AC Triac Dimming

AC Triac dimming has been applied to incandescent lamps and energy-saving lamp dimming methods earlier, and is currently the most widely used dimming method for LED dimming.AC Triac dimming is a kind of physical dimming. Starting from AC phase 0, the input voltage is chopped, and there is no voltage input until the AC Triac is turned on.Its working principle is to produce a tangential output voltage waveform after cutting the input voltage waveform through the conduction angle.

Applying the tangential principle can reduce the effective value of the output voltage, thereby reducing the power of the ordinary load (resistive load).AC Triac dimmers have the advantages of high adjustment accuracy, high efficiency, small size, light weight, and easy long-distance operation, and occupy a dominant position in the market.

The advantages of SCR dimming are higher working efficiency, stable performance and low dimming cost.

The unidirectional AC Triac consists of 4 layers of semiconductors, with 3 PN junctions: anode A, cathode K, and control electrode G, as shown below:

One-way AC Triac text symbol: AC Triac (Silicon Controlled Rectifier), CT, KG, etc. Graphic symbols:

The conditions for the AC Triac to turn on are:

A positive voltage is applied between the anode and the cathode, while a positive trigger voltage is applied to the control electrode

There are 2 ways to turn off the AC Triac:

1. Reduce the anode current to be less than its conduction maintenance current (maintenance current: the minimum forward current required to keep the AC Triac in conduction under the specified ambient temperature and the control pole is disconnected)

2. Cut off the anode power supply

For a one-way AC Triac, it mainly depends on its 5 parameters:

Rated forward average current, maintenance current, control electrode trigger voltage and current, forward blocking peak voltage, reverse blocking peak voltage

AC Triac dimming principle:

The picture shows the leading-edge phase-cut AC Triac dimming circuit. When the voltage on C2 reaches or exceeds the positive trigger voltage of the AC Triac G, the AC Triac will turn on at the leading edge of each AC voltage. When the AC Triac current drops When it reaches below its holding current, the AC Triac turns off, and must wait until C2 is recharged to above the positive trigger voltage of its G pole before turning on again. By adjusting the resistance value of R2 to change the charging speed of C2, the phase angle of the AC Triac conduction can be changed, and the range of change is close to 0°-180°