WARNING :

This project is mains operated. Do not touch any part of the circuit when power is on. Electric shock can be fatal.

DESCRIPTION : This dimmer circuit can be used to control the brightness of incandescent light bulbs, the temperature of heaters & the speed of AC motors. The max. controllable power is 2KW (i.e. 2000W) * If the dimmer is being used over long period of time, we recommend load power to be limited to 800W so that TRIAC is not overheated due to the small size of heat sink.	Schematic Click on picture to enlarge

CONSTRUCTION

Step (1) :
Mount the TRIAC on the heat sink using the mounting accessories provided. Apply small amount of silicon heat transfer compound (if available) on both sides of the mica to improve heat transfer. When done, check with an ohmmeter to ensure the center pin (MT2) of the TRIAC is fully isolated from the heat sink.

Step (2) :
Insert & solder DB3 & all the resistors. Trim the leads with a cutter

Step (3) :
Insert & solder the 0.1uF capacitors (2 pcs). Trim the leads with a cutter

Step (4) :
Insert & solder the 2M Ohm trimmer pot (VR)

Step (5) :
Insert & solder the 500K Ohm potentiometer (POT)

Step (6) :
Insert & solder the 4-contact terminal block

Step (7) :
Insert the TRIAC (with heat sink) and solder the leads then trim the leads with a cutter

TEST

Step (1) :

Hook up the circuit below. DO NOT turn on the AC mains supply just yet. You can use a incandescent light bulb (40~100W) as load for testing purpose.

Step (2) : Turn the potentiometer (POT) fully counter clockwise

Step (3) : Turn the multi turn trimmer pot (VR) fully counter clockwise

Step (4) : Turn the multi turn trimmer pot clockwise until the light bulb just starts to glow. This sets the minimum output for the dimmer

Step (5) : Now turn the potentiometer (POT) clockwise slowly & the light bulb brightness should increase accordingly

CONNECTION OF MAINS INPUT & LOAD

CIRCUIT DESCRIPTION

Angle Ф is the rotation angle of the potentiometer. When potentiometer rotates counter-clockwise, Ф increases
causing the shaded area to decrease and hence the load power.

PARTS LIST

P.C.B .	Etched & drilled printed circuit board (included)
TRIAC	BTA24 25A (Datasheet) or BT138 12A (Datasheet)
DIAC	DB3, (Datasheet)
Capacitors	(C1, C2) 0.1 uF (# 104 or 100n) AC 275V capacitors (blue or black color)
Potentiometer (POT)	B500K (linear taper)
Multi turn precision trimmer (VR)	2M Ohm (#205)
Resistors	R1 --4.7K, ( 1/4W or 1/6W) R2 --100 Ω, (or 150 Ω) ( 2W)
Heat sink, 4-contact Terminal Block, Plastic knob, 3mm screw, insulator, mica (for mounting of TRIAC)

Buy the complete set of components for this project :
(all the parts in picture)