Application of triac

What is triac used for? It finds applications in switching, phase control, chopper designs, brilliance control in lamps, speed control in fans, motors etc. Applications of Triac Next to SCR, the triac is the most widely used member of the thyristor family. In fact, in many of control applications , it has replaced SCR by virtue of its bidirectional conductivity. Motor speed regulation, temperature control, illumination control, liquid level control, phase control circuits, power switches etc.

As we know that the SCR as a unidirectional device and has a reverse blocking characteristics that prevents the current flow in reverse biased condition. But for many applications, bidirectional control of current is require particularly in AC circuits. To achieve this with SCRs, two SCRs must be connected in anti-parallel to control over both positive and negative half cycles of the input.

These are often used in motor speed controllers, AC circuits, pressure control systems, light dimmers and other AC control equipments. See full list on electronicshub. The triac is an important member of the thyristor family of devices. TRI means that the device consisting of three terminals and AC means that it controls the AC power or it can conduct in both directions of alternating current.

The triac has three terminals namely Main Terminal 1(MT1), Main Terminal (MT2) and Gate (G) as shown in figure. If MTis forward biased with respect to MT then the current flows from MTto MT2. Similarly, if the MTis forward biased with respect to MT then the current flows from MTto MT1. The above two conditions are achieved whenever the gate is triggered with an appropriate gate pulse.

Similar to the SCR, triac is also turned by injecting appropriate current pu. A triac is a five layer, three terminal semiconductor device. The terminals are marked as MT MTas anode and cathode terminals in case of SCR.

And the gate is represented as G similar to the thyristor. The gate terminal is connected to both Nand Pregions by a metallic contact and it is near to the MTterminal. The terminal MTis connected to both Nand Pregions, while MTis connected to both Nand Pregions. Hence, the terminals MTand MTconnected to both P and N regions of the device and thus the polarity of applied voltage between these two terminals decides the current flow through the layers of the device.

With the gate open, MTis made positive with respect to MTfor a forward biased traic. Similarly for a reverse biased triac , MTis made negative with respect to MTwith gate open. Until the voltage across the triac is less than the. The four possible electrode potential combinations which make the triac to operate four different operating quadrants or modes are given as. MTis positive with respect to MTwith a gate polarity positive with respect to MT1.

MTis negative with respect to MTwith a gate polarity negative with respect to MT1. In general, latching current is higher in second quadrant or mode whilst gate trigger current is higher in the fourth mode compared with other modes for any triac. Most of the applications, negative triggering current circuit is used that means and quadrants are used for a reliable triggering in bidirectional control and also when the gate sensitiv. The traic function like a two thyristors connected in anti-parallel and hence the VI characteristics of triac in the 1st and 3rd quadrants will be similar to the VI characteristics of a thyristors.

A small leakage current flows through the device provided that voltage across the device is lower than the breakover voltage. Once the breakover voltage of the device is reache then the triac turns ON as shown in below figure. However, it is also possible to turn ON the triac below the VBO by applying a gate pulse in such that the current through the device should be more than the latching current of the triac.

Similarly, when the terminal MTis made negative with respect to MT the traic is in reverse blocking mode. Triac can be triggered by both positive and negative polarity voltages applied at the gate. Hence the positive or negative pulse to. As compared with the anti-parallel thyristor configuration which requires two heat sinks of slightly smaller size, a triac needs a single heat sink of slightly larger size.

In DC applications, SCRs are required to be connected with a parallel diode to protect against reverse voltage. But the triac may work without a diode, a safe breakdown is possible in either direction. Due to the bidirectional control of AC, triacs are used as AC power controllers, fan controllers, heater controllers, triggering devices for SCRs, three position static switch, light dimmers, etc.

Triac as a switch and phase control applications are discussed below. When the switch is closed the phase voltage is applied to the gate pin. In that case the gate pin will also be isolated using an opto-coupler.

The circuit diagram for the same is shown below. V through the Light Emitting Diode. Normally a PWM signa. This is because of the internal capacitance of present between the terminals MTand MT2. The easiest way to overcome this problem is by using a Snubber circuit.

In the above circuit, the Resistor R(50R) and the Capacitor C(10nF) together form. When the POT is turned to minimum value, no voltage will be applied to gate pin and thus the Load will be turned off. The larger the load current is the worse will be the interference. Using Suppressor circuits like an LC suppressor will solve this problem. It acts just like two SCRs connected in back to back fashion and also share the same properties.

But, they do not trigger symme. Triac find its applications in electric motors. It is used in AC controlling. Effective are obtained while controlling AC power with the help of triac.

As triac ’s are directly attached to ac sources so there is a need to ensure proper safety while circuit testing. Triacs can be used for implementing a variety of useful circuit concepts. Triacs are widely used in AC power control applications.

This makes triac circuits ideal for use in a variety of applications where power switching is needed. One particular use of triac circuits is in light dimmers for domestic lighting, and they are also used in many other power control situations including motor control. As a result of their performance, trials tend to be used for low to medium power applications, leaving thyristors to be used for the very heat duty AC power switching applications. They are often used in low to medium power AC switching requirements. The basic triac symbol used on circuit diagram indicates its bi-directional properties.

Like a thyristor, a triac has three terminals. However the names of these are a little more difficult to assign, because the main current carrying terminals are connected to what is effectively a cathode of one thyristor, and the anode of another within the overall device. There is a gate which acts as a trigger to turn the device on. In addition to this the other terminals are both called Anodes, or Main Terminals These are usually designated Anode and Anode or Main Terminal and Main Terminal (MTand MT2). When using triacs it is both MTand MThave very similar properties.

Before looking at how a triac works, it helps to have an understanding of how a thyristor works. In this way the basic concepts can be grasped for the simpler device and then applied to a triac which is more complicated. For the operation of the triac , it can be imagined from the circuit symbol that the triac consists of two thyristors in parallel but around different ways. The operation of the triac can be looked on in this fashion, although the actual operation at the semiconductor level is rather more complicated. The triac structure is shown below and it can be seen that there are several areas of n-type and p-type material that form what is effectively a pair of back to back thyristors.

It can conduct current irrespective of the voltage polarity of terminals MTand MT2. It can also be triggered by either positive or negative gate currents, irrespective of the polarity of the MTcurrent. The typical IV characteristic of a triac can be seen in the diagram below with the four different quadrants labelled. Although these devices operate very well, to get the best performance out of them it is necessary to understand a few hints on tips on using triacs.

This in harmonics being generated: the less symmetrical the triac fires, the greater the level of harmonics that are produced. To help in overcoming the problem of the triac non-symmetrical firing, and the resulting harmonics, a device known as a diac (diode AC switch) is often placed in series with the gate of the triac. The inclusion of this device helps make the switching more even for both halves of the cycle.

This from the fact that the diac switching characteristic is far more even than that of the triac. Since the diac prevents any gate current flowing until the trigger voltage has reached a certain voltage in either direction, this makes the firing point of the triac more even in both directions. Triac circuits for use as dimmers are widespread and they are simple and easy to implement. Triacs have many specifications that are very similar to those of thyristors, although obviously they are intended for triac operation on both halves of a cycle and need to be interpreted as such. However as their operation is very similar, so too are the basic specification types.

Parameters like the gate triggering current, repetitive peak off-state voltage and the like are all required when designing a triac circuit, ensuring there is sufficient margin for the circuit to operate reliably. However, without making the voltage high, it can be turned on by applying the gate pulse of micro seconds to turn it on. The name DIAC comes from the words DIode AC switch.

These electronic components are also widely used in starter circuits for fluorescent lamps. As discrete components they may be contained in small leaded packages, they can be obtained in surface mount packages, in large packages that bolt to a chassis, or a variety of other packages. DIACs come in a variety of formats. DIAC circuits use the fact that a DIAC only conducts current only after a certain breakdown voltage has been exceeded. The actual breakdown voltage will depend upon the specification for the particular component type.

When the DIAC breakdown voltage occurs, the resistance of the component decreases abruptly and this leads to a sharp decrease in the voltage drop across the DIAC, and a corresponding increase in current. When the current falls below the holding current, the DIAC switches back to its high resistance, or non-conducting state. Despite this, for large applications, two thyristors are generally used.

Interestingly their behaviour is somewhat similar to that of a neon lamp, although they offer a far more precise switch on voltage and thereby provide a far better degree of switching equalisation. To resolve the issues resulting from the non-symmetrical operation, a DIAC is often placed in series with the gate. This device helps make the switching more even for both halves of the cycle.

Initially, when the switch SWis open there will not be any supply to the gate circuit and the current flow will be zero through the lamp. The Triac is most commonly used semiconductor device for switching and power control of AC systems as the triac can be switched “ON” by either a positive or negative Gate pulse, regardless of the polarity of the AC supply at that time. This makes the triac ideal to control a lamp or AC motor load with a very basic triac. This can control the flow of current over both halves of an alternating cycle. Only the Thyristor can control over the one-half of a cycle.

As a High-Power Lamp Switch. So it can be used in either direction. A Triac device comprises of two thyristors that are connected in opposite direction but in parallel but, it is controlled by the same gate. Due to the wide variety of advantages, like ability to turn ON from OFF state in response to a low gate current and also able to switch high voltages, makes the SCR or thyristor to be used in a variety of applications.

These applications include switching, rectification, regulation, protection, etc. AN8APPLICATION NOTE Figure 7. Typical circuit using triac as a bidirectional switch to control each door separately Gate control circuit In this circuit, the terminal Aof the triac is sometimes connected to the ground or to the battery voltage. Therefore, a small interface circuit is needed to drive the gate from a standard micro. TRIAC Applications and Uses 1.