Summary of 400VA AC Light Dimmer
This article describes a simple 400VA TRIAC AC load dimmer for resistive loads like incandescent lamps. It controls power by adjusting the phase of the 220VAC sine wave using a potentiometer to charge a capacitor until it triggers a DIAC and fires the TRIAC. The circuit includes an interference suppression filter but operates at lethal mains voltages, requiring safety precautions like plastic spindle potentiometers.
Parts used in the 400VA AC Light Dimmer:
- R2 potentiometer
- C2 capacitor
- R1 resistor
- D1 DIAC
- T1 TRIAC
- L1 inductor
- C1 capacitor
- Plastic spindle potentiometer
This is a simple TRIAC AC load dimmer used to control the power of a resistive load such as incandescent lamp or heater element. The max load it can handle is 400VA. Such a circuit is often found on cheap commercial light dimmers and is prooven to work reliable for the rated power.
The circuit is working by controlling the phase of the 220VAC voltage allowing the load to be powered for less than 360º of the full sine wave. Powering the load for smaller period than full sine wave delivers less power, so it has a dimming effect on the load.
Control is done throught R2 potentiometer which controls the time needed for the C2 to be charged through R1-R2. C2 is charging until it reaches the breakdown voltage of DIAC D1 which then fires the TRIAC T1. Once the TRIAC is contacting the circuit is closed and the load receives power.
The rate which C2 charges determinates the point on 220VAC sinewave where it reaches the breadown voltage of DIAC. So, slow C2 charging means that the DIAC conducts at the end of AC period and fast C2 charging means that DIAC conducts at the beggining of AC sine.
Components L1 and C1 act as interference suppression filter reducing RF emmitions.
Circuit is directly connected to mains voltage, so lethal voltages present all over the board. Take care!
The potentiometer should have a plastic spindle to provide sufficient isolation
For more detail: 400VA AC Light Dimmer
- What is the maximum load this dimmer can handle?
The circuit can handle a maximum load of 400VA. - How does the circuit achieve a dimming effect?
It controls the phase of the 220VAC voltage to power the load for less than 360 degrees of the full sine wave. - Which component determines the firing point of the TRIAC?
The rate at which C2 charges determines when the DIAC reaches its breakdown voltage and fires the TRIAC. - What components act as an interference suppression filter?
Components L1 and C1 reduce RF emissions in the circuit. - Why must the potentiometer have a plastic spindle?
A plastic spindle provides sufficient isolation because the circuit is directly connected to lethal mains voltage. - Can this circuit control non-resistive loads?
The article states the dimmer is designed specifically for resistive loads such as incandescent lamps or heater elements. - What happens if C2 charges slowly?
Slow charging means the DIAC conducts at the end of the AC period. - What happens if C2 charges quickly?
Fast charging means the DIAC conducts at the beginning of the AC sine wave.
