Triac
The triac is an active component increasingly used in montages today. Its direct use in the sector EDF makes it possible to switch loads from much smaller circuits. This component whose symbol is recalled Figure 1 theoretically works by four modes, also called quadrants, which can be summarized by the table in Figure 2 .
Figure 1
These four quadrants in fact dependent on the polarity of the anode A2 from A1 and the triac gate.
Figure 2
In the example given in Figure 3 , anode A2 will turn positive then negative while the gate is negative (removal of current) when the transistor conducts.
Figure 3
We will therefore anode A2 = A + and A-
trigger = G-
trigger = G-
Looking at the table, we say that the triac operates in quadrants 2 and 3 .
Different combinations can be obtained. I must just point out that the mode 4 be avoided, due to excessive consumption ranging above 100 mA cons only 50 mA in modes 1, 2 and 3 for a triac type 'classical'.
II models are indeed called "sensitive", requiring only low gate current of about 5 to 10 mA . This is important because the intensity of the load must be greater than the intensity of trigger, and so on dimmers trade there is, in addition to the indication of load, load indication minimum, otherwise the triac does not work.
The principle is that the triac is begun after a control pulse to zero crossing following the wave field.
The command can be impulsive and Figure 4 said such an arrangement, which is much less demanding than the continuous control of Figure 3.
Figure 4
This kind of circuit can then be fed by a network by RC from transformer if control circuit does not consume too much. A level 0 on input C blocks triac.
The engine power is maximum in this case since the triac is initiated immediately after the zero crossing of the AC voltage, but may occur in different ways for each control pulse delay in order to vary the intensity applied to the load.
A simple way to achieve this result is a network RC like the Figure 5. The offset depends on the values of these two components and R can be variable. The diac placed on the trigger allows for a phase shift even more important, it does lead until the voltage reaches 30V .
Figure 5
There are however other more sophisticated means for obtaining complete phase shifts (180 °) automatic systems for modulating the intensity according to various phenomena such as light or temperature.
The 6a and 6b indicates power applied to the load function of the delay of the control pulse relative to zero.
Figure 6a
Figure 6b
The major drawback of this type of arrangement is its ability to produce parasites and in particular on receivers MW / LW . These can be partly eliminated by the addition of a circuit comprising a network LC like the Figure 7, where the two capacitors (optional) are provided for mandatory ac class (X2) and the self calibrated according to the intensity required.
Figure 7
This provision should for circuits "dimmers", but if you just want to use the triac switch is preferable to use dedicated circuits in the zero-order wave field. We can cite for example the opto-triac JI 3041 have a "zero crossing" planned for this application and whose pinout is shown in Figure 8 .
Figure 8
Moreover, the isolation of a optotriac, some 7500 V and intensity control of a dozen milliamps provide security and ease of use for highly significant switching loads of several amperes with a voltage of 230 V or more .
Do not forget that the triacs mounts, with or without power transformer, they are not equipped optotriac or similar devices are connected directly to the mains and it must be very careful with this kind of circuit.
The Figure 9 is a universal interface for controlling various devices connected to the mains using, for example, a computer.
Figure 9
The control is performed by applying a positive level on the LED, opto triac-turn controls a triac that can be chosen according to the respective load. We can equip this interface suppression of Figure 7 .
In some cases, particularly where the load is highly inductive, it may be necessary to add a protection circuit. The Figure 10 indicates an effective way to protect the triac.
Figure 10
Finally, we must not forget to equip each of its triac sink if the power involved the need usually we start to put a radiator from a power 100 W for classic templates 6 / 8 A . Be aware however that there triacs intended for intensity 40A .
To conclude this section, the Figure 11 shows you a very simple but nevertheless sufficient, allowing you to remove doubt about how each of your triacs.
Figure 11
S1 can check the status the bulb should light, indicating the same time as the assembly is turned on.
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