Hello, readers welcome to the new post. In this post, we will have a detailed look at Introduction to DIAC. It is two dimensions or full-wave operating device that can operate in two directions or polarities in reverse and forward biasing. Its name DIAC is a combination of two words diode and AC switch.Its common applications are the switching of Triac also employed in lights dimmers.
It also parts of the circuit used to start the fluorescent lamps. In this post we will cover its working operation applications and some other related parameters. So let’s get started with Introduction to DIAC,
Introduction to DIAC
- The full form of DIAC is a diode for alternating current. Its name is the can operate in both directions forward and reverse.
- It belongs to the thyristor groups and generally employed in triggering of triac and another category of thyristors.
- Its operation is such that when applied voltage is larger than the break-over voltage that its conducts.
- The general packaging in which it exists is leaded packaging surface mounted packaging.
- In some applications, its employed with the triac so gets in single ICs.
- It sometimes is known as symmetrical diodes it is due to the symmetry of the characteristic curve.
DIAC Construction
- The structure of DIAC is like the construction of a transistor with some differences that there is no base terminal in diac and there is a similar doping level for 3 layers and it offered similar switching features for forward and reverse bias
- In the below figure, we can see the normal structure of diac. The above-mentioned terminal of diac MT1 and MT2 can seen here and used for the movement of current in two directions.
- This module is created in a structure having 5 layers and these layers close to points have a combination of positive and negative sheets.
Symbol of DIAC
- The symbolic representation of diac combination of 2 diodes linked in parallel combination having reveres structure and has 2 points.
- As the diac is two-dimensional so its terminal can not be named as anode and cathode. Its terminal is known as A1 and A2 or MT1 and MT2 here MT full form is the main terminals.
DIAC Working Operation
- The below figure indicates the working of DIAC according to their polarities. Suppose that MT1 points is at positive polarity in results P1 layers close to the MT1 get energized.
- The flow of current will take place in the order of P1, N2 P2 and N3.
- If the current is passing from MT1 to MT2 terminals then junction among the P1 and N2 and P2 and N3 will in forward biased state and pn junction for N2 and P2 will be reversed biased.
- In case if MT2 is positive polarity then layers close to MT2 will be activated and current flows in a sequence of P2 N2 P1 and N1. From this we can observe that the bidirectional behavior of DIAC is fulfill.
DIAC VI Characteristic
- The VI curve odd DIAC is like the letter Z and it exists in the ist and 3rd quadrants due to operation for positive and negative polarity.
- The part of the curve that exists in the first quadrant shows the positive cycle where the current flowing from MT1 to MT2 and the third quadrant indicates that current passing from MT2 to Mt1
- At the start resistance of DIAC is large since of the reverse bias junction among the layers so here is a small amount of leakage current passing from DIAC it is denoted as blocking state in the figure.
- When the voltage is given is close to the breakdown voltage resistance of diac loss suddenly and its operation started that causes the decrement in the voltage-current initiate rising, this step shown in the figure as conduction state.
- The value of breakdown voltage is thirty volts the value of breakdown voltage lies at the category of the component.
Advantages
- It is used for conducting and regulating both parts of the AC signal.
- it is a compact design and needs a small size heat sink for opposition to use of 2 SCR.
- It uses a single fuse for protection.
- For TRIAC triggering positive and negative gate pulses were used.
- It does not use a diode in parallel combination for reverse protection like SCR.
Disadvantages
- It provides asymmetrical switching for both parts of the AC signal.
- Asymmetrical switching provides harmonics in a system that causes different issues.
- It has a low power rating as compared to SCR.
- It is low reliable module than SCR and comes with a low switching speed.
- It has dv/dt rating low as compared to SCR
Applications of TRIAC
- TRIAC is used for low to medium-level AC power controls. It ahs asymmetrical switching use in series combination for its gate pin for providing symmetrical triggering.
- The combination of DIAC and TRIAC is called QUADRAC.
SCR vs DIAC vs TRIAC
Feature | SCR | DIAC | TRIAC |
Type | Unidirectional | Bidirectional | Bidirectional |
Use Case | DC control | Triggering TRIACs |
AC control
|
Control Precision | High | Moderate |
High
|
Symbol | Forward diode | 2 opposite diodes |
Two opposite diodes + gate
|
pins | Anode, Cathode, Gate | MT1, MT2 | MT1, MT2, Gate |
Gate Control | Yes | No | Yes |
Trigger Mechanism | Gate Pulse | Breakover Voltage | Gate Pulse |
Conduction | One Direction | (AC) |
(AC)
|
FAQS
What is the construction and working of DIAC?
- The DIAC is the 2-terminal component that is a combination of parallel semiconductor layers that helps to activate in a single direction. That devices are used for activating devices for triac. The basic design of DIAC comes with 2 pins called MT1 and MT2.
How does a DIAC work?
- The DIAC is a diode that conducts current after a break over voltage reaching. it comes with 2, 4, and 5-layer design that is like the voltage breakdown of triac without a gate pin.
What is the working principle of DIAC and TRIAC?
- DIAC is a diode that is used for AC that helps current to flow in both directions if the voltage is higher as compared to break over voltage. The TRIAC is a bidirectional SCR that has features for conducting in both directions if triggered with applications of gate pulses.
What is a DIAC equivalent circuit?
- The DIAC equivalent circuit comes with 2 parallel semiconductor layers that help current to flow in both directions. This circuit is configured as two zener diodes configured in series with reverse direction. That helps DIAC to conduct current when breakdown voltage crosses in any direction
What are parts of DIAC?
- The main parts of DIAC are 2 semiconductor layers made for conducting current in both directions. These layers are made of silicon.
What are the types of DIAC?
- DIAC comes in different types based on breakover voltage and current features. They are defined based on materials and design as compared to types. A commonly used type of circuit is standard silicon-based DIAC.
What is the difference between a DIAC and a zener diode?
- The DIAC is a bidirectional device that causes current flow in both directions when a certain break-over voltage is increasingly used for triggering and switching circuits for high-voltage projects.
- Zener diode current in one direction but also allows reversing current for certain conditions for providing low voltage control.
- DIAC is used for component activating of AC circuits and zener diode is used for providing constant voltage.
Read also
That is a detailed post about DIAC i tried to cover each and every parameters related to DIAC if you have to know further about DIAC ask in the comments. Thanks for sharing have a nice day.