TRIAC MCQ Quiz in తెలుగు - Objective Question with Answer for TRIAC - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

TRIAC:

TRIAC stands for Triode for Alternate Current

Unlike SCR, TRIAC is bi-directional.

It is ideal for operation utilizing AC power for switching purposes (operated at power frequency) 

It can control current flow for both halves in an alternating current cycle.

The TRIAC symbol is shown below.

The V-I characteristics are shown below.

Applications:

• Lighting control - especially domestic dimmers.
• Control of fans and small motors.
• Electronic switches for general AC switching and control

dv/dt protection:

• When the SCR is forward biased, junctions J1 and J3 are forward biased and junction J2 is reverse biased. This reverse-biased junction J2 exhibits the characteristics of a capacitor.
• If the rate of forward voltage applied is very high across the SCR, charging current flows through the junction J2 is high. This current is enough to turn ON the SCR even without any gate signal.
• This is called as dv/dt triggering of the SCR. This can be reduced by using the RC snubber network across the SCR.
• A snubber circuit consists of a series combination of resistance Rs and capacitance Cs in parallel with the thyristor.
• False turn – ON of an SCR by large dv/dt, even without application of the gate signal can be prevented by using a snubber circuit.

di/dt protection:

• The anode current starts flowing through the SCR when it is turned ON by the application of the gate signal. This anode current takes some finite time to spread across the junctions of an SCR.
• If the rate of rising of anode current (di/dt) is high results a non-uniform spreading of current over the junction. Due to the high current density, this further leads to form local hot spots near the gate-cathode junction. This effect may damage the SCR due to overheating.
• Hence, during the turn ON process of SCR, the di/dt must be kept below the specified limits. To prevent the high rate of change of current, an inductor is connected in series with a thyristor.

I2t rating is used to determine the thermal energy absorption of the device. This rating is required in the choice of a fuse or other protective equipment employed for the SCR. This is the measure of the thermal energy that the SCR can absorb for a short period of time before clearing the fault by the fuse.

Concept:

1. IGBT - The Insulated Gate Bipolar Transistor (IGBT) is a power electronic device commonly used in high-power applications like motor control and power supply design. However, it is a unidirectional device. It allows current to flow only from the collector to the emitter, but not in the reverse direction.
2. Bipolar Junction Transistor (BJT) - A BJT is a transistor that uses electron and hole charge carriers. These are the most commonly used transistors. However, like IGBTs, BJTs are also unidirectional devices. They allow current to flow from the collector to the emitter when the base-emitter junction is forward-biased.
3. TRIAC - The TRIAC (Triode for Alternating Current) is a three-terminal semiconductor device that can control current flow in two directions, making it a bidirectional device. It can handle both positive and negative currents and can be triggered on by either a positive or a negative voltage applied to its gate terminal. It is commonly used in AC power control applications, such as light dimming, motor speed control, and heating control.
4. Gate turn-off thyristor (GTO) - A GTO is a type of thyristor that can be turned on and off by a gate signal. However, like other thyristors, it is a unidirectional device, allowing current to flow only in one direction.

Therefore, the TRIAC (option 3) allows for bidirectional current flow out of the given options.

TRIAC:

• A TRIAC is equivalent to two SCRs joined together in anti parallel; It has two main terminal and one gate

• In the TRIACs, there will be single gate control conduction in both the directions
• It is a bidirectional device and in both the directions it will conduct
• It is available in high voltage ratings
• TRIAC is a four-layer device

• A TRIAC is equivalent to two SCRs joined together in parallel. It has two main terminals and one gate

• In the TRIACs, there will be single gate control conduction in both the directions
• It is a bidirectional device and in both directions, it will conduct
• It is available in high voltage ratings
• TRIAC is a 5-layer device

TRIAC:

• The TRIAC is a 3-terminal semiconductor device and may be considered equivalent to two SCRs connected in antiparallel.
• TRIAC are bidirectional devices. 
• It is ideal for operation utilizing AC power for switching purposes (operated at power frequency) 
• It can control current flow for both halves in an alternating current cycle.

​

The V-I characteristics are shown below.

Applications:

• Lighting control - especially domestic dimmers.
• Control of fans and small motors.
• Electronic switches for general AC switching and control

Triac:

• A Triac is a bidirectional thyristor with three terminals i.e. it can conduct in both the directions.
• Its three terminals are usually designated as MT1 (Anode 1), MT2 (Anode 2), and the gate by G as in a thyristor.
• When in operation, a Triac is equivalent to two SCRs connected in antiparallel.
• As the Triac can conduct in both the directions, the terms anode, and cathode are not applicable to Triac.
• It is used extensively for the control of power in ac circuits.

The symbol and the i-v characteristics of Triac are shown below.

A triac may sometimes operate in the rectifier mode rather than in the bidirectional mode. This may happen due to the following reasons.

• For a given value of positive gate current, a Triac may turn on with MT2 positive in the first quadrant but may fail to turn on with MT2 negative.
• With constant negative gate current, the Triac may turn on with MT2 negative in the third quadrant but may not turn on with MT2 positive.

• A TRIAC is defined as a three terminal, four layer, bi-directional semiconductor device that controls AC power, which is different from the other silicon controlled rectifiers in the sense that TRIAC can conduct in both the directions that is whether the applied gate signal is positive or negative, it will conduct. Thus, this device can be used for AC systems as a switch.
• TRIAC gives a two-quadrant operation, but Triacs can be triggered in any of the four quadrants, and two of the four possible quadrants are needed to trigger conduction during the two (positive and negative) half cycles of the AC wave.
• Quadrants I, and III or quadrants II, and III are the favored methods of triggering, as quadrant IV is much less sensitive to triggering because of the way the DIAC is constructed.
• So if quadrant IV is used with any of the other three quadrants, the positive and negative half cycles would need different values of trigger current, creating an unnecessary complication.

Characteristics of a TRIAC: The Triac characteristics is similar to SCR but it is applicable to both positive and negative Triac voltages. The operation can be summarized as follows:

• First Quadrant Operation of Triac: The voltage at terminal MT₂ is positive with respect to terminal MT₁ and the gate voltage is also positive with respect to the first terminal.
• Second Quadrant Operation of Triac
• The voltage at terminal 2 is positive with respect to terminal 1 and the gate voltage is negative with respect to terminal 1.
• Third Quadrant Operation of Triac: The voltage of terminal 1 is positive with respect to terminal 2 and the gate voltage is negative.
• Fourth Quadrant Operation of Triac: The voltage of terminal 2 is negative with respect to terminal 1 and the gate voltage is positive.

Mistake Points

• TRIAC gives a two-quadrant operation, but Triacs can be triggered in any of the four quadrants, and two of the four possible quadrants are needed to trigger conduction during the two (positive and negative) half cycles of the AC wave.

TRIAC:

• A TRIAC is equivalent to two SCRs joined together in back to back (In inverse parallel).
• It has two main terminals and one gate terminal.

• In the TRIACs, there will be single gate control conduction in both directions.
• It is a bidirectional device and in both the directions it will conduct
• It is available in high voltage ratings
• TRIAC is a four-layer device​

TRIAC:

• The TRIAC is a 3-terminal semiconductor device and may be considered equivalent to two SCRs connected in antiparallel.
• TRIAC are bidirectional devices. 
• It is ideal for operation utilizing AC power for switching purposes (operated at power frequency) 
• It can control current flow for both halves in an alternating current cycle.

​

The V-I characteristics are shown below.

Applications:

• Lighting control - especially domestic dimmers.
• Control of fans and small motors.
• Electronic switches for general AC switching and control