
	1M	1
	22k	1
	470Ω	1
	Potentiometer 500k	1
	Potentiometer 22k	1
Capacitors	PPC 0.1μF 400V	2
	Electrolytic 1000μF 16V	1
Semiconductors	Transistor BC547	1
	Diac DB3	1
	Triac BT136	1
	LED (in light-proof box)	1
	LDR (in light-proof box)	1
	Switch ON/OFF	1
	Diode 1N4148	1
	Bulb 220V	1

This circuit is for auto light dimmer which makes light slowly turn ON and OFF.

When switch S1 is ON then capacitor C1 start charging slowly and LED blink when transistor T1 start working, after voltage on C1 become 0.6V.

Also, when voltage goes more high then T1 give more current so LED become more bright and when LED turns ON LDR get low resistance and so Triac switches fast again and again.

Hence, because of this light slowly turns ON.

When switch S1 turns OFF capacitor C1 discharge slowly at base of transistor T1 so LED does not go OFF fast; so LED become less bright slowly and then fully OFF and this makes nice fade out.

So we need to adjust P2 so voltage on D1 anode is near 0.7V and this setup keep capacitor voltage near 0.5V when light is OFF and in standby.

Formula:

RC time delay formula is use to find time constant in resistor and capacitor (RC) circuit shown above.

Also, time constant (τ) show how long it take for voltage on capacitor to go around 63.2% of max value when charging or discharging.

RC Time Constant Formula:

τ = R * C

where:

• τ is time constant in seconds
• R is resistor value in ohms
• C is capacitor value in farads

To find how long charging or discharging takes, multiply time constant (τ) by number for how much voltage we want.

People mostly use 63.2% because it equals 1 – 1/e where, e is a mathematical constant.

When charging from 0% to 63.2%:

Tcharge = 0.693 * τ

When discharging from 100% to 36.8%:

Tdischarge = 0.693 * τ

In RC circuit the capacitor voltage usually follow this delay time.

How to Build:

To build a Slow Start, Fade Lamp Dimmer Circuit following steps are important for connections process:

• First, connect T1 emitter to ground and connect T1 collector to one side of LED.
• Next, connect triac anode to T1 collector and connect triac cathode to power supply positive (+).
• After that, other side of LED goes to ground.
• Also, one side of LDR goes to base of T1 and other side of LDR goes to cathode of D1.
• Then anode of D1 connect to place where SCR anode and T1 collector meet.
• Now, one side of C1 goes to base of T1 and other side of C1 goes to anode of D1.
• One end of R1 connects to base of T1 and other end of R1 connects to anode of D1.
• One side of P2 goes to where T1 base, C1 and R1 join and other side of P2 goes to ground.
• Also, one side of S1 goes to place where T1 base, C1, R1 and P2 meet and other side of S1 goes to power supply positive (+).

Modifications:

• First, turn potentiometer P2 to make D1 anode voltage around 0.7V and then choose resistor, capacitor, transistor value based on circuit need and part type.

Power:

• When we press switch S1 and turn the power ON, the LED slowly turns ON and when we release S1, the LED gradually fades and turns OFF.

Take Note:

• Check all wires and parts two times to be sure and correct and if anyone do not know much about electronics then ask someone who know or visit an technician.

Conclusion:

To conclude, this Slow Start, Fade Lamp Dimmer Circuit use different parts to make slow ON and OFF light.

Always use correct circuit diagram and right parts for good result and also be careful and follow safety when working with electric things.