TRIAC Light Dimmer

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This little circuit can be used to dim lights up to about 350 watts. It uses a simple, standard TRIAC circuit that, in my expirience, generates very little heat. Please note that this circuit cannot be used with fluorescent lights.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1	1	50K Pot
R2	1	15K 1/2W Resistor
C1, C2	2	0.068 250V Capacitor
L1	1	Lamp To Be Controlled (up to 350 watts)
L2	1	Neon Lamp
TR1	1	40502 TRIAC
MISC	1	Case, Knob, Heatsink For TR1, Wire, Socket For L1

Notes

This circuit is for 117VAC only. 220 or 240 V will burn up the circuit. L1 can be a maximum of 350 watts.

The circuit must be installed and used in a case.

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Comments

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John Dickens TRIAC Light Dimmer Wednesday, December 17, 2014 12:40:47 PM

Hi -- thanks for the video & schematic. I am new to circuitry, and there are a few things I don't understand in this schematic/video. 1. What is the purpose of the neon light? Does it do the same thing as a DIAC? 2. What does the capacitor do in this situation? What purpose does it serve? 3. In the potentiometer pot, which wires go to which port? 1, 2, 3? In a traditional dimmer switch I bought at Home Depot, it only had black wires (and a green ground). Would the 'black' go to port 1, 2, or 3 in the potentiometer (i got a 600V one). 4. If I want to make this a dimmer switch, do both the white and black wires from the plug/DC adapter need to be soldered to this circuit board? Thanks in advance, your video is really cool. J

milan TRIAC Light Dimmer Wednesday, June 27, 2012 3:22:31 PM

it works... Although it's difficult to find 2N2222 & 2N3904 transistors
(Editor's notes: Those are the two most standard NPN transistors in the world.)

anonymous TRIAC Light Dimmer Monday, December 05, 2011 4:16:45 PM

has anyone modified the circuit to be used with 220V???

E. Murphy TRIAC Light Dimmer Tuesday, December 28, 2010 7:04:12 PM

Why follow the crowd? A neon bulb is a known gas discharge voltage reference. It may well be that it doesn't do as well as a diac, but let's face it, a light bulb dimmer ain't exactly rocket science! I'd thought (yesterday) of using one to reduce 120VAC to a clipped +/- 60 V or so, rather than use a step-down transformer for a zero-crossing detector. Why? Faster changing AC voltage going in than 12VAC would be to the comparator. Get a life, folks, independent thought that doesn't always look quite right keeps the brain stimulated. Or did you come from a modern college that crushes that?

anonymous TRIAC Light Dimmer Monday, March 08, 2010 5:50:14 AM

Much better if you will use a diac than neon lamp.

anonymous TRIAC Light Dimmer Sunday, March 29, 2009 2:43:20 PM

The neon lamp in the circuit above (L2) can be replaced with a diac. When the diac's breakover voltage is exceeded, the triac gets fired. What do you think of this modification?

asskicker TRIAC Light Dimmer Friday, March 06, 2009 11:03:29 PM

this project is very bad

anonymous TRIAC Light Dimmer Friday, January 30, 2009 10:44:42 AM

1: how can you make this use more channels (16 or so) and 2: what actually controlls the dimming of this and 3:will this work with leds and not have a flickering problem ??? If not how can you make it work with leds so there is no flickering problem as it is dimmed..

anonymous TRIAC Light Dimmer Wednesday, January 28, 2009 7:22:45 PM

Why does the circuit have a neon lamp? Can it be replaced, if so, by what?

anonymous TRIAC Light Dimmer Tuesday, August 05, 2008 9:48:59 PM

can i have circuit to dim DC by dimming AC only?

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John Dickens	TRIAC Light Dimmer	Wednesday, December 17, 2014 12:40:47 PM
Hi -- thanks for the video & schematic. I am new to circuitry, and there are a few things I don't understand in this schematic/video. 1. What is the purpose of the neon light? Does it do the same thing as a DIAC? 2. What does the capacitor do in this situation? What purpose does it serve? 3. In the potentiometer pot, which wires go to which port? 1, 2, 3? In a traditional dimmer switch I bought at Home Depot, it only had black wires (and a green ground). Would the 'black' go to port 1, 2, or 3 in the potentiometer (i got a 600V one). 4. If I want to make this a dimmer switch, do both the white and black wires from the plug/DC adapter need to be soldered to this circuit board? Thanks in advance, your video is really cool. J
milan	TRIAC Light Dimmer	Wednesday, June 27, 2012 3:22:31 PM
it works... Although it's difficult to find 2N2222 & 2N3904 transistors (Editor's notes: Those are the two most standard NPN transistors in the world.)
anonymous	TRIAC Light Dimmer	Monday, December 05, 2011 4:16:45 PM
has anyone modified the circuit to be used with 220V???
E. Murphy	TRIAC Light Dimmer	Tuesday, December 28, 2010 7:04:12 PM
Why follow the crowd? A neon bulb is a known gas discharge voltage reference. It may well be that it doesn't do as well as a diac, but let's face it, a light bulb dimmer ain't exactly rocket science! I'd thought (yesterday) of using one to reduce 120VAC to a clipped +/- 60 V or so, rather than use a step-down transformer for a zero-crossing detector. Why? Faster changing AC voltage going in than 12VAC would be to the comparator. Get a life, folks, independent thought that doesn't always look quite right keeps the brain stimulated. Or did you come from a modern college that crushes that?
anonymous	TRIAC Light Dimmer	Monday, March 08, 2010 5:50:14 AM
Much better if you will use a diac than neon lamp.
anonymous	TRIAC Light Dimmer	Sunday, March 29, 2009 2:43:20 PM
The neon lamp in the circuit above (L2) can be replaced with a diac. When the diac's breakover voltage is exceeded, the triac gets fired. What do you think of this modification?
asskicker	TRIAC Light Dimmer	Friday, March 06, 2009 11:03:29 PM
this project is very bad
anonymous	TRIAC Light Dimmer	Friday, January 30, 2009 10:44:42 AM
1: how can you make this use more channels (16 or so) and 2: what actually controlls the dimming of this and 3:will this work with leds and not have a flickering problem ??? If not how can you make it work with leds so there is no flickering problem as it is dimmed..
anonymous	TRIAC Light Dimmer	Wednesday, January 28, 2009 7:22:45 PM
Why does the circuit have a neon lamp? Can it be replaced, if so, by what?
anonymous	TRIAC Light Dimmer	Tuesday, August 05, 2008 9:48:59 PM
can i have circuit to dim DC by dimming AC only?