Universal Triac Control Module with ATmega Switch and dim a variety of loads

摘要

Everyone involved in electronics knows more or less what thyristors and triacs are, how they work and how they are used. However, these components offer so many possibilities that only specialists are able to fully exploit their potential. Nowadays thyristors are mainly used in special applications with high voltages (above 1 kV) and strong currents (many kiloampères), so this article only focuses on triacs. First we look at the basic operation of triacs and the relevant parameters. Then we describe the circuitry of the control module. Figure 1 shows the author’s finished prototype. Many functions are possible with this combination of an ATmega microcontroller and a triac. Depending on the firmware, the module can be used as a simple switch or remote switch, a timer, a dimmer, or a soft-start module for switching inductive loads such as transformers or motors. A triac is a semiconductor switch that conducts current in both directions when it is switched on, which means it is an AC switch. The load current flows through the two electrodes T1 and T2 (here ‘T’ stands for ‘terminal’). These electrodes are also designated MT1 and MT2 (for ‘main terminal’), and in the past they were also called A1 and A2 (for ‘anode’). The third electrode is the gate (G), which is the control lead. Figure 2 shows the Elektor circuit diagram symbol for a triac (on the left) and a simple equivalent circuit (on the right).