Today I want to talk about light dimmers. These are electronic devices that control the amount of power that reaches the light element. This is done by firstly detecting when the mains voltage crosses the zero point and then waiting a preset time before switching on the triac which then allows the current to flow to the light. As soon as the mains voltage crosses the zero point, the triac switches off again and waits for the preset time before switching on. The earlier it switches on, the more power is allowed to reach the light element during that cycle and conversely the later it switches on the less power is supplied. Why is that worth discussing you may ask, use a simple RC and a triac and the dimmer is done. Yes and no. The humble dimmer has come a long way. It can still be done the RC way but nowadays consumers do not want to go to the switch anymore to control their light settings.
The buzzword is home automation made popular by the X10 range of powerline controlled dimmers, switches and other equipment that are available and cost effective. The trend however is to go completely wireless and that is why Zigbee and other standards are taking off on a grand scale. The humble dimmer must now be controlled completely wirelessly from the comfort of ones remote control and taking it a step further from the comfort of ones automated scene controlled home automation system. The power side is usually still being controlled by a triac circuit, but the communications side can now consist of a variety of different interfaces. One of the dangers of these types of circuits is that if the power circuit is not completely isolated then the rest of the circuit is effectively LIVE and needs to be worked on with utmost care. An easy solution is to use an isolated triac driver like the TLP3052 to drive the power element and a normal opto isolator to feed the zero cross data to the controlling element.
Old power side, new controlling element. The Zigbee wireless standard appears to be making inroads in the home and as more suppliers climb on board, more and cheaper applications will become available allowing consumers to do more with less (wires).
Marc Jarchow
46 year old entrepeneur providing MODular ElecTRONics solutions for the
Professional (custom instruments for your business),
Educator (can be used as a training aid),
Entrepeneur (can be packaged with your logo) and
Hobbyist (make your own home based products) using low cost modules to create custom applications. Information available at
modetron.com
Share this: